July 27, 2017
By Jonathan Wright
As reported by Sciencenews.org, Humpback whales in Southeast Alaska have been observed deliberately pursuing and eating freshly released hatchery raised salmon. While the overall behavior is nothing new -- Humpbacks are known for their wide range of food preferences -- it is the first time that fisheries biologists have seen Humpbacks staging specifically in established release areas to prey on juvenile hatchery fish.
Marine ecologist Ellen Chenoweth, of the Juneau fisheries center at the University of Alaska Fairbanks, stated that the whales are ""40 feet long and they're feeding on fish that are the size of my finger." The Humpbacks typically exhibit lunge feeding behavior in the shallow water of the release areas, plowing into concentrations of schooled fingerlings, and allowing their throats to balloon outward to accommodate over 7,000 gallons of sea water and fish. The water is then strained through filters of baleen and the whale engorges the meal, which undoubtedly consists of thousands of juvenile salmon.
While the coverage focused on the scientifically notable observation of interpretive feeding behaviors on the part of the whales, it did not articulate whatever concern the finding may have on the overall impact to the fisheries escapement. Obviously, a 35-ton mammal intercepting tens or hundreds of thousands of anadromous smolts the moment they hit sea water is going to be a concern to biologists and taxpayers who support fisheries efforts. However, Humpbacks are a globally protected species, with a remnant worldwide population of just 80,000 individuals. Exerting any kind of animal control would probably run into an instantaneous political buzz saw.
All Cetaceans—which include whales and porpoises—are demonstrably intelligent, and Humpbacks in particular are noted for behaviors that make them extraordinarily successful. Groups of swimming Humpbacks will encircle large schools of small fish or shrimp, blowing rings of bubbles to disorient and herd their prey into ever tightening concentrations, where finally, the whales dive in with their cavernous maws to scoop up the feast. This is arguably tool use on the part of the whales, with the bubbles serving to support a deliberately conceived and socially cooperative agenda.
Nearly 40 years ago, I was witness to whales of another species making a coordinated impact on salmon at the other end of the development scale. I had landed a gig with the US Fish and Wildlife Service working on a purse seine boat conducting census studies off the Olympic Peninsula of Washington State Our boat was harbored in Hood Canal, a large salt water inlet on the east side of the peninsula and in the southwestern margins of Puget Sound. I worked the take-up drum, winding a half mile long net on a large motorized aluminum spool.
One very calm and glassy winter morning, we were pulling the net between the 29 foot main vessel and a smaller skiff that towed the other end, working slowly across the inlet. After an hour or so, we brought the boats together to encircle our catch, and that morning, we ended up having several dozen Chinook salmon thrashing next to the boat. We were then to hand net the catch, measure the fish and record other data, and release them over the side.
In the midst of this, I became aware of a large commotion happening a hundred yards away across the water. In the still of the morning, I saw more salmon leaping from the water repeatedly, with large boils and frothing all around them. I then saw the black, four foot tall dorsal fins the Orcas. Apparently we weren't the only ones who had found good fishing this morning. My jaw dropped as I watched a pack of 25 foot long, ten ton Killer Whales decimate a school of 50lb adult salmon, tossing the fish in the air and shaking them like terriers with a rat.
It then dawned on me that we were in a potentially dangerous position. We had a bunch of alarmed Chinook herded up against the gunwale of the boat while a half dozen Orcas were going on a murderous rampage, probably within sight and well within underwater earshot of our catch. Suddenly, the 29 foot boat didn't seem like all that much protection. I turned to the captain to voice my concern, and he calmly instructed us to finish our work .... but that it might be a good idea to hurry.
Whales and salmon are part of a large and complex food chain that are being supported through conservation efforts for for both species. However, unexpected outcomes to these programs are becoming more common with changes to the environment driving survival behaviors.