CM_1980_K_22.pdf (1.596Mb)

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International Council for the Exploration of the Sea

, <:::~~1. 19 80/K: 22

\

Shellfish Committee

ABSTRACT

Results of a stratified bottom trawl survey for shrimps· (Panda1us borea·lis) in the Barents Sea and the Spi tsbergen area in 1-~av-June 19 80

by

Ana Maria Tavares

Instituto Nacional de Investiga9ao das Pescas - Lisboa - Portugal

and Per 0ynes

Institute of Marine Research Bergen - Norway

A stratified random bottom trawl survey of the shrimp grounds in the Barents Sea and the Spitsbergen area between 71°30'N and 78°18 'N, and between 10°05 'E and 35°04 'E was made in r•lay- June 1980. On the basis of the data from 60 trawling stations, the biomass of shrimps, Pandalus borealis, in the area surveyed was estimated by the swept area method to be about 65 000 tonnes ..

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The estimate is probably an underestimate due to various reasons discussed.

En Mai~Juin 1980 on a fait dans la mer de Barents et dans la zone de Spi tsbergen une recherche sur des crevettes ,· Pandalus borealis, en usant la m~thode d'{chaniillonage stratifiteau hasard avec un chalutier de rechercheo La zone parcourue est comprise entre les 71°30' 78°18' latitude Nord et 10°05' 3.5 °0 4' longitude Est.

A

partir des r~sultats de 60 stations de chalut du fond et usant la m~thode de l'aire balay~e, ^{on a} estim~ ^en 65 mille tones la biomasse de crevettes dans cette zone,

L'estimation est peut etre le minimum, tenant compte les p1usiers remarques que nous presentons. /

INTRODUCTION

Since 1970 shrimp surveys have been conducted by the Institute of Marine Research, Bergen,in the Barents Sea and adjacent ^areas~

Stations and sampling intensity were usually decided informally at sea while the surveys were conducted (ANON. 1978).

A stratified random sampling scheme was initiated on a bottom trawl survey with R/V "Mic:hael Sars" from 18 May to 11 June 1980 in the Barents Sea (Sub-area I) and off Spitsbergen (Division IIb).

The main objective was to estimate the abundance and structure of the shrimp population, and estimate sampling errors.

MATERIAL AND METHODS

R/V "Michael S'ars" is a stern trawler of 46.5 m length and has a main engine with 1500 horse power. The trawl used was the "Campelen Super" 1800 mesh with the following specifications: 30 m headline, 19 m groundrope, 40 mm mesh size in the body, and 20 mm mesh size in the codend. The boundaries of the strata were selected in

accordance with previously known shrimp concentrations (Fig. 1) ^o

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The main commercial fishing area since 1977 has been "Thor Iversen banken" (stratum 1). The area outside the Finnmark coast is called

"Nordkappleira" (stratum 7) • The two grounds north of "Nordkapp=

leira" 1 "Bananbanken" (stratum 5) and "'Tiddlybanken" (stratum 3) 1

were the best commercial fishing grounds in 1976 and 1977. The strata 61 4 and 2 were placed along these two grounds (Fig. 1).

The "Hopen" area (stratum 8) was an important fishing ground in 1974 and 1975. Strata ⁹1 101 111 12 and 13 are along the western slope of "Sentralbanken", and these strata have not been commer- cially exploited.

Only a short survey time was available for the "Spitsbergen" area.

Therefore the strata were traced only for the main fishing areas (strata 151 161 181 19).

The intention was to trawl in all of the 19 strata; however, due to shortage of time stratum 14 and 17 were not covered.

Each stratum was subdivided into rectangles of 5 minutes latitude by 5 minutes longitude. Each rectangle is assumed to be a homo- geneous· sampling unit. Within each stratum, rectangles are given consecutive numbers starting from 1 (Figs. 1 a,b,c¹d).

After fixing total number of trawl stations, the number of

stations was roughly allocated to individual strata in proportion to the size of the stratum and the expected shrimp concentrations$

Within each stratum the trawl stations were allocated to rectangles randomly.

