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    The killer whales are back!

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    Photo by Barbara Lestenkof, St. Paul Island.

    Recent sightings of killer whales posted by community members are the latest in a long history of observations around the Pribilof and Aleutian Islands. So, what do we know about them?

    Killer whales (Orcinus Orca), often referred to as Orca, are apex predators that roam all the world’s oceans. Although arguably the most famous killer whales are those in the south Atlantic that beach themselves while hunting sea lions on the Patagonian shores, not all killer whales are mammal-eaters. In the north Pacific, they are divided in three classes or “ecotypes”: residents, transients, and offshores. Residents specialize in salmon, especially chinook or king salmon, and are predictably found along the coastlines from Alaska to California. Transients eat marine mammals, ranging from harbor seals to gray whales, and overlap with Residents but are much less predictable in their movements. Less is known about the Offshore ecotype. They are found in large groups out along the continental shelf break and appear to largely specialize on eating sharks.

    Could killer whales be at least partially responsible for sea lion and fur seal declines? Among other things, this depends on the killer whale population size in the area which is a very difficult number to estimate given how widely dispersed they are. The minimum population estimate of transient killer whales in the Gulf of Alaska, Aleutian Islands and Bering Sea is 2,084 individuals based on the count of individuals using photo-identification (Allen and Anglis 2014). Springer and colleagues (2003) proposed that following a drastic reduction of gray whale numbers due to the whaling industry, transient killer whales have been switching from one marine mammal prey type to another as their populations bottom out; first Steller Sea lions, then harbor seals, then sea otters, and finally now northern fur seals. However, many other researchers do not agree with this interpretation of the data (e.g. DeMaster et al. 2006, Wade et al. 2007). Seabirds have also been declining in the Bering Sea at the same time (Byrd et al. 2008) which is not likely to have been caused by killer whales. The best evidence suggests the seabird decline may be due to less food availability, possibly a consequence of warmer ocean temperatures that occur in cycles over decades. Warming ocean temperatures point to other ecological or human-caused factors that may be the main cause of fur seal and sea lion declines in the Bering. Killer whales may be merely exacerbating a larger problem by hindering the recovery of these marine mammal populations.

    Why should we be concerned about changes in a top predator population? In short, because knowing the causes of change can help us to understand, predict and react to environmental changes that directly affect us. Changes from the top down or the bottom up of a well-connected ecosystem like the Bering Sea can lead to all sorts of unpredictable results as is occurring now with climate change. For example, the increase in global temperatures may affect the distribution of killer whales, allowing them to move further north into the Arctic. In the eastern Canadian Arctic this has already begun and killer whales are going after narwhals that used to be able to seek refuge in the sea ice. For now, however, it seems the Bering Sea killer whales are happy to feed in the Bering Sea without going anywhere else!

    There is a lot that community members can do to help solve this puzzle – from documenting

    Local children on St. George Island, Alaska look for killer whales and other marine mammals.

    Local children on St. George Island, Alaska look for killer whales and other marine mammals.

    killer whale predation incidents by pictures or videos and posting the areas and number of individuals we encounter at sea. For example, in 2006 and 2008 the St. Paul ECO and the St. George Island Institute used a community-based approach to study killer whales that included a logbook program in the local halibut fishery, collection of local and traditional knowledge, and shore-based visual surveys. See the results in the library of the Beringwatch.net webpage.
    Individual killer whales are relatively easy to identify if you happen to have binoculars with you. Look for their individually distinctive “saddle patches”, the white marks on the back behind the big dorsal fin or other marks such as notches in their dorsal fins (see picture above). You may be able to know whether the killer whale you see is the same you have seen in the last week, month or year! These observations are very valuable so please take photos and pass them on to your local Sentinels!

    Allen, B. M., and R. P. Angliss. 2014. Alaska marine mammal stock assessments, 2013. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-277, 294 p. Available at http://www.nmfs.noaa.gov/pr/sars/pdf/ak2013_final.pdf.

    Byrd, G.V., Schmutz, J. A. and Renner, H. M. 2008b. Contrasting population trends of piscivorous seabirds in the Pribilof Islands: a 30 year perspective. Deep-Sea Res. II.55:1846-1855.

    DeMaster D.P., Trites A.W., Clapham P., Mizroch S., Wade P., Small R.J. & Hoef J.V. (2006). The sequential megafaunal collapse hypothesis: Testing with existing data. Progress in Oceanography, 68, 329-342.

    Springer A.M. 2003 Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling?. Proc. Natl Acad. Sci. USA. 100, 12 223–12 228. doi:10.1073/pnas.1635156100.

    Wade P., Barrett-Lennard L., Black N., Brownell R.L.J., Burkanov V., Burdin A., Calambokidis J., Cerchio S., Dahlheim M., Ford J., Friday N., Fritz L., Jacobsen J., Loughlin T., Lowry M., Matkin C., Matkin D., Mehta A., Mizroch S., Muto M., Rice D., Siniff D., Small R., Steiger G., Straley J., Van Blaricom G. & Clapham P. (2007). Marine mammal abundance, biomass, and trends in the eastern North Pacific – a reanalysis of evidence for sequential megafauna collapse. Maine Mammal Science, 23, 766-802.

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