W, w This paper not t o be cited without p r i o r r e f e r r n c e to the a u t h o r s
g;.s&imz&k~zl;at~~~
International Council for the
Exploration of the Sea G e a r and Behaviour Comi-~ittee
APPLICATION OF RCOUSTIC STOCM ABUNDANCE ESTIMATION ON CAPELIN AND BLUE WHITING
L a r s Midttun and Odd Nakken Institute of Marine R e s e a r c h , Bergen
INTRODUC TION
The u s e of acoustics f o r fiska abundance estimation is now in a state of progressive iurprovcment. But already a t p r e s e n t the method h a s proved to give vsluable informatioils on stock abundance of both exploited and unexploited fisla stocks i n the North Atlantic.
In pra-ctical application it i s of the g r e n t e s t irrtporta.nce to take into coneideration fish behaviour and to c z r r y out the s u r v e y s aiming a t a n abundance e s t i m tion when conclitions are as fabourable a s possible.
This may be related to special spawning o r feeding seasons.
In thc following we ohell g i v e two examples of acouatic fis11 stock abv.ndz.nc\: estimiation. The f i r s t one i s the ualirrs- i;i3ii of an e-xploitcd ficii otock, namcly the Bzrents Sea Capelin, v ~ h i c h f o r the eim2 being i s th,n g r e a t e s t r e s o u r c c for the Norwegian fish m e a l production. The cecond e x a m p k i s an acoustic ctock s i z e m e a a u r c m c i ~ t of the
Norwegian Sea Blue TArhiting, an unexploited fish sto& which by this investigation can be shown t o be one of the greateat known fish stocks in the North E a s t A.tlaiztic.
- - --
A s mentioned above the method f a r an acoustic abunclcnce estirnation can not be used with the s a m e s u c c e s s under all circumstances.
The b e s t condition f o r the eclzo integration techniquc i s given if the fish atock in ~ u e s t i o n i s distributed within a definea a r e a , unmixed with other apecies and in continuous scattering layert; at rnoderatc deptho in n:id water. Conclitions a r e m o r e cornplicnted when the fish a r e forming c c h o ~ l f i o r a r e mixed with other spccies and
unfavourable s i t u a t i ~ n s a r e fsund whsn the fish arc3 distributed close to 2he b ~ t t o r n o r n e a r the s e a surface. F i s h behaviour must t h e r e f s r e bc studied and the stirveys airning a t a n abundznce estirnation should.
be ur.ldertaken when conditionc a r e a s favourz.blc a s p o o s i b l ~ . This may be related in sclrng ccases to the spawriing season o r in other c?,ses
to the feeding season. In the two ca s e s d,lt with in this paper thz blue wkiting s u r v + y was c a r r i - d out just before the spawriing season when the ider.1 conditians were f<,u,nd, whereas the c?,pelin surveys were undcrtaken during the summ cr feeding o tjason again under favourable conditions
.
The density of the grid net should be adjusted to fisli denoity i n o r d e r t o optirnize a b u n d ~ n c o ~ ~ - ~ i e a s u r e ~ e n t s . The survcy grid nct m u s t thus to some extent be f1e::iblc: and adjusted in accordancc' with thz findings a t a l l t i m e s during the survey. F i s h consentrations a r e often located i n l a r g e r units within c e r t a i n a r e a s a,nd a basic grid nvt dense enough
t o find t h e s e a r e a s should be u s r d initially, but a s soon as a f i s h field a r e a i s found, the g r i d net should be changed 2nd a d e n e e r coverage a d o p k d . Most aften the cxtension of the arei: cjf distributi:,n i s unknown b e f : ~ r e the s u r v s y s t a r t s . 1 t . i ~ then adviceablr f i r s t t c c a r r y out a v e r y raugh c o v e r a g e with the m a i n purpose to l ~ x a t e the ac'cual a r e a to be surveyed i n d e t a i l s a f t e r w a r d s . Thic tactique wi1s f ~ l l o w e d p a r t i c u l a r l y on thz bluv whiling survey; but a l s o the capclin surveya w e r e based on initial knowli7dge of the extention of the 2,ctual a r e a i n e a s t west direclion.
By adopting north s;)u.tli cwurses passing well 1rtu.t of "the echt-, r e c o r d i n g s t t on both s i d e s the survcy conductidn was undcr f~i11 cdntr3l.
The meth:>d used i s deccribud by Midttun and Nai,ckcn(l$70) and Blindheim and Nakken(l9Yl) but will be c u m m a r i z e d her^, When the zcha-soundcr
i s s e t to c a m p e n s a t e orit-way g e o m e t r i c sprcading 2nd t w ~ wayc a b s ~ r p t i ~ n (20 l a g R
+
2.:":) and the ech.1 voltages a r * s ~ u a r e d b c f ~ r e integration,then thc output jf the c c h s i n t c g r a t , ~ r i s propor.ti2ni7.1 t o nurnber %,f fish p c r unit a r e - , provided that the r e c u r d e d fiah a r a c ~ f equal s p e c i e s and size.
