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Exploration of the Sea Pelagic Fish Committee Ref. B.

ACOUSTIC SURVEY ON BLUE WHITING

IN THE NORWEGIAN SEA, AUGUST/SEPTEMBER 1985

ABSTRACT

Seven research vessels from USSR, Norway, GDR, Iceland and the Faroes participated in the fourth ICES-coordinated acoustic survey on blue whiting in the Norwegian Sea and adjacent waters.

Blue whiting were recorded over the major part of the Norwegian Sea, with the highest concentrations near the slope around Faroe Islands

The acoustic estimate of blue whiting was 4.9 mill. tonnes.

is an increase of 1.1 mill. tonnes compared to August 1984.

1982 and 1983 year-classes make up the bulk of the stock.

*General Secretary . ICES

Palcegade 2-4

DK-1261 Copenhagen K Denmark

This The

INTRODUCTION

Acoustic surveys on blue whiting, which have taken place during spring west of the British Isles, have yielded estimates of the spawning stocko For monitoring the stock, however, there was in addition a need for an estimate of the total stock.

In 1982 the first ICES-coordinated international acoustic survey on blue whiting in the Norwegian Sea took place in ~ccordance

with a recommendation from ICES (Anon. 1982). In 1983 and 1984 similar surveys were also carried out (Anon. 1983a, 1984).

The fourth ICES-coordinated acoustic survey on blue whiting in the Norwegian Sea and adjacent waters was then conducted from 27 July to 5 September 1985 (C.Res. 1984/2:9(ii)-10.)

MATERIAL AND METHODS

Five countries with the following research vessels participated in the survey:

--- ^----

Nation Vessel Survey Instrument Vertical opening period constant of pelagic

C .. 4n

I (m)

USSR "Kokshaysk" 9-10 Aug Oa83 60 Norway "Eldjarn" 29 Jul-18 Aug 0.29 15,

il "Michael Sars" 1 5 Aug-5 Sep 1.36 20, GDR "Walter Earth" 10-18 Aug *

-

³⁸

Iceland "Arni Fridriksson" 10-27 Aug 2 .. 88 17

11 "Bjarni Scemundsson" 1 0 Aug-5 Sep 2 .. 60 1 5 Fa roes ¹'Magnus Heinason" 27 Jul-14 Aug 1 ^G 33 40

' - -

*No integrator

Names of the institutes and personnel of the scientific staff participating in the cruises are given in Appendix I.

18 45

trawl

made plans and suggestions

i in t 1985 (Anon 1985)

'I' be uise of all vessels participating together with the travJl stat I: be al stations are shown on Figs 1 and ve Around Iceland and off the Northern Norwegian Coast the wa. combined with 0-group fish

inve ion_ ⁷ north of Iceland and west of Jan Mayen with capel.in inve

All the

st:anda:cdi

The echo squa surface ₉

ions,

t. one were ed with echo integrator

echo _undersa The acoustic systems of each ted aga standard target copper-

instrume constants (c

1 4n) for

t:he J_n ator values into comparable units" are

s were integrated and expressed as numbers of t s per square nautical mile sea

each five nautical mile sailed The re- of pe

identified and biolog.ical samples collected by use c trawl. The size of the trawls expressed by the

The the the

The

tical open

compos i t.ion

t.eg-rator

, are also listed in the text-table above

the t.rawlca tches echo paper record value into different

ther gave species

with analysis of basis for dividing

at sea and the conveyance of the collected data was in llowed as suggested in the Planning Group Report of 1983 1983b)

estimation f the blue whiting biomass was by the same method

~- tr1 x· e e p ·c e vi o us ye a r s (Anon ,~ 'I 9 8 4 ) ¹T he ·to ta 1 are a sur- i.vided into les of 'l⁰ latitude and 2°30' longi-

tude in which the area of blue whiting distribution were measured according to zero-linee The average integrator values for each rectangle were calculated and representative length and weight

distribution established. These were based on trawl catches within the rectangle in question, or from neighbouring rectangles.

