Spatial patterns in the biology of the chokka squid, Loligo reynaudii on the Agulhas Bank, South Africa |
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Authors: | L J H Olyott W H H Sauer A J Booth |
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Institution: | (1) Department of Primary Industries and Fisheries, Queensland, GPO Box 46, Brisbane, QLD, 4001, Australia;(2) Department of Ichthyology and Fisheries Science, Rhodes University, P.O. Box 94, Grahamstown, 6140, South Africa |
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Abstract: | Although migration patterns for various life history stages of the chokka squid (Loligo reynaudii) have been previously presented, there has been limited comparison of spatial variation in biological parameters. Based on
data from research surveys; size ranges of juveniles, subadults and adults on the Agulhas Bank were estimated and presented
spatially. The bulk of the results appear to largely support the current acceptance of the life cycle with an annual pattern
of squid hatching in the east, migrating westwards to offshore feeding grounds on the Central and Western Agulhas Bank and
the west coast and subsequent return migration to the eastern inshore areas to spawn. The number of adult animals in deeper
water, particularly in autumn in the central study area probably represents squid spawning in deeper waters and over a greater
area than is currently targeted by the fishery. The distribution of life history stages and different feeding areas does not
rule out the possibility that discrete populations of L. reynaudii with different biological characteristics inhabit the western and eastern regions of the Agulhas Bank. In this hypothesis,
some mixing of the populations does occur but generally squid from the western Agulhas Bank may occur in smaller numbers,
grow more slowly and mature at a larger size. Spawning occurs on the western portion of the Agulhas Bank, and juveniles grow
and mature on the west coast and the central Agulhas Bank. Future research requirements include the elucidation of the age
structure of chokka squid both spatially and temporally, and a comparison of the statolith chemistry and genetic characterisation
between adults from different spawning areas across the Agulhas Bank. |
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Keywords: | Chokka Loligo reynaudii Agulhas Bank Biology Spatial patterns |
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