Fish larval transport in a macro-tidal regime: Gulf of Kachchh, west coast of India

This study combines observational data with a two-dimensional numerical model results to determine the fate of fish eggs released in the Gulf of Kachchh (GoK), a semi enclosed basin on the west coast of India. Fish eggs were treated as passive particles in the model, and were released from probable spawning sites identified from the field surveys. Areas with retention of larvae above 30% have been demarcated as nursery areas. Most of these nursery areas fall in ecologically significant sites which are rich in mangroves and reefs. We find that about 80% of the particles are retained in the basin for all the three prominent seasons prevailing in the GoK. Complete retention of particles in the southern Gulf region and small quantity of flushing out in the northern boundary of the Gulf could be a major reason for sustaining an abundance of larvae in the southern Gulf. Trawler catch data at various sampling points also suggest abundance of fish in the southern GoK region. Model simulation of fish larval transport in the GoK reiterates the fact that fish larval aggregation occurs in the southern GoK during active breeding phase with varying dispersal patterns from spawning sites. Marine protected areas in the Gulf demarcated based on the ecological significance of sites reasonably corroborate with the areas of likelihood of retention of fish larvae differentiated by the model.

► For the first time modelling was done in the coastal waters of India to track dispersal of fish larvae.
► About 80% of the larvae released from spawning sites retained in the Gulf in all seasons.
► Ebb currents promote about 20% of the larvae to escape along the northern Gulf without entering the eddy zone.
► Modelling demonstrates dispersal and redistribution of larvae in the southern Gulf leading to abundant fish population.
► The study stipulates the necessity of enforcing fishing regulations to ensure sustained fishery.