CM_1955_16.pdf (219.3Kb)

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International Council for the Exploration of the Sea.

if~; r~ .~r1di't-~.f~to~a,t~t

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C .M .. 1955. _, Comparative Fishing Committee.

No.. 16 ..

Experiments ~nth large-mesh trawls in the Bear Island Area&

by G. SEetersdal

~n,~~~

The largest mesh size previously

trie~'in

furopean waters seems to be lOom. The general biology and the marketable sizes of the fish in the Barents Sea - Bear Island Areas~ however~ offer some special problems which justify trials with larger mesh sizes ..

The following experiments were oarried out in the Bear Island Area in the period lOth to the 26th of May 1954 by the vessels flThor Iversenl! (82 feet) and nPeder Ronnestad" (86 feet) belonging to the Fisheries Directorate~ Bergen ..

All the trawls used had a 50 feet headline^Q Two pair of types were ^tried~

~wine trawls with an average mesh size in the cod-end of IOcm. and 13c:m ..

respectively, and cotton trawls vdth a hemp cod-end and the same average mesh sizes of lOom. and 13cm.

The experiments were planned as series of simultaneous parallel' hauls ^$ with ohanging of gears in order to counter balanc ~ differences in fishing power peculiar to ship, ~:ound r?pe etc. of successful

hauls were made:

'*

^~~

"'\

^~~ ernT _"

Series A. 12 parallel hauls, ljWJ..ne. ^{!.. •} May loth-11th.

flThor Iversen!!

nPeder Ronnestad ^fl

lOom. Total tovving time 17 hours.

Series B ..

Series C ..

Series D ..

Series E ..

13cm" ^{fI n n} 16 ⁿ 12 hauls, twine. l'vIay 11th-13th",

IIT.I. I! 13cm. 21 hours 30 min"

lip .. R. 11 lOom.. 21 ^ff 05 ^!I 10 hauls, twine" May 21st-23rd ^e

uT.1 .. ⁿ lOom. 16 hours

lip .RQ 11 130m3 14!! 45 min~

~%-r"

9 hauls ^$ cotton/.r- .• ;, ^]flay 13th-20th.

IIT.I.^lI 13 cm .. 11 hours.

IIP.R. II 10cmo 10 !!

'!

I

n~n1.'"'

4 hauls, ootton ~. ~M~y 20th-21st.

liT .1 .. 11 10cm,. 5 hours 30 min ..

lip "R. ¹¹ 13cm., 5 ^fI

Series F. 11 hauls, twine. May 24th-26th ..

uT.I.V! lOom"

"P.R." 10cm.

10 min.

~_

The small differences in the total towing time have not been

compensate~

L-!-0r in the follOwing comparisons^c

t-b J'7'NW''';;t~ 2.

All the cod caught in each haul were measured cept in the case of series

~where only representative samples were taken~ th

~ ;i.u tJJ9-- s~igs ~'l: E aiW:-e1Th permmbage-l.ength aistrlvatisE: in serie~ F.

Series F show that the selective effect of the two 10cm. twine trawls used were almost identical. Of the other types of gears~ only one gear was available and was accordingly used by both vessels.

'-....--

Concerning ourselves with the t\nne trawls, series A, Band C, it is seen that there is a great difference in the selective effect of the two mesh sizes~

The 50% release length of the 13cmQ mesh in relation to the 10cm. mesh is about 55cm. in all three serieso

... ^{.. / ...}

- 2 -

Series "ir~ alse- show the phenomenon found in many previous experiments of this kind: fish of the larger size groups is taken in larger numbers by the widest mesh. That this difference may be of practical importance is clearly illustrated when the weight of the catches is considered~ see Fig. 4.

Here the weight of the catches from the series A~ Band C is shov"ill cmnulati veJ.y

tov~rds decreasing fish size, the unity being the average weight of a 30cme

cod multiplied by thousand.

~ The series D and E3 cotton/hemp, consist of considerably fewer hauls than

~

I

the twine series, and the results differ from those of the twine trawls in the .~ poor catches obtained by the l3cm. mesh. This may be due to some peculiarity

\ ~ this special gear.

N.r' ---

400 300_

SERIES A

TWINE

"T.I." 10 cm. Fig. L

N.

40 300 200 100

SERIES

B

TWINE I f I

/\

I \

I \ "P.R.

II

10

om. / ,/'-F"'V -1 '-\ /I ,... \-\ ~.(.:~\ /\ / v \

r /

/'~'\\/

\---\

25 . ) / \ --\

I

rl \/ \I \ \_ / ~,,-\ . ______ ::---"'~/ __ =-_

/r .-J ___ ---'_

~\\~

___ _

LengJch distribt~ti0n of cod. IVIay lOtJll~ -11th" So:c=ies B:

30 40 50 60 70 80 90 OK Series A: 12 parallell hru:la 12 paral1ell hauls May 11 tho--13th,

N

.---

SERIES C 140-TWINE 120_ 100 80 __ 60 40 20-

"T.I~" 10 cm. Fig. 2.

N 200 ~ 160 120 80 .- 40 20 90 om.

SERIES D COTTON &: HEMP

"P.R." 10 om.

\

Length distribution of cod. May 21st.-23rd. Series D: Series

c:

10 patallell hauls, 9 parallell hauls May 13th. -20tha cm.

o

cm.

N.

lOOi

SERIES

80\ COTTON

I

^{& HEMP}

~~

40L

f; ,

JL\ 1\

E

! V \1 \

I ' ! IITeI .. ^!l 10 cm ..

I I

\ \

_l

\ \

_\

I

\

\,

\

\

1\1 - \n'J

f

1/ "/ \

^/I " \ / /\ , !T

1I

;

' \ I \ I \ .... I \ t\ '\' \ d\VV~ P .. R.

/\. I

v ... ..;

V

v"

~

\

I /11 \/

\h

I 'J v ^{vI \..}

/'\1'

I

^I \.,~_

I

I

13 cm ..

60 70 ₈₀ cm"

PER 10 000

100·~---1

SERIES F

TViINE SOO

500

400_

SO 40 50 60 70 80 cm.

Fig. 3. Series E: Length distribution of cod in 4 parallel hauls May 3oth.-21st.. Series F: Percentage lebgth distribution

of cod from 11 parallel hauls May 24th. - 26th~

VVEIGHT

30

.I~ /19

^{cm .. lj}

11

I

1 - I - - - + - - l - - - i - -

I -I

1 - '1

1

I I '

. I I

I J ,

~~

^{__ 4 -___}

~

^____

^+-__ ~I~_/~1-~_

/ I

~~--4----+----+-~JH----~1 ^{- - - i}

25

20

15

lO~+-+- ^__ -+ ____ +_~~_~_~ ____ J, __ __ I

WEIGHT 10 cm"

i

~-

5

70 60

~.-+---I

. - - - - t 20 ----~---+----r---~15

I

3 ^eIDe

.~S~ER~l=E=S~B~~L+ I

____ +-__ -+_________ 5

I i

^/1

I

I . / / I

90 60 50 40 30 ^emo

WEIG:BT 10 cml

i

I

^I

: ---i

I

!

! ^I

8

- I

I

!

t1

I

I

I I·

I

I

ⁱ

I ^I

If

6 I

I ^I I

~-~r'

I

I

^I

i I

I·

+

4

-J

^{I / ; '---}

I

- I !

I ' I

i I I

I

^{/ I}

^I

2

I

i /

I

^----L-

I ^{ISERIES t I c ./ /' ~/} -li

I - - - ^- --

¹

90 80 70 60 50 40 30 cm"

Fig. 4. Cumulative weight of the catches",