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Recruitment Energetics and Coastal Assessment Program

Forage Fish and Humpback Whale Monitoring: Change in Prince William Sound

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A humpback whale feeding in the Gulf of Alaska. Photo by Steve W. Lewis. NOAA MMPA Permit #14122.

The Center’s Recruitment Energetics and Coastal Assessment Program (RECA) in collaboration with Gulf Watch Alaska’s long-term monitoring program collects data on the condition and distribution of forage fish and humpback whales within Prince William Sound during fall and winter months. During our December 2014 and April 2015 surveys, we observed shifts in whale and Pacific herring behavior that may have been a prelude to ecosystem changes observed across the Gulf of Alaska. In December 2015, adult herring failed to return to their overwintering grounds in Port Gravina. Humpback whales and seabirds, which rely on this predictable mid-winter energy source, were also absent or in greatly reduced numbers relative to earlier years. Coincidental to this event, water temperatures in Port Gravina were 4°C warmer than in 2011 and 2°C warmer than in 2013. Anecdotal observations of forage fish indicated an increase in the abundance of young of the year herring throughout the sound and a dramatic decrease in other forage fish species (capelin, sand lance, and juvenile pollock).  

Anomalous herring behavior continued into the spring. The large shoals of herring, typical of pre-spawning, were broken up into small fast moving schools. Humpback whales were present, but their foraging behavior and distribution had changed from predominantly deep dives on large, stationary shoals to surface lunges on small, shallow and dispersed schools.  Herring associated with foraging flocks of seabirds were also targeted increasingly by humpbacks. Whales either consumed all of the fish or dispersed the school, ending the foraging opportunity for seabirds. This direct competition for food occasionally resulted in seabirds being engulfed by whales.

Subsequent to these events in Prince William Sound was the declaration of an Unusual Mortality Event (UME) for large whales and seabird die offs across Alaska. While it remains to be determined how these observations are connected, they emphasize the importance of long-term monitoring and winter observations in interpreting ecosystem changes.


By John Moran

Whale recovery video - click image to play


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