Adults usually forage and live near their natal colonies and return to these sites to breed. From: Encyclopedia of Marine Mammals (Third Edition), 2018, Thomas R. Loughlin, in Encyclopedia of Marine Mammals (Second Edition), 2009. Figure 3. Holmes and York (2003) and Holmes et al. Steller sea lion distribution (in yellow) in the North Pacific Ocean. Careful attention to head and muzzle size and shape, overall coloration, and length and width of fore- and hind-flippers permits separation. 1984). comm.) Steller's sea lions occur in coastal waters of the North Pacific Rim from southern California to northern Japan, and in the Bering Sea. The upper postcanine number five is double rooted, with the crown directed backward, and does not occlude with lower postcanine five; all other postcanines are single rooted, slant forward somewhat, and have irregular conical pointed crowns. 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. Data have been grouped and totalled into 5-year periods, and are colour-coded by major breeding area. 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). C'est la seule espèce du genre Eumetopias. 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. 1996; Loughlin 1997). Steller sea lion. are generally situated in exposed areas along the outer coast, and are comprised of rocky islets and ledges. However, given the recent abundance estimates for Steller Sea Lion in B.C. A pale adult female vocalizing. 4.49). 1983; Merrick and Loughlin 1997). 1998; Loughlin et al. Les mâles sont quatre fois plus lourds que les femelles et les plus gros peuvent atteindre 1 tonne pour une longueur de 3 m.Une femelle pèse environ 270 kg pour 2,20 m de longueur. Stellers have deep voices and produce powerful low-frequency rolling roars that can be heard for long distances over the noise of wind and waves. 2007). Figure 4.49. The western population occupies the Bering Sea, Aleutian and Commander Islands, and remote locations of the Russian Far East. That idea was tried and failed, perhaps because the harvesting regime preferentially killed those females that tended to reproduce at a younger age. Given the low level of current reported kills, the level of concern for this threat is currently assessed as negligible (Table 1). 2003), otariids generally exhibit lower survival rates, and expanding populations have not attained that level of productivity. Smaller Steller sea lions, in the size range of large California sea lions, appear more muscular and powerfully built than the California sea lions, which look more rounded and streamlined. In a larger context, these management actions may also benefit Eastern Pacific Steller Sea Lions in B.C. Robert B. Steller Sea Lions may have the potential for serving as an indicator of the general status of coastal marine ecosystems. Roaring males often bob their head up and down while vocalizing. The later models suggested that over the course of the decline, the demographic causes of the decline have changed from low juvenile survival to a combination of low juvenile survival and low adult survival to an increase in survival now in combination with low fecundity. 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. 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. Northern sea lion range extending along the North American Coast, the Bering Sea, and into Asia. Acoustic disturbance such as explosions, seismic or military tactical sonar noise may cause displacement of animals from feeding areas, and disrupt foraging behaviour. Cape Olyutorsky, Russia. The eastern population is dispersed along the west coast of North America, numbers approximately 52,000 individuals, is increasing slowly overall, and is listed as “threatened” as per ESA. coast, the potential threat of accidental spills is one of local depletion, as opposed to impacting the entire population. The western population is listed as “endangered” as per ESA. The Steller sea lion (or northern sea lion), Eumetopias jubatus, is the largest otariid pinniped and one of the more aesthetically appealing sea lions (Loughlin et al., 1987).In Greek, Eumetopias means having a well-developed, broad forehead; in Latin jubatus means having a mane, as in the male. Both sexes become blonder with age. This indicates that the increase in Canada represented real population growth, and not merely a local shift in distribution (Pitcher et al. Consideration for the placement of industrial developments near rookeries should assist in mitigation of this potential chronic threat. The rest of the dorsal surface, and the palms of both foreflippers are covered with a hairless black leathery skin. As populations in B.C. 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. The low productivity of Steller Sea Lions can be attributed to a combination of low reproductive potential and high mortality. In combination, these fisheries remove millions of metric tons of fish. 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. California sea lions are the most likely species to be confused with Steller sea lions. 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. 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. Mortality of newborn pups (< 1 month) is high (Pike and Maxwell 1958; Orr and Poulter 1967). 1986; Ross 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. Longues et larges, ses nageoires pectorales lui permettent de se diriger sous l'… herring) to low-fat fishes (i.e. 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. through global climate changes) indicates that monitoring of the population is prudent. 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). The western Alaska population of Steller sea lions (Eumetopias jubatus) declined by 75% between 1976 and 1990, with subsequent continuing declines of the western stock resulting in its listing in 1997 as an endangered species under the US Endangered Species Act. 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. 