434 



Abstract.— In response to recent volun- 

 tary adoption of square-mesh codends 

 by commercial prawn trawlers in Gulf 

 St. Vincent, Australia, two new designs 

 of composite square-mesh codends were 

 investigated for their utility in 1) re- 

 ducing the bycatch of fish and 2i im- 

 proving size-selectivity of the targeted 

 prawns. The two designs (termed the 

 composite-square-2 and the composite- 

 square-3 codends I comprised mainly 

 large sections of 52-mm netting hung 

 on the bar but had different hanging 

 ratios, tapers, and small diamond-mesh 

 sections. A strategically located panel 

 of 85-mm netting was inserted on the 

 bar into the tops of the anterior sections 

 of each codend to allow small fish to 

 escape. Simultaneous comparisons 

 with a conventional diamond-mesh 

 codend (control) showed that both 

 square-mesh designs significantly re- 

 duced the incidental capture of com- 

 mercially important fish (by up to 

 96.91^ ). The numbers of prawns iPenaeiis 

 latisulcatus) were significantly reduced 

 in both composite square-mesh codends 

 (by up to 12.1'"f ) but there was no sig- 

 nificant reduction in weights of prawns. 

 There were no significant differences in 

 the selectivity parameters for prawns 

 between the two designs. The results 

 are discussed in terms of the probable 

 effects that the different square-mesh 

 configurations had on escape offish and 

 size-selectivity of prawns. 



Use and success of composite square-mesh 

 codends in reducing bycatch and in improving 

 size-selectivity of prawns in Gulf St. Vincent, 

 South Australia 



Matt K. Broadhurst 



South Australian Aquatic Sciences Centre 



PO Box 120 



Henley Beach, South Australia 5022, Australia 



Present address Universidade Federal Rural de Pernambuco-UFRPE 



Departamento de Pesca 



Laboratono de Oceanografia Pesqueira 



Av Dom Manuel de Mederios 



S/n, Dois Irmaos, Recife-PE, Brazil, CEP 52 171-900 

 E-mail address fhvhazinatruenetcom br 



Roger B. Larsen 



University of Troms0 



Breivika, N-9037, Troms0, Norway 



Steven J. Kennelly 



NSW Fisheries Research Institute 



PO Box 21 



Cronulla, New South Wales 2230, Australia 



Paul E. McShane 



South Australian Aquatic Sciences Centre 



PO. Box 120 



Henley Beach, South Australia 5022, Australia 



Manuscript accepted 12 August 1998, 

 Fish. Bull. 97:434-448 ( 1999). 



Traditionally configured prawn 

 trawls contain small diamond- 

 shaped meshes in the codend and 

 are not particularly selective fish- 

 ing gears. In addition to the tar- 

 geted prawns, they often retain 

 large quantities of nontarget organ- 

 isms, collectively termed bycatch 

 (for reviews see Andrew and Pep- 

 perell, 1992; Alverson et al., 1994). 

 In many prawn-trawl fisheries, this 

 bycatch consists of a diverse assem- 

 blage of small fish, cephalopods, and 

 crustaceans, including prawns 

 smaller than optimal commercial 

 size. The mortality of large quanti- 

 ties of juveniles of commercially or 

 recreationally important species, or 

 both, is of major concern, because 

 it may deleteriously affect the re- 

 cruitment and biomass of stocks 



targeted by other fisheries. Regulat- 

 ing selectivity of trawls to the de- 

 sired size of prawns at first capture 

 will also help to optimize yield and 

 maintain sustainability of prawn 

 stocks. 



During the past decade, many 

 studies have attempted to improve 

 selectivity of prawn-trawl fisheries 

 by altering the codends of trawls. 

 Most of these studies can be catego- 

 rized into examinations of 1) by- 

 catch reducing devices (BRDsl that 

 facilitate the escape of unwanted 

 fish (e.g. Watson et al., 1986; 

 Broadhurst and Kennelly, 1997; 

 Rogers et al., 1997); or 2) different 

 sizes, shapes, and configurations of 

 mesh that improve selectivity of the 

 targeted species by reducing the 

 bycatch of conspecifics (e.g. Karlsen 



