Whales feast when hatcheries release salmon | Science News for Students

Whales feast when hatcheries release salmon

Crowds of young fish at release sites may attract hungry humpbacks to a new type of prey
Aug 30, 2017 — 7:00 am EST
humpback feeding

Crowds of prey make eating small fish worth the effort for huge humpback whales. This also may help explain a whale innovation: dining on young salmon released by fish hatcheries.

David Csepp, NOAA/NMFS/AKFSC/ABL, National Oceanic and Atmospheric Administration/Department of Commerce

Some Pacific humpbacks have discovered a new source of convenience food.

After wintering in the tropics, these whales migrate every spring to feeding grounds in southeastern Alaska. Now, some have added a new Alaskan dining destination. They visit fish hatcheries as they are releasing young salmon into the sea, researchers report.

It’s an unusual behavior for the whales. Scientists say this is the first time humpbacks anywhere have been seen eating young salmon (SAA-mun).

The whales are “40 feet [12 meters] long and they’re feeding on fish that are the size of my finger,” says Ellen Chenoweth. She works at the Juneau Center of the fisheries department of the University of Alaska Fairbanks. As a marine ecologist, she studies how humpbacks find food. For such small prey to be worth eating, the big whales need to find a lot in one place. Young salmon streaming out of hatchery nets seem to fit the bill.

Chenoweth and her colleagues worked with the staff at five hatcheries to observe whales. All the hatcheries were near Baranof Island in southeastern Alaska. Over six years, the team recorded whether whales were around before, during and after young salmon were released. A trend emerged of humpbacks showing up at spring fish releases.

Humpbacks have a reputation for diverse and flexible diets, Chenoweth says. The salmon feasts show them adapting to a new source of prey. Her team published its findings July 12 in Royal Society Open Science.

Big gulps

Hatcheries raise the young salmon and release them to the ocean. The hope is that many will survive to become adults. This should boost the number of adult salmon available to fishing fleets. Whether whales eat enough to spoil that plan remains unknown, the scientists now say.

One upside for scientists of these whale feasts is already clear. Hungry whales in shallow water gives them a rare chance to film humpbacks dining. To catch the tiny salmon, the whales blast headfirst into their dinner. This technique is known as lunge feeding. It’s dramatic, but often hard to study.

Like a school bus going crazy, a humpback opens its jaws and speeds toward a cluster of fish. The whale then gulps a giant mouthful of fish-filled water. To allow for the biggest gulp, the whale throat swells “like a parachute opening,” Chenoweth explains.

One gulp is truly a whale of a mouthful. In a single lunge, a humpback may take in some 27,600 liters (7,300 gallons) of seawater. An amount like that is equal to about 28 metric tons (62,000 pounds). That’s enough to temporarily double the whale’s weight!

Humpback whales have no teeth. Instead, their mouths are filled with dangling fringes of what’s called baleen. As the whale swooshes the water back out, the hanging baleen snags what’s worth swallowing. For these whales, those bits add up to a salmon dinner.

Studying monster lunges is hard because humpbacks often dive deep to feed, Chenoweth notes. Scientists in a boat at the surface can’t see what gets swept in far below. They just glimpse whales back at the surface huffing to catch their breath before the next exciting plunge.

“It’s like going to a basketball game but you can only really watch players on the bench,” Chenoweth says. But when whales lunge at salmon in shallow water —such as during hatchery releases — a camera on a pole can capture the frenzy of this feast.

A humpback whale repeatedly gulps juvenile salmon recently released in this quiet cove by a hatchery in southeastern Alaska. Researchers saw dining in progress and lowered a GoPro camera on a pole for an underwater view of the whale swooping by.
E. Chenoweth et al/Royal Society Open Science 2017; NOAA fisheries permit #14122

Power Words

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baleen     A long plate made of keratin (the same material as your fingernails or hair). Baleen whales have many plates of baleen in their mouths instead of teeth. To feed, a baleen whale swims with its mouth open, collecting food-filled water. Then it pushes water out with its enormous tongue. Plankton in the water become trapped in the baleen, and the whale then swallows the tiny animals.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

colleague     Someone who works with another; a co-worker or team member.

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health.

ecology     A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

hatchery      A facility where eggs are hatched and then reared until the animals are old enough to survive on their own, at which point they typically are released into the wild (fish) or slaughtered as human food (chickens).

humpback     A species of baleen whale (Megaptera novaeangliae), perhaps best known for its novel “songs” that travel great distances underwater. Huge animals, these whales can grow up to more than 15 meters (or around 50 feet) long and weigh more than 35 metric tons.

marine     Having to do with the ocean world or environment.

migrate     To move long distances (often across many countries) in search of a new home. (in biology) To travel from one place to another at regular times of the year to find food or more hospitable conditions (such as better weather). Species that migrate each year are referred to as being migratory.

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

salmon     A popular game fish that tends to live most of its life in the ocean, then enters coastal rivers (and freshwater) to breed and lay eggs.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

seawater     The salty water found in oceans.

tropics     The region near Earth’s equator. Temperatures here are generally warm to hot, year-round.

whale     A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.

Citation

Journal:​ ​​ E.M. Chenoweth et al. Humpback whales feed on hatchery-released juvenile salmon. Royal Society Open Science. Vol. 4, July 12, 2017. doi: 10.1098/rsos.170180.