Population dynamics of the sandwich-tail whipray Brevitrygon manjajiae (Dasyatidae) from the north-eastern Arabian Sea, India

Sandwich-tail whipray, Brevitrygon manjajiae Last, Weigmann and Naylor 2023 (Family: Dasyatidae) is a small-sized, batoid species having restricted distribution in the northern Indian Ocean. The species is landed in huge quantities as bycatch in trawlers operating in the shelf areas of north-west coast of India. Disc width (DW) frequency-based stock assessment using FiSAT was conducted for B. manjajiae landed at New Ferry Wharf and Versova landing centres, trawled at 20-50 m depths off Maharashtra coast in the Arabian Sea from August 2016 to May 2018. A total of 1720 individuals of B. manjajiae (121-310 mm DW) were sampled for the study, of which males contributed 50.6% (n=870) and females 49.4% (n=850), with a sex ratio of 1:0.97. Population characteristics of B. manjajiae revealed that the species has a relatively faster growth rate with an estimated K value of 0.54 y-1, t0 of -0.72 y; asymptotic disc width (DW∞) of 347 mm with a longevity of 5.5 yrs and is overexploited (E=0.80). Keywords: Batoids, Conservation, Dasyatidae, Disc width, Fishery, Stock assessment, Trawl bycatch