Conversion of the integrated echo intensity into piomass was done by use of a fish length dependent density coefficient. The number of fish within an area is given by the product of the size of

the area (square nautical miles) and the fish density (nos. of fish per square nautical mile). The fish density can be written as

where

1

a _{b • s} ^{• C • I M}

PA is the number of fish per square nautical mile,

.. s is the mean backscattering crO$S section of the fish,

[ T s

⁼ 1

o

¹ og ob _{. s}

J

c

1 is the instrument constant, and

M is the echo integrator values.

The density coeffisient (CF-value) for blue whiting is the same as used for young cod. The value corresponds to a target strength of ~40.5 dB for a 30 cm fish:

CF 1

1l' 8 7 • 10^7. L-2.18

=

=

a b .. s

where L is the fish length in cm (Anono 1982, 1 ~84) •

The scaling factor of the instrument constant has previously been 10 to get a convenient order of magnitude, with corresponding reduction of the CF-value. This has been changed in 1985 to a factor of 4n which is more appropriate (see text-table page 2).

The standard of "1 985 therefore is

~~

times the old standard, and hence lead to a new expression of the density coeffisient:

CF' = 1 ^G 4 8 8 " 1 0 6

@ L 2 1 8

which was then used in the calculation of blue whiting biomass in August 19850

The length distribution of blue whiting in each rectangle were weighted by the average integrator value, and the number of

specimen and corresponding weight in each length group calculated by use of computer progr:arrune ^® The result of each rectangle were then summed for the sub=areas and total

Age-length keys based on analysis of otoliths sampled by the Norwegian vessels, were established and ·used for calculation of the age-composition in the stock®

All of ·the vessels but one operated a great nurnb~r of hydro- graphical stations, using either bathythermograph (XBT), CTD- sonde or Nansen water-bottles with reversing thermometer.

RESULTS

The horizontal distributions of the temperature at sea surface, 200 m and 400 m depth are shown in Figs 3, 4 and 5 respectively.

The water masses had approximately the same temperature conditions as during the similar surveys in 1984 and 1982, but somewhat warmer than in 1983 However1 at 400 m depth in the area between Iceland and ,Jan Mayen the water was not found to be below 0°C in 1985, as i t was in 1984 and 1983

Blue whiting

The relative values of blue whiting recorded during the survey are shown in Fig. 6. The distribution of blue whiting was very similar to previous years with tqe highest concentrations in the

~· southern part of the investigated area, especially around the Faroes, west of Iceland and along western Norway.

Neither in the south nor in the north was the zero-line of the blue whiting distribution defined. And signifioant concentrations of blue whiting might well have been distributed outside the area surveyed.

In the second half of July a Norwegian research vessel with other objectives than blue whiting, sprveyed the Norwegian T+ench south to 58°N. Blue whiting was observed to be at approximate!¥ the same level as found during the s~me period in 1984, (Bergstad, pers. comm.), i.e. in quite noticable concentrations.

To the north blue whiting was also observed outwith the area sur- veyed. From mid July to mid August a Norwegian +esearch vessel conducting shrimp investigations worked a fair number of bottom trawl stations in the Bear Island - Spitsbergen area. Blue whiting were caught in various numbers along the slope all the way up

to 78°30'N, i.e. off Prins Karls Forland (Fig. 7). (0ynes, pers.

cornrn. )

The total biomass of blue whiting was estimated to 4~9 mill. tonnes representing 47.2 x 109

individuals. (Table 1). Of this the 1983 year-class contributed with 2.4 mill. tonnes, the 1982 year-class with 1.6 mill. tonnes and the 1984 and the 1985 year-classes with 0.5 and 0.03 mill. tonnes respectively. The 1981 year-class and older were found to contribute together with 0.5 mill. tonnes only. The biomass by rectangle is shown in Fig. 8. The sub- areas used in the calculations are also shown in Fig. 8.

1The compositions of the stock is illustrated in for the total area and for each of the sub-areas.

The 198 year-class was the most numerous age group in all sub- areas except in the two northern, sub-area V and VI, which were dominated by ·the 1982 year-classa Of the total estimate in numbers se year-classes contributed 50% and 26% respectively.

The 0- and I-grbup constituted 5% and 1~% respectively while the year-class 1981 and older fish contributed with 5% only.

