A description of spatial and temporal aspects of the lifecycle of chokka squid Loligo vulgaris reynaudii on the inshore spawning grounds and Agulhas bank off the South Coast of South Africa

Olyott, L.J.H. (2002) A description of spatial and temporal aspects of the lifecycle of chokka squid Loligo vulgaris reynaudii on the inshore spawning grounds and Agulhas bank off the South Coast of South Africa. Masters thesis, Rhodes University.

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Abstract

The chokka squid, Loligo vulgaris reynaudii, is a commercially important species supporting a large, high-value export fishery for South Africa. This study reviewed its population dynamics and reproductive biology. Biological information collected on biannual research cruises from September 1986 to April 1999 on the Agulhas Bank as well as information from commercial vessels operating in the inshore environment collected between April 1988 and July 1989 and again between June 1999 and May 2000 were analysed. Size ranges of juveniles, subadults and adults were calculated and used to determine seasonal distribution and abundance patterns. Based on Gonadosomatic Indices (GSI) and percentages of mature squid in each month, two peak reproductive seasons in summer and winter were identified although mature squid were present all year round. Seasonal peaks in sex ratio were also apparent with males outnumbering females by up to 4:1 in the peak-breeding season. The size at which squid matured, demonstrated both spatial and temporal patterns. Squid caught in spring matured at a smaller size than squid caught in autumn and at successively smaller sizes from west to east across the Agulhas Bank. Size at maturity was highly variable especially in males where “sneaker males” were evident in both seasons. Length-to-weight linear regression revealed significant differences between maturity stages and between sexes. Females demonstrated steeper length-to-weight regression slopes than males in the peak-breeding seasons. Aspects of squid biology pertinent to fishery management were highlighted as well as potential areas where research should be directed in order to develop future stock assessment models.

Item Type:Thesis (Masters)
Uncontrolled Keywords:Loliginida, Squids, South Africa, Chokka, Loligo vulgaris reynaudii, Aghulas Bank
Subjects:S Agriculture > SH Aquaculture. Fisheries. Angling
Divisions:Faculty > Faculty of Science > Ichthyology & Fisheries Science
ID Code:2834
Deposited By: Mrs Carol Perold
Deposited On:21 May 2012 13:26
Last Modified:21 May 2012 13:26
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