Some stations, especially within stratum 6 and 7, had a rough bottom unsuitable for trawling. In these cases the first nearby rectangle was chosen during the cruise. One tow was repeated in stratum 19 and rectangle 1 due to strong current in the area and crossed doors of the gear during the first trawl haul.

The duration of the trawl was 2 hours with a mean speed of

2.5 knots in the strata 1 to 7, and only one hour trawling with a mean speed of 3 knots in the strata 8 to 19. All the stations

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were made during the day timeo

The catch of shrimp (in kg) and the number of by-catch of fish in each haul were determined (Table 1) •

Computational formulas are taken from Cochran (1977):

L

nk ^ck.

i=l ^J.

=

= 1

s. e. =

where:

=

t

_i=l

mean catch per nautical mile in kth stratum

_sample variance of kth stratum

variance of

ck

in kth stratum

standard error of ck in kth stratum

number of tows in the k stratum

catch per nautical mile in kth stratum and ith sampling unito

I t is assumed that all shrimps of fishable size present in the area swept by the trawl are caught. I t is also assumed that catch per nautical mile trawled (ck) is proportional to the density of shrimps within the stratum. The density of shrimps in stratum k as given by the swept area method is,

=

a

(5)

where a is width covered by the trawl (15 m ⁼ 0. 0081 n.m.). The biomass of the stock in stratum k is given by

where Ak is the area of stratum k.

RESULTS AND DISCUSSION

Table 2 gives results in each stratum with the precision of the estimate. The biomass of the shrimp in each stratum is given in Table 3. The biomass in the area surveyed (12 350 square nautical miles) is estimated to be 65 000 tonnes (Table 3) • These estimates

are of the biomass of shrimps available to a· 20 rnm mesh size, and they are less than the total biomass of the shrimp population.

For several reasons the trawling speed was not constant from

station to station. Therefore catch per nautical mile is assumed to be a more consistent index of biomass than catch per hour

trawling in the present survey.

Stratified random sampling permits the control and estimation of sampling errors and avoids the errors which can arise from the selection of stations ^(~1anualon ICNAF Groundfish Surveys, 1978).

The results of this survey are subject to two possible errors:

(i) A persistent error or bias in the method used is possible since i t is assumed to be a 100%

availability .of shrimp to the geare However, this may not be valid due to possible extensive vertical distribution of shrimps during certain time of the day.

(ii) The random variation of catches at different trawl stations.

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The precision of an estimate, expressed by the coefficient of variation (Table 2) , indicates the likely size of (ii) while the accuracy refers to the closeness of the estimates to the "true value" and includes both of these possible errors ..

The coefficient of variation ranges from 6% to 77% (Table 2) ^c Because of the possible error (i) the stock estimates given in Table 3 are probably underestimates ..

REFERENCES

ANON. 1978 .. Fisken og: Ha vet 1 SJERNUMMER 1₁ Institute of MariL Research, Bergen, pp. 1-28 ..

COCKRAN, W. G. 19 77. Sampling Techniques·, 3rd ed. 1 John·· Wiley and Sons, Inc.

ICNAF, 19 78. Manual of ICNAF Groundfish Surveys, 1st draft, lMi~eo

:j

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Table 1. catches of shrimp and by-catch per haul by R/V "Michael Sars" in May and June 1980 by stratum, time of hauling, distance trawled, position, direction and dep~~.

't'l=• <>C O.'t# itt~~·..a s~(u.:tr• 1'\.ault.nq (!'IC'.j

LOC I'U•l~~on

Jlsc.•n.:• - - - - Cn.r.tHl .of. l.oe. t, 1unof.

