Here, we analyze an extensive data set from the southwestern Atlantic Ocean based on commercial longline fisheries and address several aspects of its reproductive ecology and population structure. However, available information is disproportionately distributed across its range, and many aspects of its biology are still poorly understood, limiting our capacity to assess stock status and develop adequate management strategies. The blue shark (Prionace glauca) is one of the most abundant and wide-ranging shark species in the world, and also one of the most heavily fished and traded. It is not yet clear whether regional differences in median maturity exist for shortfin mako and blue sharks. Blue shark males matured at about 190-195 cm and females at 170-190 cm however these estimates were hampered by small sample sizes, difficulty obtaining representative samples from a population segregated by sex and maturity stage, and maturation that occurred over a wide length range. Shortfin mako males matured at 180-185 cm and females at 275-285 cm. New Zealand porbeagles therefore mature at shorter lengths than they do in the North Atlantic Ocean. Porbeagle shark males matured at 140-150 cm fork length and females at about 170-180 cm. Some data sets were sparse, particularly over the vital maturation length range, but the availability of multiple indicators of maturity made it possible to develop estimates for both sexes of all three species. Direct maturity estimates were made for smaller numbers of sharks sampled at recreational fishing competitions. Data on clasper development, presence or absence of spermatophores or spermatozeugmata, uterus width, and pregnancy were collected by observers aboard tuna longline vessels. Reproductive data collected from porbeagle, shortfin mako, and blue sharks caught around New Zealand were used to estimate the median length at maturity.
0 Comments
Leave a Reply. |