Decadal changes in growth, mortality and maturity parameters of Evynnis cardinalis in Beibu Gulf

We evaluated the population structure, first maturity lengths (L₅₀), growth and mortality coefficient of threadfin porgy Evynnis cardinalis in Beibu Gulf using biological data obtained from bottom trawls conducted during 1961~1962(1962), 1997~1999(1998) and 2006. Results show that the bimodal patterns of length frequency distribution in 1962 and 1998 had turned into unimodal type in 2006 and the female-male ratio increased obviously; the mean body length decreased from 108.8 mm in 1962 to 102.0 mm in 2006; L₅₀ decreased from 108.9 mm in 1962 to 95.9 mm in 2006, and growth coefficient (K) increased from 0.35 in 1962 to 0.50 in 2006, which indicates that E.cardinalis tended to be miniaturized with an increase in speed of growth and a decrease in time to mature. Slight increase in mean body length and L₅₀ from 1962 to 1998 indicates longtime overfishing of E.cardinalis did not happened in this period. The exploitation rates (E) in 1962, 1998 and 2006 were 0.49, 0.62 and 0.60, respectively, suggesting that this stock has been over-exploited since the 1990s.