Reproductive biology and fisheries of mako and blue sharks in the Pacific Ocean
Insights into the reproductive biology and fisheries of two commercially exploited species, shortfin mako (Isurus oxyrinchus) and blue shark (Prionace glauca), in the south-east Pacific Ocean
Carlos Bustamante, Michael B. Bennett
In 2005 and 2010, 1241 Isurus oxyrinchus and 1153 Prionace glauca were collected from 178 longline sets in a ship-board observer programme in coastal waters off Caldera, Chile (27°S). Catch composition was significantly biased towards I. oxyrinchus in 2005, but both species were caught in the same proportion in 2010. The sex ratio for I. oxyrinchus and for P. glauca did not differ significantly from unity within or between years. Sharks matured (L50) at a total length of 190.3 cm for male and 199.2 cm for female for P. glauca, and 180.2 cm for male I. oxyrinchus. Size-at-maturity for female I. oxyrinchus was not determined due to the near absence of mature specimens examined. Generalised additive models (GAMs) were used to examine catch per unit effort (CPUE) in relation to sea surface temperature, wind speed, time of day, hook depth and soak time. The GAMs revealed a significant effect of depth on P. glauca CPUE, and depth and wind speed for I. oxyrinchus CPUE. The predominance of small, immature sharks caught in the coastal, artisanal fishery indicates that both species may use the area as a pupping, and possibly a nursery zone during spring and summer. National data on catch composition and annual landings provide evidence of an increasing trend to land P. glauca, possibly to satisfy the international shark fin trade. Conservation measures, such as the introduction of a minimum capture size for sharks to protect the recruitment into the population, conservative fishing quotas and delimitation of fishing areas are necessary to ensure the sustainability of both species in the region.
Fisheries Research, Volume 143, In Progress, June 2013