:ll/5

~1 /S

7/6 Z1 /S

~5/5 H/5

:s1s

11/S : :!~

:o;::

~0/S

L7~0~l1Hil LS l-' t~Jl•16L7 s.o

ld llSll~lll'i ~.0

~a u600 ·.:li!OO 5. tl

~'i OS2~~a1lS 5.0 52 ~7SS~l3SS 2.>

'6 o·n~~lCJS z.s '>2 llH~lJ:ZS S.:l llS0⁴lSH S.O

n ~qsa~1uo ~.cl

ol JSiS~·J71ii S.·J 75 OSS2~07l2 ~.0

N ~,ce-to4o ;,o 1: !1522~0117 ).~

Jl l312~1'11.l 2.5 ll OIJ05~1LOS S.O

~a lJOO•lSuO '·0

6v l6\l0•1d00 l.O 20 12,5~11~) s .0 19 ~540~1740 S.·J

H 0915-LUS 5.0

H llOO~lSOO 5.0

~a ·J52s-ons s.o

t6LO•LSOS S .0 1'1S5•HS5 S.O U l'l1S~HZS '·0

>J'HS·tllS S.J

H 1-ti>~>SJO ~.S H l&S0·1S·\5 ';.a

,;,J OS20~0H S 5. ')

·:aso-1o'a s.o

'lS2S·072l LO llS()~USO s.~

7l\)•u·.~ ll<.)C:ii'.>

n"1~·.& 12'':.;•,7 n'' '"' .1 ,~ ... Ju• .ol JIJH·.~ lljH'.Il

n'' 1 ~ • • ~ JJ" s 2 • . ~ 7J⁰S'\' .o J~"~a· .u

71~-.10'.5 J-'~~\· .l 7).,H' .~ H~SO' .:l 7)~}5' .l la³~L' .0 71°19'.0 10¹S7'.J ll,H·.~ a">·1· .s

1l"t~· .G l2,t9'. ~ 7]⁰~4·.~ JZ.)H'.J 1i':1•.J l1°t7•.s 12³J'l' .~ JJ⁰JS' .~

n\)u• .a 34°~1'.1 ri"Jo• .7 H~J!)• .:!

12"J4' .S JS":1'.'J

n°J:.• .s n".:z• .J 72;,\S' .S JL.³21'.S 72°JS' .:l H"Ja• .J

·2"}0' -~ ll"liJ' .<i n>t~·.? n'<Ja'.l 7t"o4'·.2 1'J"JL'.S

7!.0'0' .'J l'l~H' .J 7t, ~~·. J ] !. ":Jl •• ) : 1° H ' . ·) :·J ~ : S ' . J 7l'"')V'~7 :?¹~2'.5 :~.};a• .1 ;o~·tl' .J n>4a• .1 n"JJ' .·J tt⁰l"i' .a Jl-:J l2 • .. s

7t..,~S'.:J J~"02'.7 n"':&' .1 ;6°·t.;• .o HJJG'.l :G:>.tS'.S 7L:lt4' .l, ~7~~;z• .0

Olr.,<;th>A C..•\ltl\

C.:J""•"I :"tl

·14'\

·14) lJS

ll S-1 1~

~·11 ~ ~·11

lOO-Jv~

:r.d-<od

laa-JH iH-lH l7C:-HO llt1-) ~3 :'ls~;H .:a?~li)Q :H~ Z11

zso-.:ss

)~0-l'll)

JCtl~ le~

<'H•I;&

!25~1 :o

l20~ Ill

H6·ll2

;s2~1n l'\3·l1S t'\Ca-tr.SS S.O 7l~l'\'.3 27>17'.5 045 l49•lH

~0/S

ll/5 S/6 5/S 5.'6 S/6 5/'i

.. S/S

,

..

.. ,.;

Sl'i !Z 6/S U 'i/6 11 :;.; l>

2/6 u 2/6 :~

2/'i ~~

1/6 a

4/6 1!

1/6 l!

1/6 19 l/6 1'?

16 L74S~l'l4S 5.'J ll⁰49'.~ 27:111' .a llS llO·lll

to ~912-0"ll 1.0 l14S~ l24S J. 0 LClS-LHS J.O ta•0·1'HO ).0 l511!-l711!

