Retrospective stock assessment of the Emperor red snapper (Lutjanus sebae) on the Seychelles Bank between 1977 and 2006

Abstract

Abstract Grandcourt, E. M., Hecht, T., Booth, A. J., and Robinson, J. 2008. Retrospective stock assessment of the Emperor red snapper (Lutjanus sebae) on the Seychelles Bank between 1977 and 2006. – ICES Journal of Marine Science, 65: 889–898. The stock status of the Emperor red snapper (Lutjanus sebae) on the Seychelles Bank was determined between 1977 and 2006 using models of yield-per-recruit (YPR) and spawner-biomass-per-recruit (SBR). Demographic parameters were derived from size frequency and size-at-age data from validated annuli in sagittal otoliths. The long lifespan (tmax = 28 years), slow growth rate (k = 0.14), empirically estimated low natural mortality rate (M = 0.12), and late age at sexual maturity (tm = 9 years for males and females combined) predisposed the L. sebae resource to overfishing. Fish became vulnerable to the gear at a mean size (Lc50 = 39.8 cm LF) and age (3.1 years) before the attainment of sexual maturity at 62 cm LF. Consequently, there was a large proportion of immature fish in landings (51.2% on average) and the full growth potential for the resource might not have been realized. For most years, the fishing mortality rates and SBR approximated the limit reference point F30%. The potential for recruitment-overfishing was identified for some years (1990 and 2004), and the dramatic increase in recent yields is further evidence that management of this fishery requires urgent attention. Previous length-based assessments probably overestimated sustainable harvest rates, which should be between 6.7% and 7.2% of the SBR.