Alaska Marine Science Symposium 2008
Humpback Whale Predation on Herring
Humpback whale (Megaptera novaegliae) predation on winter aggregations of Pacific herring (Clupea pallasii) in Sawmill Bay, Alaska: Is it a problem for the herring?
¹ Katherine A. McLaughlin, ¹ Andrew T. McLaughlin, ² John R Moran, and ²Stanley D. Rice
¹McLaughlin Environmental Services, PO Box 8043, Chenega Bay, Alaska 99574 firstname.lastname@example.org
²NOAA/NMFS, Alaska Fisheries Science Center, Ted Stevens Marine Research Institute, 17109 Pt Lena Loop Rd, Juneau, Alaska 99801
John.Moran@noaa.gov and Jeep.Rice@noaa.gov
Humpback whales (Megaptera novaegliae) have been observed feeding on herring in the early winter for a number of years in Sawmill Bay (Prince William Sound). But is the predation a major problem for herring? Herring populations in Prince William Sound have been depressed since 1993, and predation by whales in the winter may be a dominant factor. Our study evaluated the abundance and residency of humpback whales in Sawmill Bay from November 2006 through November of 2007, and will continue through the winter of 2007-2008. In the winter, a dense school of energy rich herring typically mass up in Sawmill Bay, estimated at 5,562 metric tons of herring in a basin less than 5 km2 in winter 2006-7. This energy rich prey concentrates both mammalian and avian predators during the fall and winter months. We estimated whale abundance using a combination of photo-identification techniques and shore/boat-based surveys. We identified humpback whale prey both visually, and using hydro-acoustics. During the study at least 52 individual whales have been identified utilizing Sawmill Bay. The number of whales in the Bay generally began to increase during November with 4-7 whales, peaked in mid January with 26 animals, and were absent by the beginning of May. Lower numbers, 1 - 3 whales were present from April to October in the entrances to La Touche and Elrington Passages. Winter observations suggest that the whales appear to be feeding exclusively on herring while foraging in Sawmill Bay, although capelin (Mallotus villosus) was also observed.
The study continues in the winter 2007-8, but will be expanded to include estimates of whale abundance and prey at other locations in Prince William Sound. These data will be modeled to quantify the biomass of herring removed by humpback whales. Our ultimate goal will be to assess the impacts of humpback whale predation on the Prince William Sound population of herring.
Similar observations of humpback whale abundance and residency are also being conducted at two other locations: Lynn Canal where herring populations are also struggling, and Sitka Sound where herring populations are robust.