COSEWIC Assessment and Status Report on the Loggerhead Sea Turtle in Canada 2010 - Biology

Table of Contents

Document Information

• COSEWIC Assessment Summary
• COSEWIC Executive Summary
• Species Information
  • Name and classification
  • Morphological description
  • Genetic description
  • Designatable Units
• Distribution
  • Global range
  • Canadian range
• Habitat
  • Habitat requirements
  • Habitat trends
  • Habitat protection/ownership
• Biology
  • Life cycle and reproduction
  • Physiology
  • Dispersal/migration
  • Interspecific interactions
  • Adaptability
• Population Sizes and Trends
  • Search effort
  • Abundance
  • Fluctuations and trends
  • Rescue effect
• Limiting Factors and Threats
• Special Significance of the Species
• Existing Protection or Other Status Designations
• Technical Summary
• Acknowledgements
• Authorities Consulted
• Information Sources
• Biographical Summary of Report Writer
• Collections Examined

Nesting

Loggerhead Sea Turtles nest on ocean beaches and occasionally estuarine shorelines. They seem to prefer relatively narrow, steeply–sloped, coarse–grained beaches, although nearshore contours may also influence nesting beach site selection (Provancha and Ehrhart 1987). Nesting takes place at night. Females exhibit strong fidelity for the nesting area where they hatched called “natal homing” (Bowen et al. 2005; Bowen and Karl 2007). They nest on a 2–3–year interval. During nesting years, they lay three to four clutches of approximately 112 eggs each with intervals of approximately 14 days between nesting events (Miller 1997). Nests are usually laid between the high–tide line and the dune front (Routa 1968; Witherington 1986; Hailman and Elowson 1992).

Stage 1: Egg to post–hatchling

Loggerhead Sea Turtle eggs hatch after 7–13 weeks of incubation depending on the temperature of the nest (Miller 1997), with a change of 1°C adding or subtracting approximately 5 days to the incubation period (Mrosovsky 1980). The warmer the sand surrounding the egg chamber, the faster embryos develop (Mrosovsky and Yntema 1980). Incubation period, hatchling success and size are influenced by the moisture conditions within the nest (McGehee 1990; Carthy et al. 2003).

The sex of hatchlings is dependent on the temperature of the nest; incubation temperatures above 29°C produce more or all females, and incubation temperatures below 29°C produce more or all males (Limpus et al. 1983, Mrosovsky et al. 1984; Mrosovsky 1988; Marcovaldi et al. 1997; Mrosovsky et al. 2002; Wibbels 2003). Other environmental factors (such as rainfall, moisture conditions, and shade) may directly or indirectly influence sex ratios (Mrosovsky et al. 1995; Godfrey 1997).

Hatchlings pip and escape from their eggs over a 1–3–day interval, and move upward and out of the nest over a 2–4–day interval (Christens 1990). The time from pipping to emergence ranges from 4–7 days (average=4.1 days) (Godfrey and Mrosovsky 1997). Hatchlings emerge at night, and use ambient light from the night sky to guide them to the ocean from their nest (Daniel and Smith 1947; Limpus 1971; Salmon et al. 1992; Witherington 1997; Witherington and Martin 1996; Stewart and Wyneken 2004). Immediately upon emergence, hatchlings begin a period of frenzied activity during which they move from their nest to the surf, swim, and are swept through the surf zone (Carr and Ogren 1960; Carr 1962; Carr 1982; Wyneken and Salmon 1992; Witherington 1995). Post–hatchlings spend their time in neritic waters, where they may stay for a period lasting from weeks to months (Witherington 2002; Bolten 2003). In contrast to hatchlings in the swim–frenzy stage, post–hatchling Loggerhead Sea Turtles are largely inactive, exhibiting only infrequent low–energy swimming, and they feed on a wide variety of floating items, such as the hydroids and copepods commonly associated with Sargassum (Witherington 2002).

