Prey preference and the consumption of sea urchins and juvenile abalone by captive rock lobsters (Jasus lalandii )

Abstract

Recent studies on the diet of the South African rock lobster (Jasus lalandii) have shown an increase in the consumption of sea urchins in certain areas relative to earlier assessments. Concurrent ecological surveys have demonstrated the dependence of juvenile abalone on urchins for their survival, and a radical increase in the abundance of lobsters in the area that is the main abalone fishing ground. This paper describes laboratory experiments on the consumption of urchins by lobsters, and the preferences for different prey species. Small lobsters (<68 mm carapace length) ate no urchins. Larger lobsters ate urchins of all sizes, although small urchins were preferred. The consumption rate was easily sufficient for the lobsters to have caused the documented disappearance of urchins (and juvenile abalone) in the main abalone fishing area. Lobsters showed a strong preference for mussels over all other prey offered, and for juvenile abalone over urchins, although previous field observations and laboratory experiments have shown that urchins provide shelter for juvenile abalone. However, if black mussels were available in addition to sea urchins and juvenile abalone, consumption of sea urchins and juvenile abalone declined.