CM_B3776_dalen.pdf (811.5Kb)

i i

? h

_$5

l ed without &.or _{-* %-.--} reference to the authors

i

I I I

i I International Council for C , M , 1976/B:

37

1

the Exploration of the Sea Gear and Behavious Committee F

Ref, Pelagic Fish (~orthern)

i

^{Cornmi ttee}

TARGET STRENGTH Ml3ASTJREMEN'T'S in-T4I.I ACOUSTIC BIOMASS ESTIMATION OF C A P E L I N AND 0-GI30UP FISH

John Dalen,

Ask

jell R d c n e s and I n g o l f Rat t ingen Institute of Marine Researeb, Bergen

INTRODUCTION

Echo integration is now widsly u s e d to obtain estimates of abundance of fish populations

(TIIORNE

et al 1 9 7 1 , J'OIWNESSON and LOSSE

1 9 7 3 a

MIDW'UN and NAKKEN 1973 among others),

Earlier

estimates have

mostly been worked out under the assumption that the scattering

cross section

of

the fish is proportional ^{$ 0} its weight

(URICK 1967).

This assumption introduces a bias which is dependent on the size distribution

of

the fish (NAKKEN

1 9 7 5 ) ~

However, this is overcome if one introduces a length dependent scattering cross section

(BUZETA

and M K K E N

1975,

NAKICEN and DC)BIPIIASWES

1975)

At

Institute of Maxine Research acoustic biomass estimation

of

the stock stren.gth of eapelin bas been c a r r i e d out in Sept;ember u

October each year since 1971 and I n June

-

July since

1973.

The echo integration system applied. during t h e s e cruises together with the results are given in NAIilCEN & DOMMASNES

1975.

^{The last}

year t h i s me.thodeslogy has also baon appl loti, r n c r ~ d (D&EN, IFYLEN

l

and SMEDSTAD,

i n

press), B a c k s c a t t e s - i ^pug p r o u p s r t H e a of sapelin

I

were nnst known, and A t has h i t h e r t ~ Bc+am ~ s ~ t ~ n i t c ? d t h a t the depen- dency of the density coefficient

( @ I ^su

^{f i s h bungtla} fox capelin was silmilar t o that sf sprat, B a c k aoi:t:ai;tc+ri.ng d a t a for sprat are given I n NA4eKEIVi and OLSEM

4 2.973) ,

During late summer and early autxx~riru O,-=graxxp f i s h of' .many= species occur pellagf eaiPy in _the, B a r s n - b s Sew., liC~.?,ovl.ad.ge ~1%' 'tX~e pre-

secruitment s.&oek is essential i n ii~:t~r~~~wp3i:ig t o p : ~ > s d l , e t and control f i a l n e r i e s

,

^and t h e a.dvixr~t age s f know?.:~.g g.ea:?-~:3..;3us s-bssngth for all species %n a ssgiosaz b e f o r e .$h@y a:re s,ubJec:!; 't;cb .f%r~~i.s%ai.naag f s

obvious

QDRAG.ESWD 1971).

R c s w e x w : ~ ~ t h l s klaa~~779cdgs i s i u n the B a r e n t a Sea area a s $as limilsd t o x2elat::;:.i.;rs ,um.lz-tes

(

^abundance

indices) for e a d ~ . species each yea.:~ (LPJOP;~~ I?'/%)

The method o f o b t a i n i n g tlaese %ndi.c:es h a s i.m.p.rwvsd, At present, a rme-khcud daacribed by IHAUG and E\Tk\KPdN

(1.9'73)

..used, IZere a certain number of fish o f each s p e c i e s :in. t31.e) i : ; r e ~ w I catch is used to diacrfmfnate betweer1 areas of iaca.t-i;ex:ed arid dense con-

centrations,

Bu*

8nfomakissx1 an, the eositz.iksu.-~-,:?IOTE:.~ -t;o the toea1 biomass f r o m different species can, on,,Ju,.y t ; ~ 3 S M ~ f?X.b;eZIt, ~ ~ . .be

@ extracted f r o m 'the abundance Pmdlcss ?~al:uss,

The aim o f tho present paper i s to g i ~ r d i~tlfcjrinatfon szz %he back

sca,tter&ng properties of some p e l a g i c asmd Cia-gaolap f'f sh in the t

Barsnt s Sea, in o r d e r to imparo-ve the acoa,is ti @ h.f.s~raasa eseimations i of the above mentioned categories of % i u I l c s , I