The observations of blue whiting in the Bear Island - Spitsbergen area however, were of significant larger fish with peak-lengths at 36 cm The length distributions from three parts of this area are shown on Fig 13 which also illustrate increasing size with increasing latitude.

The total weight/length relationship of blue whiting is plotted on F g "14"

DISCUSSIOl\f

During the survey ·the main feeding area of the "northern" blue whit stock was covered ^a However, due to res-trictions in vessel time. allocated the area east and south of Jan Mayen was only poorely surveyed and the eastern Norwegian Sea was not sur- veyed north of 71°N.

As recorded during the three previous years, the main concentra- tions of blue whit.ing were found to the south in the area investi- gated in Faroese Icelandic waters and towards the Norwegian west coast

•rhe estimaJced biomass, 4 .. 9 mill tonnes of blue whiting, is 1., 1 millo higher than the comparable estimate in 1984 and 2.1 mi!l:_:__ tonl1es higher than in 1 983 a The biomass and number of blue whiting year-class estimated in the three last years, are

given in the ·text-table be low

1 98 3 1984 1985 Age

t ·1 0- 6 N ·1 0- 9

Age

t. 10- 6 N •1 0- 9 Age

t. 10- 6 N •1 0- 9

years years years

0 0.22 8.5 0 0.05 2. 1 0 0.03 2.2

1 1 . 52 22.7 1 1 . 7 7 30.6 1 0.47 6.0

2+ 1 . 0 9 5.3 2 1 . 56 14.6 2 2.40 24.0 3+ 0. 41 1 . 9 3 1. 58 12.5 4+ 0.46 2.4

Total 2.83 36.5 3.79 49.2 4.94 4 7. 1

The two rich 1982 and 1983 year-classes make up the absolute bulk of the blue whiting biomass estimate (80%), and are at present the main objective of the commercial fis0ery in the Norwegian Sea ..

Compared to these year-classes the recruitment in 1984 and 1985 appears to have been at a much lower level.

Compared to spawning stock estimates in spring the 1981 and older year-classes were underestimated during the summer surveys in

1983 and 1984. The reason for this was analysed by the workshop on the blue whiting surveys which met in Bergen in May 1985 where a number of sources of biases were identified (Anon. 1985). The present estimate of the 1981 year-class and older fish (0.5 mill.

_tonnes) appears also to be an underestimate compared to the esti- mate of (1.7 mill. tonnes) the same year-classes obtained by a _Faroese research vessel at the spawning areas in the spring 1985

(Jakupsstovu and Thomsen, 1985).

·-

During a bottom trawl survey to the Spitsbergen and Bear Island area in July -August 1985, large blue whiting (Fig. 13) was caught along the entire shelfedge from 73° to 78°N (Fig. 7) and at some trawl stations in significant numbers. This area was not covered by the acoustic survey. It seems thus that the larger blue whiting have a wider distribution than the smaller blue whiting and hence only a part of i t has been surveyed.

In 982, the stock were measured to 4 6 mill. tonnes, and then an unexpected drop to ~_plill o tonnes in 1983.. For the adult part only, the difference was about 3 mill. tonnes (Anon.

1983a) ^$ Though the remaining part of the adults are only partly recorded, the results of the August surveys in the Norwegian Sea give comparable values of the stock size. The r,ebuilding of the total stock are still mainly due to the two good year-classes of 1982 and 1983

Considering the observations of blue whiting outside the area

surveyed both in north and south, the estimate of 4.9 mill. tonnes is clearly an underestimate.

REFERENCES Anon 1982

C.M

of the International Acoustic Survey on Blue in the Norwegian Sea, July/August 1982. ICES,

1-21 [Mimeo]

Anon. 1983, a) Report of the International Acoustic Survey on Blue Whiting in the Norwegian Sea, August 1983. ICES, C.M. 1983 :5, 1-20 [Mimeo].

Anon. 1983, b), Report of the Blue Whiting Planning Group for the Coordinated Acoustic Survey 1983, Copenhagen, 2- 3 March .1983. ICES C .. M. 1983 H:4, 1-12 [Mimeo].

