Observations on the biology of the Pacific sharpnose shark (Rhizoprionodon longurio, Jordan and Gilbert, 1882), captured in Southern Sinaloa, México

Abstract

The Pacific sharpnose shark, (Rhizoprionodon longurio, Jordan and Gilbert, 1882), migrates along the Pacific coast of Mexico. It is captured with gillnets and bottom long lines commonly used in the artisanal fishery of Mazatlan. From a sample of 3 464 individuals, R. longurio was observed to be a viviparous shark of small size, which is born at an average length of 31 cm total length (TL), after a gestation period of 10 to 11 months. The number of embryos showed no statistical relationship to the TL. The average number of embryos per female was 7.4 (σ = 2.01, n = 146) and sex ratio was 1:1. Observations on the growth of the claspers indicated that male maturity begins at 93 cm TL. The two smallest gravid females measured were 83 and 87 cm TL. The rest of the gravid females were at least 92 cm TL. Between 90 and 95 cm TL, the females exhibited an increase in the width of the oviducal gland and its size ranged from 5 to 12 mm. The statistical relationship between weight and length is presented in which females reach a larger size than males. The diet of R. longurio was composed principally of crustaceans and demersal teleost fishes.