Whales keep herring down, scientists says

Marine biologists said humpback whales are skipping warmer climates for the icy waters of Alaska. Marine biologists said humpback whales are skipping warmer climates for the icy waters of Alaska. (David Lyon for The Boston Globe)
By Associated Press
February 8, 2010

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ANCHORAGE - Something is holding down the herring population of Prince William Sound, and marine scientists are tailing some rather large suspects: humpback whales.

Humpbacks, once hunted to near extinction, are thriving in waters fouled 21 years ago by the Exxon Valdez, the supertanker that ran aground and leaked nearly 11 million gallons of crude oil.

The herring population crashed after the spill but should have rebounded by now. One hypothesis is that humpbacks, traditionally summer residents in the sound, are taking a big bite out of vast herring schools that form in the deep water of the sound’s fjords each autumn.

Jan Straley, a marine biology professor at the University of Alaska Southeast, and other researchers have studied whales the last two winters with surprising results. Humpbacks are showing up in significant numbers, even in winter.

When summer resident whales leave, others humpbacks move in. Some summer residents are even skipping their annual transoceanic mating and birthing trips to Hawaii and Mexico in favor of icy Alaska waters.

Record commercial harvests of herring were recorded in the late 1980s. The gash in the 987-foot Exxon Valdez on March 23, 1989, oozed oil into the sound about the time adult herring were laying eggs, which adhere to plants and rocks before hatching two weeks later into larva that feed on the spring plankton bloom, and after about 10 weeks grow into juvenile fish.

By 1993, just 25 percent of the expected adults returned to spawn. State regulators closed commercial fishing in 1993, and other than openings in 1997 and 1998, it has stayed closed.