Stage 2: Juvenile (1), exclusively oceanic

This oceanic juvenile stage begins when Loggerhead Sea Turtles first enter the oceanic zone, where they move with predominant ocean gyres for several years before returning to neritic foraging and nesting habitats (Pitman 1990; Bowen et al. 1995; Zug et al. 1995; Musick and Limpus 1997; Bolten 2003). Their movements in the oceanic stage are both active and passive relative to surface and subsurface oceanic currents and winds, and turtles may use bathymetric features for orientation (Bolten 2003). They feed primarily on sea jellies and other invertebrates (Bjorndal 1997; Witherington 2002; Frick et al. 2009).

The duration of the oceanic juvenile stage is variable, with individuals leaving the oceanic zone over a wide size range (15 cm–63 cm SCL, TEWG 2009) (Figure 3). Bjorndal et al. (2000) suggest that in the North Atlantic, recruitment out of the oceanic stage begins at 42 cm SCL. Estimates for the duration of the stage range from 7 to 11.5 years (Bjorndal et al. 2000; 2003) to 9 to 24 years (average=14.8 years) (Snover 2002). In the North Pacific, juveniles do not move to neritic habitats until they are larger than 60 cm SCL (Conant et al. 2009).

Stages 3 and 4: Juvenile (2,3), oceanic or neritic benthic juveniles

In neritic waters, Loggerhead Sea Turtles switch to a diet comprised mainly of hard–shelled, benthic invertebrates (Bjorndal 1997; Seney and Musick 2007). Genetic studies indicate that juvenile Loggerhead Sea Turtles recruit to habitat near their natal beaches, creating a modest population structure (Bowen et al. 2005). Small benthic juveniles (2) range from 41–82 cm SCL, and large benthic juveniles (3) range from 63-100 cm SCL (TEWG 2009) (Figure 3). Estimates for the duration of Stages 3 and 4 vary (for a summary, see Heppell et al. 2003b). Bjorndal et al. (2000) estimate the duration from recruitment to 87 cm curved carapace length is 13 to 20 years; Heppell et al. (2003a) estimate 14 to 24 years for growth from 45 to 92 cm SCL.

The shift to neritic waters is not unidirectional; some juveniles in neritic habitats may return to oceanic habitats, and some may never leave oceanic habitats except to reproduce (Eckert and Martins 1989; Hatase et al. 2002a; Bolten 2003; Ehrhart et al. 2003; Schroeder et al. 2003; Bass et al. 2004; Hawkes et al. 2006; McClellan and Read 2007; Casale et al. 2008; Kobayashi et al. 2008; Mansfield et al. 2009; Reich et al. 2010). Casale et al. (2008) describe Stages 3 and 4, as well as the adult life stage, as “opportunistic amphi–habitat stages” during which Loggerhead Sea Turtles choose habitat based on foraging opportunities (Figure 8).

Stage 5: Adult, neritic or oceanic

Recruitment to the adult stage ranges from 82 cm SCL, with full recruitment at 100 cm SCL (TEWG 2009) (Figure 3). Loggerhead Sea Turtles reach sexual maturity between 16 and 34 years of age, depending on the estimate as there is not consensus on this number (Crowder et al. 1994; Heppell et al. 1996; Parham and Zug 1997; Musick 1999; Dalhen et al. 2000; NMFS and SWFSC 2008), and their lifespan can be longer than 57 years (Dalhen et al. 2000; NMFS and SWFSC 2008). To estimate generation time, age at maturity is estimated by taking the mean of some published estimates. These estimates range from ~16–35 years. The mean of these is 25 years (but see Ernst and Lovich 2009, who state the range of estimates is 22–35 years). Similarly, natural mortality rate is not known, as most studies use estimates that include anthropogenic mortality sources and these are the main causes of adult mortality (e.g., fisheries bycatch). Therefore mortality rates of freshwater turtles are used as a proxy. These tend to be around 5% annually, and are often even lower (Ernst and Lovich 2009). Based on these estimates, generation time is calculated as: Gen Time = age at maturity + (1 + 1/annual rate of mortality) = 25 + (1 +1/0.05) = 25 +1 + 20 = 46 years. Another estimate using the TEWG 2009 estimate of 34 years age at maturity plus 12.5 (half of a reproductive lifespan estimated at 25 years, Pianka 1974; Dahlen et al. 2000), gives a generation time of 46.5 years (NMFS and USFWS 2008).