I

I

I

METHODS

Experfmental sat-

-

The w o r k t o o k p l a c e in a s h e l k s r e d hap a t Pkk,ogpxaagra, South V a r a n g o r

in

P i a m a s k ,

An anchored ship ~ 5 t h a r a f t a:koxagai.de .k:!?.e 3 h J . p aoxlstitk-uded the power station9 the Paboxaa-&o;ry and L h s aa.at:;t:$~!.st:5i?ii1tj-b1)?:i facilities

1 ) ⁰

The upward loo&ing transducersgwere 'mounted 'in'a ioadea

_'aludknum

I b L

frame submerged from the raft

in

ad justable'

w i s e d . : ' ~ h & fist1 w a s , . . - < i

kept in

a9

upside down position

by

a small float atlaclied

to

the fish belly in the central part of the sbund7b&ahi by

a

suspension of thin nylon gut. A hoisting device rhhde it possibi'e to 'hook the fish to the suspension at the surface and thBn lower'

it i o

the measuring position at 2.5 m depth ( ~ i ~ ,

1).

The aspect angle of the fish could be continously changed'in' the

I pitch plane. The fish was automatically tilted between -45O and

I

+ 45O to the horizontal. The overall accuracy was found to

bc . ^,

+ 2O with the worst case of deviation to be + 5'.

! 1 , 1 - . , 2 I ) m

I

i

i The equipment was calibrated three times during the field period by means of

a

hydrophone. To check the short time variation3' of the performance, three or fo qalibrations were carried

1 ^dhk

^b?

measuring the target of a rigid steel ,,sphere,

*"S'

^'idme

in' diLmeter, that was lowered into the actual position, ,

I Each fish to be measured was killed ,by hitting the frontal

part

of

1 , i , * '

' the brain by a sharp tool, When suspending the fish, care

was

I

taken to avo'id air in gills and stomach, The measurements started immediately after the fish had reached the,,meqsuying positionz,if

i ^{no other e in th} e:gbbo?anho~d, .:Wild

fish wi:thin

t

I

the sound however often

a

p ~ o b l g m wlaicb qaused con-

,

' 8 _ ^I

"'

, ..aiderable delays i n the exper

_{, x} a ; ' $

Instrumentation

1 ² shows a block diagram of the 'nstmrnentation w'hic~ also'

i

LF:iq*,

^{i :} . *

1 listed below.

' ,

hchosounder EK 38 ^A,

SIMRAD A/S

~ehqsouftd,er @K

120

A,

'1 , SICMII.4D A/S

,

Transduper, 38 kHz, dim,

10

x

10

cm SIMRAD

A/S ^,

1 % 8

T~~ansduc%r, 120

_kHz,

dim.

0

5

cm S I M R ~ D A/§

Trigger (electronic) Institute of Marine

lieseiirch

i Tiltangle indicator and control,

,

sensor and motor Institute of Flarine Research

OscilPoscop@ Dual trace 1217 ^I3 Echo Integrator QM J I

Recorder 7 7 0 2 ^I3

Signal generator Flodel 116 Signal generator

PF

1101 Frequency counter 5304 AMo me ter/counter

Electronic v s l trneter Model 2606 Hydrophorae

LC 32

I ( e w 1 e t . &

-

P a c k a r d . 5 I P l i ? A l l A/,5

fIew: e t t

-

^Packard

ldave t e c b'iarccsni

Bewi..et t

-

^Packarcl

Er%f.el & I{ jsr

Atlantic Research

The transmitted pulselengths were 0 , 6 ^ms fox- b o t h sounders.

The sounding repetition was approximately 3 , b pulses per second ^I (200 pulses per minute).

Data processing

The information recorded

on

paper cotts i s t s 0 % signal voltage arnpliGudes as function of frequency, tilkangJe, aspect, species and size,

During the analysis the f o l l o w i n g parameters were t o be read

(R)

and calculated

(c)

from each f i s h , species and a s p e c t .

