Feasibility of targeted fishing in mesoscale oceanic eddies: a study from commercial fishing grounds of Andaman and Nicobar Islands, India

Mesoscale eddies are important ocean phenomena that enhance biological productivity by mixing of water column and influence fishery catches, especially in stratified seas such as Bay of Bengal and Andaman Sea. The current study was conducted around the Andaman and Nicobar Islands (ANI), India located in the Eastern Indian Ocean. The study tested the feasibility of targeted fishing in eddies, by characterizing the mesoscale eddies in the region, towards developing operational altimetry-based fishery advisories for the fishers. We analysed fish catch data from 15,370 commercial fishing trips from the Islands using five fishing gears during 2014-17 spatially vis-a-vis the eddies delineated from Maps of Sea Level Anomaly (M-SLA). We show that 5-24% of the routine commercial catches occurred in eddies, fishery catches are positively influenced by different eddy zones and the fish catch using different fishing gear are significantly higher in some of the eddy zones. We generated experimental advisories showing locations of eddies and their zones, identified using Near Real-Time M-SLA data and guided the commercial fishers for targeted fishing in eddies. The fish Catch Per Unit Effort (CPUE) from the experimental fishing within the eddy zones was significantly (p < 0.01) higher than that from the traditional fishing grounds in the non-eddy areas. The spatio-temporal analysis of eddies around ANI during 2009-16 showed the occurrence of higher number of anticyclonic eddies, majority of which move westward and have a lifespan of less than 2 weeks and amplitude less than 4 cm. In the current study, the areas around ANI with frequent eddy occurrence and eddy density have been identified, which could aid in increasing the fishing intensity by targeting the pelagic fishes, using longlines, gillnets and ringnets. Thus, we show the possibility of using eddy fishing advisories generated from altimeter data, for augmenting the currently operational Potential Fishing Zone (PFZ) advisories that are generated using optical/thermal remote sensing data and disseminated to the coastal fishers in India. This will be helpful especially for the regions with and during periods of persistent cloud cover.