Neritic waters provide important foraging, inter–nesting and migratory habitat for adult Loggerhead Sea Turtles. However, adult Loggerhead Sea Turtles use both neritic and oceanic habitats (Hatatse 2002a; Hawkes et al. 2006; Reich et al. 2010) (Figure 8). In all three studies, females that foraged in oceanic habitats were smaller than those foraging in neritic habitats, although there was overlap (n=2) in body size in females from Japanese nesting colonies (Hatatse 2002a).

Male Loggerhead Sea Turtles never return to land after they hatch, so knowledge of their life history is hampered by access (Bowen and Karl 2007). Studies of nDNA indicate that Loggerhead Sea Turtles have a complex population structure, with male–mediated gene flow (Bowen and Karl 2007). This could be the result of male turtles not homing to their natal beach, or of mating occurring where populations overlap in feeding areas or migratory corridors (Bowen and Karl 2007). However, Bowen and Karl (2007) hypothesize that natal homing occurs in male Loggerhead Sea Turtles because it occurs in Green Sea Turtles (Chelonia mydas).

The sex ratios of juvenile and adult Loggerhead Sea Turtles are relatively poorly understood. Few rookeries have been rigorously studied over multiple years, methodologies are not standardized, and there are many variables at play (Mrosovsky 1994; Wibbels 2003; Conant et al. 2009). Conant et al. (2009) summarize available sex ratio data for North Atlantic Loggerhead Sea Turtles from all stages.

Loggerhead Sea Turtles are ectothermic reptiles. As such, their thermal tolerances affect their distribution and behaviour. Their body temperatures only exceed ambient water temperature by a few degrees (3.8°) Celsius (Spotila and Standora 1985). Preferred temperatures for Loggerhead Sea Turtles range from 13.3°C to 28°C (Hopkins–Murphy et al. 2003). Kobayashi et al.’s (2008) study of Loggerhead Sea Turtles in the North Pacific notes their occurrence in water temperatures ranging from 14.45°C to 19.95°C.

Prolonged exposure to temperatures below 8 to 10°C may cause cold stunning in Loggerhead Sea Turtles, a phenomenon in which disruption in the animal’s metabolic pathways results in a loss of buoyancy and an inability to dive or swim (Witherington and Ehrhart 1989; Morreale et al. 1992; Spotila et al. 1997). Milton and Lutz (2003) suggest that it is the rate of cooling, rather than just the water temperature itself, that precipitates cold stunning. Cold stunning can be lethal.

One additional point of interest from Hawkes et al.’s (2007) satellite tracking study of Loggerhead Sea Turtles is that females made long resting dives of up to 7 h and 24 min, effectively hibernating during colder months. This behaviour was recorded from two animals, and suggests that large numbers of adult Loggerhead Sea Turtles “sit out” cold periods in the winter while exploiting the productive waters in higher latitudes.

Hatchlings in the frenzy stage orient relative to the direction of the waves and the earth’s magnetic field (Lohmann and Lohmann 2003). In the post–hatchling neritic stage, when turtles begin to feed, they are passive relative to the currents and winds (Bolten 2003). Turtles moving into the oceanic zone use both active and passive movements relative to surface and subsurface oceanic currents, winds, and bathymetric features (Bolten 2003). Juvenile turtles are capable of assessing their position in relation to a goal using local cues, and are, therefore, capable of map–based navigation (Avens and Lohmann 2004). General homing during the juvenile neritic stage (Bowen et al. 2005) and natal homing of adult nesting females, as well as data suggesting that post–nesting females make directed migrations (Schroeder et al. 2003), indicate that Loggerhead Sea Turtles in these stages are actively dispersing. Post–nesting females will also swim against prevailing currents and correct their course if they are displaced due to ocean currents (Schroeder et al. 2003).

