Steller sea lion (Eumetopias jubatus) management plan: chapter 8
1. Species Information
- 1.1 Species Assessment Information from COSEWIC
- 1.2 Description and Biology
- 1.3 Populations and Distribution
- 1.3.1 Global Range
- 1.3.2 Canadian Range
- 1.3.3 Global Population Trends
- 1.3.4 Canadian Population Trends
- 1.4 Requirements of the Steller Sea Lion
- 1.5 Threats
- 1.5.1 Threat Classification
- 1.5.2 Description of Threats
- 1.5.3 Cumulative or Synergistic Effects of Threats and/or Limiting Factors
- 1.6 Actions Already Completed or Underway
- 1.7 Knowledge Gaps
Date of Assessment: November 2003
Common Name (population): Steller Sea Lion
Scientific Name: Eumetopias jubatus
COSEWIC Status: Special Concern
Reason for Designation: There are only three1 breeding locations in British Columbia. Although the population is increasing, they are sensitive to human disturbance while on land. Threats include the possibility of acute oil spills. There are unexplained declines in other populations to the north and west of British Columbia.
Canadian Occurrence: British Columbia, Pacific Ocean
COSEWIC Status History: Designated Not at Risk in April 1987. Status re-examined and designated special concern in November 2003.
1 Since the 2003 COSEWIC designation, a fourth location has been re-classified as a breeding site.
The Steller Sea Lion is the largest member of the eared seals, or sea lions and fur seals (Order Carnivora, Superfamily Pinnipedia, Family Otariidae; Rice 1998). Other common names used in Canada include Steller’s sea lion, northern sea lion and lion de mer de Steller. Some First Nations names for sea lion include; tukuk or tukukw (tukwašt meaning dried sea lion) in Nuu-chah-nulth Barkley Sound dialects (BSDWG 2004), in Kwakiutl sea lion are referred to as tl’íx7en (Grubb 1977), and in the Haida language, kíit or kíidaay (Lawrence 1977). The scientific name (Eumetopias jubatus) means having a broad forehead and a mane, a reference to the prominent ruff of coarse hair that mature males develop on their necks and chests, from which is also derived the name ‘lion’. Steller Sea Lions exhibit significant sexual dimorphism, with adult males (bulls) attaining a length of up to 3 m and weighing 400-800 kg, although at the start of the breeding season the largest males can weigh over 1,100 kg. Mature males develop massive muscular necks and chests, and robust heads with flatter snouts than those of females. Adult females (cows) are noticeably smaller, averaging 2.2 m and 200-300 kg (Mathisenet al.. 1962; Thorsteinson and Lensink 1962; Orr and Poulter 1967; Winshipet al.. 2001).
When dry, the fur of adults and juveniles are pale yellow to light brown, darkening to chocolate brown on their hindquarters and near their flippers, which are black and bare-skinned. Steller Sea Lions may appear greyish white when wet. Steller Sea Lion fur is comprised of short coarse hairs, which is moulted annually between late June and early December, depending on the age class (Scheffer 1964). Pups are born with a thick blackish-brown lanugo that is moulted between 3-6 months of age.
All sea lions are remarkably agile on land due to their ability to rotate their hind flippers forward and prop themselves up on their foreflippers. Steller Sea Lions can climb steep rocks and are often found many metres above the sea surface; they tend to be highly gregarious while on land and generally pack close together in dense breeding colonies (rookeries) or non-breeding haulouts (Schusterman 1981; Loughlin et al. 1987). Although Steller Sea Lions typically haul out on a regular basis, they sometimes spend many days or several weeks at sea without coming ashore (Olesiuk and Jeffries, unpublished data), and can sleep in the water, usually in groups called rafts.
Breeding colonies (called rookeries) are used by sexually mature sea lions (along with a few dependent young with their mothers) during the summer months. Steller Sea Lions have a polygynous mating system, in which bulls compete to establish territories and gain access to females; the ratio of cows to territorial bulls is generally about 10-15:1 (Gisiner 1985; Merrick 1987). Successful males will usually maintain their territory for an average of 40 days (range 20-68 days) without feeding (Gentry 1970). Most territorial males are 9-13 years old (Thorsteinson and Lensink 1962) and may hold a territory for several years in succession (range 1-7 years) (Gisiner 1985).
Females first ovulate at about 3-6 years of age. Females begin returning to rookeries in late May and give birth to a single pup within a few days of their arrival; most pups are born by early July (Gentry 1970; Edie 1977; Bigg 1985). Mothers nurse their pups on shore for about one week, before leaving on regular feeding trips that alternate one day at sea and one day on shore (Swain 1996). By about four weeks of age, pups can swim in the open ocean and mothers start moving them to nearby haulouts. Some pups continue to nurse into their third year, although most are weaned in their first or second years; some mothers may also nurse a newborn and yearling simultaneously (Sandegren 1970; Hood and Ono 1997; Milette and Trites 2003).
Use of breeding rookeries declines by late August and is at a minimum during January-April, although some animals continue to use them year-round as haulout sites (Bigg 1985). Outside of the summer breeding season, Steller Sea Lions use year-round haulouts as well as winter-haulouts that may be considerable distances from rookeries. Females with dependent young may stay at a single haulout or move their pups around between haulouts (Shusterman 1981; Loughlin et al. 1987).
Steller Sea Lions inhabit the cool-temperate and subarctic coastal waters of the North Pacific Ocean from the Channel Islands off southern California, north to the Bering Strait, and southwest along the Asian coast to Hokkaido, Japan (Fig. 1; Kenyon and Rice 1961; Loughlin et al. 1984; Loughlin et al. 1992). They presently give birth on 61 rookeries and rest at >300 haulouts across this range. Steller Sea Lions are non-migratory, but may disperse considerable distances from breeding sites (Fisher 1981; Calkins and Pitcher 1982; Loughlin 1997; Raum-Suryan et al. 2002).
Worldwide, at least two populations of Steller Sea Lions are recognized based on genetic differentiation of mitochondrial DNA (which reflects maternal lineage): an Eastern Population (California to southeast Alaska) and a Western Population (Gulf of Alaska, Bering Sea, Aleutian Islands, and Russia) (Bickham et al. 1996). Separation of the two populations in North America is further supported by a phylogeographic analysis that considers such ancillary information as population trends, distribution, movements, and morphology (York et al. 1996; Loughlin 1997). However, recent genetic sampling indicates two newly established rookeries near the western edge of the Eastern Population may have been colonized by a mixture of Western and Eastern stock animals (O’Corry-Crowe et al. 2005). Female Steller Sea Lions in Asian waters (Kamchatka Peninsula, Kuril Islands and Okhotsk Sea) appear to be genetically distinct from the other populations (Baker et al. 2005) but there is greater gene flow for males (Hoffman et al. 2006). There is also some genetic evidence of geographic segregation among the shelf (Gulf of Alaska and Alaska Peninsula) and oceanic (Aleutian Islands) components of the western population (O’Corry-Crowe 2007).
Arrows denote breeding rookeries and shaded areas denote the approximate non-breeding range of the species. The dashed line shows the separation between Asian, Eastern and Western stocks of Steller Sea Lions. (modified from Loughlin 1997 and Sease et al. 1999).
Within Canada, Steller Sea Lions occur only in British Columbia and constitute part of the Eastern Population (Bickham 2000). There are four main breeding areas in B.C.: the Scott Islands off the northwest tip of Vancouver Island, with rookeries situated on Triangle Island and the small islets off Beresford and Sartine Islands; the second area at Cape St. James off the southern tip of the Queen Charlotte Islands, with rookeries situated on the Kerouard Islands; and a third area off Banks Island on the northern mainland coast, with rookeries situated on North Danger Rocks (Figure 2).
Figure 2: Geographic Location of Steller Sea Lion Rookeries, Year-round Haulout Sites and Major Winter Haulout Sites in British Columbia
Also indicated is the major rookery on Forrester Island, Alaska. Updated from Bigg (1985) (DFO unpublished data).
The fourth breeding area was historically located off the central mainland coast on the Sea Otter Group, with rookeries situated on Virgin, Pearl and possibly Watch Rocks, but this breeding aggregation was extirpated by intense predator control programs during the 1920s and 1930s and had subsequently been used as a haulout by non-breeding animals (Bigg 1985). An increasing number of pups have been born on Virgin and Pearl Rocks in recent years and based on the 2006 abundance survey the site was reclassified as a rookery (Figure 2). In addition to the four breeding sites, there are about twenty-three haulout sites distributed mainly along the exposed outer coast that are used continuously throughout the year, as well as numerous winter sites used on a seasonal or irregular basis.
The offshore distribution of Steller Sea Lions is not well defined. In general, most Steller Sea Lions appear to feed within about 60 km of shore during summer, and can range over 200 km from shore in winter (Kenyon and Rice 1961; Merrick and Loughlin 1997). They appear to feed over the continental shelf and along the shelf break (Kajimura and Loughlin 1988). Steller Sea Lions captured in B.C. and fitted with satellite tags ranged widely along the B.C. coast, but rarely ventured more than 50 km from shore (Olesiuk and Jeffries, unpublished data).
Between the late 1950s and 1970s, overall abundance of Steller Sea Lions in the North Pacific (range-wide: Japan to California) was believed to have been stable at about 250,000-300,000 individuals (Kenyon and Rice 1961; Loughlin et al. 1984). Abundance subsequently declined to about 116,000 by 1989, 97,500 by 1994-95, and 95,000 by 1999-2002.