Anon 1984 International Acoustic Survey on Blue Whiting in the Norwegian Sea, August 1984 ICES, C.M. 1984/H:67, 1-21 [Mimeo]

Anon 19850 Report of the Workshop pn the International Acoustic Surveys of Blue Whiting in the Norwegian Sea, Bergen 6-'1 1 May 1 9 8 5 ICE S , C ,. M . _ 1 9 8 5 I H : 6 , 1 - 2 7 [ Mime o ] . Jakupsstovu, S H 1 and Thomsen, B .. 1985 An acoustic estimate

of the blue whiting spawning stock in April 1985.. ICES, : 59 , 1 ~ 8 [Mime o ]

·---~-

APPENDIX Icl

Blue whiting acoustic survey, Norwegian Sea, 1985.

Survey period 9 20a8

I

Vessel

"Kokshaysk"

&.9 7-18 8 "Eldjarn"

Research Institute

Polar Research Institute of Marine Fisheries

and Oceanography - PINRO - Murmansk USSR

Havforskningsinstituttet Bergen, Norway

Scientific staff Isaev N.A., Zubov Shapovalov B.J., Kapenizov B. L., Antropov N. V~,

Melnikov S.D., Ignatjev Ju. G.

Anthonypillai Blindheim J. , Dommasnes A., Eklund 0., Folkestad E., Romslo, A.

V.'

B. J . '

'l 5. 8-5 ~ 9 "Michael Sars" Havforskningsinsti tuttet Kolbeinson S.,

Bergen, Norway Kvinge, B, L~vheim L., Monstad T. (coordi- nator), Nilsen J.H., Tangen 0.

10 18.8 "Walter Earth" Institut fur Hochsee- Schul tz N •

1 ^{U {I' I}

e

^lt

') • 2 7 ~ 8 "Arni

Fridriksson"

10>8"~5.9 "Bjarni Scemundsson"

27.7 14o8 ¹⁹Magnus Heinason"

fischerei und Fisch- verarbeitung, Rostock, GDR

Hafrannsoknastofnunir, Reykjavik, Iceland

"

Fiskirannsoknarstovan Torshavn, Faroe Islands

Sveinbj~rnsson, S.

Vilhjalmsson, H., Helgason1 V.

Malmberg, S.A.

Halld6rsson 0. , Reynisson, P., Magnusson J.V.

Olapson, J.

Jakupsstovu S.H. 1, Mouritson, R. ¹

Thorns en ¹ B. ¹ Thomsen, J.K.

"

I

- - - -

Area VII I

Year~

class Biom. N Biom. N

1985

I

^- - - -

I

1984 ^{I I} 2.5 34 56.5 946

1983

I

19.2 195 148.9 1628

1982

I

^{11. 6 99}

I

175.2 1364 1981+

I

! ^{1.8 13 92.6 472}

Sum

I

^{35. 1 341 473.2 ~-41 0}

Area size 5600 34696

Density 6.3 61 13.6 127

- --' --~ -~---

i

I

n

Ill IV V

I

VI

I

Total

Biom. N Biom. N Biom. N Biom. N Biom. N ! Biom. N

ij

I

12.4 1088 ' 13. 1 1104

I

1.3 54 ^{- -} - -

l I

^{26.8 2246}

1482

I

^I

122.6 ^! 184.9 ²³⁶⁸

I

^80.2 896 18.8 218 ^5.1 59

!

470.6 ⁶⁰⁰³ 520 !2404.9

743.8 7323 11039.1 10453 302.7 3020 91.1 811 60.1 23950 460.7 3723

I

^651.6 5230

I

^60.4 514 115. 1 839 108.8 756 11583.4 12525 129.5 714 127.8 698 0.6 4 77.8 3B2 32.3 160

l

^{462.4 2443}

l

146 9. 0 14330 2016.5 19853 445.2 4488 302.8 2250 206.3 1495

i

^{4948.1 47167}

109653 83524 _i 7550 54415 28915

I

³²⁴³⁵³

13.4 ^{- - -} 131 24. 1 238 59.0 594 ^{- - - - - ~--} 5.6 41 7. 1

~ 5~ '-~

^{15.3 145 - ~}

I

^I

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.