'lS5J~ij642

oaoo-·noo

La50·115a J.O 2. 5 J.O l.O 120·110 l.O UH'l~19l0 l.O 15Jf;~l6 16 l.O l5~2·l6~Z l.O l7lS·l91S l.O l140·lHO 3.0 01Yl~l0~0 l.O 201~-1125 J.O ll 062 S-07 25 J. 0 20 1110~1aLO J.O 1100•1200 1.5

·'~5S~Il64S 2.5

75°55' .4 JO"<::'l' .J 7>"SJ'.5 n"n· .o

75°29' .J Jl:>l6' .0 75°21' .o n"'o1• .'J 7S:~:l' .9 JO:~SEI' .0 75.,14' .a H"n· .a 1s"oa· .·:J jo"za• .a

H⁰04' .6 ll⁰Jl' .0 ,..,.,, •. J ;o:~JS' .o H"u• .0 J0"4S'. 7 74°)4',7 1'l.,~9'.il 14°1 l'. r. Jo"co • .o 78°<H' .0 ll⁰17' .S 71!.,:l0' .o 12°Jl• .6 78::~16' .) LO"H' .0 78°11' .a 1:J²~a·.o 15°)7',0 l5°Sl' .o

75°SCJ'.l 16°~5' ,0 7-s"•,r;• .o 17°11J' .a

74°49' .o u;"JI!' .o

H"H• .J 17°19' .S llS

:zs

140 270 2JS LJS llS 225 lH lOS 220 LJS ll'J lOO 295 JLS tJS HS 0?0 270

llO-ll7 12s~n1 J5S·lSl )l}•ll6 l65-J72

)47~)54

J7 2· l8ol Hi5·lS7 J7S~J17 )62·129 Ji!O-J71!

)1;2-]14 2SJ- 24EI 245-245 124-JCa 2'J4·lC8 Ha-1&1 lll-12') 251·281 Ho-J 29 JCO•JOl

1nr""'P .. ,ten t•·ll

V10

LOO tSJ l8S

!01 Jl 23S HO

ua

70 s;

l4

lJO

~liO

::o

~~

l6S 105

HO zao

lSO

~10 t6a 400

LS

as.

.;a 1CS

:eo

li•J 101!

t sa

l7~

60 ,21']

l'JS 400 H

?0 )]

450 125 )0 l Sl

~5 l l

lS

tS

lL

l"

14 10 l2

\l•JO 148 627

L4

;:j

11 2')

)) tSS 7)')

:&o HO 1170 lll.6

24 )2 25 Sll 22'1

so

14 49 Sl

ll9

•ll 11;

t-47 52 S) 68 ae l) 5 48'J'S

;7 l l

ll

lSO lll t'J l'l

147 U6

1l ll1

!0 11) )0

lCC.2

11)0

2l0 210

zo

2'H 140 41 120

~ ..

?a

1~6

182

126

20

i'01ar c:c<J Other I~•·•

140 JU SH 840 6915 22J!>

8184

Z:JO 59a 27&5 500 2))0

uss

70'3S 5706 4Ul

100 l20

15200 L 75SO 1H5 22'1}5 15 ~0 1800 650 1640 qFt4

1350 1080 6)0 720 679}

21 lO )25 440 Sl

Zll SUJ

Hl

<HJ

~62 Hl~

Jll

~:ol 594 316 684

~01

\ }7'1

807 l20ii 7S7

..:ea LJS

l ~1

6C.2 10~

,.,

lCS

')L

~\

110 47) l4C )20

254 Hil 44AS a1H 818 )276 707 1492 191 12) lJH

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TABLE 2. Mean catch per nautical mile of shrimp on Bare~ts Sea and Spitsbergen area in May-June 1980, and estimates of precision.

