Navigating the Predator Gauntlet: Impacts of Nearshore Marine Fishes on Hatchery and Wild Juvenile Salmon in Southeast Alaska
University of Alaska Fairbanks
- Douglas Duncan, MS program
Hatcheries invest significant resources into salmon production to support lucrative and culturally important fisheries in Alaska. A key measure of success for hatcheries is the number of salmon that return to spawn of those released when young. However, the productive marine waters that support salmon are also a fertile environment for predators. Releases of hatchery fish can act as a “dinner bell,” attracting predators to release sites. This pulse of salmon smolts into the environment can also lead to higher predation rates on wild fish by increasing local predator densities. This predator gauntlet is the major source of mortality for smolts during the vulnerable first phase of their marine life, yet surprisingly few studies have quantified predation impacts on hatchery smolts. This study will provide insight into the fate of hatchery smolts by assessing the impacts of abundant predatory fish on young salmon in estuaries. We will measure densities and diets of two abundant predators known to consume smolts—Dolly Varden and staghorn sculpin—at natural rearing areas and release sites for one of the largest hatcheries in Southeast Alaska. Predators will be sampled before and after release of hatchery smolts to test the hypotheses that there will be a higher density of predators at hatchery release sites relative to natural rearing areas and that predation on smolts will be greater following release events. Our work will inform hatchery release strategies that reduce predation risk to smolts and provide an improved understanding of ecological factors that affect early marine survival of salmon.
Young salmon are subject to extremely high rates of predation during their early period in the nearshore marine environment. Understanding where, when, and what sizes of smolts are at highest risk of predation will help hatchery managers identify release strategies that improve survival of hatchery salmon. The three largest hatchery associations in Southeast Alaska released more than 450 million smolt and contributed $171 million to the economy in 2008. Therefore, even a small increase in the percentage of released smolts that return to spawn can translate into millions of dollars for Alaska’s coastal communities.
Why is this an Alaska Sea Grant project?
Our study addresses Alaska Sea Grant Goal 3 in the Sustainable Fisheries and Aquaculture theme area. We are partnering with Douglas Island Pink and Chum, Inc. (DIPAC), one of the largest hatchery associations in Alaska, which is sponsoring a large portion of this research. Hatchery managers will be engaged in every stage of the research, so that our study design will be ideally suited to provide information they can directly use for improving smolt release strategies that support sustainable hatchery production. This study is also relevant to Goal 1 in the Healthy Coastal Ecosystems theme area. By examining predation impacts on hatchery and wild smolts, our study will contribute to a more complete understanding of the ecological factors that affect early marine survival of salmon.
Douglas Island Pink and Chum, Inc. (DIPAC)
Alaska Department of Fish and Game, Mark, Tag, and Age (MTA) Laboratory
Dr. Carolyn Bergstrom, University of Alaska Southeast
What researchers learned
From May to September 2016, we sampled nearshore fishes during 7 sampling periods at 4 sites in the Juneau area. Although predator stomach contents have not been fully processed, we saw evidence of predation on salmon smolts by both predator species, particularly during May and June. In addition, we conducted a series of successful pilot feeding trials with staghorn sculpins in the lab; full experiments will be performed this summer to estimate the quantity of salmon smolts that sculpins are capable of consuming. To date, we have worked with 17 volunteers in the field and lab, including undergrads, grad students, faculty, and agency employees. An undergraduate at University of Alaska Southeast completed a 3-credit research internship under the guidance of the PI and graduate student. This spring and summer we will have a new team of undergraduates working with us, including two NOAA Hollings Scholars.