Estimates of age, growth and mortality of spotted catfish, Arius maculatus (Thunberg, 1792), off the Coast of Yunlin, Southwestern Taiwan

Abstract

Spotted catfish is a benthic species that can be found abundantly off the coast of Yunlin in southwestern Taiwan. Its biological parameters are little known. In this study, life history parameters of this species were estimated using samples caught by bottom trawling. The spotted catfish was the major bycatch species which comprised 32% of the total catch. The growth parameters estimated by length frequency analysis were: asymptotic fork length (L_∞ = 34.4 cm), growth constant (k = 0.28 year^-1) and age at length 0 (t₀ = -0.57 year^-1). The total mortality, natural mortality, fishing mortality and the exploitation ratio were 1.29, 0.86, 0.43 year^-1 and 0.24, respectively. Although spotted catfish is not a target species of bottom trawling, the high fishing mortality and exploitation ratio suggest that they are the major by-catch species, and hence more attention should be paid to the dynamics of this stock. According to the monthly length distribution, the smallest fish (median = 2 cm) appeared in July 2009, which implies that the spawning season of spotted catfish is in June or July. However, the results of this study are preliminary, therefore other methods, such as ring reading of hard tissue, should be utilized to verify the growth parameters of spotted catfish.

Key words: Age and growth, mortality, exploitation rate, spotted catfish