Very few juvenile salmon return to spawn. Many are consumed by larger fish who eat them as they migrate from rivers or hatcheries to the ocean.
That’s a problem for hatcheries that release millions of young salmon, called smolts, into the waters of coastal Alaska.
Alaska Sea Grant funded research on chum salmon predation by two common nearshore fish species, Dolly Varden and Staghorn Sculpin. The researchers, including University of Alaska Fairbanks student Douglas Duncan, found that both of these predators consumed lots of chum salmon. In fact, these predators’ stomachs were consistently full with a variety of items, including salmon.
For his master’s degree, Duncan spent three years studying whether the release of hatchery fish can act as a “dinner bell,” attracting predators to release sites. Duncan concluded that Dolly Varden and sculpin were abundant at a variety of times, not just when hatchery salmon were released. Dolly Varden had a higher proportion of chum salmon smolts in their diet than sculpins, likely because Dolly Varden are more mobile. But neither species is the “smoking gun” of salmon mortality at marine entry. There are likely many challenges to salmon during their marine phase, and more work is needed on this important, but less understood, part of their life cycle.
During his thesis defense this month, Duncan said his advice is to maintain productive, healthy estuaries to best limit predation on salmon. Predators likely consume a sampling of what is available, and so salmon smolts may fare better when there are other fish around.
The research was supported by Douglas Island Pink and Chum, Inc. (DIPAC), one of the largest hatchery associations in Alaska. Duncan is the recipient of the Ladd Macaulay Graduate Fellowship in Salmon Fisheries Research, funded at UAF through an endowment provided by DIPAC. The Juneau-based hatchery association produced $262.9 million worth of salmon in wholesale value between 2008 and 2012.
Duncan will soon graduate with a MS in Fisheries from the College of Fisheries and Ocean Sciences at the University of Alaska Fairbanks. Doug works with Anne Beaudreau, his advisor and a fisheries faculty member at UAF. Over 50 volunteers helped to collect fish for this multi-year study.