The drop in overall abundance of Steller Sea Lions was attributable to declines in the western part of their range. Historically, the Western Population (Russia to Gulf of Alaska) was much larger than the Eastern Population (southeast (SE) Alaska to California), and accounted for roughly 90% of total abundance between the 1950s and 1970s (Kenyon and Rice 1961; Loughlin et al. 1984; Trites and Larkin 1996). The decline appears to have begun in the eastern Aleutian Islands in the mid-1960s, and spread to the western Aleutian Islands and Gulf of Alaska in the late 1970s. Numbers dropped precipitously during the 1980s, and continued at a much slower rate through the 1990s (York et al. 1996). By 1999-2002, the Western Population was estimated to have numbered about 50,000 individuals (Burkanov 2000; Sease and Stinchcomb 2003), a decline of about 80% from levels present during the 1950s to 1970s. The precipitous decline of the Western Population has made the Steller Sea Lion one of the most intensively studied marine mammals in the world (see NMFS 1992, 2008; Loughlin 1998; Hunter and Trites 2001; Dalton 2005).
Predator control programs in B.C., Washington, Oregon (Rowley 1929) and California (Pearson and Verts 1970) during most of the 20th century (1900 – 1970) resulted in the Eastern Population of Steller Sea Lions becoming severely depleted by the time the species was protected under the Fisheries Act in Canada in 1970 and under the Marine Mammal Protection Act in the U.S. in 1972.
Steller Sea Lions were not known to breed in SE Alaska during the early 1900s and were not subjected to major control programs. The first rookeries became established in SE Alaska during the 1930s or 40s when the intense killing had begun in southern parts of the range, and the species appears to have flourished in the 1950s and 60s even as breeding populations were reduced in B.C. While predator control programs were underway, dispersal of breeding females from rookeries in B.C. may have contributed to the rapid expansion of new rookeries established in SE Alaska (Calkins et al. 1999; Pitcher et al. 2003, 2007), and dispersal patterns appear to have changed over time. Forrester Island accounted for much of the growth until the early 1980s, but its growth rate has subsequently slowed, and newly established rookeries in central-northern SE Alaska as well as other rookeries in B.C. have accounted for much of the more recent growth (Pitcher et al. 2007).
In contrast to the Western Population, the Eastern Population has been growing in recent years (DFO 2008; Olesiuk unpublished data; Calkins et al. 1999; Pitcher et al. 2003, 2007). In 2002, the Eastern Population was estimated to number about 46,000 – 58,000 individuals (Pitcher et al. 2007), compared with approximately 45,000 Steller Sea Lions in western Alaska (Angliss and Outlaw 2007) and 16,000 in Asia (Burkanov and Loughlin 2007).
Historical counts of Steller Sea Lion rookeries in B.C. date back to the early 1900s, and provide an index of the size of the Canadian breeding population (Bigg 1984, 1985; DFO 2008). It is estimated that about 14,000 animals (all ages, including pups) were present on rookeries in 1913-19 (Fig. 3), which was prior to any large-scale kills. Steller Sea Lions in Canada and neighbouring waters were subjected to predator control programs during most of the 20th century.
Prior to the species being protected in the 1970s, the Canadian government conducted intensive culls of Steller Sea Lions at rookeries, for the mandated purpose of protecting salmon fisheries (Figure 4). Limited commercial harvests were also conducted for hides and for mink food. Numbers on rookeries in B.C. had been reduced to 4,550 by 1961 and 3,390 animals (including 940 pups) by the time the first aerial survey was conducted in 1971. Thus Steller Sea Lions in B.C. were depleted to about one-quarter of their historic size by predator control and commercial harvesting (Bigg 1985; DFO 2008).
Assessments of the abundance, distribution and status of Steller Sea Lions in B.C. were initiated in the 1970s and 1980s (Bigg 1984, 1985, 1988) and continue to the present day (DFO 2008; Olesiuk et al. unpublished data). Province-wide aerial surveys have been conducted in B.C. at 4-5 year intervals since the species was protected under the Fisheries Act in 1970 from targeted harvest, or culling. Surveys are conducted during a brief time window between late June and early July, representing the period by which most pups have been born, but most are still too young to have begun to disperse from rookeries (Bigg 1985; DFO 2008).
Figure 3: Historic Trends in Total Numbers of Steller Sea Lions (Pups, Juveniles and Adults) on Breeding Rookeries in B.C., Forrester Island, Alaska, and Other New Rookeries in SE Alaska
The thin blue lines show the distribution of animals among main breeding areas in B.C. (modified from Bigg 1985 and Olesiuk et al. 2008).
Figure 4: Total Numbers of Steller Sea Lions Reported to have been Killed in B.C. as Part of Control Programs and Commercial Harvests During 1913-70
Data have been grouped and totalled into 5-year periods, and are colour-coded by major breeding area. Comparison with Figure 3 shows the impact these kills had on populations. (Data from Bigg 1984).
B.C. aerial surveys indicate that numbers of pups and non-pups on rookeries increased at a mean rate of 3.5% and 3.9% per annum respectively, which has resulted in a tripling in the size of the breeding population since the early 1970s (Figure 5) (DFO 2008). Similar trends have been observed on neighbouring rookeries to the south in Oregon and to the north in SE Alaska (Figure 5), which combined constitute 90% of the Eastern Population (Brown and Reimer 1992; Calkins et al. 1999; Pitcher et al. 2007). This indicates that the increase in Canada represented real population growth, and not merely a local shift in distribution (Pitcher et al. 2007). Based on estimated pup production during the last range-wide survey in 2002, the total size of the Eastern Population is estimated to be between 46,000 to 58,000 animals, with about one-third (33% of pups and 34% of non-pups) occurring in Canadian waters. Abundance in Canadian waters was estimated to be 20,000-28,000 based on the most recent survey in 2006 (DFO 2008).
The needs of Steller Sea Lions can be partitioned between the time they spend on land when they come ashore to rest and reproduce, and the time they spend at sea where they travel and forage. The species is gregarious while on land, and animals gather at traditional rookeries and haulout sites, some of which have been used for over a century. Steller Sea Lions forage on a variety of prey items, primarily small or medium-sized schooling fish, and foraging habitat varies in relation to prey distribution and abundance.
Terrestrial Habitat
The terrestrial sites used by Steller Sea Lions in British Columbia generally fall into three distinct categories: 1) rookeries where animals congregate during May-August to give birth, mate, and nurse pups; 2) year-round haulouts that are usually occupied continuously; and 3) winter haulout sites that are used less regularly, mainly during the non-breeding season (Bigg 1985). Rookeries generally have peripheral haulout sites associated with them that are occupied mainly by non-breeding males and juveniles during the breeding season. In most cases animals continue to use rookeries as haulout sites throughout the year, albeit in much reduced numbers.
Steller Sea Lions exhibit high site fidelity for breeding and birthing. Studies of marked individuals indicate that most females tend to return to their rookeries of birth, and will return faithfully to a single rookery each year (Raum-Suryan et al. 2002). The three main breeding colonies in B.C. were all well established when the first sea lion survey was conducted in 1970 (Newcombe and Newcombe 1914), and have been used continuously despite disturbances caused by predator control programs and commercial harvests (Pike and Maxwell 1958; Bigg 1985; Olesiuk unpublished data). The fourth breeding site in the Sea Otter Group was eradicated by predator control programs, although sea lions continued to use the site as a non-breeding haulout. Pupping has resumed at the site, and based on pup counts during the 2006 survey, the site was recently reclassified as a rookery.
Figure 5: Recent Trends in Counts of Steller Sea Lion Pups and Non-pups on Rookeries
In a) southeast Alaska; b) British Columbia; and c) Oregon
(updated from Pitcher et al. 2007).
Although Steller Sea Lions generally return to breed on their natal rookery, there may also be some exchange between neighbouring rookeries (Calkins and Pitcher 1982, 1996). Of 31 females branded as pups on Forrester Island, several were observed to have given birth at other rookeries, including 400 km away at Cape St. James (Raum-Suryan and Pitcher 2000; Raum-Suryan et al. 2002).
Terrestrial habitats for Steller Sea Lions comprise some of the most isolated, barren outcroppings in the North Pacific Ocean. Haulouts are typically located in regions that have relatively high currents, high salinity, low surface temperatures and shallow waters, presumably reflecting high ocean productivity and hence optimum feeding areas (Ban et al., unpublished data). Essential haulout features seem to include relatively flat terrain, accessibility, protection from swell and waves, and absence of terrestrial predators such as bears and wolves (Edie 1977). Sea lions use protected areas during storms, and wet areas during extremely hot weather (Edie 1977). Access to high ground is also important for whelping, although older animals that are capable of going to sea will use lower and more exposed areas. Rocky ledges are preferred breeding substrate in B.C. rookeries, although increasing numbers of animals have recently begun breeding on the gravel beaches along the eastern (leeward) side of Triangle Island (Olesiuk, unpublished data).
The twenty-three year-round haulout sites in B.C. are generally situated in exposed areas along the outer coast, and are comprised of rocky islets and ledges. Approximately half of the sites were noted to exist during the first surveys in 1913 (Newcombe and Newcombe 1914), while about one-quarter appear to have been colonized since aerial surveys were initiated in the early 1970s. Year-round haulout sites are widely distributed in B.C., and provide sea lions with habitat for resting all along the outer coast. Steller Sea Lions can also rest in the water during storms or heavy swells when haulouts are awash, or when they are near concentrations of prey without suitable nearby haulouts; this rafting behaviour often occurs in groups (Kenyon and Rice 1961; Olesiuk and Bigg 1988).
Many winter haulouts are situated in protected areas, such as the Strait of Georgia, Strait of Juan de Fuca and Queen Charlotte Strait. In addition to natural substrates, wintering haulouts include log booms, floats, jetties and docks. In southern B.C., winter haulouts are often shared with subadult and adult male California sea lions (Zalophus californianus) (Hancock 1970; Brenton 1977; Bigg 1985).
