Filling gaps in the biology and habitat use of two spurdog sharks (Squalus japonicus and Squalus brevirostris) in the East China Sea.

The conservation and management of sharks requires appropriate information on their biological and habitat characteristics. Data needed for the conservation and management of two dominant demersal shark species in the East China Sea, the spurdogs (Squalus japonicus and Squalus brevirostris), are inadequate. To remedy this, we analysed biological, catch and abiotic data from bottom trawl surveys conducted in 2000–05 and 2008–14 from within the East China Sea. The precaudal length of male and female S. japonicus at 50% sexual maturity was 396.1 and 459.9 mm respectively, whereas for S. brevirostris it was 289.6 and 354.9 mm respectively. Prey overlap was high between species, with lanternfishes the most important prey. The fractional trophic level was 4.33 for S. japonicus and 4.31 for S. brevirostris. We estimated spurdog habitat using a generalised additive model. Depth affected the presence of both sharks, with latitude also affecting the presence of S. brevirostris. These two spurdog species were spatially segregated over the continental slope, and body-length and sex-ratio distributions suggested that there was a maturity-based segregation within and among species. The results of this study improve our understanding of the population dynamics of these spurdog species, their reproduction and diet, fundamental information required for their conservation and for improved fisheries management. Biological characteristics and habitat use of two data-deficient spurdog shark species, namely Squalus japonicus and Squalus brevirostris , are described from fishery-independent bottom trawl surveys. Prey overlap was high between species and estimated length at sexual maturity suggested that populations of either species have not declined. Body length and sex ratio distributions of these two spurdog species suggest that they segregate over the continental slope and that there was a maturity-based segregation. [ABSTRACT FROM AUTHOR]