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). Endangered for the western subspecies and Least Concern for the eastern (Loughlin’s) subspecies. Adult females are about 2.5 m and 273 kg. Steller sea lions may be affected by commercial fishing directly through incidental catch in nets, by entanglement in derelict debris, by shooting, or indirectly through competition for prey, disturbance, or disruption of prey schools (Alverson, 1992). Therefore, availability of high quality prey near rookeries appears to be a potentially important limiting factor. These reserves were established in 1971 by the Province of British Columbia to protect biodiversity. 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. Threats and status Steller sea lions have been important to the native people living near them for millennia. Females with dependent young may stay at a single haulout or move their pups around between haulouts (Shusterman 1981; Loughlin et al. Methods should be continually reviewed and revised to minimize lethal interactions. Within Canada, Steller Sea Lions occur only in British Columbia and constitute part of the Eastern Population (Bickham 2000). California. LesBaleines • July 27, 2018 84 Pins • 11 Followers Post Comment. dumping offal, habituation of animals to fishing gear), and increased monitoring and enforcement around Steller Sea Lion haulouts and rookeries. 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. 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. The hindflippers have short hair covering part of the proximal end of the flipper, and the rest of the dorsal surface, and the entire sole is covered in black leathery hairless skin. unpublished data). The highest concentrations are found in old males, while females transfer much of their burden to their pups during lactation (Lee et al. Therefore, there is much rookery contact all year around, and fecal discharge following feeding is near shore and on haul-out sites rather than 100 to 200 km offshore, as occurs with Northern fur seals. Females can nurse juveniles in their third year. 1999; Rosen and Trites 2000a; Shima et al. Glenn R. Van Blaricom, ... Robert L. 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. Key knowledge gaps for Steller Sea Lions in B.C. Steller Sea Lions exhibit high site fidelity for breeding and birthing. occurs on the Scott Islands, an oil spill in that area during the breeding season could have a significant impact on breeding animals. Abundance in Canadian waters was estimated to be 20,000-28,000 based on the most recent survey in 2006 (DFO 2008). Steller's sea lions feed extensively on groundfish species, such as walleye pollock, targeted by fisheries. Since 2000, the trend has been a slight increase in numbers overall, but the western Steller sea lion DPS remains Endangered under the US Endangered Species Act. eider de Steller. Adult females and juveniles have no crest and have only a minor forehead dip in front of the eyes and appear to be almost flat from the crown to the tip of the nose. 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. 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. However, the perception that the unexplained portion of the decline of the Western Stock began in the eastern Aleutians may be colored somewhat by changes that likely resulted from the massive harvests of pups (the entire annual production for three straight years) and associated disturbance of adults at the largest of the rookeries in that region in 1970–1972. Maniscalco et al. Predation by Killer WhalesAs outlined in ‘Limiting Factors’, killer whales are an important predator having the potential to limit Steller Sea Lion populations. The effects of threats are often difficult to distinguish from one another, or from natural limiting factors. However, many of the 100 or so salmon farms currently operating in B.C. 4.50(a)). Determination that competition with fisheries is contributing to the decline could result in forced reduction of fishing effort, with great economic loss and political discord. 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. 2000; NMFS 2001; Gallucci et al. (modified from Loughlin 1997 and Sease et al. The current estimate of the population is 5.4 million (Hammill and Stenson, 2007); approximately 18–20% of the population is young of the year. Steller Sea Lions are widely perceived to be an important component of the coastal marine ecosystem, and contribute to the eco-tourism industry. Basic knowledge of seasonal and regional feeding habits of sea lions in B.C. 1999; McFarlane et al. 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). 1999); selective-fishing by humans can cause changes in fish stocks (Pauly et al. 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. 9:33. 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. 2006). Unfortunately, rescue or rehabilitation of animals entangled in marine debris is usually neither technically, nor practically feasible. 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 groundfish fisheries of the Gulf of Alaska and the Bering Sea are the most valuable and highly capitalized of the fisheries in the coastal waters of the US. 1999). However, a spill affecting a rookery during the breeding season could result in a significant population-level impact. localized prey depletion from fishing or disturbance). has averaged about 185 million kg over the last decade (DFO 2007). Follow. Moreover, studies such as Trites et al. Measures to reduce the perceived competition between sea lions and fisheries for ground fish stocks include the establishment of “buffer” (no-trawl) areas to include important locations where the sea lions breed, feed, and rest, as well as specifying a pollock harvest which is more evenly distributed over the remaining areas and spread throughout the year. They once bred in the Channel Islands, but are now rarely seen south of Monterey Bay. Because of these dynamics and the very long south-to-north and warm-to-cold-water distribution of the Steller range and the lack of long-distance migration cycles, certain discrete or local colonies and herds have been unequally affected. 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. 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. About 70 percent of the Steller sea lion population resides in Alaska.
Atalanta Bergame Pays,
Médecin Généraliste Lyon 2 Confluence,
Gorge Du Doux,
Pierre De Volcan Mots Fléchés,
Gratte Ciel Villeurbanne Aujourd'hui,
Pneu Tubeless Moto,
Rationalité Limitée Et Rationalité Parfaite,
Regroupement Familial Suisse Permis B,