BIOLOGICAL ASPECTS OF THE SHARKS RHIZOPRIONODON LALANDII AND RHIZOPRIONODON POROSUS (CARCHARHINIDAE-CARCHARHINIFORMES) CAPTURED BY ARTISAN FISHING IN ISLA FUERTE, COLOMBIAN CARIBBEAN

Abstract

Some biological aspects of the sharks Rhizoprionodon lalandii (Brazilian sharpnose shark) and R. porosus (Caribbean sharpnose shark), such as maturity and sexual segregation, biological indexes (gonadosomatic index, hepatosomatic index, and condition factor), and stomach contents were studied. Between September and December 2007 a follow-up of the captures of those sharks by the artisan fishing carried on around Isla Fuerte was made. 49 individuals of the Caribbean sharpnose shark were analyzed, 55 % of them immature or juvenile; as well as 39 specimens of the Brazilian sharpnose shark, 59 % of them immature individuals. Rhizoprionondon porosus showed a sex ratio (male:female) 9:1 and R. lalandii 1:9, giving evidence of sexual segregation. A significant correlation exists between the gonadosomatic index and the condition factor (r= 0.93, p= 0.002, n= 7) for the females of the Brazilian sharpnose shark in stage 4 of maturity. On the other hand, in agreement with the index of relative importance, bony fishes and shrimps were the main prey items of R. porosus and R. lalandii, respectively.