Wealth of Steller studies barely touch theories of sea lions' decline

welchlanieLR.jpg In 1751, Georg Wilhelm Steller published the first scientific paper on Steller sea lions. Since then, 272 papers and articles have been written about the species. To learn more about what scientists have learned about Steller sea lions over the past two centuries, check out an annotated bibliography compiled by Andrew Trites and Andrea Hunter that has just been published.

It identifies areas of research that have been undertaken to date and whether they address the leading hypotheses proposed to explain the population decline in Alaska. In all, Trites and Hunter found 111 publications in scientific journals, and 161 other documents, such as technical reports, unpublished reports and dissertations.

According to the first newsletter from the North Pacific Universities Marine Mammal Research Consortium, the total number of Steller sea lion articles published per decade has risen exponentially from four in the 1940s to 128 in the 1990s. Most of the studies have focused on population distribution, population dynamics, ecology, census data, nutrition and behavior. Subject areas that have received less attention include predation on Steller sea lions, captive studies, metabolism and parasitology.

Only 21 percent of the 272 scientific articles contained information relevant to testing one of the 12 hypothesized causes of the Steller sea lion decline. The most frequently addressed hypothesis concerned juvenile mortality, found in 25 papers. This was followed by starvation, competition with fisheries, human predation and regime shifts. Only one of the 272 articles addressed the role that killer whale predation may be playing in the decline of sea lions.

To date, more than 9,228 pages pertaining to Steller sea lions have been printed, or 1,148 pages of primary publications and 8,080 pages of other publications. The relative number of articles that address or provide significant information about hypothesized causes of the population decline are few, roughly 30 percent of the literature per decade.

Sea lion statistics

Sea lion census counts by the California Department of Fish and Game show total populations going from 968 animals in 1930 to 12,600 animals in 1958 to 18,400 sea lions in 1961 to a whopping 160,000 to 180,000 in 1995.

Biologist Doyle Hannan, in a presentation before the CDFG, estimated the following California sea lion consumption figures in pounds for commercial species in 1995: anchovy, 4.1 million; sardine, 89.3 million; squid, nearly 155 million; whiting, 9 million; rockfish, 17.6 million; and salmon, 6.7 million.

Hannan said: "The bottom line: Lots of seals and sea lions eat lots of fish. More than fishermen these days! Preservationists claim the oceans are dying, yet they are supporting huge pinniped populations. Why is it only human use of fish resources is an issue?"

Agency changes otters’ listing

The U.S. Fish and Wildlife Service has decided that sea otters along the Aleutian Islands do not warrant a listing as "depleted" under the Marine Mammal Protection Act. However, the species could still be listed as threatened or endangered under the Endangered Species Act.

Any listing holds the potential to constrain fishing because of increased regulations and area closures. Sea otters throughout the Aleutians have dropped about 70 percent in the past decade, researchers say.

The Center for Biological Diversity petitioned the FWS to list the species as depleted in August, but the agency found there was not enough information to warrant any action.

Furthermore, according to a Nov. 2 notice in the Federal Register, the FWS "determined that the statewide population of sea otters in Alaska is larger than presented in the petition," and that "the best available scientific information indicates that multiple stocks of sea otters exist in Alaska."

The agency identified three distinct populations of sea otters in Alaska: those in Southeast, which are growing; those in Southcentral regions, which are either stable or growing; and those in Southwest Alaska, which are undergoing declines. Many researchers blame the decline of otters there on predatory killer whales.

Kodiak-based free-lance writer Laine Welch can be reached via e-mail at ([email protected]).

Updated: 
12/02/2001 - 8:00pm