Biological Observations of Shortfin Mako Shark (Isurus oxyrinchus) on Spanish Surface Longline Fishery Targeting Swordfish

Also posted as IOTC-2021-WPEB17(AS)-INF07

Reproductive data of 92 pregnant females were observed in 19,905 females across the Atlantic, Indian and Pacific oceans. Overall sex-ratio showed a slight but not significant predominance of females in the Atlantic and a slight but significant predominance of males in the Indian and Pacific. Litter-size varied from 3 to 17 (mean 11.6 embryos). The sizes of the females with embryos were ≥ 250cm FL. The SST range in which specimens were distributed was 12.7º31.5ºC but 16.5º-28.5ºC for females with embryos. The results show that the lower the SST the greater the mean size of the embryos. Several areas for parturition are described but no restrictive seasonality was identified in any of the hemispheres neither within any ocean, suggesting diverse periods with a peak in the boreal autumn (33.3%) and in the southern spring (48.6%). The data confirms low availability of pregnant females in all areas observed and low occurrence of gestation and parturition suggesting either that these phases are more likely occur in other areas, or that these pregnant females are not easily accessible to this oceanic fishing gear.