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Reassessing hatchery mating policy in Alaska: is non-selective mating unnatural?


Megan McPheeFisheries Division
School of Fisheries and Ocean Sciences, University of Alaska Fairbanks
David TallmonFisheries Division
Scott VulstekAuke Bay Laboratory
National Oceanic and Atmospheric Administration



Hatcheries are an important component of the Alaska salmon socio-environmental system, generating a commercial ex-vessel value of $120 million and $600 million total economic output annually in recent years (2012-2017; McDowell Group 2018). Alaska is also obligated to produce hatchery salmon for harvest under the Pacific Salmon Treaty (PSC 2019). However, salmon hatcheries are a source of considerable controversy within the State of Alaska, primarily due to potential risks to wild stocks related to competition in the ocean and deleterious genetic 1 effects on wild populations when hatchery fish stray into natural spawning habitat. The precautionary principle codified in Alaska’s Policy for the Sustainable Management of Fisheries requires that management actions, including hatchery operations, consider “the needs of future generations and [avoid] potentially irreversible changes” [5 ACC 39.222(c)(5)]. As such, the genetic effects of hatchery practices have been subject to much scrutiny throughout the development of salmon hatcheries in the state. Alaska Department of Fish & Game also has in place a ‘Genetic Policy’ (Davis et al. 1985) that addresses both the potential risks to wild stocks in terms of genetic diversity and population genetic structure as well as potential genetic risks to hatchery populations, and provides recommendations for how to minimize both. Alaska’s Genetic Policy is over 30 years old, though, and is based largely on theoretical treatments of genetic risks and mitigation strategies. We now have the genetic tools necessary to evaluate these principles empirically, allowing us to advance genetics policy for hatchery management in Alaska out of the theoretical realm, with more realistic context based on data from real salmon populations. Outbreeding depression is identified in the Genetic Policy as a potential risk of hatchery programs to wild salmon populations. The policy assumes first that wild populations are locally adapted, and second, that hatchery populations are likely to diverge from source wild populations through random genetic changes (‘drift’) as well as through adaptation to the hatchery
environment. Outbreeding depression would occur if divergent hatchery fish stray onto wild spawning grounds, successfully interbreed, and alter the genetic composition of the next wild generation, thereby reducing the wild population’s average survival and reproductive success. One way to reduce the probability of outbreeding depression is to minimize the degree to which the genetic composition of the hatchery population is changed by hatchery practices. This involves managing the hatchery population in ways that reduce genetic changes due to artificial selective forces and demographic effects.
The Genetic Policy does not prescribe specific mating practices for hatcheries, but one charge of the policy is to avoid artificial selection for certain traits, either consciously or unconsciously.


The issue

Wild and hatchery salmon stocks contribute hundreds of millions of dollars to the Alaska economy annually. However, there is a great deal of controversy surrounding the use of hatcheries and the Genetic Policy of the State of Alaska used to guide hatchery production management. Despite the controversy, there is minimal understanding of how well hatchery production protocols mimic natural mating strategies or impact the maintenance of genetic variation and individual fish size in hatchery broodstock. We will examine reproductive success of alternative mating strategies (jack versus full-size males) and the mating structure of a wild coho salmon population, its impacts on female salmon size, and compare these results to practices used in Southeast Alaska coho hatcheries. We will explore how the incorporation (wild) or exclusion (hatchery) of jack males may affect the maintenance of population level genetic variation and the size of female offspring in hatchery broodstock.

Why is this an Alaska Sea Grant project?

The results of this project have major implications for salmon hatchery practices and therefore, great economic impact on coastal communities and economies that depend upon sustainable salmon management.

How will researchers conduct their study?

We will make use of an unprecedented collection of high-quality coho salmon abundance data coupled with genetic samples collected at the Auke Creek weir. Genotypes from all returning adult coho offspring (2012-2018) of individuals that spawned in 2010, 2012, 2013 and 2014 will allow us to examine the fitness of jacks and full-size males, the size of their offspring, and how hatchery broodstock management affects the maintenance of genetic variation.