Now, in a breakthrough study, the University of Alaska Fairbanks-led researchers have revealed that salmon hatcheries represent a sort of double-edged sword for wild salmon.
While hatcheries dramatically increase the wild salmon population, they also threaten the very genetic diversity on which the species relies for long-term resiliency.
Increasing Numbers and Decreasing Genetic Diversity (Photo : PATRICK T. FALLON/AFP via Getty Images)
Salmon hatcheries, which were to supplement the declining wild salmon populations, have been highly successful at increasing the numbers of these fish in the North Pacific Ocean.
Currently, more than 5 billion young salmon are released every year, and the pink salmon harvests are booming off places like Prince William Sound, Alaska-from around 4 million salmon to a staggering 50 million fish.
Abundance at a Price
This success story comes with an unexpected downside: loss of morphological diversity among wild salmon populations.
The researchers discovered that straying of large numbers of hatchery salmon into natural spawning grounds and interbreeding with wild salmon occurs.
A straying hatchery fish intermingle and breeds with the wild population, passing along its hatchery-origin gene variants, typically less variable than the wild-type ones.
Genetic Homogenization by Straying Hatchery Fish
Researchers are concerned about the phenomenon of hatchery fish straying into wild populations.
According to Samuel May, lead author of this study, even a small fraction of hatchery-origin fish straying often can likely be impactful because such a great number of fish are released.
The research, done via the Alaska Hatchery Research Project, applied simulations based on real-world data to forecast the lasting effects of this trend on wild salmon recruitment and resilience.
The simulations reiterate, once again, a paradoxical scenario: increased wild fish population sizes were associated with reduced genetic diversity.
The life-history diversity characteristic of wild salmon attuned to the local conditions was thus compromised by hatchery fish, often bred under different environmental pressures that intuited similar traits in diverse populations.
This can potentially undermine the ability of wild salmon to adapt to future environmental challenges.
How do we balance hatcheries with wild salmon conservation?
The balanced hatchery-wild salmon management would need a holistic approach where substitutive experimental designs are used more precisely to explain competitive dynamics between hatchery and wild fish; periodic ecological and genetic impact assessments in determining the effects of hatchery fish on wild stocks; initiation of hatchery reforms help reduce potential risks.
Hatchery fish straying needs management for many reasons, including to avoid genetic homogenization.
Decent habitat conditions for wild salmon need to be sustained and rehabilitated as much as possible to allow the species to sustain themselves naturally and reduce dependence on hatchery supplementation.
Public education and stakeholder involvement can build support for sustainable practices, while policy and regulatory changes must accommodate new scientific findings so hatchery inputs match conservation goals.
These measures provide for the maintenance of salmon populations' growth without giving away the genetic diversity and ecological well-being of wild stocks.
This University of Alaska Fairbanks study highlights the thin line between effective conservation and preservation of genetic diversity.
It calls for nuance in hatchery practice so that enhancement does not come at the cost of reduced evolutionary potential and the ecological stability of species.