L ( R ) : Fish length ( c m )

TJ

(R)

: I \ I a x f m w m observecl voltage ampa itucle

( v )

FV

(I{) : Interval o f t i l t a n g k s within w h i c h . TS 2 TS _{l n a x}

-

6

dB (degrees)

TS

( c )

Pfaximurn observed target strengLh

m a x

Target strength, T S , was cal-culated f ~ o m tho f ollow-i.ng equation

TS = 20 l o g

--z,-_

⁺ L ^>< ,;

TJ

,

^r

~qhere U is observed v0.L Lnge a r n 1 > 3 i t ~ 1 d e , 1: _r is the obshsrveri voltage

a m p l i t u d e f rorn the sererence sphere which has t h e target s t r c n g t h

'r

^is

..

^{38.1 dI3 at j d s a L} c o n d b t i-ctn.7 w h i c I z ;$a:+ t,he v a l u e

T * 1"

u s e d j n

(I),

RESULTS

B e s i d e s vaLues of t h e t,arget s t , r e n g t h i t i s 01' inlpor-tance t o f i n d t h e dependency between t a r g e t s t r e n g t l l and I e n z t h of t h e f i s h . To e s t a b l i s h t h i s we assume a L i n e a r re.Lation between t a r g e t s t r e n g t h and t h e l o g a r i t h m of t h e f i s h l e n g t h , that i s

'J'S = m log L

+

b ( 2 )

m and b a r e d e t e r m i n e d by l i n e a r r e g r e s s i o n a n a l y s i s .

It was o r i g i n a l l y planned t o measure t a r g e t s t r e n g t h of a l l l e n g t h g r o u p s o f c a p e l i n , However, due t o c f i l ' f i c u l t i e s i n c a t c h i n g and t r a n s p o r t i n g t h e s m a l l e r c a p e l i n from t h e f i s h i n g grounds i n t h e Barones S e a s o u t h t o t h e measuring s i t e a t Varanger, t a r g e t s t r e n g t h measurements c o u l d o n l y be made f o r l e n g t h g r o u p s 13 cm t o 18 cm. ?'his w a s c o n s i d e r e d t o few d a t a t o a p p l y a l i n e a r r e g r e s s i o n , and i t w a s d e c i d e d t o combine t h e s e d a t a w i t h p r e - v i o u s l y measured t a r g e t s t r e n g t h d a t a from o t h e r fish of t h e o r d e r C l u p e i f o r m e s . PerLinent d a t a f o r f o l l o w i n g s p e c i e s o f Clupeiformes were i n c l u d e d .

S p e c i e s Iief'erence

C a p e l i n

ca allot us

~ l o s u s ) ( * r e s e n t measurements)

H e r r i n g ( C l

-

upea h a r e n g u s ) N A K J a N &: O L S E N ( ~ ~ ~ ~ ) Salmori ( ~ a l m o s a l a r ) R D T T L N G E N

,

u n p u b l i s h e d

Sprat, ( S ~ r a t t u s sprat t u s ) NAfULEN & OLSEN

(19'73)

These d a t a have been combined and p l o t t e d i n F i g , ' % , and r e s u l t s from t h e l i n e a r r e g r e s s i o n a r e shown i n T a b l e l.,

The o b s e r v a t i o n s and t h e r e s u l t s of t h e l i n e a r r e g r e s s i o n f o r cod

adus us --

morhua), s a i t h e ( P o l ~ a c h i u s

---

v j r e n s ) and sand e e l (rlrnrnodytcs sp.) a r e shown i n F i g s , 4 ,

5

and 6 , and '1'abl.e 2.

T a r g e t s t r e n g t h m e a s u r e ~ n e n t s o f 10 specimens o f haddock

a ad us

acgl ef i n u s ) w e r e made, IYAKKICN and OI,S-;TlCN ( 1977) a l s o m e a s u r e d

-

t a r g e t s t r e n g t h of laaddock ( I 5 spccirncns) but. t h e trleasurcments w e r e o n l y p u b l i s h e d a s mean v a l u e s ('l'abl s 3, N.II\lCISN ancl OLSEIV 1 9 7 3 ) b e c a u s e t h e y felt, t.he o b s e r v n i . i o n s t o f e w t o imr~ke a Linear recrcwsi o n . P'ig.

7

rlr~d 'l"1bl o 2 colnl)irlc t k i s p r e s e n t . . m e a s u r e m e n t s

c,f' b a r i r f o c k w i t h t , l l o s t : of' U,Il\'KICN ; i r l ( l O i , 5 b ' Y ( 19'7'4)

.

Fig.

