A recent U.S. Geological Survey estimates that the Pacific walrus population nearly halved between 1981 and 1999, the last year for which demographic data are available. The study notes that the decline was most severe in the mid-1980s, and then moderated in the 1990s. Currently, the USGS is working to obtain more recent population data of the Pacific walrus. This information will be vital because the U.S. Fish & Wildlife Service is expected to determine whether the Pacific walrus should be listed as threatened under the Endangered Species Act in 2017.
A recent U.S. Geological Survey estimates that the Pacific walrus population nearly halved between 1981 and 1999, the last year for which demographic data are available. The study notes that the decline was most severe in the mid-1980s, and then moderated in the 1990s.
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Currently, the USGS is working to obtain more recent population data of the Pacific walrus. This information will be vital because the U.S. Fish & Wildlife Service is expected to determine whether the Pacific walrus should be listed as threatened under the Endangered Species Act in 2017.
"We integrated data from many sources," said lead author of the study research statistician Rebecca Taylor, with the USGS Alaska Science Center in Anchorage. "These included annual harvest records, 6 age structure surveys and 5 population size surveys conducted at various times over the 32 year study. The age structure data—collected between 1981 and 1999—were particularly informative, and enabled us to quantify the population decline and the birth and death rates that caused it."
Scientists think past walrus population dynamics were affected mainly by harvest. Previous work suggests the population probably increased rapidly in the 1960s due to reduced hunting and reached or exceeded the size that could be supported by food resources in the late 1970s to early 1980s. The decline quantified by the USGS analysis was probably initiated by this overabundance of walruses and exacerbated by a return to the relatively high harvests of the 1980s.
"The decline probably was prompted by these historical reasons, but we can't rule out other possible contributing factors," said Taylor. "The environment isn't static, and food may have become less available to walruses over time, possibly because of sea ice loss." Sea ice is important to walruses because they rest on it between dives to the ocean floor to eat clams and other invertebrates.
In 2011, due to the combined threats of harvest and sea ice loss, the USFWS determined that listing of the population as threatened under the Endangered Species Act was warranted but was precluded by higher priorities. The agency is under a court order to make a listing decision in 2017.
This research effort is part of the USGS Changing Arctic Ecosystems Initiative. The results of this new study were published in the online journal Marine Mammal Science on September 5, 2014.
Read more at USGS Newsroom.
Walrus image via Shutterstock.
