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The dynamics of fauna in coastal ecosystems are influenced by seasonal patterns in the oceanographic environment. It is well known that the monsoon along south-west coast of India influences the movement and spawning of fishes. Thus, they have direct effect on the richness, abundance and evenness of fish diversity in the ecosystem. This study investigates how the monsoon affects the commercial gillnet fishery along the coast of Goa. Fishing experiments were conducted in popular gillnet fishing grounds and the temporal pattern in diversity indices between October 2013 and September 2014 was assessed. A total of 124 fish species (40 families), 16 crustacean species (4 families) and 9 molluscan species (8 families) were recorded. The species diversity was found to be significantly different during the monsoon season and the species abundance distribution followed a geometric series during this period indicating signs of ecosystem perturbations. The economic and biological aspects of gillnet fishing in relation to the monsoon season in Goa are also discussed.

In this study, the ecological impacts of introduction of cage aquaculture employing small cages integrating shellfish and finfish in coastal water bodies of Goa, situated in the west coast of India were analysed using Ecopath with Ecosim model. A multispecies cage aquaculture system incorporating Lutjanus argentimaculatus, Etroplus suratensis and Perna viridis was established in an estuarine ecosystem. The Ecopath model identified 12 functional groups starting from detritus (trophic level=1) to large benthic carnivores (trophic level=3.72). The ecosystem statistics such as total system throughput (8672 g m-2 year-1), gross efficiency (0.001), primary production/respiration (1.4), net system production (1028.2 g m-2 year-1) and system omnivory index (0.26) indicated that the ecosystem was highly productive and in a developing stage. With a medium rate of recycling (Finn’s Cycling Index=11.7%), high system throughput, high system overhead (79%) and moderate omnivory index (0.26), the food web was found to be immature having an organized trophic network with high production. Simulations of the various expanding scenarios for the cage culture within the ecosystem were explored using Ecosim. A scenario in which two cages each for pearlspot and red snapper and 20 mussel ropes was identified as a sustainable solution without sacrificing the threshold biomass for the functional groups of fish species [WU1] . The study provided useful insights and methodology towards assessing aquaculture in coastal ecosystems in terms of ecosystem structure and function.

Seasonal fish species composition, catch rate and catch value in the small scale fishery of a tropical monsoon estuary along southwest coast of India

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