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

Abstract

Models that account for sex‐specific behavior and population dynamics are becoming more common in the stock assessment of sexually dimorphic fishes. However, such models can be data intensive and require some knowledge or assumptions about the sex ratio of fishery landings. A recent stock assessment review of Summer Flounder Paralichthys dentatus identified the need to account for sex‐specific fishing mortality in the assessment model; however, no data on the sex composition of the catch were available. Fishery‐independent, sex‐specific information for this species is collected annually by the National Marine Fisheries Service's Northeast Fisheries Science Center during their bottom trawl survey. Sex at age from the survey could be applied to the fishery landings if the probability of landing a given sex at a given age is equivalent for fish collected by the survey and those in the landings. To generate the first regionally comprehensive database on the sex ratio of Summer Flounder landings and to determine the efficacy of using survey sex‐at‐age keys to estimate the sex of landed fish, we recorded the sex composition of the commercial and recreational catches of Summer Flounder (n = 31,912) in 2010 and 2011. When (1) trawl survey length data were left‐truncated to simulate the minimum retention sizes in the fisheries and (2) age–length keys generated from fishery‐dependent data were applied to length frequency distributions from the survey to simulate the growth rates of landed fish, the sex‐at‐age pattern in the survey‐derived data closely resembled the patterns in the catch. However, statistically significant differences in sex at age remained between the catch and the survey‐derived data. We hypothesize that these differences are attributable to differences in the spatiotemporal distributions of the sexes and of the survey and fishing effort. Received March 9, 2015; accepted June 23, 2015

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

“…Further, the scarcity of large males implies that these older individuals may stay farther offshore, as has been hypothesized in past work (Morson et al. , ). As a result, the habitat preferences of such individuals cannot be characterized by the findings presented here.…”

“…Females dominated the captured fish larger than 45 cm (Figure ), and the sex ratio of observed flounder legal for recreational harvest was more extreme than those reported by the fishery‐dependent sampling efforts of Morson et al. (, , ) and the 2013 Benchmark Stock Assessment (NEFSC ). This discrepancy is perhaps due to the greater emphasis on shallower depths in this study.…”

“…; Morson et al. , , ). Females dominated the captured fish larger than 45 cm (Figure ), and the sex ratio of observed flounder legal for recreational harvest was more extreme than those reported by the fishery‐dependent sampling efforts of Morson et al.…”

“…) and may even be available from recreational anglers or party and charter vessels (Morson et al. ). Such predictions could provide further insight into the finer spatial characteristics of the species’ sex‐specific habitat preferences.…”

“…Sex was determined by visual inspection of the gonads as in Morson et al. (). Small individuals with underdeveloped gonads that were unable to be sexed were excluded from analyses.…”