Easy pickings Dr Ellen Chenoweth/NOAA Fisheries permit #14122

No such thing as a free lunch? Not so for these whales. Humpback whales in south-east Alaska seem to have found their own chain of fast food restaurants: salmon hatcheries. While making a good meal for the whales, the habit may prove harmful to the local fishing industry.

Hatcheries aren’t fish farms, but salmon nurseries. The idea is that the juvenile fish released into the ocean from the hatcheries increase the number of salmon available to catch without leading to overfishing of the wild stocks.

Wild salmon spend the first part of their lives in streams where competition is fierce and many don’t make it. Hatcheries make sure enough salmon survive this crucial life stage, breeding them in captivity for six to 18 months before releasing them into the wild.


Ellen Chenoweth at the University of Alaska Fairbanks first became interested in humpbacks feeding on juvenile salmon when she saw videos that hatchery staff had taken of whales swimming close to their hatchery’s release sites to feed.

Normally whales feed at depth, out of sight, which makes their feeding habits difficult to study. They filter water through their baleen to catch krill and small fish – but seem to be equally at home around these new, human-made shallow hatcheries. “Whales are fascinating: mammals like us, but perfectly at home in an alien environment,” she says.

No escape

Her team monitored five hatchery release sites in protected coves on the eastern side of Baranof Island between 2010 and 2015, recording whales’ behaviour every morning and afternoon. The researchers also tagged individual whales to track where they feed.

They found that while hatchery salmon isn’t an important food source on a population level, it does appear to be vital for a small number of whales for a period of a few weeks. “For the individuals that appear to specialise there, it is part of a seasonal feeding strategy and, in some cases, they return year after year,” says Chenoweth.

What makes feeding at hatcheries so impressive is how these animals are able to feed among the network of docks and holding pens in relatively shallow water, very close to shore, where the hatchery salmon is released The team suspect that whales may be using some of these obstacles as barriers to keep their prey from escaping.

Humpbacks are well known for their ability to learn new behaviours and dietary diversity, so “in that respect the findings here are not surprising, but it is an important demonstration that helps to bracket how quickly whales can exploit a newly available resource”, says Andrew Read at Duke University in Durham, North Carolina.

The study is a good example of the challenges posed by successful conservation, he adds. “Now the [humpback whale] population has recovered, managers can focus on developing effective and innovative solutions to interactions, such as the ones described in this paper,” Read says.

Journal reference: Royal Society Open Science, DOI: 10.1098/rsos.170180

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