Biological observations on the Bengal guitarfish Rhinobatos annandalei Norman, 1926 from the Eastern Arabian Sea, India
Biological data for the little known Bengal guitarfish Rhinobatos annandalei Norman, 1926 (Rhinopristiformes: Rhinobatidae) are presented based on specimens collected from bycatch of commercial shrimp trawlers, gill netters and bag or dol netters operating in the Arabian Sea at depths of 2-70 m off the north-west coast of India. Five hundred ninety-three specimens measuring 30.0 to 95.0 cm total length (TL) and weighing between 64.0 to 3300 g total weight (TW) were collected for the study. The length-weight relationships (LWR) were significantly different between the sexes (p<0.001) and for the combined sexes was derived as TW= 0.000604 TL3.408256 (r2= 0.997). The co-efficients â€˜aâ€™, â€˜bâ€™ of the LWR were estimated as 0.000621, 3.410115 (r2= 0.999) for females and 0.000766, 3.333872 (r2= 0.999) for males. The lengthÂ at maturity (TL50) for females and males was estimated to be 61.0 and 63.3 cm TL, respectively. In a single female, the number of embryos ranged from 2 to 11 and the size at birth was estimated between 25.0 to 30.0 cm TL. The overall sex ratio favoured females at the rate of 1.6:1. An analysis of the stomach contents (%IRI) revealed that R. annandalei mainly fed on Solenocera spp. (18.7% IRI), along with P. sculptilis (0.5% IRI), P. stylifera (0.4% IRI), Loligo spp. (0.4% IRI) and sciaenids (0.3% IRI). Since, the species is poorly studied and assessed as â€˜Data Deficientâ€™ in the IUCN red list criterion, it is anticipated that the biological results from the present study, will update information on the species thereby enabling more effective management decisions.
Keywords: Arabian Sea, Diet, Length at maturity, Length-weight relationship, Reproductive biology, RhinobatosÂ annandalei