Bjorndal (2003) notes that there is little quantitative information on the interaction of Loggerhead Sea Turtles with their environment or with other species.

Hybridization

Molecular genetics have confirmed hybridization between the Loggerhead Sea Turtle and Kemp’s Ridley Sea Turtle (Lepidochelys kempii) (Karl et al. 1995; Barber et al. 2003), the Loggerhead Sea Turtle and Hawksbill Sea Turtle (Eretmochelys imbricata) (Karl et al. 1995; Witzell and Schmid 2003), and the Loggerhead Sea Turtle and Green Sea Turtle (Karl et al. 1995; James et al. 2004).

Diet

The diet of oceanic stage Loggerhead Sea Turtles is poorly studied. The most comprehensive review is Bjorndal (1997), who considers the stomach contents of oceanic juveniles found in the Azores and Madeira. These contained salps (including Pyrosoma atlanticum), jellyfish (including Pelagia noctiluca), amphipods that associate with jellyfish (Hyperia medusarum), pteropods (Hyalaea tridentata), the crab Nautilograpsus (=Planes) minutus, the barnacle Lepas anatifera, sygnathid fish Entelurus aequoreus, squid, gastropods (including Janthina spp. and Pterotrachea spp.), and other pelagic coelenterates (primarily siphonophores). In the north Pacific, pelagic Loggerhead Sea Turtles primarily feed on gastropods (Janthina spp.) and Velella velella.

Natural predators

Predation of eggs and hatchlings occurs on almost all nesting beaches. The most common predators at the primary nesting beaches in the United States are Ghost Crabs (Ocypode quadrata), Raccoons (Procyon lotor), feral hogs (Sus scrofa), foxes (Urocyon cinereoargenteus and Vulpes vulpes), Coyotes (Canis latrans), Nine–banded Armadillos (Dasypus novemcinctus), and Red Fire Ants (Solenopsis invicta) (Stancyk 1982; Dodd 1988).

During the juvenile oceanic stage, Loggerhead Sea Turtles are depredated by large carnivorous fish or mammals found in that environment (Bjorndal 2003). Neritic juveniles and oceanic stage juveniles and adults are depredated by large sharks, including Tiger Sharks (Galeocerdo cuvieri), Bull Sharks (Carcharhinus leucas) and Great White Sharks (Carcharodon carcharias), and Killer Whales (Orcinus orca) (Compagno 1984; Witzell 1987; Fergusson et al. 2000; Simpfendorfer et al. 2001; Bjorndal 2003).

Neritic Loggerhead Sea Turtles in the Northwest Atlantic are also harmed by algal blooms such as a red tide. The species that causes most red tides is Karenia brevis. Although Loggerhead Sea Turtles that wash ashore alive during red tide events can recover from symptoms of acute brevitoxicosis (uncoordinated and lethargic despite an otherwise robust appearance), red tides (n=4) along the west coast of Florida have been the cause of Loggerhead Sea Turtle mortality (Redlow et al. 2003).

The lineage of the Loggerhead Sea Turtle stretches back more than 24 million years (Bowen 2003). This longevity is an indication of its ability to adapt to natural changes in both the marine and terrestrial environments it inhabits. However, the ability of Loggerhead Sea Turtles to survive anthropogenic threats is in doubt. The species is in decline worldwide and, given available information about anthropogenic threats to juveniles and adults in neritic and oceanic waters, it has the potential to continue to decline (Conant et al. 2009). Conant et al. (2009) determined that the Loggerhead Sea Turtles found in the northwest Atlantic Ocean and the North Pacific Ocean have a high likelihood of quasi–extinction. Quasi–extinction is a threshold at which the persistence of the species is in question, and in this case was determined using a risk index called “susceptibility to quasi–extinction” (Snover and Heppell 2009). (See Fluctuations and Trends and Limiting Factors and Threats).