8

s h ~ w s the relation between nlaxii~iunl clorsal aspect target strength and mean angle be tween points of' ha.1 d' m a x i m u r n amplitude

(6 dB

points) for cod, haddock and saithc,

D I S C U S S I O N

We would l i k e to pay some specific a t L e n t i o n to how to reduce the data by linear rcgssssion analysis i . , e , what regression to use ( R I C I U ~ I ~

1 9 7 3 ) . In

order to make a d e c i s i o n one should discuss;

%

-

what kind of -arark?iab.i.Li c y a n d

error

wlaich are

involved in the v a r i a t e s , ^,

2

-

what distaributitsns tho v a r i a t e s make,

3 -

whalt has the sanapling rnetklod b e e n and

4

-

^{i s}

^the

regression used r , s d e s c r i b e a relationship, or to m a k ~ psedict%sns, or b o k h ,

Most

of

the variability

in

targo$ ~Lrength-?ength. observations

we

find to be inherent I m h the nrnateria-tl mare than in the process

itself of measuring Xengeh and measuring and calculating target strength.

The

observations are f r o m a non-rxkdasaua sample which forms an open-ended non-normal distribution,

i

Primarily the regressions are needed to dscribe a certain relationship, secondarily howev6;.~, they wui b.6 be tlsaci to pre- dict target strength from lengkh a b a e r - v a k i o n s ,

These statements lead do %he c o n c l u s i - o n t h a t functional regression (least geometric mean regsesslon) 4-s $-+reif"ea-a$it-? to predictive

regression (

I

e n s t mean square r e g 3 - o s s i n n ) , Tlxp.: -8"Ii11ctional regression represerits the Pine which m i a z i m j :zes the sulri of the products of the v e r t i c a l anti k~orixont,a.b r ' 8 i s l n n c c of _{e a c h} point

from the Zjne. T h e sJ ope of t,ho d i n e i s

e n t t h e q u a n t i t i e

-

X and y = Y

- - ^Y.

(1975)

shows t h a t o b s e r v t

r e n g t h can be u s e d t o o ween s p e c i e s and l e n g t h t a r g e t s t r e n g t h i s

TS = m l o g L

+

rnax

O r a p p l i e d f o r t h e d e i i s i t y coefficient (NA%CKEN 1975)

CI i s a i n s t r u m e n t c o n s t a n t and C $ s a c o n s t a n t f o r a give^, S

LJn,fyr$unately t h e d a t a o b t a i n e d d u r i n g t h e presenl; measure:;leqt s ,.L,wer;e < , t o few t o g i v e l e n g t h dependency of' t h e d e n s i t y

coefficient

i . I " " ' $ 9 f +

i , i S Qqs - a t a from c a p e l i n o n l y , Ilowever, t h e c a p e l i n b e l o n g s

s y s t e m a t i c a l l y t o t h e o r d e r C l u p e i f o r m e s , and i n g e n e r a l , with

2 d + 3 -

t h e e x c e p t i o n of c e r t a i n deep-sea s p e c i e s ( ~ ~ ~ ~ ~ R S I I A L I , 1 9 6 0 ) ~

<- 1

a l ! ~ ~ e ~ i f orrn f i s h have physostomus swim b l a d d e r s ( F N L ~ N

1 9 6 7 ,

1968)

,'

o s s e o u s bone t i s s u e , i n t e r m u s c u l a r bones, c o m g % r a t i v e l y rn,any, v e r t e b r a e , f i n s w i t h o u t s p i n e s and c y c l o i d s c a l e s , Clupeiform f i s h t h e r e f o r e have common s t r u c t u r a l components t h a t a r e

a c o u s t i c a l l y i m p o r t a n t , and one f e e l s t h a t e h i s j u s t i f i e s t r e a t i n g

i "

^' t h e a c o u s t i c d a t a f o r s e v e r a l . C J u ~ e i f o r m e ' s to g e t h e r . The o b t a i n e d v a l u e s of m f o r a number of s p e c i e s of 0-group f i s h a r e l i s t e d i n T a b l e 2 . The v a l u e f o r cod shows a decrease i n dB/decade compared

t o ,$,hat o f l a r g e r f i s h measured by NiZKKISX and O L S E N

( 1 9 7 3 )

y h i l e

! t P i

t f o r s a i the shows a i n c r e a s e i n , dB/decad

I t i , ~ well known (I,C)VF:

