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Population biology and assessment of the white-spotted spinefoot, Siganus canaliculatus (Park, 1797), in the southern Arabian Gulf


Author's address: Edwin Grandcourt, Marine Environmental Research Centre, Environment Agency-Abu Dhabi, PO Box 45553, Abu Dhabi, United Arab Emirates.


The age, growth, mortality, reproduction and resource status of Siganus canaliculatus in the southern Arabian Gulf were investigated using a combination of size frequency, biological and size-at-age data. Defined structural increments consisting of alternating translucent and opaque bands in transverse sections of sagittal otoliths were validated as annuli. The maximum absolute age estimate was 7.8 years. Parameter values of the von Bertalanffy growth function fit to size-at-age data (males and females combined) were: k = 1.0, L = 24.8 cm (LF), to = −0.1 years. Fish in spawning condition were only observed between April and July although patterns in gonadosomatic indices suggested a second but less well defined spawning event in November. The mean sizes and ages at first sexual maturity were 21.5 cm LF (1.9 years) for males and 25.7 cm LF (2.1 years) for females. Fish were fully recruited to the fishery at a size (L100 = 19.7 cm LF) that was smaller than the sizes at which sexual maturity was attained. The annual instantaneous rate of fishing mortality (F = 0.85 year−1) (0.26–1.44 year−1 95% CI) was considerably greater than the target (Fopt = 0.33 year−1) and limit (Flimit = 0.44 year−1) biological reference points, indicating that the stock is overexploited.