High reproductive potential of the commercially exploited shark Squalus suckleyi in the major fishing grounds of the western North Pacific.

The present study examined body length (precaudal length, PCL) and age at sexual maturity, as well as fecundity and maternal investment in the Pacific spiny dogfish Squalus suckleyi, a long-term commercially exploited shark in the western North Pacific, using samples caught in several fisheries and across seasons. The PCL and age at 50% sexual maturity of males were 60.6 cm and 9.4 years, respectively, and those of females were 73.1 cm and 17.8 years, respectively. The PCL and age at 50% maternity were 77.4 cm and 19.7 years, respectively. General or generalized linear models revealed that capture by different fishing method did not significantly correlate with sexual maturity and maternity rates or litter size. Other general linear models revealed an increase in offspring size with maternal size, but litter size was not affected by embryonic development. These findings indicate that the reproductive potential of Pacific spiny dogfish is relatively high throughout the whole North Pacific region because of a smaller size and earlier age at sexual maturation in both sexes. In addition, pregnant females displayed no resting phase and produced 0.45 more embryos per centimetre of PCL in their lifetime after the onset of maturity, which is higher than in the eastern North Pacific. We suggest that these qualities are not a consequence of stock decline associated with the long-term exploitation of the species, but that its high reproductive potential has likely contributed to the long-term stability of the landings in Japan. SIGNIFICANCE STATEMENT: While reproductive potential has been determined for many fish species, such information is scarce for Pacific spiny dogfish. We evaluated the reproductive characteristics of this species in the major fishing grounds of the western North Pacific. The productivity and rebound potential of sharks is extremely low compared with those of bony fishes. However, our results indicate that even if the reproductive potential has a small effect on the population dynamics, it should not be ignored for sustainable stock utilisation.