Prey Requirements and Marine Habitat
Over 50 species of fish and invertebrates have been identified in the diets of Steller Sea Lions (Wilke and Kenyon 1952; Pike 1958; Spalding 1964; Pitcher 1981; Kastelein et al. 1990; Sinclair and Zeppelin 2002). In British Columbia, preferred prey appears to include small or medium-sized schooling fishes, such as herring, hake, sandlance, salmon, dogfish, Eulachon and sardines, and bottom fish such as rockfish, flounder and skate (Pike 1958; Spalding 1964; Olesiuk and Bigg 1988, Trites and Olesiuk, unpublished data). In addition to fish, squid and octopus are sometimes consumed, but their importance was likely exaggerated in earlier studies because cephalopod beaks likely accumulate in stomachs over extended periods (Bigg and Fawcett 1985). Crabs, mussels, clams and other invertebrates are occasionally recovered in stomachs and scats, but these may represent secondary prey that had been consumed by the prey species eaten by sea lions. Steller Sea Lions have also been observed to prey on gulls (O'Daniel and Schneeweis 1992) and other pinnipeds, including neonate fur seals (Gentry and Johnson 1981) and harbour seals (Pitcher and Fay 1982, E. Mathews, University of Alaska, Juneau AK, pers. comm.). Predation on other pinnipeds seems quite uncommon, but may be locally significant.
Prey requirements of Steller Sea Lions vary seasonally and with age and sex, and depend on the type and quality of prey (Perez 1994; Rosen and Trites 1999, 2000b,c). Bioenergetic models predict that daily food requirements for Steller Sea Lions in the wild are approximately 15-20 kg for mature females and 30-35 kg for mature males (Winship et al. 2002). For females, these daily energy requirements represent about 14% of body weight for a 1 year old and 7% for a mature individual. Mean consumption in the SE Alaska population was estimated at 17 kg per individual per day (Winship and Trites 2003). Sea lions that consume more low fat fishes such as gadids require significantly more prey than those that consume fattier fishes such as herring (Trites and Donnelly 2003; Winship and Trites 2003).
There is relatively poor understanding of how Steller Sea Lions use their aquatic habitat At sea, Steller Sea Lions are commonly seen alone, or in groups of several animals (Bonnell et al. 1983). Animals feeding on small schooling fishes appear to feed co-operatively in groups of up to 100 animals that dive and surface in synchrony (Fiscus and Baines 1966; Loughlin et al. 1983; Loughlin and DeLong 1983; P. Olesiuk, Fisheries and Oceans Canada – Pacific Region, Science, pers. comm.). Foraging appears to occur primarily at night based on satellite telemetry (Loughlin et al. 1998; Loughlin et al. 2003) and diurnal haul out patterns (Withrow 1982; Higgins 1984; Milette 1999), but can vary seasonally depending on the type of prey consumed (Olesiuk and Jeffries, unpublished data). Steller Sea Lions can dive to depths of at least 310 m (Andrews 1999) and stay submerged for over 8 minutes (Swain and Calkins 1997), with most dives in the range of 15-50 m and lasting 1.5-2.5 min (Merrick and Loughlin 1997; Swain and Calkins 1997; Loughlin et al. 1998; Andrews 1999; Swain 1999).
Animals are generally observed within 60 km of land and in water depths less than 400 m, but may venture several hundred kilometres offshore and occur off the continental shelf (Kenyon and Rice 1961; Merrick and Loughlin 1997). Telemetry and branding studies have shown that animals are highly mobile, and may travel hundreds of kilometres and utilize numerous haulout sites over the course of a few weeks or months (Merrick and Loughlin 1997; Loughlin et al. 1997, 2003; Raum-Suryan et al. 2002). Steller Sea Lions captured and tagged in B.C. have been subsequently tracked up to 1,700 km, ranging north to Alaska or south to California (Calkins 1981; Fisher 1981; Loughlin, pers. comm.; Olesiuk, unpublished data). Steller Sea Lions also occasionally venture into freshwater (Jameson and Kenyon 1977; Roffe and Mate 1984; Beachet al. 1985). In B.C., sea lions are occasionally seen rafting as far as 35 km upriver (Olesiuk, unpublished data). Steller Sea Lions also congregate in estuaries during autumn to feed on pre-spawning salmon and at the mouth of the Fraser River in spring when Eulachon are running (Bigg 1985; Bigg et al. 1990, Olesiuk unpublished data). Major wintering areas of sea lions off southern Vancouver Island have shifted, presumably in relation to changes in distribution of pre-spawning herring (P. Olesiuk, pers. comm.).
Foraging trips tend to be more localized during the summer breeding season (<20 km) than during other times of the year (60-160 km). (Bonnell et al. 1983; Merrick and Loughlin 1997). In summer, reproductive females are confined to foraging within commuting distance of rookeries, as they must regularly return to attend pups. In contrast, non-breeding animals during summer and all animals during the non-breeding season (September-May) are more flexible and movements are likely related to the availability of forage fish. Foraging ranges of immature non-breeding animals appear intermediate to the summer and winter foraging ranges of adults (Merrick and Loughlin 1997).
The Steller Sea Lion is the largest species of otariid and the only one that resides and breeds year-round in Canadian waters. The species occupies a niche intermediate to the inshore distribution of harbour seals (Phoca vitulina) that generally occupy more protected waters, and the pelagic distribution of northern fur seals (Callorhinus ursinus) that generally occur over the continental shelf and along the shelf break. The role of seals and sea lions in complex marine ecosystems remains poorly understood and studies are required to assess the contribution of the Steller Sea Lion in large and complex ecosystems (Beverton 1985; Bowen 1997; Merrick 1997; Trites 1997).
Due to the recent declines in Alaska, the British Columbia rookeries at the Scott Islands and Cape St. James now represent the second and sixth largest breeding aggregations in the world. Based on overall pup production in 2002, B.C. supports about 16% of the world’s population and about 33% of the Eastern stock (another 31% occurs in southeast Alaska within 50 km of the Canadian border). Steller Sea Lions are widely perceived to be an important component of the coastal marine ecosystem, and contribute to the eco-tourism industry.
Steller Sea Lions are top marine predators. In SE Alaska, Steller Sea Lions are estimated to consume about 140 million kg of fish annually (Winship and Trites 2003); assuming a similar diet, the B.C. population would consume another 110 million kg annually. In comparison, the total annual commercial fish landing in B.C. has averaged about 185 million kg over the last decade (DFO 2007). Basic knowledge of seasonal and regional feeding habits of sea lions in B.C. are still lacking, and much of the information that does exist has been collected anecdotally as part of other studies. As Steller Sea Lions recover from predator control programs and harvests, it is likely that prey resources will ultimately limit sea lion populations, but it remains unclear to what extent sea lions themselves might limit their prey populations.
Steller Sea Lions also compete with other marine predators, including other species of pinnipeds, whales, seabirds, sharks and flatfish (Livingston 1991; Tamura and Ohsumi 2000; Wespestad et al. 2000; NMFS 2001; Gallucci et al. 2006). Over the last century, competition with California sea lions (Zalophus californianus) has increased dramatically (Lowry and Maravilla-Chavez 2005), which could adversely affect Steller Sea Lions. California sea lions appear to have displaced Steller Sea Lions from traditional rookeries in the Channel Islands off California, and have extended their non-breeding range north into B.C. (Bigg 1988; P. Olesiuk pers. comm.) and occasionally as far as Alaska (Maniscalco et al. 2004). California sea lions migrating along the coast of Oregon appear to displace Steller Sea Lions (Mate 1975); the two species often share the same winter haulout sites (P. Olesiuk pers. comm.) and consume the same prey species (Olesiuk and Bigg 1988).
Steller Sea Lions are an important prey species for Transient Killer Whales (also called transients), (Morton 1990; Baird and Dill 1995; Ford et al. 1998; Matkin et al. 2007; Wade et al. 2007), which may selectively prey on pups and juveniles (Barrett-Lennard et al. 1995). Transient Killer Whales are listed under the Species at Risk Act [SARA] as threatened, and could be vulnerable to fluctuations in their prey species. In B.C. and adjacent waters, Steller Sea Lions were found to be the second most important prey for transients (Ford et al. 1998), and a survey of the entire northeast Pacific Ocean reported Steller Sea Lions to be the sixth most commonly observed prey of these whales (Wade et al. 2007). Large sharks may also prey on Steller Sea Lions in the southern part of their range (Stroud 1978; Ainley et al. 1981) and sleeper sharks are a potential sea lion predator in Alaska (Sigler et al. 2006).
Steller Sea Lions may have the potential for serving as an indicator of the general status of coastal marine ecosystems. The species is widely distributed in coastal waters, has a long lifespan, congregates on rookeries where breeding populations can be readily censused, and occupies a position near the top of the marine food chain. The recent declines in the Western Population of Steller Sea Lions in Alaska are now widely believed to be associated with broader ecosystem processes that are not well understood; this demonstrates that the ability to monitor Steller Sea Lion populations far exceeds our understanding of the complex ecological processes that regulate these apex predators. As populations in B.C. and neighbouring waters have now recovered past historic high levels, natural population regulatory mechanisms might become a factor governing the status of Steller Sea Lion populations.
Limiting factors are the natural processes that limit population size or growth. Steller Sea Lions are inherently a relatively long-lived and slow-reproducing species. The maximum productivity level has not been determined for this species, but it is likely low. For U.S. stock assessments, a theoretical maximum growth rate of 12% is generally assumed for pinnipeds. While this may be appropriate for phocids (e.g. Olesiuk et al. 1990; Olesiuk 1999; Bowen et al. 2003), otariids generally exhibit lower survival rates, and expanding populations have not attained that level of productivity. For instance, severely depleted populations of California sea lions sustained exponential growth rates of only about 6.1% (Lowry and Maravilla-Chavez 2005) and northern fur seals about 8.6% per year (York, pers. comm. cited in Angliss and Outlaw 2007). Recovering Steller Sea Lion populations along the west coast of North America have sustained growth recovery rates of only about 3.1% per annum and have exhibited no signs of density dependence as populations increased, but it is not known whether this represents the maximum intrinsic rate of increase for the species or whether some stressor has been inhibiting recovery throughout this region for the past 40 years (Pitcher et al. 2007). Regardless, the productivity of Steller Sea Lions is probably lower than other pinnipeds, making it less resilient to perturbations and stresses, taking longer to recover from such impacts.
