Diet of Cape fur seals Arctocephalus pusillus pusillus at three mainland breeding colonies in Namibia. 1. Spatial variation

Abstract

The diet composition of Cape fur seals Arctocephalus pusillus pusillus was investigated from three breeding colonies in Namibia between January 1994 and April 2002 using scat analysis. Otolith numbers were corrected for those lost during digestion before determining the percentage numerical abundance of prey in each sample. Otolith diameters were corrected for erosion during digestion and then converted to fish length and mass to determine the percentage mass of prey in samples. In all, six main groups of teleost prey were identified, consisting of at least 48 species and 19 families. Cape Cross seals mainly consumed Cape horse mackerel Trachurus trachurus capensis, whereas lanternfish Lampanyctodes hectoris were negligible in their diet. At Van Reenen Bay and Atlas-Wolf Bay, the two southerly colonies, lanternfish were numerically prevalent in scats but not important in terms of mass. Cape hake Merluccius spp. and goby Sufflogobius bibarbatus featured in scats from all three colonies. The species in the pelagics prey group were of lesser dietary importance, with round herring Etrumeus whiteheadi being most prevalent in the south at Van Reenen Bay and anchovy Engraulis encrasicolus and sardine Sardinops sagax most prevalent in scats from Cape Cross. The difference in the prevalence of prey in seal diets seems to be related to fish distributions.

Keywords: Arctocephalus pusillus pusillus, breeding colony, Cape fur seal, diet, Namibia, scat analysis, spatial variation

African Journal of Marine Science 2006, 28(1): 57–71