Diet of the yellowtail surgeonfish Prionurus punctatus (Gill, 1862) on the rocky reef of Los Frailes, Baja California Sur, México

We investigated the diet of the yellowtail surgeonfish Prionurus punctatus (Gill, 1862), determined from the stomach contents of 120 individuals, caught monthly from November 2004 to October 2005 on the Los Frailes reef, B.C.S., Mexico. Of all organisms caught, 86 had food in their stomachs, and 34 were empty. In order to characterize the diet by sex, by size and by season, the frequency of occurrence and gravimetric methods were used in the combined index of relative importance (IRI). We determined that the yellowtail surgeonfish P. punctatus is a strict herbivore; overall, we identified 25 food items, of which 15 algae belonged to the Class Rhodophyceae, 7 to the Chlorophyceae, and 3 to the Phaeophyceae. According to the IRI, the most important algae in the diet were: Rhodophyta (20.48%), Gracilaria sp. (15.98%), unidentified organic matter UOM (12.56%), Chlorophyta (9.75%), Hypnea musciformis (9.15%), Jania mexicana (6.17%), Sphacelaria sp. (4.29%) and Dictyotaflabellata (4.05%). The diversity of the diet was intermediate (H′ = 2.48); the diet also varied according to size and season. This could be due in part to size segregation in yellowtail surgeonfish; with smaller sizes feeding in shallower areas, and medium and large sizes feeding in deeper areas. The availability of algae on the reef on which P. punctatus feed varies spatially as well as with the season.