The low productivity of Steller Sea Lions can be attributed to a combination of low reproductive potential and high mortality. Most otariids, including California sea lions and northern fur seals, wean their young at a few months of age, and tend to reproduce annually. In contrast, Steller Sea Lions often continue to nurse their young into the second or third year (Pitcher et al. 2003). Since lactating females are less likely to carry fetuses to term, the extended period of parental care typically results in longer intervals between consecutive births and overall reduced reproductive performance (Pitcher et al. 1998).
Mortality of newborn pups (< 1 month) is high (Pike and Maxwell 1958; Orr and Poulter 1967). Juvenile mortality is difficult to estimate due to potential sampling biases, but appears to be high, with about 48% of females and 26% of males surviving to three years of age (Calkins and Pitcher 1982; York 1994). The higher mortality rates for males’ results in a progressively skewed sex ratio favouring females. Mortality rates are significantly lower for adults (~10-15% per year for females, and ~13-25% for males). The principle cause of death for pups is drowning due to limited swimming abilities at this age preventing them from hauling out of the water or steering in strong tidal currents (Orr and Poulter 1967; Edie 1977). Being bitten, tossed or trampled by older animals, and being abandoned or separated from their mothers also contributes to pup mortality (Orr and Poulter 1967; Gentry 1970; Sandegren 1970; Sandegren 1976). In marine mammals, density dependence is generally thought to be expressed primarily in the parameters that affect reproductive rates, especially of younger animals (i.e., age at first reproduction, fecundity rates, and juvenile survival) (Eberhardt 1985; Fowler 1987). Juvenile mortality has been implicated as the main driver in the steep declines of the Western Population in the 1980s (York 1994), with reduced adult female natality and survival playing a lesser role (Holmes and York 2003). The slower decline in the 1990s may be attributable to improved juvenile and adult survival, although natality rates appear to have continued to drop (Holmes and York 2003). The ratio of pups to non-pups provides an index of relative birth and survival rates. The surprisingly high ratio of non-pups to pups observed in surveys along the west coast of North America suggests that increased juvenile survival (as opposed to increased natality rates) may have been an important factor influencing growth of the Eastern Population (Pitcher et al. 2007).
The factors that ultimately limit Steller Sea Lions and other marine predators can be broadly categorized as bottom-up processes mediated by the availability and quality of prey, and top-down processes mediated by predators (including direct kills by humans).
Prey Availability and Quality
Steller Sea Lion populations are ultimately limited by the availability of suitable prey. A shift in the quality of diets from fatty fishes (i.e. herring) to low-fat fishes (i.e. walleye pollock) has been implicated in the decline of Steller Sea Lions in the Gulf of Alaska and Aleutian Islands (Alverson 1992; Alaska Sea Grant 1993; DeMaster and Atkinson 2002; Trites and Donnelly 2003). Controlled-feeding studies have shown that sea lions, particularly young animals, consuming large amounts of low-fat prey such as pollock, may be unable to maintain body mass (Rosen and Trites 2000c; Azana 2002). In the wild, these young animals would typically still be dependent on their mothers, who may have difficulty meeting the high energetic costs associated with lactation (Winship et al. 2002; Pitcher et al. 2003). Therefore, availability of high quality prey near rookeries appears to be a potentially important limiting factor.
Diversity of the diet has been shown to be inversely correlated with the severity of declines of the Western Population in the Gulf of Alaska, with the steepest declines occurring in areas with the least diverse diet (Merrick et al. 1997). Diversity of the diet in the increasing Eastern Population appears to be high (Trites et al. unpublished data). Reduced rates of body growth (Calkins et al. 1998), and a direct correlation between body condition and the proportion of animals maintaining late-term pregnancies (Pitcher et al. 1998) provides further evidence of nutritional stress during the steep declines in the Western Population observed during the 1980s (NMFS 2008).
The acute impacts that reduced prey availability can have on pinnipeds is evident from the abrupt declines in California sea lion and northern fur seal pup production on San Miguel Island coinciding with El Niño events (DeLong and Antonelis 1991; Melin and DeLong 1994; Melin et al. 1996; Melin and DeLong 2000).
Steller Sea Lions also consume many of the same prey resources sought by other predators, including humans (McAlister and Perez 1976; Kajimura and Loughlin 1988; Fritz et al. 1995; Wada 1998; Trites et al. 1999); selective-fishing by humans can cause changes in fish stocks (Pauly et al. 1998).
Predation
The question as to whether top-down forcing as a result of predation by Transient Killer Whales could also limit sea lion populations has garnered much attention in recent years. In 1992, a killer whale stranded in Prince William Alaska had 14 flipper tags from Steller Sea Lion pups in its stomach. While data on predation rates are lacking, simulation models have shown that Transient Killer Whales could potentially have a significant impact on Steller Sea Lion populations, and in particular could inhibit the recovery of depleted populations (Barrett-Lennard et al. 1995).
Maniscalco et al. (2007) estimated that killer whales consumed 3-7% of the Steller Sea Lion population in Kenai Fjords annually, and 11% of pups born at their main study site on Chiswell Island, which could be significant for a species with such an inherently low rate of productivity. Preliminary calculations indicate that even if killer whale predation accounted for all natural mortality, the net annual production of Steller Sea Lion populations in B.C. and the entire Eastern Population could only support roughly 26 and 77 killer whales respectively (Olesiuk, unpublished data).
There are several threats which may affect this population in British Columbia. Threats (both natural and anthropogenic) have caused, or are causing, or may cause harm, death or behavioural changes to a species at risk or the destruction, degradation and/or impairment of its habitat to the extent that population-level effects occur.
The effects of threats are often difficult to distinguish from one another, or from natural limiting factors. For example, exposure to contaminants may render animals more susceptible to natural diseases, and disturbance of sea lions at haulout sites and rookeries may displace them into the water, making them more vulnerable to predation by killer whales. In addition, because animals concentrate at a limited number of breeding sites, they may be more vulnerable to both catastrophic accidents, or localized threats affecting early survival (e.g. localized prey depletion from fishing or disturbance).
Section 1.5.1 provides a tabular summary of the risk assessment rating threats in terms of population-level impacts to Steller Sea Lions. The ‘current level of concern’ and ‘mitigation potential’ for each threat is identified (Table 1). These assessments allow for prioritisation of recommended management and other actions to prevent this population from becoming threatened or endangered, and provide an indication of the mitigation feasibility for a threat. Definitions of the terms used for rankings are available in Appendix I (Table 4).
Section 1.5.2 provides detailed descriptions of twelve historic, current and potential threats to the Steller Sea Lion population in B.C., as well as the uncertainties surrounding population level effects. This text provides the background information used to determine the overall level of concern for the impact of each threat to the Eastern Population (Table 1).
Although there is considerable uncertainty regarding the total impact of threats on Steller Sea Lions in Canadian waters, the continued growth of the local Steller Sea Lion population suggests it is currently within sustainable limits. However, with a population growth rate of about 4.5% per annum, a relatively small increase in human-induced mortality could become an important factor if conditions for Steller Sea Lions deteriorate, or if combined with other threats.
Threats were assessed based on their current likelihood of occurrence and severity of impact on the B.C. population. In addition, the certainty of an effect on the B.C. population was incorporated into the assessment to provide a measure of confidence in the rating of current ‘level of concern’ and to provide an indication of areas where further monitoring or study may be useful in addressing uncertainties or knowledge gaps. Where certainty of effect on the population is not demonstrated, weight of scientific evidence for other pinnipeds or marine mammals may be deemed adequate to contribute to the assessment of the level of concern for a threat.
The mitigation potential column (Table 1) refers to the likelihood that measures (future or existing) will adequately mitigate or prevent negative effects to the population. It should be noted that the current level of concern column reflects the concern for impacts from a threat at this time, and future assessments may result in levels of concern that differ from those presented here. Therefore, the importance of long-term monitoring of the population cannot be overstated.
Table 1: Summary of Threat Classifications and Mitigation Potential for Listed Identified Threats to the Eastern Pacific Steller Sea Lion Population
| Threat | Most vulnerable age class | Limiting factors which are likely to be affected | Severity of population-level impact | Uncertainty of Effect |
Current Level of Concern | Mitigation Potential | |
|---|---|---|---|---|---|---|---|
| Prey Reduction | Fisheries Competition | Juveniles Reproductive Females |
Prey availability Direct impact: Survival Chronic prey limitation may result in decreased reproductive rates |
Potentially High | Medium | Moderate, potentially High |
High |
| Environmental Change and Variability (e.g. Regime Shift)* | Juveniles Reproductive Females |
Prey availability Potential for altered distribution Occurrence of natural diseases Direct impact: Survival Chronic prey limitation may result in decreased reproductive rates |
Potentially High | Medium | Moderate, potentially High |
None, if due to natural fluctuation Low, if due to anthropogenic effects on climate |
|
| Environmental contaminants | Un-regulated Persistent Organic Pollutants (POPs) e.g. PBDEs |
Pups, Adult Females |
Prey quality Increased susceptibility to disease Impaired reproductive rates |
Moderate | Medium-High | Moderate | Low-Medium |
| Regulated POPs e.g. DDT |
Pups, Adult Females |
Prey quality Increased susceptibility to disease Impaired reproductive rates |
Moderate | Medium-High | Low - Moderate | Low -Medium | |
| Disturbance | Physical disturbance when on terrestrial habitat | Pups on rookeries | Pup survival Territorial and breeding behaviours |
Low, at haulouts Moderate, at rookeries |
Medium-High | Low -Moderate | High |
| Acoustic disturbance when in aquatic habitat | All | Habitat use (i.e. displacement from feeding areas) Foraging success Chronic prey limitation may result in decreased reproductive rates |
Likely Low | Medium | Low | High | |
| Toxic Spills | Pups Adult Females, at rookeries during breeding season |
Habitat use Direct impact: Survival |
Low Moderate for Scott Island and Cape St. James rookeries |
Medium-High | Low -Moderate | Low-Medium | |
| Incidental take - fisheries and aquaculture | Unknown | Direct impact: Survival | Low | High | Low | Medium | |
| Entanglement in marine debris | Juveniles and Sub-adults | Foraging success Direct impact: Survival |
Low, potentially severe effects on individual animals | Medium | Low | Medium | |
| Illegal kills | Juveniles and Adults | Direct impact: Survival | Unknown | High | Low | Medium | |
| Predation by Killer Whales* | Pups, Juveniles and Adults |
Direct impact: Survival | Potentially High | Medium | Low | None | |
| Predator control programs | Historically affected all age classes Currently not applicable |
Direct impact: Survival | Historically High Currently Low |
Low | Historically High Currently Negligible |
High | |
| First Nations harvest | All | Direct impact: Survival | Low | High | Negligible | High | |
| Disease and Parasitism* | All | Effects can be enhanced by synergistic effects of threats Direct impact: Survival Reduced reproductive rates |
Unknown | Medium-High | Unknown | Low | |
Mitigation potential refers to the likelihood that measures (future or existing) may mitigate or prevent negative effects to the population. This assessment is a current view of the state of threats to the population, and as such assessment ratings may change over time. Asterisk (*) denotes naturally occurring threats to the population (i.e. limiting factors whose effects can be increased by human activities).