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1/)

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p;::::l^, ''._) ,_,___'-,

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'z z,~lz ^[

I _{_ o x o x oo x 'z z} 6 z z z z z z ' '\ z

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^{x / x o I /x} I ,'-..._I o I I I I~

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^z,:::__7L

63ol

_{, I} \l

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'vf _j f

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62"_, ' o ⁰/ 1-1 \G-,o_j ', ' .·'

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^-~---x\

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z,;,=

o - o - o '11

61o _{: //} o/

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/9 o-o\ ^o ,

a~ _{o / c 1} ~ ~t

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~

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z 1

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0 3

591 _~ ...

58°

rl{b~.

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• 'i?~,

57 , -^{T T} 3 T s 01 3 0 0 ~--.-,- .--~--~ 2 s ⁰ , - - · r -20 ⁰ -~ 15 , - -T ~ '00 j r -TA , . A ~ '1;5p 50 ----.---, - , - 00 ~0~-,-~~~~r---~-.-,~.-~-.~-~~--_j

5 2~

Fig. 2. Cruise tracks and hydrograph 11 stations, August 1985. 1) CT D-so

3) Nansen water-bottles with reversing thermometer. e, 2) Bathythermograph (XBT),

w

l

i

73ol

I

i

72"-l

71ol

I

70°~

69ol

68°~

61

°J

60°1

59°

58°

1

I

s 7°

L.-

^{T T - ,} _35° ^{' -} _30° ^{--,--- I}

~~-

^{---,--- ,-::--r- '}

25° 20° 15°

3 4

~

12~ ) ^.. ~~

12 7-

ri;:,~

~.

' )

~~;~::1

'\?

~ ~

^{1/ --,} -,0 ---,

-- TA ' 1l. ~ 0

, ~ I

0 ' 5

• 0

Fig. 3. Temperature (t°C) at sea surface, August 1985.

11

-..l.

~

t ⁰⁽ 0 m

' ' ''

⁾⁰

4:\~T-~~~~J

10° 15° 2C⁰

74°

3 4

6 9°

68°

Ul ... 3//

/ /

B~v-8

~ ^f

.·~

ri;,C

'lie

57°L~,.-.--,----,--,~~~~~~~~~!Jll~L~~~r--r-41f-~~~~~

⁰⁰

Fig. 4. Temperature (t°C) at 200 m depth, August 1985.

0 rn r--

I I I

I

\

\

\

\

\

\

\

\

\

\ I I

I I

- --0~ - - 0~- ~ -0:;:-- 0~

c-- r-- r-- ...0 ...0

C>

0 0

0 Lr\

0 0

0 If)

0 0

0 Lr\

0 r-- Lr\

"'

Lt')

00 m

0 0 .::::r +.J ro

0 u

+.J

(])

!...

:::s

+.J ro

!....

(])

0. E

(])

1- 01

.

l.L.

73'~

72°j

I

I

71'1 70'1

so

I

~-/\_/

251

69'-

6801

-....]

35°

57°+-~--~--.-.-~~--~~--~~~~~~~~~~.-.-~~~~-,~~~-.~~~--~~~~~.---~F=~--~~-.~~~~~~~~

25° 20° 15° 10° 5° Oc 5° 10° 15° 2C⁰

30°

Fig. 6. Distribution and relative abunc:fance of blue whiting, August 1985. Echo intensity in m2

/(n.mile)2 ., 4TI.

0

0 0

0

?t

~

^0-100

~

^100-500

7(

I

^{> 500}

Fig. 7. Observations of blue whiting (filled symbols) as by-catch in bottom trawl catches, ¹¹Michael Sars" 15 July - 15 August 1985. Hatched ^I doubled hatched and black areas show areas with different numbers of specimens caught per hour of trawling. (From 0ynes I P. unpublished).