There is currently no direct stock assessment of Loggerhead Sea Turtles in Canadian waters. Data for abundance in Canadian waters have been compiled from: McAlpine et al. (2007); Ledwell (2007); Brazner and McMillan (2008); the Canadian Sea Turtle Sightings Database (2009); Lawson (pers. comm. 2009); and Spaven (pers. comm. 2009). The population and nesting trend status of nesting stocks contributing to, or most likely to contribute to, the Loggerhead Sea Turtles found in Canadian waters comes from three recent analyses conducted in the United States: Recovery Plan for the Northwest Atlantic Population of the Loggerhead Sea Turtle (NMFS and USFWS 1998); An Assessment of the Loggerhead Turtle Population in the Western North Atlantic Ocean (TEWG 1999) and the Loggerhead Sea Turtle 2009 Status Review Under the Endangered Species Act (Conant et al. 2009). Their data were derived as follows:

Recovery Plan for the Northwest Atlantic Population of the Loggerhead Sea Turtle (NMFS and USFWS 1998)

Although numbers of nests and nesting females have high annual variability, nesting beach surveys can provide a valuable assessment of changes in the adult Loggerhead Sea Turtle female population because individuals exhibit strong nest site fidelity (Bowen et al. 2005). The value of the assessment depends upon surveys conducted over a sufficiently long time and using standardized effort and methods (Meylan 1982; Gerrodette and Brandon 2000; Reina et al. 2002). Within a nesting season, the number of females is directly related to the number of nests deposited. Clutch frequency for Loggerhead Sea Turtles has been reported as 3 to 5.5 nests per female per season. The conversion from number of nests to number of nesting females is a simple division of nests divided by clutch frequency, calculated over the number of years of available data. Subpopulations are identified as Recovery Units defined as subunits of the species that are geographically or otherwise identifiable and essential to the recovery of the species. There are five Recovery Units for the northwestern Atlantic population of Loggerhead Sea Turtles (Figure 9):

1. Northern Recovery Unit (Florida/Georgia border through southern Virginia)

2. Peninsular Florida Recovery Unit (Florida/Georgia border through Pinellas County, Florida)

3. Dry Tortugas Recovery Unit (islands located west of Key West, Florida)

4. Northern Gulf of Mexico Recovery Unit (Franklin County, Florida, through Texas)

5. Greater Caribbean Recovery Unit (Mexico through French Guiana, The Bahamas, Lesser Antilles, and Greater Antilles)

Figure 9. Location of the four identified Loggerhead Sea Turtle recovery units in the United States. NRU: Northern Recovery Unit; PFRU: Peninsular Florida Recovery Unit; DTRU: Dry Tortugas Recovery Unit; NGMRU: Northern Gulf of Mexico Recovery Unit. From NMFS and USFWS 2008.

An Assessment of the Loggerhead Turtle Population in the Western North Atlantic Ocean (TEWG 1999)

Population trends were estimated for Loggerhead Sea Turtles found in the Western North Atlantic based on nest census data that included only those beaches that were most consistently surveyed; these beaches tended to represent a majority of all nesting activity for each subpopulation. Subpopulations were defined as the five Recovery Units identified in NMFS and SWFSC (2008). Trends were estimated using both simple linear regression and Bayesian state–space modelling approaches.

Status Review Under the Endangered Species Act (Conant et al. 2009)

Populations for each Loggerhead Sea Turtle DPS (see “Designatable Units”) were assessed using two independent analyses.

1. Risk of quasi–extinction. Quasi–extinction is a threshold at which the persistence of the species is in question, and in this case was determined using a risk index called “susceptibility to quasi–extinction” (Snover and Heppell 2009). The approach is based on stochastic projections of observed trends and variability in the numbers of mature females at various nesting beaches. The analysis is based on the available time–series data on the numbers of nests at nesting beaches.

2. Threat matrix analysis. This is a deterministic stage–based population model focused on determining the effects of known anthropogenic mortalities on each DPS with respect to the vital rates of the species. Anthropogenic mortalities were added to natural mortalities, and possible ranges of population growth rates were computed as another metric of population health. This analysis is based on the known biology of the species and anthropogenic mortalities independent of observed nesting beach data.

