Rapid Decline of Kittlitz’s Murrelets in Alaska

The Problem

• Kittlitz’s murrelet (Brachyramphus brevirostris), a small seabird whose breeding range is restricted to the coastlines of western Alaska and the Russian Far East, is apparently in serious decline in Alaska, and has been nominated as a candidate for listing under the U.S. Endangered Species Act (ESA).
• According to studies by the U.S. Fish and Wildlife Service (USFWS), Kittlitz’s murrelets in Alaska have declined by as much 84% in Prince William Sound since 1989, and may disappear from the region completely within 30 years. The species’ local population in the Malaspina Forelands apparently declined by at least 38%, and perhaps as much as 75%, between 1992 and 2002. In the Kenai Fjords area, it’s estimated that the Kittlitz’s murrelet population has declined by as much as 83% since 1976. The USFWS predicts that, if present trends continue, the species could disappear from the Glacier Bay region sometime in the next 40 years.

The Causes

• The cause, or causes, of the species’ decline in Alaska remain uncertain, although some hypotheses have been advanced. At least two known causes of human-induced mortality of Kittlitz’s murrelets have been identified—oil spills, and incidental entanglement in fisheries—although their impact on population levels have not been determined.
• Because they are small-bodied, near-shore divers, murrelets are vulnerable to being caught and drowned in gill nets used for salmon fisheries. The same traits make them highly susceptible to oil spills.
• It is believed that the Prince William Sound population may have been severely impacted by the 1989 Exxon Valdez oil spill, but their low numbers and scattered distribution precluded an accurate determination of the extent of mortality.
• It is possible that murrelets are disturbed by marine vessel traffic or even helicopter flights over their nesting areas; the birds’ preferred habitats, near tidewater glaciers, are prime destinations for tour and cruise ships, and the species’ primary breeding areas in Alaska—the Kenai Fjords, Prince William Sound, and Glacier Bay—are all experiencing increases in tour operations.
• One hypothesis that is gaining currency among researchers is that a significant part of the species’ decline in Alaska may be related to the retreat of tidewater glaciers. Most glaciers in Alaska, including many of those surrounding Glacier Bay and Prince William Sound, have been receding since the turn of the century; studies in other regions have recorded low biological productivity in fjords with receding glaciers, as a result of increased sedimentation and lowered salinity. These factors could result in fewer forage fish for the murrelets, while the sedimentation might reduce the birds' ability to see and catch prey.
• It is also possible that broader changes in the marine environment, prompted by over-fishing and both natural and anthropogenic climate change, among others, may have caused changes in the Kittlitz’s murrelets’ available prey species.

The Context

• Assessing the impacts on, and status of, the Kittlitz’s murrelet is difficult because much about their numbers and trends remains uncertain. It is believed, however, that the global population is less than 20,000 and is perhaps as low as 9,000.
• The highest murrelet densities can be found along the glaciated coasts of southern and southeastern Alaska. Little is known about the species’ winter distribution. Most North American murrelets appear to spend the winter in the open waters of the Gulf of Alaska or the Bering Sea. Russian-breeding birds winter in ice-free waters of the Bering Sea and the Sea of Okhotsk, perhaps as far south as northern Japan.
• The declines in Kittlitz’s murrelets reflect a wide range of changes in the marine environment of the Gulf of Alaska and Bering Sea region, including declines in Steller sea lions, harbor seals, sea otters, and several taxa of waterfowl, as well as a series of anomalous events including several mass mortalities of seabirds. The favored explanation for these changes is a complicated interaction of human impacts including historical whaling and fishing, on-going over-exploitation by commercial fisheries, and natural and anthropogenic climate changes.

Further Reading

Day, R.H. and Nigro, D.A.  2004.  Is the Kittlitz’s Murrelet exhibiting reproductive problems in Prince William Sound, Alaska?  Waterbirds 27(1): 89-95.

Day, R.H., Nigro, D.A. and Prichard, A.K.  2000.  At-sea habitat use by the Kittlitz’s Murrelet Brachyramphus brevirostris in nearshore waters of Prince William Sound, Alaska.  Marine Ornithology 28: 105–114.