This paper not to be cited without prior reference to the authors

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1 Ths paper not to be cted wthout pror reference to the authors ' nternatonal Councl for the Exploraton of the Sea C.~11974/F:45 Demersal Fsh (N) Commttee OBSERVATON~ FROM THE BARENTS SEA N SPRNG 1973 a~ THE DSCARDNG OF COD AND HADDOCK CAUGHT N BOTTOt~AND MDHATER TRA~VLS FTTED WTH DOUBLE COD ENDS by Arvd Hylen and Odd M. Smedstad nsttute of Marne Re'search Box Bergen Norway NTRODUCTQN Dscardng of Arcto-Norwegan cod and haddock from hred Norwegan commercal trawlers fshng along the Fnnmark Coast and n the Bear sland area wth slghtly dfferent chafers was studed by Hylen ( ). Smlar studes were made n the begnnng of Aprl and June 1973 off the East Fnnmark Coast. j1ethods AND M~.TERAL A Norwegan trawler was hred for the perod 2-9 Aprl and another for the perod 9-19 June Commercal bottom and mdwater trawls made of polypropylene wth a mesh sze of 130 mm n the cod ends were used. A chafer of the double cod end type wth the same mesh sze as the cod end was used 1n some of the hauls. t was fastened to the anteror part of the cod end. The number of hauls wth the dfferent gears are gven n Table 1. ' Observers from the rlarne Research nsttute Bergen had the responsblty of the samplng program. They measured a representatve part of the fsh used for human consumpton and dscarded from as many hauls as possble. The total number of fsh n these two categores were estmated for each haul by rasng the length frequences of the samples to the total. Total' weght of each speces caught n the observed hauls was calculated from the length compostons and the length/weght relatonshp.

2 - 2 ~ RESULTS Dscardng rates of cod from' catches taken n Aprl wth bottom trawl wthout chafer were estmated to 34% by numbers and 13% by weght (Table 1). Correspondng fgures for the hauls wth bottom trawl ftted wth double cod end ~ere 26 and 11% respe6tvely. The dscardng from the bottom trawl catches n June were of the same order. Experments wth mdwater trawl wth sngle and double cod end gave dscardng rates of 34 and 39% by numbers and 18 and 22% by weght respectvely. The smallest cod retaned n the bottom and mdwater trawls ftted wth double cod end was 17 and 28 cm respectvely whle the smallast fsh caught n bottom and mdwater trawl wth sngle cod end Was 16 and 32 cm respectvely (Table 2). Accordng to market demand most of the cod 39 cm and less were dscarded. The 50% selecton length for landng were cm n the bottom trawl c~tcbes and 40 cm for the mdwater trawl catches (Table 3). All fsh more than 44 cm were landed for human consumpton. Dscardng rates for haddock n bottom trawl catches were n the order of 3-9% by weght whle no dscardng was observed from the mdwater trawl catches. Snce haddock was mush less abundant n the catches than cod both n Aprl and n June the estmated rates may be less sgnfcant (Table 1). Haddock as small as 16 cm were retaned n the bottom trawl wth double cod end whle the smallest fsh caught n the mdwater trawl was 37 cm (Table 4). Fsh up to 44 cm was dscarded but few more than 39 cm. t s of nterest_n ths connecton to get an dea of the loss of cod and haddock f a hgher effectve mesh sze would have been used n the experments. Ths can be estmated by knowng the selecton ogve for the speces and the gear. The selecton ogve characterzed by the selecton factor and the selecton range between the 25-75% and 5-95% retenton langth are known from many selecton experments wth bottom trawl n the Barents Sea Bear sland and Sptsbergen area (Anon ). Grand mean selecton factor for Arcto-Norwegan cod n trawl made of polypropylene s 3.67 (Anon. 1971). Experments wth a double cod end chafer and the same mesh sze n both cod ends have shown a reducton n the selecton '/

