Non Technical Summary

The catches and bycatches from 91 prawn haul fishing trips throughout the Richmond, Manning, Wallamba and Shoalhaven Rivers were sampled between September 1998 and June 1999. A total of 43 finfish and 5 invertebrate taxa were identified in bycatches. The composition and structure of bycatches varied little between locations within each estuary, but differed significantly between estuaries.

Small fishes (< 15 cm TL) of little economic value, including Herrings, Perchlets and Siphonfish, primarily dominated bycatches in all estuaries. Other species abundant in bycatches included Forktail catfish and Many-banded sole in the Richmond River, Estuary catfish and Silver biddy in the Manning and Wallamba Rivers and Tailor, Silver biddy and Bream in the Shoalhaven River. Several species important in other commercial and recreational fisheries were recorded in bycatches, including Silver biddy, Bream, Tailor, Sand Whiting, Mulloway and Dusky flathead, but they generally occurred in low numbers (< 20 individuals of each species caught per fishing trip), the notable exception being Silver biddy. Most bycatch species were discarded in good condition.

Mean prawn catch to bycatch ratios by weight for each estuary ranged from 1:0.07 to 1:0.52, which are amongst the lowest reported for any prawn fishery in the world, and are considerably less than those reported for other net-based prawn fisheries in NSW. The estimated total weight of bycatch from seining in each estuary ranged from 1.7 to 17.6 t during the 10-month fishing season. In catching an estimated 131 t of prawns in all 4 estuaries, the fleet took an estimated 27 t of bycatch throughout the survey.

The relatively low levels of observed bycatches in the seine fishery were attributed to the small size of nets (40 m headline length) and the relatively short time (3-15 minutes) it took to do each individual seine. The data indicate that discarding in this fishery probably has minimal impact on other interacting finfish fisheries in these estuaries.