Observer-based survey of by-catch from prawn trawling in Botany Bay and Port Jackson, New South Wales

Catches and by-catches were surveyed in the commercial prawn trawl fleets of Botany Bay and Port Jackson, two estuaries in the Sydney metropolitan area (NSW, Australia). Catches were surveyed in all tows during replicate fishing trips in each month during the 1990-91 and 1991-92 prawn trawl seasons in each estuary. Significant species-specific variabilities in abundances were detected between estuaries, between years, and between early and late in the fishing season. The mean annual ratio of by-catch to catch of prawns (by weight) was 2.5:1 for Botany Bay and 1.8:1 for Port Jackson. A mean annual by-catch (+/- 1 s.e.) of 142 +/- 14 t was taken from the Botany Bay fishery and 38 +/- 3 t from Port Jackson. These by-catches included large numbers of small recreationally and commercially important finfish: a mean annual by-catch of 1.52 +/- 0.20 million fish from Botany Bay and 219 +/- 23 thousand fish from Port Jackson. Despite uncertainties about the impacts of such by-catches on interacting commercial and recreational fisheries, it is recommended that strategies for the reduction of such by-catches be considered.