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ICES Journal of Marine Science: Journal du Conseil 2006 63(9):1649-1664; doi:10.1016/j.icesjms.2006.06.011
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© 2006 International Council for the Exploration of the Sea

Spatio-temporal patterns in maturation of the chokka squid (Loligo vulgaris reynaudii) off the coast of South Africa

L.J.H. Olyotta,*, W.H.H. Sauerb and A.J. Boothb

a Department of Primary Industries and Fisheries Queensland, GPO Box 46, Brisbane, Queensland 4001, Australia
b Department of Ichthyology and Fisheries Science, Rhodes University PO Box 94, Grahamstown 6140, South Africa

*Correspondence to L. J. H. Olyott: tel: +61 7 3405 6822; fax: +61 7 3224 2805. e-mail: Leonard.Olyott{at}dpi.qld.gov.au.

Knowledge of the temporal and spatial characteristics of chokka squid (Loligo vulgaris reynaudii) biology in South African waters is limited, so the possibility of there being a geographically fragmented stock was examined by investigating the distribution of maturity patterns for the species, covering all known spawning areas and using both historical and recent data. Gonadosomatic indices (GSI) varied between year-round consistency and apparent seasonal peaks in both summer and winter; there was no clear spatial pattern. Monthly percentage maturity provided further evidence for two peak reproductive periods each year, although mature squid were present throughout. Sex ratios demonstrated great variability between different areas and life history stages. Male-biased sex ratios were only apparent on the inshore spawning grounds and ranged between 1.118:1 and 4.267:1. Size at sexual maturity was also seasonal, squid maturing smaller in winter/spring than in summer/autumn. Also, squid in the east matured smaller than squid in the west. Although the results from the present study do not provide conclusive evidence of distinct geographic populations, squid likely spawn over a significantly larger area of the Agulhas Bank than previously estimated, and squid on the west coast of South Africa may return to spawn on the western portion of the Agulhas Bank. It remains likely, however, that the east and west coast populations are a single stock and that migration of juveniles to the west coast and their subsequent return as sub-adults is an integral but non-essential and variable part of the life history.

Keywords: biology, chokka squid, Loligo vulgaris reynaudii, spatial, temporal, variability

Received 19 December 2005; accepted 29 June 2006.


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