Addressing caveats in current skate fisheries management: a comparative study on the morphometry and life history traits of commercially important skates blonde ray Raja brachyura and thornback ray Raja clavata.

Abstract European skate fisheries management lacks species-specific measures due to data limitation and issues in species-specific reporting. Given these caveats, detailed information on commercially relevant skate stocks at species level is warranted. The morphometry and life-history parameters of 152 individuals (59 Raja brachyura, and 93 R. clavata) were determined for samples collected by observers within commercial fisheries, and two scientific surveys (December 2020 - August 2021) in the Southern North Sea and Eastern English Channel. The morphometry significantly differed between R. brachyura and R. clavata. Morphometric shape descriptor ratios were considered and proven more succesful in species discrimination than linear morphometric measurements. Length-weight relationships indicated faster growth for R. clavata. Age was assessed by visual inspection of enhanced vertebral centra, allowing derivation of von Bertalanffy growth parameters. The macroscopic maturity was determined, and the relationship between body size and sexual development was ascertained in maturity ogives following logistic regression. Maturity assessment revealed interspecific and intersexual differences where male R. clavata matured at the smallest size (L50 = 654 mm) and earliest age (A50 = 10.8 yrs) while female R. clavata matured at the largest size (L50 = 839 mm) and latest age (A50 = 11.5 yrs). The morphometry of congeners R. clavata and R. brachyura significantly differs, which is reflected in the life history traits: length-weight relationships, growth, and reproductive biology. These interspecific differences once again highlight the need for species-specific data collection and management considerations of commercially relevant skate stocks in the Northeast Atlantic Region.