1971

S11113:L'I'h 1970) ' t h a t t h e r e i s a #change i n t h e d i r e c t , i n n a J r e f - L e c t i o n of' fish as tjle fisl.1 s i z e , oi- v a t h e r I,/ A ( w h e r e I , i .s f i s 1 1 J engLh a n c l h is wnvc-lenl;t,h)

,

d e c r e a s e s . 'There wi ll be ;i r e d u c t , i o n in t.lra r ~ u u ~ b e r - o f ' l o b c s

,

^and consequent I y

(' " a n increi*.c,c: o f t , h e VV-on~7;lo, I'ig. ti S ~ I O W : C ~ t h r e l a t i o n ~ b c t w e e n

r n a x i t r l ~ ~ n ~ d o r ~ 1 i i I ~ i s p e c t t i t r t ~ e t s t ? - ( - n f ; t h ancl t l i c ? ;rr~{.;lt? b e t w e e n t h e

6

dB points i l l the dir'ectlvity p a t t e r n . for t h e .?.measured cod and saithe. Tire pe elations found k q r NAbCICTCN and O I S E N

(1973)

are also indicated, The angle between Lhe

6

^{d B} p o i n t s for cod increases with decreasing. fish size, (or deskeas-ang L / A ) , f o r saithe the angle does

not

seem Lo e x e e s d 25 0

,

T i n i s 1na:y be due to different structure and reflecting prapcrties a P t h e swim-bladders of cod versus that of saithe,a phsnomonon a l r e a d y indicated by M I D T T U N and

HOFF ( 1 9 6 2 ) and

MIDTTUN and NMffLEN ( 1 9 7 ~ ) ,

The

t i l t angle distribution will thus be of greater i m p o ~ - t a n c e in abundance estimation

of

0-group

saithe

than for O - t g r ~ ~ p c o d *

Abundance e s . t i m a $ j . on

When different categories o f fish, x , , a , size g r o u p s species are mixed and thus simultaneousPy contribuke to the echo, then the integrated echo intensity M can be w r i t t e n

MIP is the contribution to

the

integrated echo intensity from

length group, I of

s p e c i e s

1 ,

M e 2 is _.the c o n t a x i ' b ~ r t i o n from length group 2 of species 1. and s o

on,

aIltogethes m l e n g t h gx-OUPS from each of the p species, W e must assume that f ~ e q u e n t sampling, usually with a pelagic t r a w l , shows khs t r u e density ratios between df

ff

_erenf length gxbo.ups and species, FoXkswing NAICKEN and D O M M A S W S

(1975)

:

k is the proporti.on of t h e l e n g t h Lr;.~oup of' species of the ai

total catch, (T'otal n length grotapa l['n*;uam eaclln of p species) and

A

. is the d e n s i t y p e r unit, a r e a o E' that particular

a x

category of fish.

F u r t h e r

where Cai i s the density c o e f f i c i e n t for E e i ~ g t h group

i

of species a.

T h e relationship between the fish density and integrated echo intensity

is

lill~,lar b ~ l o w a cer.kain den.si.ty ( ' L ' I ~ o ~ ~ w E ^{~ 1 d .} T ' G G 3 E '

1970

MIDTTUN and N.AKXmN

1973

RWI'TLMGEN i n press.

) .

^{T h i s}

leads

to:

By ap9lying this method absolute f i s % density can b e calcxla-kcd for the different species w h e r e the clerl3rEty cocfrr"icients are laown

(

e q o

5, Table

1 and 2).

T a b l e 1. Functional regression ( T S , ~ ~ ~ = in loglOL c b) for for f~-sqtaen.c$es 38 1dIz 1 2 0 _kHz m) calculated slope, b) c o n s t a . . n t of regression, r) correlation coefficient,

N)

x c u m b e s o f fish measured.

Table 2. Calculated slope (m) an.& c s n s t x n t (b) of regression

Lines,

TS=

m

l s g l O L

+

'b, 'the correlation c ~ e f f i c i e n t

( s )

and the

number o f f i s h rueaaxxred ( N ) .

... ... ... ^. ... ... . . .

I I,-.m.-" *b---.,." -*L.*,v, ".," -<.... ". .-.'. ^a-. ,...*

"-

^{.- - -.}

i I

i

1

^{I, i I}

i

^{Species i Frequency}

I

^N

¹

^m

ⁱ

^{b j r , Length range}

i

t

i I

^t

i lcHz

1

^!

