Variation in evacuation rates of different foods skew estimates of diet in the western rock lobster Panulirus cygnus

Abstract

Knowledge regarding differences in evacuation rates of diet items from a consumer’s stomach is important when using gut content analysis to quantify consumer diet. Evacuation rates of three diet items (pilchards, crabs and coralline algae) from the foreguts of western rock lobsters (Panulirus cygnus) were compared in aquaria. To determine evacuation rates, lobsters were allowed to consume offered food over a 90-min feeding period before being killed at 4, 6, 8, 10 and 12 h after the feeding period concluded. Diet items differed in their rate of evacuation from lobster foreguts with coralline algae evacuated most rapidly, followed by crabs, then pilchards. The evacuation of crabs and pilchards was still not complete 12 h after the feeding period concluded. Food not evacuated after 12 h predominantly consisted of hard components of the lobster diet, indicating that it is these components that account for slower evacuation. Observed variation in evacuation rates between diet items may skew the results of studies that use gut content analysis to quantify the diet of western rock lobsters.