Fishery and geospatial mapping of pelagic elasmobranchs from mechanised gillnetters of Tharuvaikulam, Thoothukudi, south-east coast of India

Abstract

The pelagic elasmobranchs fishery of multiday gillnetters (MGNs) of Tharuvaikulam, Thoothukudi was studied during 2015-2016. Fishery data revealed that MGNs targeting scombrids and other large pelagic fishes also contribute to the pelagic elasmobranch landings accounting for 7.67 and 5.3% of total elasmobranchs landed at Tharuvaikulam during 2015 and 2016 respectively. The catch per unit effort (CPUE) varied from 2.09 to 175 kg (2015) and 13 to 124.95 kg (2016). In total, 15 species of pelagic elasmobranchs were recorded during the study period, which includes 7 species of sharks and 8 species of rays. The pelagic elasmobranchs fishery of Tharuvaikulam depends mainly on two species namely bigeye thresher, Alopias superciliosus and spinetail devilray, Mobula japanica. The geospatial mapping revealed that fishing grounds of MGNs was between 77° to 80°E longitudes and 7° to 9° N latitudes with depth ranging from 50 to 200 m. The persistence of fishing grounds of pelagic elasmobranchs was identified by classifying the fishing areas of Gulf of Mannar Biosphere Reserve (GOMBR) into seven zones. The results showed that more fishing happens in Zone 4, off Thoothukudi between 78° to 79°E and 8° to 9°N followed by Zone 7, off Kanyakumari between 77° to 78°E and 7° to 8°N. Seasonal analysis revealed that along with the targeted groups, the CPUE of pelagic elasmobranchs was higher during the pre-monsoon season. The present paper illustrates the zonal distribution of pelagic elasmobranchs in the fishing grounds of MGNs in GOMBR, along the south-east coast of India and the results of the study would serve as baseline information for formulating future management plans.