Life-history parameters of white stumpnose Rhabdosargus globiceps (Pisces: Sparidae) in Saldanha Bay, South Africa, with evidence of stock separation

Abstract

White stumpnose Rhabdosargus globiceps were sampled over 24 months in Saldanha Bay on the west coast of South Africa. The species is a rudimentary hermaphrodite, with < 1% of mature fish having simultaneously developed ovaries and testes. Spawning activity extended from September to March and peaked in October and February. Mature males developed spawning colouration in spring, which can be used as an indicator of spawning activity. The amount of abdominal fat correlated with the spawning cycle in both sexes, suggesting that abdominal fat reserves are used in the development of gonads. Seasonal variation in the condition index suggests a slightly greater investment in reproduction by males than females. Females grew slightly faster than males and attained a larger size. The Saldanha Bay fish grew more rapidly and matured earlier than fish from populations on the south coast of South Africa. Age-at-50% maturity was 2+ for females and 1+ for males, and size-at-50% maturity was 222 mm (fork length) for females and 194 mm for males. It is necessary to use area-specific growth and life-history parameters for the assessment of the stock status of white stumpnose in South Arica.

Keywords: growth; life history; reproduction; Rhabdosargus globiceps; Saldanha Bay; stock separation

African Journal of Marine Science 2010, 32(1): 23-36