3 - 3 - ~ factor for cod up to 40% (Anon. 1967). Applyng a reducton n the selecton factor 'of 20% would gve an effectve mesh sze of 104 mm. The length composton whch would have been obtaned wth a sngle cod end and a mesh sze 130 mm or 145 mm could then be estmated. Applyng the same selecton for landng as. estmated from the descrbed experments would have gven mmedate losses by weght for the Aprl experment of 21.2 and 41.4% respectvely (Table 5). Correspondng losses for the June experment would have been 8.4 and 21% respectvely. By landng all the fsh caught wth the hgher effectve mesh szes the mmedate losses would be smaller. Hgher effectve mesh szes n the cod end would have reduced the dscardng of small fsh. Mesh szes of 130 or 145 mm and sngle coh end n the Aprl experment would have lead to dscardng of 6.2 or 0.2% of th'e recorded dscardng by numbers~ Correspondng fgures for the June experment would h. been 14.1 or 0.5% respectvely..~- J Smlar calculaton for the mdwater trawl catches have not been made because of lack n our knowledge of the selectvety n ths gear. A comparson of the length composton of catches taken n Aprl wth bottom trawl and mdwater trawl show that cod less than 25 cm and more than 79 cm were represented only n the bottom trawl catches (Table'2 and 6). However the length groups cm were more abundant n the mdwater -trawl catches. A relatvely hgh number of haddock cm were caught n bottqm' tr'awl. length groups whch were mssng n the mdwater trawl catches. However the length groups cm were more abundant n the mdwater trawl than n bottom trawl catches. ';> SUM~1ARY Dscardng practse of cod and haddock was studed on board two Norwegan trawlers hred for fshng off the East Fnnmark Coast one n the perod 2-9 Aprl and one n days 9-19 June Bottom and mdwater trawls wth double and sngle cod ends were used. The cod end and the chafer were made of polypropylene and had a mesh sze of 130 mm. Dscardng of cod caught n bottom trawl ftted wth double cod end was n the order of 27/0 by numbers and 11:;~ by weght. Correspondng fgures for mdwater trawl catches were 39% by numbers and 22% by weght.

4 - 4 - Dscardng of haddock from the same bottom trawl hauls was 3-7% By weght and no dscardng was observed from the mdwater trawl catches. A sngle cod end n the experments wth bottom trawl ftted wth double cod end would have reduced the dscardng of cod t~ 1/5-1/7 by numbers. A sngle cod-end and a me~h sze of 145 mm would have gven 'neglegble dscardng. REFERENCES ANON ' Report of the CES/CNAF Horkng Groups on selectvty analyses..cooperatve Research Report Ser. 1 A: ANON Co-opted members' report. Selectvty experments. Cooperatve Research Report Ser. B 1965: HYLEN A Utkast av torsk fra tralfangster. Fskets Gang 51: On the estmaton of cod and haddock dscarded by trawlers usng dfferent chafers.cooperatve Research Report Ser. B 1966: MARGETTS A. R. SETERSDAL G. VON BRANDT A. and TRESCHEV A The 1959 nternatonal Arctc trawl mesh selecton ex~erments. Coo~eratve Research Report Ser. A 2:

5 Table 1. Dscardng of Arcto-Norwegan cod and haddock caught by hred Norwegan trawlers off the East FnnmorkCoast. - COD No. Landngs Dscard Per cent dscarded Gear Date of Hauls No. v!eght (kg No. ~Jeght (kg) No. ~1eght (kg Bottom trawl sngle cod end 2-9 Aprl double 11 t Mdwater trawl sngle cod end t double t 11 f Bottom trawl double cod end 9-19 June HADDOCK Bottom trawl sngle cod end 2-9 Aprl ' t t double t l Mdwater trawl sngle cod end t double t 11 t Bottom trawl double cod end 9-19June ::._-;.

6 Table 2. Length compostons of Arcto-Norwegan cod caught by hred Norwegan trawlers off th~ East Fnnmark Coast. Total June 1973 Bottom trawl double cod end Landed Dscarded ~ --- _.-._J --_!': Aprl 1973 Length.. (cm)' Bottom trawl Mdwater trawl Sngle cod end Qou be cod end Sngle cod end Double cod end. Landed Dscarded Landed Dscarded Lanc<!ed Dscarded Landed Dscarded _ ~ C} ;

7 ~ 'Table 3. Percentage retaned for landng by length of cod caught by hred Norwegan trawlers off the Ea&t:'Fnnmark Coast Aprl 1~73 9 ~ 19 June 1973 Length Bottom trawl Mdwater trawl Bottom trawl (cm) double cod end Double cod end Sngle cod end double cod end!! ; 3 45 : ' ~ :: Table 4. Length compostons of Arcto-Norwegan haddockcaught by hred Norwegan trawlers off the East Fnnmark Coast. 2-9 Aprl June 1973 ]1gth Bottom trawl Mdwater trawl Bottom trawl S~ngle cm) Sngle 'cod end Double cod end Double double cod end cod end cod end ' Landed Dscarded Landed Dscarded Landed Landed Dscarded ! / TOTAL ; L ~ ~------~- _ '

8 '. Table 5. Estmated loss (%) n landngs of cod from the bottom trawl c~tches f a hgher effectve ~esh sze n the cod end had been used. Date. Same dscardng practce No dscardng mm mesh 145 mm mesh 130 mm mesh 145 mm mesh.' N W N W N H N 2-9 Aprl June W J - ' Table 6. Relatve length compostons of cod and haddock caught n Aprl 1973 by bottom and mdwater trawl wth double and sngle cod ends~ Mesh sze n cod end and double cod end 130 mm. Sngle cod end Double cod end Length (cm) Bottom trawl Mdwater trawl Bottom trawl ~ldwater trawl -r : COD ; : HADDOCK ;k<+ --