A large and extensive seabird die-off occurred in Alaska in summer 1997.
Short-tailed Shearwaters died from the western Gulf of Alaska to the Chukchi Sea. Other species also died in parts of this area: Black-legged Kittiwakes on the Alaska Peninsula, and murres and some other species in small parts of the west and north. Mortality lasted from mid-May to early September and spanned about a week in each area.
This die-off was very
widely reported, considering that the entire
area has no roads
and few human residents. Calls came from villagers, fishermen, and diverse
biologists. Ground surveys were conducted on 21 beaches and aerial surveys
on four. (Numbers of birds on beaches suggest relative mortality but are
not precise indices.) Cooperators sent specimens from 20 locations.
The first phase of
the die-off involved Common Murres in western
Alaska in the last
week of May. Dead birds were reported in waters between Nunivak Island
and the mainland, and 1-2/km were counted on beaches.
The next reported mortality
was in waters of northern St. Lawrence
Island at the end
of July. Several hundred carcasses included murres, Horned Puffins, Black-legged
Kittiwakes, Short-tailed Shearwaters, and small numbers of other species.
During the first week
of August, Short-tailed Shearwaters and
Black-legged Kittiwakes
died on both sides of the Alaska Peninsula (the "tail" of Alaska that extends
southwest towards the Aleutians). "Thousands" of dead birds were reported
in tide rips near shore. The die-off covered the entire lower half of the
peninsula, as confirmed by a 2-day aerial survey. Beaches surveyed by foot
had 5-50 dead Short-tailed Shearwaters and 1-20 Black-legged Kittiwakes/km.
Dead storm-petrels also were reported on one beach.
Short-tailed Shearwaters
began dying over a huge area of the Bering
Sea at about the same
time. Freshly dead birds (as well as flocks of live ones) were seen on
both sides of the Aleutian Islands as far west as Adak in the first week
of August, on the Pribilofs and near Anadyr (Russia) a week later, and
on the north shore of Bristol bay in the third week of August. Densities
on beaches ranged from 50/km on Adak to 350/km on Nunivak Island.
Mortality of Thick-billed
and Common Murres, Black-legged
Kittiwakes, and Short-tailed
Shearwaters was reported in the Chukchi Sea between Kotzebue and Point
Hope in the last week of August. A few shearwaters were found at Cape Lisburne,
on Alaska's northwest corner.
Numerous reports were
received of birds behaving unusually. Flocks
of shearwaters were
seen feeding within 100m of shore. Shearwaters and kittiwakes in the Gulf
of Alaska were attempting to grab food out of fishing gear and sometimes
perching on vessels. Flocks of shearwaters commonly included moribund birds
that did not fly at the approach of a vessel. Several shearwaters were
seen up to 30 km inland on rivers and freshwater lakes. Murres had lower
than normal breeding success in the Pribilofs (G.V. Byrd and A.L. Sowls,
unpubl. data). Dead birds were thin and light in weight.
Most Alaskan seabirds
appear not to have been affected. There was
no mortality in the
northern and eastern Gulf of Alaska. No species died off other than those
listed above, although 38 species breed in Alaska and 2 shearwaters visit
during the summer. Breeding success of kittiwakes, which is highly sensitive
to availability of suitable prey at the surface, was normal in most areas
studied, including the Pribilof Islands (G.V. Byrd and A.L. Sowls, unpubl.
data). (Data on kittiwake productivity are still being analyzed for some
breeding colonies.We have none for 1997 on the south side of the Alaska
Peninsula, unfortunately.)
Unusual conditions prevailed at sea in the Gulf of Alaska and southern Bering Sea in summer 1997. Surface waters were very warm, and waters in eastern Bristol Bay were highly stratified (G.L. Hunt, unpubl. data). Several researchers and fishermen reported extensive areas of weirdly beautiful pale-aqua water in the Bering Sea. Hunt has identified this phenomenon as a bloom of Coccolithophorid phytoplankton.
The condition and behavior of the birds, and what is known so far about water conditions, suggest that starvation was an important factor in the 1997. However, necropsy of specimens from various locations will help indicate whether disease or parasites may have contributed significantly. Further information about oceanographic conditions also will help.--Vivian M. Mendenhall, U.S. Fish and Wildlife Service <vivian_mendenhall@mail.fws.gov>