Prey Reduction - Fisheries Competition
Steller Sea Lions consume many of the same prey resources exploited by other predators, including humans (McAlister and Perez 1976; Kajimura and Loughlin 1988; Fritz et al. 1995; Wada 1998; Trites et al. 1999). Commercial harvesting can deplete local abundance and availability of prey (Lowe and Fritz 1997; Fritz and Brown 2005), and harvesting surplus production on a continual basis could affect resilience and amplify the effects of natural prey fluctuations. Because nursing females are restricted to foraging within commuting distance of rookeries during the first few months after giving birth, prey availability around rookeries may be critical in ensuring successful early survival of pups and their nursing mothers.
It is now widely acknowledged that the decline of the Western Population of Steller Sea Lions was, to at least some extent, driven by a change in diet resulting in reduced body growth, birth rates and ultimately survival (Calkins and Goodwin 1988; Calkins et al. 1998; Pitcher et al. 1998; see review by Trites and Donnelly 2003). However, debate continues over the relative influence of fluctuations in environmental conditions and regime shifts that may be the result of global warming, as well as the effects of whaling and commercial fisheries (Pascual and Adkinson 1994; Fritz and Ferrero 1998; Pauly et al. 1998; Trites et al. 1999; Rosen and Trites 2000a; Shima et al. 2000; Benson and Trites 2002; Fritz and Hinkley 2005; Trites et al. 2006; Trites et al. 2007). For additional, prey information see "Environmental Change and Variability".
There are several commercial fisheries that target important known summertime prey species of Steller Sea Lions in British Columbia: sardine, herring, hake, salmon and groundfish. All are currently managed to prescribed catch levels, which are believed to be sustainable. Steller Sea Lion are known to feed on a variety of prey species, and it is not known whether limitations in one prey species alone may limit population growth. Overall prey availability and regional species composition may be altered by natural or anthropogenic factors, and fisheries management will need to balance the needs of a continually growing Steller Sea Lion population with that of fisheries. The non-summer diet of Steller Sea Lions is poorly understood, and as information becomes available, additional species may be identified as important components of the year-round diet of Steller Sea Lions in B.C.
The potential for mitigation of this threat is high (Table 1) as fisheries extractions may be managed directly through Fisheries and Oceans Canada. However, as Steller Sea Lions and their prey are trans-boundary species, adequate mitigation may require additional collaboration and cooperation with U.S. fisheries management.
Given the unrestrained, exponential growth of the Steller Sea Lion population during the last 45 years, competition for prey with commercial fisheries does not appear to have had an effect on the population, leaving moderate concern for impacts. Reduced availability of a high quality prey supply has had a demonstrated negative effect on Steller Sea Lion in the Western Population (Calkins and Goodwin 1988; Calkins et al. 1998; Pitcher et al. 1998; see review by Trites and Donnelly 2003), and prey requirements will continue to increase as the Eastern population continues to grow. Therefore, there is some concern for potential population-level impacts in the future (Table 1). This illustrates the importance of continued monitoring of fisheries, ocean conditions, and the clarification of seasonal prey requirements to forecast any increase in competition with fisheries for prey resources. All of this may assist in development and application of appropriate management measures.
Prey Reduction - Environmental Change and Variability
The degree of natural ecosystem change (which often occurs in discrete steps termed ‘regime shifts’) is dependent on a number of factors, many of which are poorly understood and the causes of which are not always apparent. While regime shifts may be forced by global climate change affecting oceanographic processes (e.g. changes in ocean temperatures, or species distribution), shifts may also occur through processes such as decadal oscillations or El Niño events. Fishing can also cause changes in fish stocks and functioning of marine food webs (Pauly et al. 1998).
As mentioned in ‘Limiting Factors’, climate change and large-scale regime shifts can affect biota throughout the North Pacific (Sinclair et al. 1994; Beamish and Bouillon 1993; Sinclair et al. 1996; Anderson et al. 1997; Anderson and Piatt 1999; Hare et al. 1999; McFarlane et al. 2000; Benson and Trites 2002), and such changes may affect Steller Sea Lion prey distribution within B.C. and range-wide (NMFS 2008). Increases in ocean temperatures resulting from global climate change might be expected to shift the distribution of Steller Sea Lions northward (NMFS 2008), and indeed the species has been disappearing from the southernmost part of their breeding range on both the North American and Asian coasts (Pitcher et al. 2007; Burkanov and Loughlin 2007). The centre of distribution of the breeding population on the west coast of North America has shifted northward from the Columbia River (46.0ºN) in the 1920s to central B.C. (51.5ºN) by 2002 (Pitcher et al. 2007).
The acute impacts that reduced prey availability can have on pinnipeds is evident from the abrupt declines in California sea lion and northern fur seal pup production on San Miguel Island coinciding with El Niño events (DeLong and Antonelis 1991; Melin and DeLong 1994; Melin et al. 1996; Melin and DeLong 2000). A regime shift that alters prey abundance from a high to low energy prey species (e.g. herring to gadids) may affect sea lion vital life history parameters (Trenberth 1990; Springer 1998; Benson and Trites 2002; Trites et al. 2007), resulting in population decline.
Currently, the Steller Sea Lion population in B.C. has exceeded historic peak abundance levels. As populations continue to grow, and prey requirements increase, Steller Sea Lions may become more susceptible to prey shortages. The concern for impacts on population viability from regime shift or climate change is moderate. However, should extreme ecosystem changes occur that result in decreased prey availability, there may be high concerns for population level effects. The high uncertainty regarding occurrence and effects of single regime shift events, or the effects of chronic long-term alterations in ocean conditions (i.e. through global climate changes) indicates that monitoring of the population is prudent. Clarification of seasonally important prey may assist in forecasting impacts to occurrence and distribution of prey species resulting from regime shift.
Environmental Contaminants – Persistent Organic Pollutants
Persistent environmental contaminants such as organochlorine pesticides (e.g. DDT), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polybrominated diphenyl ethers (PBDEs) bioaccumulate in marine food chains. The magnification of such chemicals with increasing position in the food web predisposes many marine mammals to becoming highly contaminated.
In some cases, levels of persistent environmental contaminants have been associated with adverse health effects in free-ranging pinnipeds. Field studies suggest linkages between contaminant levels and reproductive impairment (Helle 1976a,b; Addison 1989), premature births (DeLong et al. 1973; Gilmartin et al. 1976; Martin et al. 1976), birth defects (Arndt 1973), skeletal deformities (Bergman et al. 1992), suppression of the immune response (Mos et al., 2006) and disruption of vitamin A and thyroid hormone physiology (Tabuchi et al. 2006, Mos et al. 2007). Captive feeding studies of harbour seals have also demonstrated deleterious effects of persistent contaminants on the reproductive, immune and endocrine systems (Brouwer et al.. 1989; de Swart et al.. 1994; Ross et al. 1995; Reijnders et al. 1986; Ross et al. 1996) . Results in many of these studies are consistent with the pattern of effects in PCB- or dioxin-exposed laboratory animals (Ross et al. 1997; Ross 2000).
Nursing pups are exposed to particularly high levels of contaminants because fat-soluble chemicals such as PCBs are readily transferred through their mothers’ lipid-rich milk (Hickie et al. 2005). While most persistent contaminants are not likely to cause acute toxicity, they are considered to be endocrine disrupting compounds (‘hormone mimics’; Colborn et al. 1993). As such, they may alter the normal growth and development of exposed animals. In addition, effects may not be notable until a stressful co-factor is implicated, such as a fasting period or period of food shortage which may increase the mobilization of fat-soluble chemicals or add to the stress upon the immune system (Jepson et al. 2005). An additional example might be the introduction of a new virus to a naïve pinniped population, in which contaminant-associated toxicity may cause an increase in vulnerability, virus transmission, disease severity and/or mortality (Ross 2002).
As has been shown in other marine mammals, contaminant concentrations in Steller Sea Lions (predominantly organochlorines) are linked to age and gender. The highest concentrations are found in old males, while females transfer much of their burden to their pups during lactation (Lee et al. 1996). Barron et al. (2003) found that PCB levels in Steller Sea Lions appeared to be declining in the Gulf of Alaska in recent years and that current levels are not a threat, but concentrations of PCB in the 1980s were higher in Steller Sea Lions than in any other pinniped and could have posed a health risk.
In B.C., there have been few systematic studies of contaminant levels in Steller Sea Lions, although studies have recently been initiated to evaluate PCBs and PBDEs. PCB, dioxins, furans and organochlorine pesticides are considered to be regulated, ‘legacy’ contaminants as a result of national and international restrictions on their use, production and/or by-production. However, many new, unregulated chemicals are considered as ‘emerging’ concerns. These include the flame retardant PBDEs, which are doubling every four years in the environment (Hites 2004; Ross 2006). Because PBDEs resemble PCBs, it is likely that PBDEs will be increasingly recognized as a threat to the health of wildlife, including Steller Sea Lions.
