Research shows historic decline in Pacific walrus population

research-shows-historic-decline-in-pacific-walrus-population

A recent study by scientists at the USGS quantified the historic Pacific walrus population and found that their numbers roughly halved between 1981 and 1999. The 18 year decline identified by the study was not steady across that period. The decline was most severe in the mid-1980s, and then moderated in the 1990s. 

If the moderating trend has continued up to the present time then the population might be stabilized. That, however, cannot be determined until more recent data are collected and analyzed. USGS is working to obtain the data needed to close the gap from collection of the last demographic data to the present day. 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. Population dynamics, such as those investigated in this USGS study, will be a critical factor in the decision.

“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.

Taylor’s analytical approach allows the incorporation of new data to understand more recent population dynamics.  In 2013 and 2014, the USGS, USFWS and the Alaska Department of Fish & Game jointly surveyed walruses in Bering Strait and the Chukchi Sea to estimate current age structures and test a new method of estimating population size using a genetic mark-and-recapture approach. Another survey is planned for 2015.

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.

Source: USGS

Reference:

  • "Demography of the Pacific walrus (Odobenus rosmarus divergens): 1974–2006" – Rebecca L. Taylor, Mark S. Udevitz – Wiley – September 5, 2014 – DOI: 10.1111/mms.12156

Featured image: Walruses in the Chukchi Sea during a tagging survey onboard the Norseman II in June 2010. Author: Sarah Sonsthagen, USGS

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One Comment

  1. I lived in Nome, Alaska for 5 years from 1978-1983. I had lived in Alaska for many years prior and continued to live there for several years after. I don’t remember there being a problem with sea ice during the years I was in Nome, nor do I remember any reports from gov’t officials or the Eskimos that lived there and hunted. What I can tell you there was a problem with was hunting. And not subsistence hunting. All Alaskan marine mammals are restricted from being hunted by anyone other than Eskimos. There are plenty that hunt legally and only for food. But when I was living there, there were also plenty of Eskimos that hunted purely for heads and oosiks. The heads are prized for carving and mounting, while the oosiks (the penis bone of the walrus) are removed and sold to tourists. I was not aware of any system in place, while I was there, that would require any walrus head mount to be certified to have been taken legally. I do remember one occasion where some friends and I drove many miles West of Nome on the beach. In that time we counted 62 dead walrus, 1 dead killer whale and 4 seals. All the walrus were missing their head and oosik, as was the seal. The killer whale was missing his head. I was told by a friend that the teeth would be extracted and used for carving and sale. I was also told that unscrupulous Eskimos, hard up for easy money, would ride around in their boats, shoot at will whatever they saw and however many they saw. Let them sink and then wait for whatever to wash up on the beaches where harvest would be much easier. If they didn’t wash up…oh well. And you can do the math: while I was there, I eventually found out who would sell a “black market head mount” (usually those involved in the drug trade) and once had the pleasure of seeing one of the most beautiful pieces of artwork I had ever laid eyes on…a head mount with carved tusks and scrimshaw on the skull that was priced at $1,100.00. Upon seeing that head mount I thought of those 62 headless walrus I had previously seen on the beach. And since I worked at a Tourist gift shop, I knew that just a plain, cleaned and polished walrus oosik would bring approx. $50.00. I’m not saying that a decline in food supply for a growing population of walrus didn’t contribute to declining walrus numbers in the 1980’s…but I do believe all the facts should be accounted for. And these practices I have witnessed with my own eyes. I have no idea if these practices still continue or to what extent they might continue.

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