Data from Atlantic Canadian waters

McAlpine et al. (2007) summarized historical reports of Loggerhead Sea Turtles in Canadian waters, and introduced the first data on Loggerhead Sea Turtles from the Canadian Sea Turtle Network, which included Loggerhead Sea Turtle sightings from 1998–2000. This sighting information has been updated for this report (n=81) (CSTSD 2009). Sightings information in the CSTSD was obtained through a voluntary sea turtle reporting program targeting commercial fishers in Atlantic Canada (Martin and James 2005a). The data are limited not only to those who were aware of the program, but to those who were willing to call in what is a reluctant reporting climate (Martin and James 2005b). In addition the Loggerhead Sea Turtle was listed as a secondary species of interest to the program, with the majority of effort directed to raising awareness about the Leatherback Sea Turtle. The sightings themselves are limited by fishing effort.

Brazner and McMillan (2008) reviewed data recorded by the International Observer Program (IOP) about the Canadian Atlantic pelagic longline fleet from 1999–2006 (which includes information from Javitech 2002 and Javitech 2003) within Canada’s Exclusive Economic Zone. Observer data from before 1999 were not reviewed because turtles were recorded only as “unspecified sea turtle,” not by species. Observations from 1999–2000 were considered underestimates because only those turtles brought on board the boat were recorded when most of the turtles were released by line cutting over the side of the boat. Observer coverage (~10.6%) was estimated as the proportion of total commercial landings that were observed in a given year, season and region. Catch of Loggerhead Sea Turtles per unit of effort was estimated using the total landings from the fishery and the percentage of observer coverage. Difficulties in matching data from the IOP and total landings databases (e.g., estimated vs. actual weights, missing values) introduced bias into estimates of Loggerhead Sea Turtle bycatch; hence, bycatch estimates should be considered minimum numbers, with actual bycatch potentially considerably higher.

Data from Pacific Canadian waters

The British Columbia Cetacean Sightings Network, which also maintains sightings of marine turtles, has records of 31 unidentified sea turtles (Spaven pers. comm. 2009; Wild Whales 2010) some of which may be Loggerhead Sea Turtles. The British Columbia Cetacean Sightings Network is a network of over 1,800 observers across British Columbia, including whale watching operators, lighthouse keepers, charter boat operators, tugboat captains, BC Ferries personnel, researchers, government employees, recreational boaters and coastal residents (Wild Whales 2010). Observers report their sightings via the project website, toll–free line and logbook program (Wild Whales 2010).

Northwest Atlantic Nesting Populations

The following estimates of numbers of nesting females (NF) at each Recovery Unit was calculated from the mean number of nests (NN) derived over a stated timeframe (NMFS and SWFSC 2008). Numbers of NF are approximate and are based on 4.1 nests per female.

Northern Recovery Unit: NF=1,272; NN=5,215 (1989–2008)
Peninsular Florida Recovery Unit: NF=15,735; NN=64,513 (1989–2007)
Dry Tortugas Recovery Unit: NF=60; NN=246 (1995–2004, excluding 2002)
Northern Gulf of Mexico Recovery Unit: NF=221; NN=906 (1995–2007)
Greater Caribbean Recovery Unit: Statistically valid analyses of long–term nesting trends are not available for this unit.

Atlantic Canadian Population

There has been no formal scientific study of the abundance of Loggerhead Sea Turtles in Canadian waters.

Loggerhead Sea Turtles (n=701) in Canadian waters were reported by the International Observer Program. Those animals were incidentally captured by the Canadian Atlantic pelagic longline fleet from 1999–2006 within the Canadian Exclusive Economic Zone, and were found concentrated in offshore areas along the Western Scotian Shelf and Georges Bank off Nova Scotia, and near the Grand Banks off Newfoundland (Brazner and McMillan 2008). Given the degree of IOP coverage (~10.6%), Brazner and McMillan (2008) estimate the incidental catch for the fishery as a whole during that time period was 9,592 Loggerhead Sea Turtles (average=1,199 annually).

