Abstract:
A seasonal fishery from December to May each year exists for a small-sized clupeid, Ehirava fluviatilis in an estuary on the West coast of Sri Lanka. Two kinds of lift nets are used for catching this species. The theoretical weight of 50 mm fish, as calculated from length-weight relationship that was used as an index of body condition (942 mg) is considerably higher than that of a reservoir population (540 mg). In contrast to feeding habits reported from the reservoir population in which rotifers were the major food items, E. fluviatilis in the estuary feeds mainly on copepods. Size at first maturity of this species is also higher in the estuarine population than that reported from the reservoir population.
From the length frequency samples collected approximately in bi-weekly intervals, growth and mortality parameters were estimated using FiSAT software package. Total mortality coefficient (5.73) calculated on the basis of asymptotic total length (54.3 mm) and growth constant (2.00 yr-1) indicates that E. fluviatilis population in the estuary has a high turnover rate. Relative yield-per-recruit analysis performed by incorporating probabilities of capture indicates that the fish stock is underexploited and that the fishing strategy can be optimized by decreasing size at first capture from the present value of 45.8 mm to about 26 mm at an exploitation rate of about three times higher than the present level. The high total annual production of E. fluviatilis of 15.9 tons that is equivalent to an annual yield of 23.2 kg�ha-1 could be due to its ability to withstand heavy fishing mortalities through high turnover rates.