The impact of fisheries interactions on the foraging behaviour of Indian Ocean Humpback Dolphins along the Sindhudurg coast of Maharashtra
Photo by Ketki Jog
The coastal district of Sindhudurg hosts about 25,375 fishers. Fishery operations include artisanal mechanized and non-mechanized crafts, using cast-nets, shore-seines, gillnets (mono/multifilament, mesh-size: 0.5 cm -38 cm) and commercial mechanised gear like trawlers and purse-seines.
With several small seasonal and perennial rivers acting as nutrient influxes, there is an abundance of prey species like mullet, sardines, mackerel and pomfret. This habitat is therefore ideal for the Indian Ocean humpback dolphin (Sousa plumbea).
Dolphin depredation of gillnet, shore-seine and purse-seine fisheries targeting common fish like mullet, pomfret (Pampus sp.), mackerel (Rastrelliger kanagurta) and sardines (Sardinella sp.) is a frequent occurrence in this region. These interactions lead to considerable economic damage and strong negative perceptions of dolphins. Fishers describe instances where dolphins habituate to gillnets fishing for mullet, sardine and mackerel. Similar habituation is observed in harbours where dolphins associate with vessels bringing in the day’s catch, having learned to exploit the discards (personal observations).These behaviours suggest that local fisheries shape the foraging strategies of at least some dolphin individuals. Given their ease in exploiting highly concentrated food sources from fishing gear, such short-term benefits to dolphins appear to outweigh the cost of interacting with fishing nets potentially leading to dolphin mortality. Studies also indicate that local dolphin populations have high site fidelity, adding to the likelihood of local extinctions.
Attempts are currently being made to understand the nature of these interactions and estimate the scale of cetacean entanglements and bycatch. Present management strategies are based on fragmented documentation of interactions, e.g., the state government of Maharashtra announced a compensation scheme in 2018, promising an amount of ~US$400 for the safe release of entangled dolphins (Mumbai Mirror 2018). Systematic understanding of the underlying causes of these interactions, however, is lacking.
Moreover, there is an urgent need to quantify their effects on fishers’ livelihoods and the efficacy of current mitigative measures to inform an adaptive management process. With this project, we will assess the ecological and socio-economic significance of cetacean-fishery interactions along the Sindhudurg coast of Maharashtra to inform their management.
The main aim of this project is to inform the management response to direct interactions between dolphins and fisheries in Sindhudurg by identifying the factors associated with dolphin depredation and entanglement in fishing gear, assessing the impact of dolphin depredation and bycatch on fishery operations and livelihoods, and stakeholder perceptions of current management measures.
Principal Investigator: Ketki Jog, supervised by Emeritus Prof Helene Marsh (College of Science and Engineering), Amy Diedrich (College of Science and Engineering), Alana Grech (ARC Centre of Excellence for Coral Reef Studies) and Dipani Sutaria (Adjunct Professor, College of Science and Engineering)
Funding: James Cook University International Post-graduate Research Scholarship, The New England Aquarium Marine Conservation Action Fund (Anderson Cabot Centre for Ocean Life), Society for Marine Mammalogy (Small grants scheme)