The CSTSD has 81 records of Loggerhead Sea Turtles from 1997–2009. The structure of data collection in this instance does not allow for extrapolation to the total number of Loggerhead Sea Turtles in Canada, though it does support the seasonal presence of the species in Canadian waters (Martin and James 2005a; James et al. 2006).

Sightings and observer data collected to date suggest a seasonal population of juvenile Loggerhead Sea Turtles in Atlantic Canada, as does the presence of Loggerhead Sea Turtles in contiguous American waters (Ladzell 1980; Witzell 1999; Javitech 2002; Bolten 2003; Ehrhart et al. 2003; Javitech 2003; Ledwell 2007; McAlpine et al. 2007; Brazner and McMillan 2008; CSTSD 2009; James pers. comm. 2009; Lawson pers. comm. 2009). Although COSEWIC criteria usually focus on the number of mature adults in a population, it is important not to underestimate the importance of the juvenile life stage in Loggerhead Sea Turtles to the species’ survival. Mixed–stock analyses of juvenile Loggerhead Sea Turtles indicate that individuals from genetically distinct nesting assemblages mix extensively in oceanic habitats (Bowen et al. 2005; Bowen and Karl 2007). Therefore, impacts on this population reverberate throughout the nesting habitat (Bowen et al. 2005; Bowen and Karl 2007; Brazner and McMillan 2008; Alfaro Shigueto et al. 2008; Mansfield et al. 2009). Using a stage–based matrix model, Crouse et al. (1987) noted that improving survivorship of the large juvenile and adult stages appeared far more effective in ensuring population maintenance and growth than did increases in egg survivorship or fecundity. Following on this study, Crowder et al. (1994) calculated stage–specific reproductive values:

• Transition from eggs/hatchlings to small juveniles = 40% increase in reproductive value

• Transition from small juveniles to large juveniles increases reproductive value 4.4x

• Transition from large juveniles to sub–adults increases reproductive value more than 14.3x

• Transition from sub–adult to adult increases reproductive value an additional 2.8x

North Pacific Nesting Population

Nesting beaches in Japan, which are the primary contributors to the North Pacific Loggerhead Sea Turtle population, host approximately 2,000 mature females annually (Conant et al. 2009).

Pacific Canadian Population

Abundance of Loggerhead Sea Turtles in Pacific Canada is low; there are no confirmed sightings of Loggerhead Sea Turtles in Pacific Canada (McAlpine et al. 2007, Spaven pers. comm. 2009). However, sightings of Loggerhead Sea Turtles off the coasts of Washington and Alaska suggest that they may occur in British Columbia occasionally (Hodge 1982; Bane 1992; Hodge 1992; Hodge and Wing 2000; McAlpine et al. 2007). Sightings of unidentified sea turtles (n=31) by the British Columbia Cetacean Sightings Network may include Loggerhead Sea Turtles (Spaven pers. comm. 2009; Wild Whales 2010). However, current understanding of oceanic and neritic habitat for North Pacific Loggerhead Sea Turtles indicates the animals occur south of Canadian waters. In oceanic zones, they are found south of 44° N latitude (Bowen et al. 1995; Koch et al. 2006; Peckham and Nichols 2003; Peckham et al. 2007; Kobayashi et al. 2008).

Current data on Loggerhead Sea Turtles in the Canadian context are insufficient to determine fluctuations and trends in the population. It is relevant to use trends from nesting beaches known to, or most likely to, contribute to the Loggerhead Sea Turtles found in Canadian waters as proxies. Generation time for Loggerhead Sea Turtles is estimated at 46 years (50 years according to NMFS and USFWS 2008). Trends for both the northwest Atlantic and north Pacific populations of Loggerhead Sea Turtles are declining (NMFS and USFWS 2008; Conant et al. 2009; TEWG 2009).

