Evaluation of the sensitivity of biological reference points to the spatio-temporal distribution of fishing effort when seasonal migrations are sex-specific

Abstract

Offshore lingcod (Ophiodon elongatus) in British Columbia (B.C.) make seasonal migrations that differ by sex: in winter most adult males aggregate in shallow water and most adult females aggregate in deep water, while in summer both sexes distribute equally in deep and shallow water. We developed a semi-age structured delay-difference model that accommodates sex-, and age/depth-specific seasonal migration and examined the sensitivity of biological reference points for B.C. offshore lingcod to migration pattern and the allocation of fishing effort across seasons and depths. When a migration pattern with a homogeneous distribution of males and females in shallow and deep water throughout the year was assumed, the estimated maximum sustainable yield (MSY), biomass at MSY (B MSY), and percent spawning per recruitment at MSY (%SPR MSY) were robust to changes in effort allocation. However, when a migration pattern that assumed a winter distribution of 95% of adult males in shallow water and 95% of adult females in deep water was used, the estimated MSY, B MSY , and %SPR MSY were markedly sensitive to changes in effort allocation. These results suggest that incorporating sex-, age/depth-, and season-specific structuring in stock assessment models could enable improved evaluations of management options for B.C. lingcod and other species with sex-and season-specific migrations.

Evaluating Summer Flounder Spatial Sex‐Segregation in a Southern New England Estuary

“…Nonetheless, relatively few stock assessments incorporate sex‐specific life history characteristics due to the intensive data required (Okamura et al. ; Terceiro ) and uncertainty in whether local patterns represent stock‐wide characteristics. Although some of these data are available from fisheries‐independent surveys or landings (Wang et al.…”

“…Incorporating sex-specific information in fisheries stock assessments can be critical in understanding the structure and resiliency of fish populations. Research on several fish species has indicated that failing to account for sexual dimorphism in fish growth and natural mortality (Swain 1997;Swain and Morin 1997;Wang et al 2007;Gerritsen et al 2010;Su et al 2011;Loher et al 2016), differing fishery selectivity (Gerritsen et al 2010;Myers et al 2014;Loher et al 2016;Gonçalves et al 2017), and/or spatiotemporal sex-segregation (Swain 1997;Gerritsen et al 2010;Loher and Hobden 2012;Okamura et al 2014;Gonçalves et al 2017;Haugen et al 2017) may bias biological reference points and compromise the success of management strategies. Nonetheless, relatively few stock assessments incorporate sex-specific life history characteristics due to the intensive data required (Okamura et al 2014;Terceiro 2018) and uncertainty in whether local patterns represent stock-wide characteristics.…”

“…Research on several fish species has indicated that failing to account for sexual dimorphism in fish growth and natural mortality (Swain 1997;Swain and Morin 1997;Wang et al 2007;Gerritsen et al 2010;Su et al 2011;Loher et al 2016), differing fishery selectivity (Gerritsen et al 2010;Myers et al 2014;Loher et al 2016;Gonçalves et al 2017), and/or spatiotemporal sex-segregation (Swain 1997;Gerritsen et al 2010;Loher and Hobden 2012;Okamura et al 2014;Gonçalves et al 2017;Haugen et al 2017) may bias biological reference points and compromise the success of management strategies. Nonetheless, relatively few stock assessments incorporate sex-specific life history characteristics due to the intensive data required (Okamura et al 2014;Terceiro 2018) and uncertainty in whether local patterns represent stock-wide characteristics. Although some of these data are available from fisheries-independent surveys or landings (Wang et al 2007;Su et al 2013;Morson et al 2015;Loher et al 2016;Haugen et al 2017;Terceiro 2018), there is little information characterizing spatial variability or describing the sex-composition of fishery discards, further complicating incorporation of sex-specific information into stock assessments.…”

Estimating the Sex Composition of the Summer Flounder Catch using Fishery‐Independent Data

“…Recent work suggests that the inclusion of sex structure in stock assessment models is important for sexually dimorphic fishes. For example, if growth rates or natural mortality differ between male and female fish (Wang et al 2005;Su et al 2013), if sex-specific migratory behavior and fishing effort are not evenly distributed in space and time (Okamura et al 2014), or if fishery selectivity is sex specific (Myers et al 2014), then the absence of sex structure in the assessment model can bias biological reference points. In light of these recent findings, sex-structured assessment models are becoming more common in describing the population dynamics of fishes that have sexually dimorphic characteristics and/or behavior (Clark and Hare 2006;Wang et al 2007;Fenske et al 2011;Su et al 2011;McGilliard et al 2013).…”

A Lagrangian approach to model movement of migratory species

“…The migration cycle observed in many iteroparous species can vary in extent (i.e., distance or timing) for subgroups within a population, for example, for different age or size groups (Ressler et al 2007), sex (Okamura et al 2014), or substocks (Carlson et al 2014). This variability can lead to spatial segregation of subgroups within a fish population.…”