Demographic resilience of brook trout populations subjected to experimental size-selective harvesting

Shannon H Clarke; Gregory R McCracken; Shelley Humphries; Daniel E Ruzzante; James W A Grant; Dylan J Fraser

doi:10.1111/eva.13478

Demographic resilience of brook trout populations subjected to experimental size-selective harvesting

Evol Appl. 2022 Sep 18;15(11):1792-1805. doi: 10.1111/eva.13478. eCollection 2022 Nov.

Authors

Shannon H Clarke¹, Gregory R McCracken², Shelley Humphries³, Daniel E Ruzzante², James W A Grant¹, Dylan J Fraser¹

Affiliations

¹ Department of Biology Concordia University Montreal Quebec Canada.
² Department of Biology Dalhousie University Halifax Nova Scotia Canada.
³ Lake Louise, Yoho, and Kootenay Field Unit, Parks Canada Radium Hot Springs British Columbia Canada.

Abstract

Sustainable management of exploited populations benefits from integrating demographic and genetic considerations into assessments, as both play a role in determining harvest yields and population persistence. This is especially important in populations subject to size-selective harvest, because size selective harvesting has the potential to result in significant demographic, life-history, and genetic changes. We investigated harvest-induced changes in the effective number of breeders ( ${\hat{N}}_{b}$ ) for introduced brook trout populations (Salvelinus fontinalis) in alpine lakes from western Canada. Three populations were subject to 3 years of size-selective harvesting, while three control populations experienced no harvest. The ${\hat{N}}_{c}$ decreased consistently across all harvested populations (on average 60.8%) but fluctuated in control populations. There were no consistent changes in ${\hat{N}}_{b}$ between control or harvest populations, but one harvest population experienced a decrease in ${\hat{N}}_{b}$ of 63.2%. The ${\hat{N}}_{b}$ / ${\hat{N}}_{c}$ ratio increased consistently across harvest lakes; however we found no evidence of genetic compensation (where variance in reproductive success decreases at lower abundance) based on changes in family evenness ( $\hat{FE}$ ) and the number of full-sibling families ( ${\hat{N}}_{fam}$ ). We found no relationship between $\hat{FE}$ and ${\hat{N}}_{c}$ or between ${\hat{N}}_{fam}$ / ${\hat{N}}_{c}$ and $\hat{FE}$ . We posit that change in ${\hat{N}}_{b}$ was buffered by constraints on breeding habitat prior to harvest, such that the same number of breeding sites were occupied before and after harvest. These results suggest that effective size in harvested populations may be resilient to considerable changes in N_c in the short-term, but it is still important to monitor exploited populations to assess the risk of inbreeding and ensure their long-term survival.

Keywords: effective population size; fisheries management; genetic compensation; population genetics.