;

measured (cm)

!

!

, - - . M - - - * - - - - = . . - . . - ~ , -

i ^--..-

_.

_-&

i

^".d

,..---..-.-,--.---.-- -..-

I

I

I ^I

i

^I _! ^I

1

^Cod

, 38

i

32

'

^{2 1 . 9}

i ^63.5

^{0 . 8 ~ i}

j

4 , 7 -

^20.5

I

^I

i I. 20

'2 39.4 87.1

0.90 ;

^I g o o -

^16.5

1

^!

/

^{Saithe 38 25}

1 ⁷

^78.0

1 ^{0.524 7.1} -

^14.5

I

j 1

i ' Haddock

I

i

i

I

^{Sand eel}

i

120.

38

1 2 0

38

...

11 2 4

34.8

78,6

10.84. i

7.1 -

^14.5

I ;

1 8 . 7 59.4 j oa9!j

^7.2

-

^48.0

2 8 . 9

74.0

0.97

1

^7,,6

-

^48.0

22 20

1

^{I IrPj,5}

¹

^{97.2 j}

^{o 0 8 o}

^{9 , 2}

^-

^18.5

! i

:. ^{. . . L}

REFERENCES

ANON, 1975.

Re;;asrt

of a meeting to

consider

young fish

BUZE'PA, R ,

and

NAKKEN,

0, 1975, Abundance estimates of the spawning stock of blue whiting (~icromesistius

outassou ou is so,

1810))

in the area west of the 1 gritish Isles in 1972-1974, FiskDir.Skr.Ser.

HaarUnders?, g: ^245m257a

DALEN,

J,, HYLEN, A, and SMEDSTAS), 0, $976, Acoustic abundance estimates of cod

and

haddock in the Barents Sea in February 1976. (1n press),

3RAGESUND, 0 , 1971, Comparative analysis sf yeas-class strength among fish-stocks in the North Atlantic. FiskDira Skr,SersHaVUBPderso 4-6: ^4-9-64.

FAILEN, G, 1967. Morphological aspects on the hydrographic function ~f the gas bladder of Clupea harengus L.

Acta,Univ.Lund. ~ ( 1 )

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L-49,

) F P L ~ L ~ N , G ,

1968, The gas bladder as a hydrostatic organ in Thymallus

k,,

Osmerus esperlanus L, and Mallotus villosus Mtl11,

F i s m i r r S k r . S e r , I - I a v U n d e r s

KAUG, A, and NAKKEN,

0.

1973. Echo abundance indices of 0-group fish in the Barents

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1965-1972e IntsCoun.Explor,

ethods in Fisheries Research.

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PfimeoJ

JOIIANNESON,

_{K . A ,}

and LOSSE,

_{G . F ,}

1 9 7 3 e Some resu1,'ts of observed abundance estimates in several UNDP/FAO resource survey projects

,

M

1-77. pimeo]

I,0VE9

_{R O N ,}

1971. Dorsal aspect target strength

o f

an individual

fish, J,Acoust,Soc,Am,, s:

^814-823.

MABSHALL,

N,B, 1968,

S w i m b B a d d ~ % : r . ~ . 2 ; l r ' . i : s f deep-sea f i s h e s

in

relation .ka t h . ~ + : ? r ~;3yst::sma.%ica and biology.

31 2 1 . L 8 L 2 2 ,

9 &-?.,*

MIDTTUN, L , w d H O F P p

I, 1962s

Maaes8.r.eiraea1:ks sf r e f l e e t i o n of

sound by fish , ~ ' ~ ~ ~ L ~ ~ J ~ ~ v ~ ~ f ~ ~ ~ ~ ; L t L ~ s ~ ; A ~ ~ 2 ~ ~ n . d e rs : 1-18,

MIDTTUPJ, L , and NAKKEN, 0 ,

1971,

O n a c o u s klc i d c m t i f i c a t i o n , sizing and ab,isndanea e s t i ~ n a ~ i e t m sf fish, FiskDir.

s

1s.l~

s

^s H : s ~ ~ ~ a d ~ a g ~ D ,

,-.ui

^I:

: ⁶

^I: 8

.

