Research Document - 2008/021

Size at 50% maturity for Atlantic herring in the southern Gulf of St. Lawrence (NAFO 4T)

By C.H. LeBlanc and R. Morin

Abstract

DFO Fisheries Management Branch requested Science advice in November 2007 to determine whether the current 24.5 cm fork length size limit corresponded to the size at 50 % maturity for the southern Gulf of St. Lawrence (sGSL) Atlantic herring stocks (NAFO 4T). The herring population in the sGSL consists of a spring and a fall spawner component. Herring samples from the annual herring acoustic surveys and the annual groundfish surveys from the years 1995 to 2006 were chosen for the analysis because they were considered to be unbiased for gear selectivity. Immature and mature classes were generated from gonad maturity data. We fitted logistic models to the observed proportion of mature fish at each length to determine the median fork length (L₅₀) at maturity for both the spring and the fall spawning components. We estimated confidence limits of L₅₀ alternatively by bootstrapping the observed number of mature and immature herring within each year and spawning group, both on non-weighted and weighted maturity data. There were no significant differences of the L₅₀ at maturity between sexes but some differences between areas. Inter-annual variations in L₅₀ was highly significant, thus the data were analysed by year. After considering both spawning groups separately, the differences in L₅₀ were not significant for most years and the data was combined. To determine the most appropriate L₅₀ values, the models were fitted to the weighted acoustic survey biological data and the confidence limits were obtained by bootstrap simulations. The mean fork length at maturity (L₅₀) for the southern Gulf of St. Lawrence Atlantic herring stocks for the years 1999-2006 is estimated at 23.5 cm.

Complete document (PDF, 976 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.