Genetics of century‐old fish scales reveal population patterns of decline

Michael H.H Price,Terry D Beacham,Brendan M Connors,John R Candy,John D Reynolds,Jonathan W Moore,Brenda Mcintosh

doi:10.1111/conl.12669

Michael H.H Price, Terry D Beacham + Show 5 more

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https://doi.org/10.1111/conl.12669

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Abstract

AbstractConservation scientists rarely have the information required to understand changes in abundance over more than a few decades, even for important species like Pacific salmon. Such lack of historical information can underestimate the magnitude of decline for depressed populations. We applied genetic tools to a unique collection of 100‐year‐old salmon scales to reveal declines of 56%–99% in wild sockeye populations across Canada's second largest salmon watershed, the Skeena River. These analyses reveal century‐long declines that are much greater than those based on modern era abundance data, which suggested that only 7 of 13 populations declined over the last five decades. Populations of larger‐bodied fish have declined the most in abundance, likely because of size‐selective commercial fisheries. Our findings illustrate how a deep historical perspective can expand our understanding of past abundances to a time before species incurred significant losses from fishing, and help inform conservation for diminished populations.

Highlights

Declines in population abundance of many of Earth’s biota are outpacing species extinctions (Hughes, Daily, & Ehrlich, 1997), and disrupting ecosystems and human cultures
Population diversity has shifted between time periods, such that the proportion of all wild fish returning to the Skeena River that are not from the Babine population has declined by 1/4
Using modern molecular tools and century-old fish scales we show that wild sockeye salmon populations in Canada have declined more over the last century than are currently recognized

Summary

Introduction

Declines in population abundance of many of Earth’s biota are outpacing species extinctions (Hughes, Daily, & Ehrlich, 1997), and disrupting ecosystems and human cultures. Managers rarely have the historical information required to assess changes in abundance over more than a few decades, even for common species (Bonebrake, Christensen, Boggs, & Ehrlich, 2010) The absence of such historical data can lead to a shifting baseline syndrome (sensu, Pauly, 1995), whereby abundances in recent decades are incorrectly assumed to be the appropriate baselines against which to quantify trends, and assess current status. This can impair the characterization of risk, hide a legacy of stressors, and delay conservation action (Soga & Gaston, 2018). Salmon can exhibit large fluctuations in abundance, which at times are

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