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

Investigators

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

Student

Synopsis

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.

Overview

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.