Modelling the relative impacts of trawling and longlining on Cape hake Merluccius capensis on the inshore Agulhas bank

A Geographic Information System (GIS) is used to elucidiate vertical and horizontal patterns of distribution of Merluccius capensis on the inshore south coast (20°-27°E) of South Africa. Catch data used to compare the size distribution in catches made by commercial trawls and longlines off the South Coast (20°E). Results show that M.capensis size increases with depth and that the distribution of fish < 30 cm is mostly west of 23° E with isolated pockets east of that region. No seasonal differences were found in the distribution of this species. Spatial mapping of survey trawl and longline grounds of the Agulhas bank whereas longlines operate over rocky areas. Size comparisons of the catches of the two fishing methods reveal that longlines catch very few fish that are < 60 cm whereas trawl cataches are dominated by M. capensis of length < 60 cm. Analyses also revealed sex compostion in longline cataches to be different to that of trawls. All these results are discussed in relation to the ecology of M. capensis and the areas where data come from. Using size selectivity properties, the potential impacts of longlining and commercial trawling on the South Coast M. capensis (east of 20° E) are modelled with a yield per recruit and spawner biomass per recruit model. First, the age-specific selectivity vectors of the two fleets are estimated from catch data (length frequencies).

Grantor dc:publisher.institution

Department of Biological Sciences

Year dc:date.issued

2001

Author dc:creator

• Jayiya, Terence Phinda

Advisors dc:contributor.advisor

• Field, John G
• Moloney, Coleen
• Leslie, Rob

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/6105

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/6105