Samp1ings Numbers Mean catch Sample Sampling Coefficient, Locality units of per n.mile v~riance variance of variation

Hauls ck(kg/nom) sk v (ck) s.e./ck

Thor Iversen (1) 64 8 48o13 852ol3 106.62 .21

Out Thor Iversen (2) 98 5 43.12 296a63 59.33 .18

Tiddly (3) 62 5 13.84 117.07 23.41 . 35

Out Tiddly (4) 85 5 48.60 163.80 32.76 .12

Banan (5) 16 4 39.75 26.25 6.56 .06

Nav Vardct> (6) 63 6 48.00 209.20 34.87 .12

Nordkappleira (7) 24 6 50.33 373.47 62.24 .16

Hop en (8) 10 2 2.83 9.39 4.69 .77

w.

Sentralbanken (9) 8 2 24.17 34.72 17.36 .17

w.

Sentralbanken (10) 8 2 34 017 1.39 .69 .02

w.

Sentralbanken (11) 8 2 30.00 72.00 36.00 .20

w.

Sentralbanken (12) 6 2 54.17 34.72 17.36 .08

w.

Sentra1banken (13) 8 2 30.00 200.00 100.00 .33

Isfjordrenna (15) 5 2 99.17 2334.72 1167.36 .34

W. Forlandet (16) 3 2 27.50 12.50 6.25 .09

Storfjordrenna (18) 21 3 89.78 5088.48 1696.16 .46

Kveithola (19) 5 2 36.60 1210.32 605.16 .67

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TABLE 3. Mean catch per nautical mile, biomass and standard error of the biomass of shrimp on Barents Sea and Spitsbergen area in May-June 1980. "Michael Sars" survey.

Area Mean catch Biomass Standard

Locality (sq. n .m.) per. n.m. ( t) error of

the biomass

Thor Iversen ( 1) 1600 48.13 9508 2038.70

Out Thor Iversen ( 2) 2450 43.12 13044 2329.29

Tidd1y (3) 1550 13.84 2464 926.38

Out Tidd1y ( 4) 2125 48.60 12751 1500.73

Banan (5) 400 39.75 1963 126.42

Nav Vard~ ( 6) 1575 48.00 9334 1147.30

Nordkapp1eira ( 7) 600 50.33 3728 584.42

Hop en ( 8) 250 2.83 87 66.71

w.

of Sentra1banken ( 9) 200 24.17 597 103.00

w.

of Sentra1banken ( 10) 200 34.17 843 20.48

w.

of Sentralbanken (11) 200 30.00 741 148.20

w.

of Sentra1banken ( 12) 150 54.17 1003 77.21

w.

of Sentra1banken (13) 200 30.00 741 247.00

Isfjordrenna ( 15) 125 99.17 1531 527.52

w.

of For1andet (16) 75 27.50 255 23.18

Storfjordrenna (18) 525 89.78 5820 2669.50

Kveitho1a (19) 125 36.60 565 379.75

TOTAL 12350 651.60

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1s·l

• ~

74"~--

I

~

73'1

2"~

I ( m·l I ^I

I

I F 17o•f.

t

r

- 10 -

30" . ^35~

~KONG ~ KARLS LAND

STORBANKEN

.. \

.. :, ,.:' ... ~r"~ .•... --·-·-~, ... ;

:: ... ~ (·~:-.;

.. ··

.•·

so·

:--,-~.-:~

Fige le Sampling strata used in May and June 1980 in the Barents Sea and Spitsbergen areas for the shrimp survey with R/V "Michael Sars".

J~

.·;/I

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~

1"30'

I"

73"

1-

30'

L ~

G) a G) G§) 17 2 G) 10 15 18

G) 6 11 14 19

4 5 12 13 @

Fig. la.

