This paper not to be cited "litbout prior reference to the mithor. ObservationS on Fiah Behn;viour in tbe Trawl. . by 11.

Transcription

1 This paper not to be cited "litbout prior reference to the mithor C.11:. 1912/B:9 Genz. arid Bebaviour Comnii.ttee ObservationS on Fiah Behn;viour in tbe Trawl. by 11. strzysewski x ). Oboervatioris on tho bohaviour 01' borring" cod and floundor in the bottom tr~wl entrance and i ts codend hd.vo been carriod out on the research vessel mit "Dr Lubecki" (24 m long, 240 HP) in the Baltic Sea at a depth 01' metres... '.. a 1J:ca.11 mewh sizo (50 mm; and in i ts final' part 36 mm). so that oven small herring. could not pass through tho not out"sido (Figure 1).. The trawl usod during tbe re~earcboporationswas mado' 01' tho netting (PA) w!th n order t6 obsorve throughwh1cb part oi the trawl entrance the' individual fisb are entering, the trawl was equipped' with a horizontal wall 01' netting witb a. mesh sizo 01' 40 and 20mm,. situatad betwaen the trawl lateral linee; Tho beginning 01' tbe horizontal '-lall of netting was situatod on the tra;wlgroundrope heigbt and wns contmuod to the codend (Figura 2)~. n the further investigations tbe front ~a:t of the borizontal \Tall of netting Was removod and Was only kept in the codend tf~gure 3)..' '. '... l1easuring tests 01' the trawl' entranco oponing..;.. cnrried out by the difference' 'batbygraph - showed that the vertical opening a.:1ounts from 2~9 to 3.2 m, while the borizontal ~ll 01' netting beginning, was situated 1.5 m ovar the ground ropo. ; n the second case,"there the trawl was equipped with the horizontal wall of netting only in its codend, it uas possible to corl'irm tbo trend of fioo bebaviour in tbe trawl on i ts entoring t~"rard the upper or lower' cod~nd part basis;. The results.obtainod arg shown in Table 1, uhich inc1udes tbe quantitative and percentage relations 01' the'fish üntrance to tbe uppür and m'1or part 01' tbo trawl' equippe~ with tbe horizontal wall 01' netting as illuntratod'in Figura 3.,Duringthe catches, 'hcrring and cod appeared together witb a. notable preponderanco of.berring. He~..!!ß:. AS far as berring i8 concerned it seams clear tbat'lt enters by tbe tra.wl entrance main1y at its upper part (Table 1). Tbe only sporadical case took p1aco intho period 01' May, Tbis experiment, however, should not be taken into consideration for tho smallfish quantity. This ahmts us to think tbat the mo8.ns obtained in vnrious oj..'1lorimenits - a:1ounting to 97.4% 01' berring ontoring through. tbe uppor trawl entranco - arc realistic, because particulnr results show only minimal doviationso. ;cr Süa. FiSheries nstitute, A1eja Zjednoczonia. 1, ' Gdynia, Polo.nd~

2 .' f,... )~. \ " " < '.... As the traul was. towed close to tbe bottom, it was possible to suppose tbat tho herring movement from tbe front part of the trawl to its final part (Table 2) undergoes distinct cha.i1ges. in relation to the trawl admission entering. ;;. Throu@;h the uppe~ part of 'tbe' code~~ orüy 60.2% enter while 39~6% herring ~nter tbrough tbc lower part~ This phenomenon :Ls prob8.bly due.to tbe fact, that once herring have actimlly entered tbe trawl they tend to disperse' towards tbe vertical suxface lookfng for a way to escape from the trawl. '. Cod enters the trawl in a different way eompared to' heitinb'. n the upper part' of the trawl open.1ng cod was observed only in 27 ~ 3% and in the lowg'r part in 721) 7% (Tablc 1)...,.., '.'.. However, in thc investigations carrl.ed out in p.pkil 1970, it was bbserved that dod enter into the upper and lm'lor Pi:l.rt of the trawl more or less in tbe. same m8.nner _.. ' ~... '.'.'." ":,,,.~ : >''''. Duo to this i t is necessary to bo earof-.ll in drawing, arty conclusj.ons in,spite. of thefact,. tbat the average rosulto for tbo antire period under investigations indicate tbat thc majority of.fioh enter ihto the lower part of the trawl. ", tis possible, that there are periodical' cbanges in cod beh~vlouf~ Nevertheless, this phenomenon should be studied ir.i a greater number of observations arid should be carried out all year round. Fromtbe present investigations it appears tbat cod enter into tbe lower part of tbc codend in 74.0% (Table 2). Comparing this result witb the observations during tho 'similar research period (Table 1),.it is see'n,,that tbe difference is not so important. Tbus, it cnn be sugicstcd, tbat 'cod, which remain in thc bottom layer up to 1.5 m, once it has entercdinto tbc trawl does not disperse vcrtically, but continues,to stayat the same level from ",hieh it entered the trawl.... Flounder ".. During the investigations, the quantity of flounder was very small. However, even from tbis small quantity of information it "TaS possiblc to conelude that 80% of flounder enter thc trawl through its lower part. observed entering thc eodend.. Tbe sane' proportion was Tbe investigation conducted have shown tbat by menns of tbe trawl partition it is.possible to dra~rn eonelusions as to how fish are entcring into tbe particular trawl sections.

3 - 3 - Tab1e 1. The number of fish which have entered into the fore part of the trawl in its upper and lower part _.._-'.. -"._-~----_ Trawl Part.. _- - Fish Up!er L Lower Number Date }-- --:----, of of the % Number of % trawls catch species Number of \ specimens specimens 0 Herring V- " V v- 70 " X,X - 70 Total without catches 45 of May 1970 Cod V- 70 " X,X Total F10under X Tab1e 2.!. The number of fish which have entered from the trawl to the codond into i ts upper and 10l.'ler part. Codend Upper Part Fish Lower PC!-rt Number Date of of the species Number of Number of?~ specimens specimens % trm.,ls catch -- Herring X - 70 Cod X - 70 F10under i X - 70

4 '7 ~ b: 0 ::s: -J \,(\ \,(\ '" ~" qllo, ~lid 792 3~ 13h 13~ O!}Omm 13lt O~Omm , m tn 1~2 oomm '' , /8 210 ~ \ Details 0/ ehe trawl and the wall of netting used to the investigg tions. FiJ.l

5 C.M.1972/ B: 9 '. the Nal/of nelting the trawl Uppel' patt. Me tl'()wl /owej' PClJ-t Oiaglt1m ()f Me lfont wdh fhe uall of netnng he iran! vpper pa,.t the codend tvtth lhe wall 01 helling c:q:) Me flt2wl ('lae,. pa;t ljiag,.am of Me trawl wilh the wal! of netbi?g in Me codenci Fig.?