^I

-

MIDmUPJ, L , and NAKKZN, 0 , %973a Sums r s o u % % s of abundmce ^I Ex33 3- ^CB r ~ ~ ~ ~ ~ ~ , p - & a ; ~ ~ - g ~ ; ~ & ~ - ~ ; ~ J ~ ; ~ ~ $ 2 ~ - & ~ ~ F i.s he r i e s ^- R s s e a x * g & Bsrgsns.

8.97"$(1,7E$,3::

a.mnlfz;t, 1;iinneo~

RA.KKEN, 0.

3L9750

O n %he problem o f d s - k s r m % : n l . r i g khe r e l a t i o n s h i p between integrated scba i r ~ t ; s n s $ i t y and fish density,

NAKKEN, 0 , and DOMMASNES; .A,

197,:i0

The ag?lpl.i@ation of an echo fntegra%ion. An. i:~vss'ii;iga-t:L~33::i.~; on the stock strength of the Baren.ts Sea oatrje:L$r~ ~~a.23e~t::.cas ~ v l l l o s u ~

,

NAKKEN, 0 , and Fish O L S E N , K, ^* -.---,,, _Jnt

1973@

, C o u n , E : ~ B c j ~ ~ ? 3 e a ^{' X} T a r g a t ,_,.-~-.-r~-I'.-&~- s t r e i ~ g t l a 5 ^IIYD Acoustic Methods msasussments of

1

in F Bergen 1 3 7 3 7 i

pirne

--

^o

7

RDTTINGEN, I, 1 9 7 6 ,

^{O n the} x w S . a t f o n 'bs.tween echo intensity and

f i s h dens it y

,

~ ~ ~ g r ~ ~ J ; ~ L ~ ~ & ; ~ A ~ ~ ~ ~ & . ~ ~ r ~ i 3 e x's

. ^{( in}

press)

SEIIBATA,

K, 1970,

Stsady o n details of ul ts-aaonlc refluetion from ind2.vidual f 5 a h , ~ - ~ : ~ ~ = , G ~ ~ ; b ~ ~ L ~ & f f T d T d a & ~ ~ k ~ Unilr.

29

: 1-82

r.d.-

THORNE,

_{R , E ,} and WOODEY, J,C,

13'70U

Stack assessment by echo i n t e g r a - t ion and its a.pp.bica t i.an t;o J~zrrenile Soekeye s a l m o n in E a k : s Washiagt;on, i+iv,of Wash.

C o l B , F i . ~ h , C $ ~ i . c ; u 3 - ; 1 1 ~ * na,

70

$-, 2 , I L ~ ~ E " P ~

---,--, ^----: - , ~ " ~ % ~ , ~ - , , , . . r m ~ ~&-,A

--..

^~-.%.~

I

THORNE,

R . E ,

,

REEVES, J , E . and _MKLL,KUN, A , E ,

19'71,

Estimation of the Lake populaLBon fn Port Susan, Washington, using a n echo integrator, Y,Fisb,RsseBoard

Can.

28

( 9 ) :

1275-1284,

-

URICK,

R.J. 1967.

M c Graw-HI11 Book Company, New Yorke 342

Pe

Fig.

1. Experimental set-up vessel, raft, framemounted

transducers and surpensian arrangement.

Fig.

3,

Maximum dorsal target strength

versus

length of Clupeiformes. 1 ) Herring, 2 ) Salmon,

3 )

Sprat

-25 . .

-

-30.

and

4)

~ a - p e l i n . Observed values and regression l i n e ,

38KHz . 12OKH.z

i

. - I 0 - 2 + - 3

a - L

-

m

0 -35.

-

I I- 0 z

W w

I- V)

I- W 0 -LO -

rz

2

-15 -1

I

-50 .

Y=18Alog L-62.7 10

---- ^I

L 6 8 1 0 2 0 LO 6 0 80 100 L 6 8 10 2 0 LD 6 0 50 103

L E N G T H IN Chn

ANGEL B E T W E E N 6 d 0 POINTS, DEGREES

F i g , 8. C o r r e s p o n d i n g v a l u e s o f m a x i m u m d o r s a l t a r g e t a t 38 kHz s t r e n g t h and a n g e l between p o i n t o f hal'f-'maximum a m p l i t u d e ( 6 db p o i n t s )

.

1) c o d , 2 ) s a i t h , 3 ) and 4 ) cod and s a i t h e (NAKKEN and OLSEN 1 3 7 3 )

.