This weight of evidence regarding effects and persistence of regulated and unregulated pollutants on Steller Sea Lions leaves concern for effects to the population viability. As the environmental presence and overall usage of emerging, unregulated persistent organic pollutants (POPs) is increasing, the level of concern for this threat is moderate1, while concern for regulated, legacy contaminants is deemed low to moderate (Table 1). However, one might expect the population to be more susceptible during periods of prey limitation and nutritional stress, when lipids with their high concentrations of contaminants are mobilized. As uncertainties on the level of toxic loading in Steller Sea Lions in B.C. remain, monitoring of this threat and mitigation of sources of pollution are recommended.
Though point sources of contamination can be regulated and monitored, potential to implement mitigation measures for this threat is rated low-medium, due to the difficulty in mitigating or managing non-point sources and long-range airborne transport of contaminants. Additionally, sources of contamination that originate in Canada may be mitigated, whereas for contamination that may originate in international waters, the mitigation potential is very low from a Canadian management perspective.
Disturbance on and around Terrestrial Habitat
Repeated disturbances of breeding or haulout sites by aircraft, boats, pedestrians, construction, or fishing activities (e.g. geoduck and urchin dive fisheries) can lead to animals temporarily leaving haulouts and rookeries (Sandegren 1970; Calkins and Curatolo 1980; Johnson et al. 1989; Brown 1997) and can eventually lead to permanent abandonment (Pike and Maxwell 1958; Kenyon 1962).
Vessel disturbance of pinnipeds at haulouts can reflect a suite of influences, including vessel type and number, speed, and distance from animals (Henry and Hammill 2001; Szaniszlo 2005). Interestingly, self propelled vessels (such as kayaks) are demonstrated to elicit behavioural responses from pinnipeds on haulouts (Henry and Hammill 2001), possibly due to these disturbance stimuli illustrating perceived predation risk (Deecke et al. 2002; Frid and Dill 2002). Nonetheless, Steller Sea Lions at winter feeding sites often habituate to chronic disturbances, and some haulout sites are located in high traffic areas close to major urban centres such as Vancouver and Victoria (Bigg 1985; P. Olesiuk pers. comm.). Acute noise disturbances, such as blasting or demolition, near haulouts may result in stampeding of Steller Sea Lions, resulting in pronounced, localized (as opposed to population-wide) disturbances.
Although habituation to human activities may occur at haulouts, Steller Sea Lions are vulnerable to disturbances on rookeries. Human intrusion onto rookeries during breeding season (e.g. to census animals, capture pups for tagging or branding) appears to be highly disruptive and often causes animals to escape into the water or to nearby haulouts (Lewis 1987; Scordino 2006; Olesiuk, unpublished data). Disturbances can result in increased pup mortality due to drowning, trampling or separation of pups from mothers. Recovery times of haulout sites from disturbances such as scat collections is highly variable, ranging from as little as a few hours to as much as a couple of weeks (Kucey 2005; J. Etzkorn, Carmanah Lighthouse, B.C., pers. comm.), but disturbance of rookeries may persist over a number of years (Olesiuk, unpublished data). Additionally, disturbance may have energetic costs for both pups and mothers, should feeding or nursing opportunities be disrupted.
Breeding site fidelity is another factor in disturbance of rookeries. During the control programs conducted prior to 1970, some breeding animals were likely displaced to other rookeries, but the majority of sea lions continued to return to sites that had been heavily disturbed for many consecutive years. At the Sea Otter Group rookery, in spite of intense annual culls, animals continued to use the rookery for 17 years before the colony was completely eradicated. Thus, Steller Sea Lion reproductive biology may not have the plasticity to adapt to disturbances near breeding colonies.
As mentioned above, severity of population level impact is low for haulouts, but moderate for disturbance to rookeries due to site fidelity, potential energetic costs for mothers and pups, and pup survival (Table 1). The mitigation potential for management of this threat is high. At present, access to rookeries is strictly monitored and permits are required for entry onto a known rookery site. Vessel disturbance of pinnipeds is managed via guidelines for viewing marine mammals. Based on the criteria listed above, level of concern for disturbance is rated low to moderate. It should be noted that U.S. regulation maintains a 3 mile no-entry zone surrounding rookeries (in western Alaska), further illustrating the sensitive nature of rookery disturbance.
Acoustic Disturbance in Aquatic Habitat
Operations related to oil and gas exploration, alternative energy development (e.g. wind and wave energy), and other resource extraction (e.g. methyl hydrates) have the potential to disturb animals as they produce both chronic (i.e. from vessel or construction activities) and acute (i.e. seismic surveys) underwater noise.
Acoustic disturbance such as explosions, seismic or military tactical sonar noise may cause displacement of animals from feeding areas, and disrupt foraging behaviour. Canadian seismic surveying standards assist in mitigation of this threat. The Statement of Canadian Practice with respect to the Mitigation of Seismic Sounds in the Marine Environment set out minimum standards that must be met during marine seismic surveys in all non-ice covered marine waters in Canada (http://www.dfo-mpo.gc.ca/oceans-habitat/oceans/im-gi/seismic-sismique/statement-enonce_e.asp). As Steller Sea Lions are able to surface or exit the water to avoid acute noise stress, the concern for acute noise disturbance at feeding sites is low. However, there is currently interest in expansion of offshore fossil fuel exploration and extraction activities, and as such, assessment of this threat should be ongoing as new information on occurrence and frequency of activities in relation to Steller Sea Lion rookeries and feeding areas becomes available. Continued review of development and exploration proposals will ensure that Steller Sea Lion habitat requirements are considered in sustainable development plans.
Chronic noise stress in important foraging areas and near rookeries could have a long-term effect on Steller Sea Lion vital rates and body conditions; however, given the remote locations of rookeries at present, concern remains low (Table 1). Consideration for the placement of industrial developments near rookeries should assist in mitigation of this potential chronic threat. General increase in vessel traffic (motorized and self-propelled) along the B.C. coast has increased the number and frequency of visits to haulout areas. Such in-water acoustic (or visual) disturbance from vessel activity may contribute to increased energetic cost should foraging be disrupted on a long-term scale. Mitigation potential for underwater acoustic disturbance, particularly surrounding rookeries, is high given the National Park Reserves protection surrounding two of the rookeries, and potential review and revision of guidelines and protocols for acute noise disturbance of marine mammals.
Toxic Spills
Sea lions may be impacted by catastrophic accidents such as toxic spills (St. Aubin 1990), although the impact on a population-wide scale has rarely been established. The main threat is likely through contact with heavy oil accumulations when the source of the spill is near important habitats such as rookeries and haulout sites, and to a lesser degree from absorption through the skin, incidental ingestion of oil directly or through feeding, exposure to vapours, and partial fouling of pelage from fresh oil (Smith and Geraci 1975; Engelhardt et al. 1977; Engelhardt 1987; St. Aubin 1990). Sea lions are insulated by a subcutaneous layer of blubber, so oiled fur does not interfere with thermoregulation. Steller Sea Lions with tar lodged in their throats or around their lips, jaw and neck have been observed in Alaska (Calkins and Pitcher 1982).
During the 1989 Exxon Valdez oil spill (EVOS) in Prince William Sound, oil did not persist on the coats of Steller Sea Lions for as long as it did on harbour seals (Calkins et al. 1994a), but sea lions were observed in the vicinity of the oil spill and metabolites in the blood showed they had been exposed to hydrocarbons. Premature births were more common and pup production was somewhat lower in the year following the spill, but limited data prior to EVOS and the ongoing population decline in the area made it difficult to assess the statistical significance of the impact (Calkins et al. 1994b; Loughlin et al. 1996).
Several Steller Sea Lions with small patches of oiled fur were observed during the Nestucca spill that spread along the west coast of Vancouver Island in 1988 (Harding and Englar 1989). Because the population is widely dispersed along the entire B.C. coast, the potential threat of accidental spills is one of local depletion, as opposed to impacting the entire population. However, a spill affecting a rookery during the breeding season could result in a significant population-level impact. Considering that over 70% of pup production in B.C. occurs on the Scott Islands, an oil spill in that area during the breeding season could have a significant impact on breeding animals.
As a population-wide impact has been illustrated to be unlikely, concern for catastrophic spills affecting the population has been rated low (Table 1). However, given that a spill near a rookery (e.g. Scott Islands) during breeding season might impact a large proportion of animals at once, an additional moderate concern is applied for impacts to rookeries during breeding season (Table 1). As spills are accidental, the timing and locations of spill events are difficult to predict. There are currently Canadian regulations and measures to minimize the risk of accidental spills (e.g. Transportation of Dangerous Goods Act) and mitigate effects through remediation of habitat and other measures. The potential for mitigation of this threat is considered low to medium due to the inherent difficulty in, and low success of, post-spill clean-up measures (Graham 2004), particularly in isolated, remote areas.
Incidental Take in Fishing or Aquaculture Gear
Steller Sea Lions are killed incidentally in various fisheries (particularly drift gillnet fisheries for salmon), and there is incomplete fisheries observer coverage to adequately monitor by-catch levels. Animals can get trapped in trawl nets or caught (entrapped) in drift and gill nets, and ultimately drown (Loughlin and Nelson 1986). Unfortunately, once an animal is entangled the potential for rescue or rehabilitation is extremely low, from both a technical and practical standpoint. Annual by-catch in U.S. waters in recent years has been estimated at about 25 animals per year (Loughlin and York 2000; Angliss and Outlaw 2007). No such estimates are available for fisheries in B.C.