0

²⁴ ²⁵ ⁴⁸ ⁴⁹ ⁶⁴ ⁶⁵ ⁸⁰ ⁸¹ @ ²⁹ ⁴⁰ ⁴¹ @ 53 64

2 23 26 47 50 @ ⁶⁶ @ 82 27 36 39 42 51 54 63

3 22 27 46 51 62 67 78 17 26 31 38 43 50 55 @

4 21 28 45 1

CV

⁹ ¹⁶

cw

²⁵ ³² ³⁷ ⁴⁴ ⁴⁹ ^@ ⁶¹

5 20 @ ⁴⁴ 2 7 10 15 19 25 33 36 @ 48 57 60

5 19 30 43 3

i

⁵ ¹¹ ⁽ⁱ⁾ ²⁰ ^{231 34} ³⁵ 46 47 58 59

7 18 31 1 42 4 I 5 I 12 13 21 22 93 8 17 32 41 52 51 58 77 83 92 I 94

9 16 33 40 s:; 60 69 76 84 91 95

10 18 34 39 54 59 70 @ 85 90 96

11 14 35 38 55 58 71 74 86 89 97

12 13 36 37 56 57 72 73 87 88 98

9 30 31 52 53 74 75

10 29 32 @ 54 73 76

11 28 33 so 55 72 77

~ --

12 27 34 49 56 11 78 1 9 24 25 38 39 50 51

13 26 35 48 I 57 70 79 2 10

I@

²⁶ ³⁷ ⁴⁰ ⁴⁹ 52

14 25 36 @ 58 69 80 3 11 22 Zi 36 41

G

⁵³

15 24 17 46 J 59 58 81 4 @ 21 28 35j 42 47 54

l a 1s I ²³ ³⁸ ⁴⁵ @ 57 82 5 13 20 291 34j 43 46 55

2 7 17 22j@ 44 61 66 83 6 14 ! 19 30 ® ^:.4¹⁴⁵¹⁵⁶

3 6 18 21 40 43 62 55 at. 7 1s I 18 31

4 5 19 '@ 41 :.z 1 53 64 83 8 16 117 32

1 8

0

¹⁶ ⁴³ ^ss^I⁵⁷

2 7 10 15 44 55 58

1 10 11 @ ²¹ ³⁰ 01 ⁶ ® ¹⁴ ^1.5 ⁵⁴ ⁵⁹

24 2 9 12 19 22 29 4 5 12

cw

⁴⁶ ⁵³ ^@

0'

23 G) 8 13 18 23 28 31 36 37 42

l@_

52 51 22 4 7 14 17 24 7:1 J2 35 38 41 48 G_i) 62

21 5 6 15 16 25 26 J3 34 @ ⁴⁰ 49 50 63

Strata 1 to 7 subdivided into 5'x5' rectangles.

Legend: 1= trawl station.

-

62 51 16 {~

59 58 57

1

_I

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"" ^'•·'

76°

1-

....

f -30'

"'

~

75°

1-

f-o

!---

30'

Fig. lb.

- 12 -·

"'"--· ' ' ^'

I

^I

Q)

^t. ⁵ ⁸ ⁹

2 3 6 7

@)

_-

-

1

CD

⁵ ⁸

2 3 ⁶ ⁷

-

1 t. ⁵ ⁸

0

³

0

⁷

_-

CD

⁴ ⁵ ⁸

2 3

G)

⁷

.

1

CD

⁵

2 3

0 01

G)

⁴ ⁵ ⁸

2 3 6

GJ _-

zgo _30° _31° 32°

I 1

^I

^'!'

Strata 8 to 13 subdivided into 5'x5' rectangles.

Legend: ^1~trawl station.

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... _I ₁

.

^-~ ⁱ Î ^-1 Î Î

t-

-

jCD j0j

³

_I

^I^I

J

~

I I

I

1

101

I . ⁵

_I

2

10

^I

..._

i

I

j

I

3if~· ---~---~---~---~---L---~ I

Strata 15 and 16 subdivided i~to 5'x5' rectangles~

Legend: l= trav1l station.

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I 130'

r-.

I

I ,.

I

_I

! 76°

/CV

1 6 1

a

Q) s

¹ 9 3

~.

¹ ¹⁰

- 14""'

15 116

14

1,7

®

¹⁸

12

119

I

11 1 20 20 1

I

\{)I

Fig. ld. Strata 18 and 19 subdivided into 5'x5' rectangles. Legend: 1= trawl station.