© 2006 International Council for the Exploration of the Sea
A refined fish consumption model for lactating Cape fur seals (Arctocephalus pusillus pusillus), based on scat analyses
a Avian Demography Unit, Department of Statistical Sciences, University of Cape Town Rondebosch 7701, South Africa
b Lüderitz Marine Research, Ministry of Fisheries and Marine Resources PO Box 394, Lüderitz, Namibia
*Correspondence to S. Mecenero: tel: +27 21 6503648; fax: +27 21 6503434. e-mail: smecener{at}adu.uct.ac.za.
A refined fish consumption model for lactating Cape fur seals in Namibia during the eight-month lactation period, which allows for spatio-temporal variation in the diet as determined by scat analyses, has been developed. Previous estimates of prey consumption by Cape fur seals have been based mostly on coarse diet composition models. Sensitivity analyses showed that the energetic requirement and mass of lactating females (bioenergetic variables), as well as the energetic density of prey (diet variable), contributed most to the uncertainty in consumption estimates. Uncertainty in the remaining input variables had minimal effects on the estimates of food consumption. The consumption of commercial prey (horse mackerel, hake and pelagic fish) was greatest by the colony at Cape Cross. The model estimated that a female of average mass 55 kg ingested, on average, 11% of her body mass per day. This model is easily applied to other age/sex classes of the seal population. It permits improvement of the estimates of prey consumption by seals, which are useful for assessing levels of competitive interactions between seals and fisheries or other predators, or the impacts of seals on prey species.
Keywords: Cape fur seal, fish consumption, lactating females, model, Namibia, scat analysis, spatial variation, temporal variation
Received 6 May 2005; accepted 8 June 2006.