Northwest Atlantic

Results from both the Recovery Plan for the Northwest Atlantic Population of the Loggerhead Sea Turtle (NMFS and USFWS 1998), and An Assessment of the Loggerhead Turtle Population in the Western North Atlantic Ocean (TEWG 1999) are included. Numbers represent annual decline rates.

Conant et al. (2009) calculated a declining trend for the Northwest Atlantic DPS among the Recovery Units for which it had sufficient data (Northern Recovery Unit; Peninsular Florida Recovery Unit; Northern Gulf of Mexico Recovery Unit, and Greater Caribbean Recovery Unit). On Mar 10, 2010, The National Marine Fisheries Service and the U.S. Fish and Wildlife Service issued a proposed rule to change the status of North Pacific and Northwest Atlantic Loggerhead Sea Turtles from “threatened” to “endangered” under the Endangered Species Act. The NMFS and USFWS also proposed listing loggerheads around the globe as nine separate populations, each with its own threatened or endangered status.

North Pacific

Data exist for some Japanese nesting beaches back to the 1950s and clearly indicate a significant population decline (Kamezaki et al. 2003). Data from the 1970s suggest a period of population stability for nesting females. In the 1980s, there were increases in nesting numbers. The 1990s, however, was a period of consistent decline in annual nesting, dropping numbers below those from the early 1980s. Two beaches in particular suffered major declines: Hiwasa (89% decline) and Minabe (74% decline). The lowest nesting numbers recorded for most beaches were during 1997–1999. (All data on Pacific nesting from Kamezaki et al. 2003.) Snover (2008) recently confirmed a general downward nesting trend in Japanese nesting beaches from 1989 (between 6,000–7,000 nests) and 2007 (between 3,000–4,000 nests).

Conant et al. (2009) calculated a high susceptibility to quasi–extinction (SQE) for both the North–west Atlantic and the North Pacific Ocean DPS. SQE for Loggerhead Sea Turtles was given a value of 0.3. The North Pacific DPS reached SQE = 0.3 at approximately 3% of the current female abundance. In each DPS, the threshold of SQE = 0.3 was reached at QET < 0.3, indicating high likelihood of quasi–extinction over a wide range of QET values (Conant et al. 2009).

Loggerhead Sea Turtle populations worldwide are in decline and have the potential to decline in the future. As noted above, Conant et al. (2009) argue that the northwest Atlantic and north Pacific populations have reached the quasi–extinction threshold.

The highly–migratory behaviour of Loggerhead Sea Turtles makes them a shared resource among many countries. Therefore, international conservation efforts are interdependent (NMFS and USFWS 2008). The loss of any of the world’s discrete population segments (n=9) would result in a significant gap in the range of the taxon (Hatase 2002b; Conant et al. 2009).

In the Atlantic Ocean, Canada hosts a juvenile population of Loggerhead Sea Turtles (Ladzell 1980; Witzell 1999; Javitech 2002; Bolten 2003; Ehrhart et al. 2003; Javitech 2003; Ledwell 2007; McAlpine et al. 2007; Brazner and McMillan 2008; CSTSD 2009; James pers. comm. 2009; Lawson pers. comm. 2009). Mixed–stock analyses of juvenile Loggerhead Sea Turtles indicate that individuals from genetically distinct nesting assemblages mix extensively in oceanic habitats (Bowen et al. 2005; Bowen and Karl 2007). Juvenile Loggerhead Sea Turtles have the highest reproductive value to the species (Crowder et al. 1994). Mansfield et al. (2009) note that “localized sources of mortality affecting juvenile loggerheads will ultimately translate to population impacts among all USA loggerhead subpopulations.” Crowder (2000) and Lewison et al. (2004) discuss the responsibility of nations whose pelagic longline fisheries, like Canada’s, take Loggerhead Sea Turtles as bycatch; they state, “the basin–wide distributions of both pelagic longline effort and sea turtles…suggest that effective protection for loggerheads and leatherbacks will require coordinated international action.” The importance of conserving the population of Loggerhead Sea Turtles found in Atlantic Canadian waters should not be underestimated.