7

~~~

^{t)Q~ Q}

~0--

I

t-

1 O

~V

^I

~.._ ~ ^I ~·

--!'

l

Tl :'if

·-

^·,;

-;jJ

0

^{~ ~}

^llV

^{+ 8 14 10. 14 16 21 16 20 13}

²

~

D

t' ^,-~-

J _{4 13 12 12 19 19 25 17} 36 15 + ^I

.

^{f '}

3

~··

-

/

~~

^{9 38 32 31 28 25 19 22 0 :~J...-}

:. ^/

/?~

' /-

^{9 18 41 35 40 29 26 - 8 27}

^.

'(!,cr.A?

⁸

·~ ^w

^{1 + 7 19 "54 29 24 126 27 67 85}

^3~-;

^{56 .5}

13 311 20 9 9 9 27 30 30 30

'

~

7 76rr 43 19 20 45., ._28 56 94 ... 16

V

.

N

^{.u;~ :J.l~}

^{.,.. '}

D 25 87 65 114 47 29 15 38

70 148_:J-29 219 100 19 8

~9

.

D

.

^{81 97 ~78} ~ ^{156 59 5 15}

_~

.. (.

.

253 204 163 48 23

,£)

A

El

^~

114 131 6.7 ~- 12

'

.

. -~~r~

. ~ \

- ^{I - I " I •}

7

70

o9

68

67

(rt,

65 64

63

62

ol

60

1)9

58

s'1

15 2~

Js" 3'o• is" i'"~ ,·s· 10" s" ^o'" s· 10

~

'-0

Fig. 8. Biomass of blue whiting (in 1000 tonnes), August ·1985. Markings of sub-areas I-VII.

10 5

0

20 ^<

0 -

10 15 20 25 30 35 40

. 9. Total length distribution of blue whiting ^w~ghted by abundance, Norwegian Sea, August 1985. N: 47.2 .. 10 specimens.

.

0 2 3 4 5 6 7 8 9 10 11 12 13 14 15+

. 10. Total age coryposition of blue whiting, Norwegian Sea, August 1985.

N: 4 7. 2 .. 10 specimens.

cm

10

20 V N

=

2.3

10

40 IV ^{N = 4.5}

30 20 10

20 ^Ill

N = 19.9

10

20 ^{II N =14. 3}

10

20 ^N = 4. 4

10

VII ^N = ^{0. 3}

20 10

10 15 20 25 ^{30 35 40}

Fig. 11. Length distribution of blue whitin§l weighted by abundance in sub- areas I-VII (see Fig. 8). N in 10 specimens.

cm

4-0 ...-- 20

11 -= ,__,

.

^{= "} ,...--,

^.

V _•

⁰ ~ ^~

...,... 9

...

^I r;=• -re Q ₉ ...,... I I ^N T""

⁼

^2.3 •

20

60 IV ^N

=

^4.5

40

20

^. n

_..-- ^r--I

^{. .}

III N

=

19.9

40

r -

20

n . _0

^_ ...

. ^.

II ^{. -} N

=

14.3

40

r---

20

n . 0

-""'"""'-

-

^-~

^{. .}

I . - _.-- N

=

^4.4

[]

_C":l =

.20

.

_..--

. . .

VII N

=

^0.3

. -

20 .

0

^,--,

.

^I

.

0 2 3 4 5 6 7 8 9 10 11 12 13 14 15+

F . 12. Age co~positi.ons of blue whiting in sub-areas l:-VU ( s·ee· Fig. 8). · N in 10 . specimens.. .

20 10

0/o

30 20 10

0/o

20 10

Fig. 13.

B. _{N = 294}

c.

_N

₌

₂₃₆

I

f r - ---r-- • -

20 25 30 35 40 cm

Length distribution of blue whiting caught as by-catch in bottom trawl in three

different areas (A-C) at Bear I si and - Spitsbergen, July I August 1985. (See Fig. 7).

(From (l)ynes, P. unpublished) .

(\J

w

g

3 50

0

0

300

0 0

250 0

0 0

200 ⁰

0

0 0

150 ⁰

0

0

0

100 ⁰

0

0

0

so

^{0 0}

0 0

0 0

0 0

0 0 ⁰

0

10 15 20 25 30 35 40 cm

Fig. 14. Total length /weight relationship of blue whiting in the Norwegian Sea, August 1985.

j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j