Age and growth and a preliminary stock assessment of stonebream Neoscorpis lithophilus (Pisces : Scorpididae) along the KwaZulu-Natal coast, South Africa

Abstract

The age and growth of the endemic scorpidid Neoscorpis lithophilus was investigated by use of whole otoliths from specimens collected along the KwaZulu-Natal coast, South Africa. Comparison between counts of growth increments from whole and sectioned otoliths showed no significant difference. Marginal increment analysis and oxytetracyline labelling were used in an attempt to validate the annual periodicity of growth increment deposition. A von Bertalanffy growth function gave an acceptable fit to the length-at-age data and the parameters L_∞ = 413.4 mm fork length, K = 0.222 year^–1 and t₀ = –0.981 described the growth of N. lithophilus for both sexes combined. The study revealed that N. lithophilus is a reasonably fast-growing species reaching an age of at least 10 years. Total fishing mortality rate (Z = 0.44 year^–1) was estimated from the slope of the descending limb of a catch curve, natural mortality (M = 0.29 year^–1) was estimated by empirical methods and fishing mortality (F = 0.15 year^–1) by subtraction. Yield and spawning biomass per-recruit modelling revealed that the stock of N. lithophilus off KwaZulu-Natal is not overexploited.