Characterizing catch variability in a multispecies fishery: implications for fishery management

Abstract

Exploiting several fish species simultaneously reduces variability in daily catches. The reduction depends on the number of species, the catch-frequency distributions of individual species, and the level of co-occurrence of species in the catch. We explore theoretically the reduction of variability (coefficient of variation; CV) in the total catch by combining the distributions of daily catches of individual fish species, including zero catches, into a total catch frequency distribution. Theoretical findings are tested with an example from a stationary lift-net fishery for schooling small pelagic species around Ambon Island in the Central Moluccas, Indonesia. This fishery catches over 30 species, all with high daily variability (CV = 2.2–13.4). The reduction of variability in the total catch (CV = 1.7) is a result of the dominance and independent occurrence of the three main species. We conclude that in this fishery the information value of the total catch as an indicator of the catches of the individual species is low.