Low levels of bycatch from estuarine prawn seining in New South Wales, Australia

We present estimates of the composition, catch rates and quantities of bycatches taken in the seine fishery for school prawns (Metapenaeus macleayi) in coastal rivers in New South Wales, Australia. Observers sampled 91 fishing trips throughout the Richmond, Manning, Wallamba and Shoalhaven Rivers between September 1998 and June 1999 and identified a total of 43 finfish and 5 invertebrate taxa in bycatches. Multivariate analyses indicated that 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 primarily dominated bycatches in all estuaries, except the Shoalhaven River. Dominant species in bycatches included Herklotsichthys castelnaui, Arius graeffei and Zebrias scalaris in the Richmond River, H. castelnaui, Siphamia sp., Ambassis spp., Gerres subfasciatus, Cnidoglanis macrocephalus and Acanthopagrus australis in the Manning and Wallamba Rivers and Pomatomus saltatrix, G. subfasciatus and A. australis in the Shoalhaven River. Several species important in other commercial and recreational fisheries were recorded in bycatches, but generally in low numbers, the notable exception being G. subfasciatus. Mean prawn catch-to-bycatch ratios by weight for each estuary ranged from 1:0.07 to 1:0.52, which are considerably less than those reported for other net-based prawn fisheries. 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. Across all four estuaries, in catching an estimated 131 t of prawns 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 a combination of the small size of nets (40 m headline length) and the relatively short time (3–15 min) it took to operate each individual seine. The latter also led to observations that bycaught fish were in particularly good condition when discarded. The data indicate that discarding in this fishery probably has minimal impact on other interacting finfish fisheries in the region.