Reproductive success of jack and full-size males in a wild coho salmon population

Abstract

Despite the wealth of research on Pacific salmon Oncorhynchus spp. life histories there is limited understanding of the lifetime reproductive success of males that spend less time at sea and mature at a smaller size (jacks) than full-size males. Over half of returning male spawners can be jacks in some populations, so it is crucial to understand their contribution to population productivity. We quantified adult-to-adult reproductive success (RS) of jacks and their relative reproductive success (RRS) compared to full-size males in a wild population of coho salmon in the Auke Creek watershed, Juneau, Alaska. We used genetic data from nearly all individuals (approx. 8000) returning to spawn over a decade (2009–2019) to conduct parentage analysis and calculate individual RS. The average adult-to-adult RS of jacks (mean = 0.7 and s.e. = 0.1) was less than that of full-size males (mean = 1.1 and s.e. = 0.1). Jack RRS was consistently below 1.0 but ranged widely (0.23 to 0.96). Despite their lower average success, jacks contributed substantially to the population by siring 23% of the total returning adult offspring (1033 of 4456) produced between 2009 and 2015. Our results imply that jacks can affect evolutionary and population dynamics, and are relevant to the conservation and management of Pacific salmon.

Alternative life‐history strategy contributions to effective population size in a naturally spawning salmon population

“…The data and scripts that support the findings of this study are openly available in Dryad at https://doi.org/10.5061/dryad.2280gb5z6 . The raw data that supports the findings of this study are available in the supplementary material of King et al 2023 at http://doi.org/10.1098/rsos.221271 .…”

“…Genotyping and parentage assignment methods were the same as those presented in King et al ( 2023 ). In brief, we employed a contract lab (GTseek LLC) to extract and sequence tissue samples of all returning individuals from 2009 to 2019 using the “genotyping‐in‐thousands” (GTseek LLC) protocol (Campbell et al, 2015 ).…”

“…We then quantified the percent of returning adults from stray parents that spawned in 2013–2015. For additional details, see King et al ( 2023 ).…”

“…In some Pacific salmon species, jacks spend reduced time in saltwater and can make up anywhere from <1 (Sockeye Salmon O. nerka ; Quinn et al, 2001 ) to >50% of returning males (Coho Salmon O. kisutch ; King et al, 2023 ). Observational studies show that jacks participate in spawning (Gross, 1985 ; Healey & Prince, 1998 ).…”

Inferring precocial Chinook Salmon production through single‐parentage assignments

“…In other studies, precocial males contributed 8% of fry in an artificial stream (Schroder et al 2012) and were estimated to produce, on average, one-third of the anadromous offspring in a natural setting (Ford et al 2015). In Coho Salmon O. kisutch, jacks were shown to have lower average success than fullsized males, but they still sired 23% of returning adult offspring (King et al 2023b). Although the proportion of adult offspring produced by precocial males in this study system is within the range of previous observations, it is on the lower end of the distribution.…”