Reproductive biology of female blue shark Prionace glauca in the southeastern Pacific Ocean

Abstract

An understanding of reproductive biology is important in evaluating the potential impacts of fisheries on shark population dynamics. Reproductive biology of the female blue shark (Prionace glauca) was evaluated using data collected in the Chinese Longline Fishery Scientific Observer Programme in the southeastern Pacific Ocean during July–November 2003 (Trip 1) and February–December 2006 (Trip 2). The fork length of gravid females varied from 170 to 246 cm (mean = 201 cm) in Trip 1 and from 168 to 220 cm (mean = 188 cm) in Trip 2. Gravid size was significantly different among months. The relationship between the proportion of gravid females and female size could be quantified by a logarithmic model. Litter size varied from 13 to 68 (mean 35) and was weakly correlated with maternal size. The sex ratio of captured blue sharks was significantly different from 1:1, while the sex ratio of pups was not significantly different from 1:1. Pup size (combined sexes) ranged from 12 to 39 cm FL, with mean of 27 cm. No significant differences were detected in length distribution and median length between female and male pups. This study suggests that there are large spatial and temporal variations in key reproductive parameters of the blue shark, which should be considered in the assessment and management.