Alternate explanations of the dispersal pattern of galjoen Dichistius capensis

Abstract

The movement behaviour of galjoen Dichistius capensis (mm total length) was studied by using a tag and recapture technique. A total of 25 191 galjoen was tagged at four sites in South Africa. Three of the sites were in fully protected reserves (two in the De Hoop Marine Protected Area, one in the Tsitsikamma National Park), whereas the fourth site was at the Cape Peninsula where fishing is permitted. In all, 2 174 fish were recaptured, some of them several times. The vast majority of fish were caught at the site of release. After correcting for differences in recovery effort between the release sites and other areas, it was estimated that 95% of tagged fish remained at the release site. The remaining 5% moved throughout the South African range of galjoen, which was separated from the Namibian range. There was no evidence to suggest that movement is linked to season, age or sex. Although not territorial, galjoen do hold home ranges, which were estimated to be no larger than 1.38km in extent, but probably much smaller. Two likely models, the polymorphic and the tourist, are advanced to explain the movement behaviour. The polymorphic model is a combination of two movement patterns, one resident and another nomadic. The balance between the two may represent a mixed evolutionary stable strategy. The tourist model does not differentiate between fish. Each fish spends its time at a small number of widely separated sites, moving between them as conditions dictate. The tag and recovery data do not favour one model above the other unequivocally.

African Journal of Marine Science 2005, 27(1): 141–156