Factors affecting spatial variability in seine net catches of fish in the surf zone of False Bay, South Africa

Abstract

Ichthyofaunal assemblages at 11 surf zone localities along the perimeter of False Bay South Afnca were sampled by seine netting at monthly intervals between July 1991 and June 1993 Sampllng localit~es were selected to encompass as wide a range of physical vanables as possible incorporatlng sheltered, exposed, sandy and mixed-shore habitats, thus providing a colnprehensive assessment of the factors lnfluenclng surf zone fish assemblages Data collected at each site were averaged over the 2 yr p e i ~ o d in order to highlight the influence of various physical environnlental vanables on the abundance and co~nmunity structure ot these assemblages Athenr~a brevlceps, Liza rlchardsonii and Rhahdosarg~ls g loh~ceps were numeiically domlnant at all sites together providing between 69 and 99%) of the catches Overall catches of juvenile flsh exceeded that ot adult fish, making up almost 53 of the catch Fish abundance (no ind per 100 m') and number of species recorded at each site ranged from 6 to 199 and from 12 to 31 respectivel) Multivdriate analyses Indicated that the deglee of wave exposure the presencc of emergent rock on the shore dnd turbid~ty were responsible for most of the spa t~a l vanab~l i ty in abundance and community structure observed Although of lesser importance abundance of detached macrophytes salinity dnd water temperature also played a role in structuring fish assemblages Species specific preferences for varying combinations of these var~ables are responsible for fluctuations in the structure and overall abundance of assemblages in different a r e a