North Pacific right whale (Eubalaena japonica) COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
Whaling
Traditional whaling around Japan and Korea greatly reduced the population of right whales from the western North Pacific (Gaskin 1987). In the eastern North Pacific, Monks et al. (2001) states that right whales were hunted by central and northern Nuu-chah-nulth (Nootkan) tribes and they were pursued whenever they were seen. The Haida of the Queen Charlotte Islands also may have whaled, although it is unknown whether right whales were taken (Acheson and Wigen 2002). Various aboriginal peoples from Washington State were known to take this species (Mitchell 1979), although it was not usually the main target of their hunts, nor was it taken in great numbers (Brownell et al. 2001).
Commercial open-boat whaling for right whales began in the North Pacific in 1835 and was most intense during the decade 1839-1848, which accounted for approximately 80 percent of the historic commercial catch of right whales (Scarff 1991, 2001). The estimated right whale catches by American whalers amounted to at least 14,500 animals (Best 1987, IWC 1986), and Scarff (2001) estimates that the total whaling-related mortality during the period 1839-1909, including mortality of struck-but-lost whales and non-American whalers, was in the range of 26,500-37,000 animals.
Although right whales received some international protection starting as early as 1935, important North Pacific whaling countries--Japan and the Soviet Union--did not sign the international convention and continued whaling through World War II (Scarff 1986). The first comprehensive prohibition on commercial whaling, including shore-based whaling agreed to by all the major North Pacific whaling nations, did not take effect until 1946. However, “research whaling” was still permitted under this treaty and Japan legally took 13 right whales and the Soviet Union killed 10 right whales during the 1950s and 1960s.
Illegal whaling in the North Pacific also occurred on a much larger scale. Brownell et al. (2001) factored in illegal hunting by the Soviet Union in order to address the question of the present status of North Pacific right whales. Hundreds of right whales were illegally hunted in the Kuril Islands and the Okhotsk Sea, and 372 were killed in the eastern North Pacific, notably the Gulf of Alaska and southeastern Bering Sea (Yablokov 1994, Zemsky et al. 1995, Tormosov et al. 1998, Doroshenko 2000, Brownell et al. 2001). Remnant populations may have been gradually recovering from intense commercial whaling until the 1960s, when these illegal Soviet catches compromised this recovery (Brownell et al. 2001).
In Canadian waters, aboriginal whaling is not illegal but it is not currently practiced in British Columbia. Should aboriginal whaling be renewed in British Columbia, it is very unlikely that right whales would be targets.
Population Numbers and Genetic Diversity
Eastern North Pacific right whales have a critically small population (maybe a few tens of animals), which could result in low reproduction from the demographic effects of small population size and they are at high risk from stochastic effects, which could limit their recovery.
Marine Traffic and Ship Strikes
Ship strikes are the most significant documented human-induced source of mortality for right whales in the western North Atlantic (Knowlton and Kraus 2001). It is not known to be a significant source of mortality in the eastern North Pacific. However, this threat is likely under-reported for all whales in the waters off western Canada due to the remoteness of most of the coast.
Entanglement in Fishing Gear
Entanglement in fishing gear is another major source of mortality for western North Atlantic right whales (Kraus 1990, Kenney and Kraus 1993, Knowlton and Kraus 2001, Clapham et al. 1999, IWC 2001b). It is possible that right whales in the eastern North Pacific are also vulnerable to this source of mortality given the use of similar types of fishing gear in their historic range. T. Miyashita reported an entangled whale in the Okhotsk Sea in 1992 (Brownell et al. 2001). The Russian gill net fishery was implicated in the death of two right whales: one in 1983, and the other off the Kamchatka Peninsula (Russia) in 1989 (NMFS 1991, Kornev 1994). Although entangled whales have not been reported in the Bering Sea and further south into Canadian waters, there are extensive fisheries in the eastern Bering Sea and entanglements can be considered a threat to right whales.
Noise
Right whales are thought to use sound for communication, navigation, attracting mates, or detection of predators and prey (Clark 1994, McDonald and Moore 2002). Sources of ambient noise from human activity include seismic testing for oil and gas exploration, active sonar and explosives testing by the military, underwater noisemakers to deter marine mammals from fishing nets and fish pens, marine experiments that involve the use of loud sounds, and increasing levels of noise from everyday boat and ship traffic (Anonymous 2000).
Man-made noise could potentially interfere with acoustic communication, particularly since the major sound energy from shipping overlaps the lower frequencies of right whale signals (Richardson et al. 1995, Kenney 2001). It is possible that high levels of ambient noise in the ocean could lead to displacement from migration routes or important habitats, disrupt the communication ability of right whales such as mating calls over large distances, perhaps reducing mating opportunities. Such activities should be of concern in Canadian waters, particularly in areas where oil and gas exploration, pipeline construction, high levels of marine traffic and military exercises are conducted or proposed.
Climate Change and Food Supply
Climate-driven regime shifts can cause major changes in ecological relationships over large-scale oceanographic areas (Francis and Hare 1994), and are manifested faster at lower trophic levels in marine ecosystems (Benson and Trites 2002). Right whales feed exclusively on zooplankton, and primarily on large calanoid copepods. They have a narrow range of acceptable prey species and require prey in high concentrations. The presence of such concentrations is dependent upon physical factors, such as water structure, currents, and temperature. This combination of a narrow range of prey, and the requirement of high concentrations of prey dependent upon physical factors might make the right whale more sensitive than other cetaceans to impacts from global climate change (Kenney 2001).
Pollution
The effect of pollution and contaminants on the recovery of eastern North Pacific right whales is unknown. In general, right whales feed on copepods in various depths of the water column from the surface to the bottom. In convergent zones and slicks where surface currents concentrate flotsam and jetsam, they are susceptible to ingesting contaminants, oil, and floating garbage.
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