412 



Abstract. - Two experiments were 

 conducted in the New South Wales oce- 

 anic prawn-trawl fishery, 1 ) by compar- 

 ing catch from a conventional codend 

 with that from two new codend designs 

 with square-mesh panels and 2) by 

 showing the effects on catches of a short 

 delay in haulback of trawls with square- 

 mesh panels. The two new codend de- 

 signs incorporated panels of netting 

 (85-mm mesh) sewn such that the 

 meshes were square-shaped (measur- 

 ing 7x11 bars) and inserted lengthwise 

 and widthwise into the tops of the an- 

 terior sections. Simultaneous compari- 

 sons among these designs and a conven- 

 tional codend showed that both designs 

 performed similarly by significantly re- 

 ducing the weights of bycatch that 

 would be discarded (by 46% and 38%, 

 respectively) without significantly re- 

 ducing the catch of the prawn Penaeus 

 plebejus. The second experiment showed 

 that juvenile red spot whiting, Sillago 

 flindersi, an important commercial fin- 

 fish, escaped from the square-mesh 

 panels in the trawl during a 10-15 sec- 

 ond haulback delay Trawls without any 

 haulback delay showed no significant 

 reduction in the bycatch of this species. 

 The results are discussed in terms of 

 the probable behavior of fish in the 

 modified trawls and in terms of the 

 implications that factors such as 

 haulback delay may have on the sur- 

 vival of fish escaping through square- 

 mesh panels in codends. 



Effects of square-mesh panels in 

 codends and of haulback delay on 

 bycatch reduction m the oceanic 

 prawn-trawl fishery of New South 

 Wales, Australia 



Matt K. Broadhurst 

 Steven J. Kennelly 

 Gerard O Doherty 



Fisheries Research Institute, NSW Fisheries 



PO. Box 2 1 Cronulla. New South Wales 2230. Australia 



Manuscript accepted 8 February 1996. 

 Fishery Bulletin 94:412-422 ( 1996), 



In many of the world's prawn-trawl 

 fisheries, significant numbers of 

 nontarget organisms (collectively 

 termed "bycatch," sensu Saila, 

 1983) are caught incidentally with 

 targeted prawns. This bycatch often 

 includes a large and diverse assem- 

 blage of small fish, some of which 

 are juveniles of commercially and 

 recreationally important species 

 ( for reviews see Saila, 1983; Andrew 

 and Pepperell, 1992;Alversonetal., 

 1994; Kennelly, 1995). The inciden- 

 tal capture and mortality of large 

 numbers of these juveniles has been 

 of worldwide concern in recent years 

 because it may reduce the potential 

 biomass and yield of stocks that 

 form the basis of other fisheries 

 (Gordon, 1988; Foldren, 1989). 



In New South Wales (NSW), Aus- 

 tralia, oceanic prawn trawling in- 

 volves approximately 300 vessels that 

 usually operate during the night from 

 11 ports. This fishery is valued at 

 approximately A$ 17 million per an- 

 num and primarily targets the east- 

 ern king prawn, Penaeus plebejus, 

 although a significant proportion of 

 the total income is derived from the 

 sale of legally retained bycatch 

 (termed "byproduct"), which com- 

 prises several commercially impor- 

 tant species offish, crustaceans, and 

 cephalopods (see Kennelly et al., 

 1992). However, a recent survey ex- 



amining the spatial and temporal dis- 

 tributions and abundances of the 

 catch and bycatch from four ports in 

 this fishery showed that juveniles of 

 commercially important species com- 

 prised a significant portion of the 

 bycatch (Kennelly 1 ). Athough many 

 of these juveniles showed large tem- 

 poral and spatial variability in their 

 occurrence, some (e.g. red spot whit- 

 ing, Sillago flindersi, and eastern 

 blue spot flathead, Platyeephalus 

 caeruleopunctatus), were consistently 

 caught in large numbers throughout 

 the sampling period. Although there 

 are few data available on the popula- 

 tion structure and dynamics of the 

 key bycatch species or on the extent 

 of their post-trawl mortalities, the 

 quantities involved have raised con- 

 cerns regarding potential detrimen- 

 tal impacts of prawn trawling on fu- 

 ture stocks of these species ( Kennelly, 

 1993). We therefore began an inves- 

 tigation that examined various modi- 

 fications to trawling gear and trawl- 

 ing practices that minimize undesir- 

 able bycatch while maintaining 

 catches of prawns and commercial 

 byproduct. 



1 Kennelly, S. J. 1993. Study of the by- 

 catch of the NSW east coast trawl fishery. 

 Final report to the Fisheries Research and 

 Development Corporation, P.O. Box 222, 

 Deakin, ACT, 2600, Australia. Project No. 

 88/108. ISBN 7310 2096 0, 520 p. 



