Biology of the stakes Bathyraja brachyurops and B. griseocauda in waters around the Falkand Islands, Southwest Atlantic

The distributions and length compositions of two large, abundant skates, broadnose skate Bathyroja brachyurops and grey-tail skate B. griseocauda, were studied using an extensive clataset (similar to 48 000 skates) collected from the commercial fishery and research cruises on the southeastern Patagonian Shelf around the Falkland Islands between 1992 and 2006. Bathyroja brachyurops mostly inhabit the shelf at depths shallower than 250 m, whereas B. griseocoudo are found deeper (> 250 m), off the shelf break and slope. Small individuals of both species are most segregated spatially. Growth increments on caudal thorns and vertebral centra revealed that B. brachyurops grow slower and have a shorter lifespan, attaining a maximum total length of 121) cm at 20 years, compared with B. griseocauda (similar to 150 cm at 28 years). Maturity is attained at 8-10 years for male and female B. brachyurops, and at 15 and 17 years for B. griseocauda, respectively. Spawning takes place on spatially segregated spawning grounds, B. brachyurops reproducing above the shelf break, and B. griseocauda just below the shelf break throughout the year, with a smaller proportion of females of both species laying eggs in winter.