Biology and management of the Cape gurnard, Chelidonichthys capensis (Order Scorpaeniformes, Family Triglidae) in South Africa

McPhail, Amanda Sue (1998) Biology and management of the Cape gurnard, Chelidonichthys capensis (Order Scorpaeniformes, Family Triglidae) in South Africa. Masters thesis, Rhodes University.

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Abstract

The South African demersal trawl fishery, as with most trawl-directed fisheries worldwide, has a substantial bycatch component. With increasing commercial emphasis being placed on retained bycatch, an urgent need has arisen to investigate these species. In the past the bycatch component has received little research or management attention. Members of the gurnard family Triglidae make up up to 2.4 % of the South African hake-directed demersal catch and are thus considered an important bycatch species. The catch history and biology, including population structure, reproduction, feeding, age, growth and mortality, of the Cape gurnard, Chelidonichthys capensis, sampled from the Agulhas Bank, South Africa, were thus investigated. Males (mean TL = 366mm) were significantly smaller than females (mean TL = 411mm). The sex ratio was close to parity, males being more dominant in commercial trawls and less dominant in research trawls. Gonad maturation and gonadosomatic indices showed this species to have an extended spawning period with peaks in reproductive activity during September, January and April. First approximations of size at 50 % maturity were similar for females (349mm TL) and males (348mm TL) but differed significantly in terms of age (3.6 years and 4.6 years respectively). Otolith growth marks were validated as annuli using marginal zone analysis. The maximum age estimated was 16 years for a female of 675mm TL and recruitment to the commercial fishery was estimated as taking place in the fifth year of growth for both males and females. Gut content analysis showed C. capensis to be an opportunistic feeder preying preferentially on the benthic crustaceans Goneplax angulata and Mursia cristimanus. Landings from the commercial linefishery were insignificant whilst those for the commercial trawl fishery ranged from 500 tonnes to 3250 tonnes b~tween 1984 to 1995, and indicated that this species forms an important component of the South African trawl fishery bycatch. A first approximation of fishing mortality (0.36 year-I) for the inshore commercial trawl fishery was higher than that of natural mortality (0.25 year-I) suggesting some fishing pressure on this species on the Agulhas Bank. However this fishing mortality value was significantly less than that for Fo.1 (4.78 year-I) that was estimated using a yieldper- recruit model. VIII

Item Type:Thesis (Masters)
Uncontrolled Keywords:Scorpaeniformes, Cape Gurnard, Chelidonichthys capensis, South Africa
Subjects:Q Science > QL Zoology > Chordates. Vertebrates > Fishes
Divisions:Faculty > Faculty of Science > Ichthyology & Fisheries Science
Supervisors:Buxton, Colin and Hecht, Tom and Sauer, Warwick
ID Code:3085
Deposited By: Mrs Carol Perold
Deposited On:04 Jul 2012 13:20
Last Modified:04 Jul 2012 13:20
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