Research shows how jack salmon contribute to population and genetics

In the world of commercial fisheries management and Pacific salmon research, jack salmon haven’t received nearly as much attention as their larger relatives, but that may change as a result of an Alaska Sea Grant-funded project. 

Jacks are male salmon that reach sexual maturation and spawn at a younger age than full-size males. In some populations and some years, jacks comprise as much as 50% of the male population that returns to natal streams for mating, but their small size makes them difficult to count, and of lower value for commercial purposes. Because jacks aren’t always monitored, their contribution to salmon populations has not been well understood.

Alaska Sea Grant funded a research project led by University of Alaska Fairbanks (UAF) College of Fisheries and Ocean Sciences professor Megan McPhee, who worked with University of Alaska Southeast professor David Tallmon and UAF Fisheries graduate student Erika King, to examine the role that jacks play in salmon population dynamics and evolutionary dynamics. 

The research compared the reproductive success of jacks to that of full-size males, and examined the contribution of jacks to the genetic diversity in a population of Coho salmon. The study found that jacks had lower reproductive rates than regular-size males, but they fathered 23% of the adults returning to spawn. The research also concluded that jack presence in the population increased genetic diversity by 13%, and that removing jacks from the population generally reduced genetic diversity.

The project relied on data available through NOAA’s Auke Creek Research Station in Juneau. “We were able to do the work we did because of this really robust data set­, which was an entire decade of demographic and genetic data from the Auke Creek Coho population,” said King.

King explained that each and every adult salmon is intercepted at Auke Creek on its way to spawn, and manually transported over the fish weir. Since 2009, every returning adult Coho salmon has been sampled for genetic analysis, and about 33% are sampled for age, sex, and length. The research team used these genetic data to analyze 8,000 individual adult male salmon, including jacks, from 2009 to 2019.

These new findings have the potential to guide hatchery practices to better mimic the mating strategies of wild salmon stocks and ensure the maintenance of genetic variation.  The results are also relevant for managing wild salmon populations, providing new insights about how salmon will respond to stressors like climate change and informing how to protect and recover vulnerable stocks.

“This is compelling evidence that jacks should not be ignored in the study, monitoring and management of Pacific salmon,” said King. King graduated with her MS in Fisheries and now works at the Alaska Department of Fish and Game in their habitat division. This research project, like many that Alaska Sea Grant supports, has a dual benefit to contribute to workforce development in Alaska and to train the next generation.