Preliminary assessment of the biology and fishery for the narrow-barred Spanish mackerel, Scomberomorus commerson (Lacépède, 1800), in the southern Arabian Gulf

The population biology and fishery for Scomberomorus commerson in the southern Arabian Gulf were investigated using a combination of size frequency, biological and size-at-age data. Transverse sections of sagittal otoliths showed structural increments consisting of alternating translucent and opaque bands, which were used to estimate age. Edge analysis revealed an annual periodicity of formation with opaque zones being deposited between May and July in association with increasing seawater temperatures. The maximum absolute age estimates were 16.2 years (males) and 15.3 years (females). Initial growth was rapid with fish reaching more than half the asymptotic size by their second year and there were no significant differences in growth characteristics between sexes. Parameter values of the von Bertalanffy growth function fit to size-at-age data (males and females combined) were: k = 0.21, L∞ = 138.6 cm (LF) and t0 = −1.9 years. Spawning occurred between April and August, the mean sizes and ages at first sexual maturity were 72.8 cm LF (1.9 years) for males and 86.3 cm LF (2.1 years) for females. The size at which fish were fully recruited to the fishery (62.6 cm LF) was considerably smaller than both the mean size at first sexual maturity for females and the size at which yield per recruit would be maximised (95.6 cm LF). Furthermore, the annual instantaneous fishing mortality rate of 0.62 year−1 (0.46-0.79 year−1 95% CI) was by far in excess of the precautionary target (Fopt = 0.13 year−1) and limit (Flimit = 0.17 year−1) biological reference points, indicating that the resource is heavily over-exploited. The results suggest that an increase in mesh size regulations for gillnets in combination with a substantial reduction in fishing effort will be required if resource conservation and stock rebuilding objectives are to be achieved. The study also highlights the need for a strategic regional approach to the assessment and management of this highly migratory species.