Decline of the Steller Sea Lion in Alaskan Waters Untangling Food Webs and Fishing Nets (2003) / Chapter Skim
Currently Skimming:
2. The Environmental Setting
2. The Environmental Setting
Pages 26-38
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From page 26... ...
Physical perturbations, particularly those in upper-ocean temperature, could affect Steller sea lions by changing the distribution and abundance of sea lion prey, competitors, or predators. The physical environment in the western range of the Steller sea lions is profoundly influenced by atmospheric phenomena (e.g., wind stress, heat flux, precipitation)
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From page 28... ...
Tree-ring reconstructions for coastal Alaska and North Pacific surface temperatures provide evidence of multidecadal climatic regime shifts over the past three centuries, though the amplitude of this variability was weak in the mid-1980s (e.g., Ingraham et al., 1998; D'Arrigo et al., 2001; Gedalof and Smith, 2001~. Studies of tree-ring records (Ingraham et al., 1998)
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From page 29... ...
The newly described oscillating control hypothesis (OCH) relates ecosystem changes to changes in atmospheric and oceanic features of the southeastern Bering Sea (Hunt et al., 2002~.
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From page 30... ...
Because low water column temperatures can change the distribution of some forage fish species, the OCH explains why Steller sea lions, other pinnipeds, and piscivorous seabirds may thrive even under cold conditions if forage fish become more available as prey. Warm regimes occur during years when sea ice is either absent or retreats before there is sufficient sunlight to initiate an under-ice bloom.
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From page 31... ...
Unlike the shallow eastern Bering Sea shelf, in the Gulf of Alaska depths greater than 150 m often occur close to the coast. Numerous islands provide habitat for the Steller sea lion.
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From page 32... ...
The allocation of carbon fixation to respiration, storage, and export, as mediated by coupling of pelagic and benthic carbon cycles, is of major interest (Walsh et al., 1989; Walsh, 1995; Rivkin and Legendre, 2001~. Although hemispheric climate variability has been tied to regime shifts, threshold responses in the regional Gulf of Alaska and/or Bering Sea biological ecosystem are more elusive yet critical to understanding the environmental factors potentially acting on the decline of Steller sea lion populations in the region.
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From page 33... ...
The small-mesh Gulf of Alaska trawl survey data analyzed by Anderson and Piatt show an apparent major redistribution in the relative abundance of species closely associated with the 1977 regime shift (see Figure 2.4~. As the relatively cool era of the early 1970s switched to a relatively warm era (in Gulf of Alaska sea surface temperatures and ocean bottom temperatures and wintertime coastal Alaska air temperatures)
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From page 34... ...
Schematic diagram indicates the relative abundance of select marine mammals, fish, and shellfish in the Gulf of Alaska. To clarify multiyear trends a 10-year running average was applied to groundfish, forage fish, and Tugidak harbor seal molt count data.
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From page 35... ...
NPPI, North Pacific Pressure Index; BC SST, British Columbia sea surface temperature from lighthouse stations; trends were smoothed by taking 3-year running averages. SOURCE: Reproduced from Anderson and Piatt (1999~.
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From page 36... ...
Only Arctic cod (Boreogadus saida) occur regularly in the cold pool, whereas the subarctic walleye pollock are variable, moving to the outer continental shelf in cold years (when the cold pool expands)
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From page 37... ...
Data from 1996-2002 on bowhead, fin, and humpback whale population trend data came from Robyn Angliss, National Oceanic and Atmospheric Administration, Marine Mammal Lab in Seattle, personal communication, 2002. Data for the northern fur seal annual pup counts on the Pribilofs came from Anne York, National Marine Fisheries Service, Marine Mammal Lab, Seattle, personal communication, 2002.
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From page 38... ...
, together with anecdotal evidence of declines in shrimp and forage fishes.
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