breeding grounds in the Yukon-Kuskokwim Delta; seabirds such as
common murres, thick-billed murres, and red-legged and black-legged
kittiwakes have also declined significantly in the western Gulf of
Alaska and Aleutian Islands.
Steller sea lion populations in the Bering Sea and western Gulf of
Alaska have declined by approximately 80 percent. In parts of the Gulf
of Alaska, harbor seal numbers have dropped by as much as 90 per-
cent. Sea otter numbers in the Aleutians have fallen by 70 percent
since 1992 and, in some areas of the archipelago, at least 95 percent
since the 1980s.
According to a 1996 report by the National Research Council
(NRC) of the National Academy of Sciences, the region is responding
to a series of natural and anthropogenic impacts that date back decades
and even centuries. According to this “cascade hypothesis,” large
reductions in whales and some fish as a result of over-exploitation
increased the amount of food available for other fish and invertebrates,
so that by the 1960s and early 1970s, the Bering Sea ecosystem
changed from one dominated by capelin to one dominated by pollock.
This change was intensified in 1977 by what is known as a “regime
shift,” in which the region’s sea temperatures increased, to the benefit
of groundfish (except for cold-water species such as turbot) and the
detriment of species such as capelin and sand lance.
According to the NRC thesis, as a result of this regime shift, Steller
sea lions, which previously fed on capelin and herring, were deprived
of their primary food source and forced to subsist on the less nutri-
tionally valuable pollock, initiating the demise of that species.
Environmentalists and many researchers argue that the sea lions’
decline is exacerbated, or their recovery impeded, by intense fishing for
pollock.
A 1998 paper in Science argued that the decline of sea lion popu-
lations was forcing orcas, which normally fed on the pinnipeds, to
switch their attentions to sea otters, and that it was this increased pre-
dation that was largely responsible for the sea otters’ disappearance in
the region. A further result is an increase in the sea urchins on which
sea otters prey, and consequent deforestation by the urchins of kelp
beds in the region. This plethora of natural and human-induced
Alaska and the Western Arctic 105