Stomach contents of the Pacific sharpnose shark, Rhizoprionodon longurio (Carcharhiniformes, Carcharhinidae) in the SE Gulf of California, December 2007-March 2008.

Abstract

Abstract. The feeding habits of the sharpnose shark Rhizoprionodon longurio of the SE Gulf of California are described using the stomach contents of 251 specimens (136 males and 115 females) obtained weekly from December 2007 to March 2008 in the two main landing sites of the artisanal fishing fleet of Mazatlan. Total length (TL) ranges were 52-120 cm (females) and 60-140 cm (males). The mean TL values (79.00 ± 13.52 and 79.72 ± 17.65 cm TL for females and males, respectively), were not significantly different (Mann-Whitney test, P =0.373). TL distribution showed two modal groups (juveniles: 52-80 cm, mode 72.5 cm, and adults: 85-140 cm, mode 92.5 cm). Out of the 395 preys identified in 235 stomachs with identifiable contents, the most important were cephalopods (Index of Relative Importance, IRI = 93.06%), mainly Argonauta spp. (IRI = 92.93%). The total IRI value for fish was 5.9%, mostly represented by Oligoplites refulgens and Oligoplites sp. (joint IRI value = 4.83%). Diversity, equitability and dietary breadth indexes tended to be lower in juveniles than in adults, but ANOSIM analysis did not show differences related to age and sex. The results indicate a specialized feeding behaviour, with Argonauta spp. as preferred prey. This behaviour does not agree with all previous information on R. longurio , and is probably due to the local availability of this prey.