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Fishery Bulletin 97(3), 1999 



I 



ences in behavior between sexes or 

 between mature and immature indi- 

 viduals but could also lead to differ- 

 ences in efficiency. Of particular con- 

 cern is a possible difference in net 

 efficiency between mature and imma- 

 ture males because such a difference 

 could lead to a bias in the estimates 

 of the carapace width at maturity 

 and thereby affect commercial mini- 

 mum width regulations. 



We estimated net efficiency with 

 an experimental approach pioneered 

 by Engas and Godo ( 1989) that uses 

 an auxiliary net attached beneath the 

 trawl net to capture crab escaping 

 under the footrope. If the auxiliary 

 net spans the fishing width of the 

 trawl net, from wing-tip to wing-tip, 

 and captures everything passing be- 

 neath the footrope, then efficiency is 

 estimated as the quotient of the trawl 

 catch divided by the total catch of 

 both the trawl and auxiliary net 

 (Walsh, 1992; Dickson 1993b). The 

 crux of such an experiment is then 

 to design an auxiliary net with a 

 footrope that exerts sufficient bottom 

 contact to capture everything pass- 

 ing beneath the trawl footrope with- 

 out causing enough added drag to al- 

 ter the fishing efficiency of the trawl. 

 Unlike the trawls examined in the 

 studies of Engas and God0( 1989) and 

 Walsh (1992), the 83-112 trawl lacks 

 bobbins or rollers on the footrope and 

 instead has a footrope consisting of 

 a simple, rubber-wrapped cable. This 

 difference in trawl design required several distinct 

 differences in the design of the auxiliary net. In this 

 paper we examine the application of this auxiliary 

 net to estimate the efficiency of the 83-112 eastern 

 trawl for snow and Tanner crabs. 



Materials and methods 



Description of the trawl and auxiliary net 



The 83-112 eastern trawl is a two-seam trawl with a 

 25.3-m headrope and a 34.1-m fpotrope consisting of 

 a simple rubber-wrapped cable intended to remain 

 in close contact with a smooth bottom (Fig. 1; see 

 Armistead and Nichol, 1993, for a detailed net plan). 

 The trawl is towed behind 1.8 x 2.7 m steel "V" doors 



Auxiliary net 



Auxiliary net footrope 



Figure 1 



The 83-112 eastern trawl net and the auxilary net. The dashed lines show the 

 corresponding attachment points on both the trawl and auxilary nets, but the 

 two nets are sewed together along the entire edge of the auxilary net. 



weighing 816 kg each, which are connected to each 

 wing with two 55-m bridles. Wing and throat sec- 

 tions of the net are made of 10.1-cm (stretched mea- 

 sure) nylon mesh, the intermediate section is made 

 of 8.9-cm mesh and the codend is made with a double 

 layer of 8.9-cm mesh lined with 3.1-cm mesh. 



The auxiliary net was hung beneath the trawl net, 

 attached at the wing tips and along the top of the 

 wings (Fig. 1). Unlike the auxiliary net designs of 

 Engas and Godo (1989 ) and Walsh ( 1992 ), our auxil- 

 iary net lacked a headrope, used the belly mesh of 

 the trawl as the top panel, and had a single codend 

 rather than three separate codends. The mesh used 

 in the auxiliary net was the same as that for the 

 trawl, but the footrope was longer ( 38.2 m) and was 

 constructed of 16-mm long-link steel chain intended 

 to be sufficiently heavy to excavate buried crab. An 



