Investigations on fishery and biology of nine species of rays in Mumbai waters

Abstract

Annual landings of rays by trawlers operating from New Ferry Wharf, Mumbai during 1990-2004 ranged from 205.7 t to 765.1 t with an average of 502.8 t constituting nearly 1 % of trawl catches. The trawling effort increased from 0.95 million hours (mh) in 1990 to 1.73 mh in 2004, whereas the catch rate declined from 0.65 kg h-1 in 1990 to 0.24 kg h-1 in 2004. There were two peak periods of abundance, September-December and February-April. Fourteen species of rays constituted the fishery, of which Himantura alcockii (50.1 %), Himantura bleekari (13.9 %), Amphotistius imbricatus (8.5 %) and Himantura uarnak (8.1 %) formed the mainstay of the fishery. Information on biology of H. alcockii, H. bleekeri, A. imbricatus, Pastinacus sephen, Dasyatis zugei, Gymnura japonica, G. poecilura and Mobula diabolus is also presented. It appears that the resource of rays off Mumbai may not be able to withstand any further increase in fishing effort. Innate biological characteristics such as limited brood size, late maturation and capture of spawning stock are the causes of continuous decline. Conservation measures are required to protect this resource from further depletion.