Rates of entrapment in finfish aquaculture installations are currently reported via voluntary means in the Pacific Region, which may limit the information regarding these types of interactions. Information from voluntary reporting between 2004 and 2008 indicates only one animal was positively identified as a Steller Sea Lion (drowned as a result of entrapment) and another 12 pinnipeds could not be identified to species2. Accuracy in reporting of species identification has not been determined. However voluntary industry-based training is conducted. Implementation of standardized, voluntary reporting mechanisms is also being pursued to promote improved reporting and documentation of these occurrences. This will result in future improvements regarding information on entrapment rates of Steller Sea Lions in aquaculture gear. At present, there are no aquaculture facilities in Alaska, therefore there are no data available for comparison with incidental take of Steller Sea Lions elsewhere.
Improved reporting on marine mammal entanglements and entrapments by aquaculture operators has led to increased reporting on incidences, however this does not necessarily reflect an increase in number of incidents overall. The level of concern is rated low for this threat, based on the current population estimates for the Steller Sea Lion in B.C. (Table 1). However, proactive measures including siting of aquaculture operations away from haulouts, gear modification (both fisheries and aquaculture), and all reasonable non-lethal means of control at aquaculture sites, to minimize risks of entanglement or entrapment is being used. Methods should be continually reviewed and revised to minimize lethal interactions.
Entanglement in Marine Debris
The increasing prevalence of synthetic debris (net fragments, plastic bags and packing bands, etc.) is a growing problem worldwide and has been implicated in the declines of other species of pinnipeds (Fowler and Merrell 1986; Fowler 1988). Debris such as net fragments and packing bands can get caught around the necks of sea lions, leading to abrasion or cutting deeply into tissue as animals grow. Steller Sea Lions occasionally take fish from troll gear, and it is not uncommon to see animals that have swallowed hooks and are hooked internally with salmon flashers dangling from their mouths. Unfortunately, rescue or rehabilitation of animals entangled in marine debris is usually neither technically, nor practically feasible.
Entanglement rates for Steller Sea Lions in Alaska have been estimated at about 0.07% for adults, with packing bands and net debris being the most common material (Calkins 1985; Mate 1985; Loughlin et al. 1986; Stewart and Yochem 1987; Fowler 1988). On recent research surveys in B.C., approximately 0.2% of animals counted had either debris around their necks or fishing gear hooked in their mouths or throats (Olesiuk, unpublished data). However, as Fowler (1988) noted, much of the debris found at sea or washed ashore may be too large for an animal to transport, so the observed rate of entanglement could represent a small fraction of numbers actually being entangled and drowned at sea. Entanglement of pups and yearlings has not been observed, and it is unclear whether these age groups are able to avoid debris or whether entanglement of smaller animals results in 100% fatality. The marine debris documented to cause entanglements results mainly from lost fishing gear. Modifications to fishing gear may reduce the risk of harmful entanglements and should be considered a potential for successful mitigation of this threat.
The severity of a population-wide impact on Steller Sea Lions as a result of entanglement in marine debris is unknown, however as entanglements have been recorded, it is evident that this threat affects some proportion of the population. Further research may be necessary to address knowledge gaps on the rate of entanglements and their effect on a population-wide scale. Currently, the level of concern regarding entanglement in marine debris is low (Table 1).
Illegal Kills
Illegal and undocumented killing of Steller Sea Lions is likely to occur in B.C., particularly since the species is perceived to have a negative impact on fish stocks and is known to depredate fishing operations. Several cases of illegal kills have been documented (DFO unpublished data), and mortality may also occur outside of the legal parameters assigned to permit holders (e.g. for predator control or subsistence harvest). However, data on these activities are currently lacking, and incidents that occur in remote locations are inherently more difficult to document or monitor. In some remote areas, fishing operations are located near rookeries and haulouts, and further exacerbating the interaction between fisheries and sea lions is the conditioning of pinnipeds to dumping sites for offal and other fish remnants.
The extent of illegal killing of pinnipeds is poorly understood and the impact of such activity at a population-level is unknown. However, given the recent abundance estimates for Steller Sea Lion in B.C. (DFO 2008), it is unlikely that this threat currently impacts population viability (Table 1). Mitigation of this threat requires outreach and communication with affected parties, and education on modification of some practices (e.g. dumping offal, habituation of animals to fishing gear), and increased monitoring and enforcement around Steller Sea Lion haulouts and rookeries. As such there is moderate potential for successful mitigation of this threat.
Predation by Killer Whales
As outlined in ‘Limiting Factors’, killer whales are an important predator having the potential to limit Steller Sea Lion populations. Predation rate on Steller Sea Lion may be increased due to synergistic effects with other threats or limiting factors. The potential for altering predation rate by killer whales due to environmental variability, changes in prey availability (i.e. increased distance required for foraging excursions), or increased incidence of disease may increase the impact of this natural threat on the population viability of Steller Sea Lions in B.C. Impacts on other killer whale prey, such as harbour seals, could result in a shift in killer whale diet and increased predation on sea lions. Disturbances that cause animals to enter the water or move to other sites could also increase exposure to killer whales. Additionally, an increasing trend in population growth for Transient Killer Whales (Ford et al. 2007) indicates that there is potential for the predation rate to increase. Simulation models have shown that Transient Killer Whales could potentially have a significant impact on Steller Sea Lion populations, and in particular could inhibit the recovery of depleted populations (Barrett-Lennard et al. 1995). Preliminary calculations indicate that even if killer whale predation accounted for all natural mortality of Steller Sea Lions, the net annual production of the Steller Sea Lion population in B.C., and the entire Eastern Population could only support roughly 26 and 77 killer whales respectively (P. Olesiuk, unpublished data). This suggests there are also other sources of mortality for these sea lions.
As the Steller Sea Lion population is currently experiencing uninhibited population growth, and alternative prey such as harbour seals are also at high levels, concern for predation-induced population decline is at present minimal (Table 1). Given that mitigation measures for predator-prey interactions are extremely unlikely, monitoring of both the Steller Sea Lion and Transient Killer Whale populations will assist in determining long-term trends in abundance and distribution of both of these species within B.C., and range-wide.
Predator Control Programs
For most of the 20th century, the main factor limiting Steller Sea Lions along the west coast of North America was predator control programs. In B.C., government predator control programs eradicated a major rookery on the Sea Otter Group by the late 1930s, and numbers of sea lions breeding at the remaining rookeries had been reduced to about one-quarter of historic levels by the late 1960s (Bigg 1985). In Washington, the state government offered a bounty payment for Steller Sea Lion kills, and abundance along the Washington coast fell from several thousand in the early 1900s to fewer than a hundred by the late 1940s. Large bounty kills were also made in Oregon in the 1920s (Pearson and Verts 1970), and harassment and killing by bounty hunters and fisherman also reduced abundance of Steller Sea Lions and apparently eliminated several breeding sites in California (Rowly 1929). The Eastern Population of Steller Sea Lions had been severely depleted by the time the species was protected under the Fisheries Act in Canada in 1970 and the Marine Mammal Protection Act in the U.S. in 1972. The only portion of the Eastern Population range that escaped large culls was southeast Alaska, where there are no records of the species breeding or being abundant in the early 1900s.
From 1990 to 2003, legal predator control at finfish aquaculture operations in B.C. constituted one of the largest known sources of human-induced mortality for Steller Sea Lions in the North Pacific (Angliss et al. 2001; Jamieson and Olesiuk 2001). Quarterly reports filed by licence holders indicate that a total of 362 Steller Sea Lions plus 21 sea lions for which species could not be identified, were killed from 1990 (when the first permits were issued) up to 2003. The number of Steller Sea Lions killed annually was initially low (averaging less than 10), but escalated in the late 1990s and peaked at 91 in 1999 (Jamieson and Olesiuk 2001), likely as a result of a shift in winter distribution of sea lions from Barkley to Clayoquot Sound (P. Olesiuk pers. comm.). In 2004, license conditions were modified to remove Steller Sea Lions from the permits to eliminate the use of lethal control for this species due to the COSEWIC designation of this species as special concern. However, many of the 100 or so salmon farms currently operating in B.C. waters possess permits to use lethal means of control for harbour seals and California sea lions, and it is possible that Steller Sea Lions could be shot as a result of being mis-identified as one of these species. Given the low level of current reported kills, the level of concern for this threat is currently assessed as negligible (Table 1).
First Nations Harvest
Traditionally, Steller Sea Lions were hunted by aboriginal peoples in B.C. for use as a food source (Bigg 1985), and whiskers continue to be used on some traditional ceremonial garb. Use of sea lions by First Nations people appears to have declined during the 1800s and sea lion meat has not been an important dietary staple since the early 1900s (Bigg 1985). It is unknown whether subsistence harvesting prior to the 1900s regulated the Steller Sea Lion population in B.C.
Aboriginal hunting of Steller Sea Lions for subsistence and cultural purposes does occasionally occur in Canada, but harvest levels are unknown. First Nations people may hunt sea lions without a licence; nevertheless, Fisheries and Oceans Canada works with First Nations to encourage the use of Communal Licences with harvest limits to ensure removals do not exceed sustainable limits. Given that there are no commercial harvest licences issued for Steller Sea Lions in B.C., and there is very limited subsistence harvest of Steller Sea Lions, the level of concern associated with harvesting is rated as negligible (Table 1). Continued communication with First Nations groups interested in harvesting pinnipeds will assist in assessing future level of concern for population-scale impacts due to harvest.
Disease and Parasitism
Steller Sea Lions in both B.C. and Alaska have exhibited positive screenings for several pathogens (Calkins and Goodwin 1988; Sheffield and Zarnke 1997; Burek et al.. 2003, 2005; Lambourn et al.. 2006), and in general parasites are common to the species (Dailey and Hill 1970, Dailey and Brownell 1972, Fay and Furman 1982, Shults 1986, Gerber et al.. 1993; all cited in NMFS 2008). Although parasites and diseases may have little impact on otherwise healthy animals, effects could become significant if combined with other stresses (Haebler and Moeller 1993). Anthropogenic stressors can also increase the incidence of disease, or introduce foreign pathogens into the population.
Pathogens and diseases from terrestrial sources or exotic species are a concern in terms of exposure of the population to new biological contaminants. Sewage outflow, storm-water and agricultural runoff may play important roles as vectors for pathogens or disease, as do multi-species rehabilitation-reintroduction programs that include pinnipeds.
Mitigation of terrestrial sources of pathogens and exposure to exotic species affecting marine mammals will assist in reducing the risk of transmission of foreign diseases to the Steller Sea Lion population in B.C. Measures to minimize the risk of exposure of rehabilitated pinnipeds to pathogens carried by terrestrial mammals may decrease the likelihood of transmission of disease to pinniped populations. Further, management of sources of outflow and runoff may assist in mitigating this threat. However, given the high degree of uncertainty regarding disease effects, the primary action is to address knowledge gaps on terrestrial sources of pathogens and their potential effects on Steller Sea Lions.
The effects of threats and limiting factors can be difficult to distinguish from one another, making conclusions regarding causes of population decline often difficult to ascertain. Although there is considerable uncertainty as to the total impact of threats on Steller Sea Lions in Canadian waters, the continued growth of the local Steller Sea Lion population suggests it is currently within sustainable limits, and individual or combined effects of threats and limiting factors are not prominent enough to force population decline, or to limit population growth. Nevertheless, with a population growth rate of less than 5% per annum, a relatively small increase in human-induced mortality could become an important factor if conditions for Steller Sea Lions deteriorate, or if combined with other threats. Therefore the importance of targeted research programs addressing knowledge gaps, and long-term monitoring of the population and of identified threats cannot be overemphasized.
Harvest Controls
The conservation and management of Steller Sea Lions in Canada falls under the authority of the Fisheries Act (1985), more specifically the Marine Mammal Regulations (1993) of that Act. With the exception of First Nations peoples, no person can fish for or disturb any marine mammal, unless explicitly authorized by a licence. Under s.6, First Nations people may hunt sea lions without a licence for food, social or ceremonial purposes; however, the use of Communal Licences with harvest limits is common, to ensure removals do not exceed sustainable limits.
Since 1970, the management approach for pinnipeds in British Columbia has not provided for commercial harvest or culls. The only licences issued that allow for killing of sea lions have been to protect stocks at fish farms and herring impoundments from predation. Limited harvests are permitted of “nuisance animals” as defined in the Marine Mammal Regulations (a licence is required under section 26.1(1)(c)), and harvests are monitored to ensure removals are within sustainable levels. In response to Steller Sea Lions being COSEWIC-designated as special concern in 2003, predator control nuisance seal licences issued under section 26.1(1)(c)), since 2004 have prohibited the killing of Steller Sea Lions.
Protection from Disturbance
Section 7 of the Marine Mammal Regulations (Fisheries Act) prohibits the disturbance of marine mammals, unless authorized by a fishing licence or scientific licence. Proposed amendments to these regulations would also provide specific protection from some forms of disturbance such as swimming with, or feeding marine mammals. In addition, guidelines (Be Whale Wise: Marine Mammal Viewing Guidelines for Boaters, Paddlers and Viewers, 2006) have been established to address disturbance from close approaches whether on land or sea, and are often followed for pinniped viewing. Management and educational programs, for the purposes of achieving compliance with the guidelines, have been implemented for the ecotourism industry (e.g. Pacific Whale Watch Association Best Management Practices (http://pacificwhalewatch.org/ ) and the public). Furthermore, the Statement of Canadian Practice with respect to the Mitigation of Seismic Sound in the Marine Environment was developed as a national code of conduct in response to public concerns over the potential impacts of seismic surveys on marine life.
Protection of Habitat
The Fisheries Act (ss. 35, 36) contains provisions for habitat protection and prevention of pollution of marine mammal habitat. The Steller Sea Lion breeding colonies at Triangle and Beresford Islands are located within Anne Vallee (Triangle Island) and Beresford Island Ecological Reserves, respectively. These reserves were established in 1971 by the Province of British Columbia to protect biodiversity. Ecological reserves are closed to entry except as authorized by permit. Environment Canada (Canadian Wildlife Service) is leading a federal government initiative to establish a Marine Wildlife Area (MWA) in the Scott Islands, which will fulfill objectives of the Species at Risk Act by protecting habitat for several nationally listed species at risk, including Steller Sea Lions.
The Steller Sea Lion breeding colony at Cape St James is located within the Gwaii Haanas National Park Reserve and Haida Heritage Site, cooperatively administered by the Parks Canada Agency and the Council of the Haida Nation. Gwaii Haanas National Marine Conservation Area (NMCA) in the southern Queen Charlotte Islands is proposed under the Canada National Parks Act and National Marine Conservation Areas Act to extend 10 km offshore from Gwaii Haanas National Park Reserve and Haida Heritage Site potentially protecting marine habitat for Steller Sea Lion in the area. NMCAs are managed for sustainable use, and protected from industrial activities such as marine dumping, mining, and oil and gas exploration and development.
Numerous Steller Sea Lion haulouts around B.C. are also protected within National or Provincial Parks, such as Pacific Rim and Gulf Islands National Park Reserves, Race Rocks Ecological Reserve, and others.
Department of National Defence (DND) ‘Maritime command order: marine mammal mitigation procedures’ (DND 2007), mitigates disturbance from tactical sonar use by the Canadian military. The Canadian Environmental Protection Act, Polybrominated Diphenyl Ethers Regulation (July 2008) has recently been passed in Parliament. This regulatory tool restricts manufacture and use of several types of PBDEs in Canada, and is a first step toward long term reduction in environmental toxic effects from PBDEs. Additionally, the Canada Shipping Act, Regulation for Prevention of Pollution from Ships and for Dangerous Chemicals addresses marine pollution and debris. These codes of practice and regulatory tools may assist in mitigation of effects to Steller Sea Lion habitat.
Following the coming into force of SARA in 2003, several marine recovery strategies and management plans for ‘at-risk’ marine mammals have been developed. These documents include recommended actions for recovery, protection and management of listed marine mammal species. In a larger context, these management actions may also benefit Eastern Pacific Steller Sea Lions in B.C. Please refer to Section 4 ‘Associated Plans’ for specific recovery strategies and management plans with actions relevant to the protection and management of Steller Sea Lions in B.C.
Fisheries and Oceans Canada, Conservation and Protection Branch responds to, as necessary, and investigates reports of unauthorized lethal take (including attempts) and disturbance to all marine mammals, in the course of general operations. Targeted enforcement of disturbance is focusing on whale oriented viewing, but also addresses the disturbance of pinnipeds, especially when hauled out near populated areas. However, these activities do not significantly overlap with Steller Sea Lion distribution.
Information to assist enforcement and response to incidents is collected by the Marine Mammal Response Program (1-800-465-4336). These initiatives provide information on pinniped incidents, and provide capacity for response actions on a case-by-case basis.
Given the trans-boundary distribution and high mobility of Steller Sea Lions, population assessments need to be coordinated among jurisdictions. This is especially true for B.C. and southeast Alaska, as the largest breeding aggregation of Steller Sea Lions on Forrester Island is situated less than 50 km north of the international border. Following a recommendation of the National Marine Fisheries Service (NMFS) Steller Recovery Plan (NMFS 1992), effort has been made to standardize census techniques (Olesiuk et al. 2008) and coordinate survey schedules between each state and province (DFO 2008), culminating in the first comprehensive assessment of Eastern Population over its entire range (Pitcher et al. 2007).
Key knowledge gaps for Steller Sea Lions in B.C. include diet composition and annual prey requirements, both by age class and by season. The seasonal abundance and distribution of prey species is also poorly understood, as are potentially important foraging areas. As such, the spatial and temporal distribution of fisheries may become increasingly important as these knowledge gaps are addressed and our understanding of Steller Sea Lion feeding ecology is expanded.
Several natural limiting factors are currently poorly understood. In some cases, there are research programs addressing these uncertainties, but results are so far unavailable or inconclusive. Information on key vital rates of Steller Sea Lions are required to determine age and sex specific fecundity and survival rates, age at weaning, and age of first reproduction that regulate population productivity. Further genetic samples of the population within B.C. may foster an increased understanding of dispersal among rookeries, and the genetic makeup of individuals re-colonizing the rookery on the Sea Otter Group.
Seasonal changes in diet or prey requirements are at present unclear for the Steller Sea Lion population in B.C. Of particular uncertainty is their diet outside of the breeding season. Several studies on the summer diet of Steller Sea Lions have indicated that forage fish, such as herring, sandlance and sardines, as well as other mid-sized schooling fishes such as salmon, hake and rockfish (see `Prey Requirements` section) may be important dietary components (Pike 1958; Spalding 1964; Olesiuk and Bigg 1988, Trites and Olesiuk, unpublished data). Additionally studies to address the distribution of these prey will assist in identifying important geographic feeding areas (particularly adjacent to rookeries), and temporal or geographic areas having potential for fisheries interactions.
The importance of killer whale predation as a limiting factor remains somewhat uncertain. While predation by transients is significant, the specific importance of different sex and age classes of sea lions in the diet of transients is unknown. Increasing knowledge of the seasonal distribution of Transient Killer Whales and their diet will assist in determining the degree to which predation regulates Steller sea lion population growth in B.C.
Anthropogenic threats affecting sea lions in North America that require further clarification include:
- The effects of research activities such as disturbances at haulouts and especially rookeries and hot-branding on pup survivorship
- Baseline levels of chemical and biological pollutants in the B.C. population
- The significance of specific fishing and aquaculture gear types (e.g. troll vs. seine nets) in terms of risk of entanglements
- The spatial and temporal distribution of fisheries with respect to important sea lion haulouts and rookeries, as well as the frequency of fisheries interactions, illegal kills or entanglement incidents
1 Regulated and unregulated contaminants of concern are listed in Appendix II.
2 The vast number of pinniped entanglements (110 out of 170) can be attributed to shark guards used at one site, and these have since been removed (DFO unpublished data).
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