Whcra:
,
,'J.n
is the a r e a density i n number p e r unit a r e a , ~ / ( a . m i l e ) 2,
M i n t e g r a t o r deflecti.>n in mm and C i s a canstnnt dzpcnding on fish s p e c i e s and s i z e .
When mixed recdrdingo .)ccur, i t i s necessc?ry to d i s c r i m i n a t e between thz s p e e i e s , and find the contributivn to the int.,grntdr r e c o r d i n g s f r o m .?ach specidc. VJhk2n £i& ~f diffcrcnt ldngth o c c u r i t i s n e c e s s a r y t.> I c i l ~ w ~ the 1-ngth corrpositit;n \,.E the s t x k and thc t n r g e t strength/length r c l a t i o n f:>r thc s p e c i e s i n question.
On b o a r d the Norwegian r e s e a r c h v e s s e l c i t i s therel~zjre r . ~ u t i n s procedurcr t 9 identify the echo recordinge by t r a w l c a t c h e s whinnever the recordinga apparently changee. It i s also ruutine to s c r u t i n i z e the ac;)ustic data s a c h day and t o decicle which s p e c i e s of f i s h Islav(:: contributed t10 .the integrzted echo i n t ~ n s i t y . Thin a n a l y s i s i s d.rjnr by esrperieizced peapl2 i;n b a s i c : ~ f c x a m i n a t i m a£ t r r ~ w l c a t c h z ~ and e c h ~ rec.>rd.ings.
During the investigatians r e p g r t e d i n this pap2r th.;! 6 echo i n t c g r a t a r s 3nbmy.d the G. O. S a r o w c r e c-jnnectcd to the S i m r a d scientific sounder E M 30.
The
5 upper ckac.nxlels w e r e norrr-ally adjuated to i n t e g r a t e i n 50 m depth s l i c c s down tu 250 m , while the 6th channcl worked betwi2cn 250 and 449 m. Curing the blue whiting s u r v c y a slightly different setting was adopted in a r d e r to include e l s o the dccpcr p n t :>f the f i s h l a y ~ r s . A l l channcls have a b . ~ t t o r n stop functian which stops the integr7.tion just abave bottom.Thi: integrated e c h ~ intensities w e r e read p e r nautical mile, a v e r a g e d f o r each 25 n. m i l e s (running rneans) and plotted a l m g the c o u r s e line.
The clt~terminatilin af C i n the e q u n t i ~ n 1 wao c a r r i d d cut a6 fullows:
F i e h t r a c e s w e r a c\~untccl .jn the r e c ~ r d i n g pnpcr when single fiah could be distinguished. Th:: c ~ r r t p l i n g vLJlume (and i r z - . ) "f the ccho s ~ u n d v r
w x c f ~ u n d f r 3 m .ibczrvl;d. fre*:uency d i s t r i b u t i ~ n s ~f the d e t c c t i ~ n s c c t b r anglc (Blindheim and Nakken 1971) o r f r ~ r r thc dirdctivity d i a g r a m (of the t r a n s d u c e r . Numblrrs of fioh p e r unit a r e a wns calculnted by di viding thc: f i s h countc with t h ~ irresp spond ing sa-mpling n x e a s . Finally C velues were sbtaincd f r o m c a r r r n p ~ n d i n g values f o r
f J'
2nd M.Cnpelin
The capelin survey i n 1971 ( F i g 1) w e r c undertakcn under favourable coilchitions. The fish w e r e clistributed over widc a r e a s i n scattering layero and thin ~ c h o a l s wc11 abovv t& buttom, and practically unmi::cd with other cpecic:~. The a r c a intcgratiori of Fig. gave a s r c s u l t
Q 2
(t. 3.10 mm (nm) ,
The c - nditions for integratioil in August 1972 (Fig, 3) w c r e m o r e diificullt than i11 Scptexnber 1971. 111 thc wcntern p a r t of the B a r e n t s Sea, the cnpi:lir.i was distributed c l a s e to t h z bateom. over widc a r s a s . E'urtlzer e a s t capelin and polar cod v e r y often wei-c sxtensively mnixed, and a t time6 i t wc?,,s
iimpossibl;: to d i s c r i m i n ~ ~ t e bstween the two specics on the e c h o g r a r ~ . The a r e a integration Fig, 4:. showsd 6, C. mm (nrn) 2
.
, -
V a l u c ~ c i ? C f o r cnpelin w c r c obtained only duringSthi. 1971 survay. Thc nu-ixb~rr; varied f r x m 1. U, 2 . 2 ton/mm/(nrn) 7,
,
and the rnean of S vslucn w e r c 2.1, tc;n/nxn(~~rn) 1.
This i a iri good acc0rclanc.u with th;:value obtained by Dr2geound and. Monstad (1772) i n the Newfoundland a r c a .
By multiplying th:: obtaincd. valuc of C, by the rcsulto of the a r e a
integration of Fig. a. 2 and I , the smount of capclin v ~ i t h i n the investigated a r c a c f o r thr: tvia y c a r s 19'il and 1972 w e r e found to bc 10.1 and 13.5 million tons r e opoctively.
Bluc Whiting
The uurvey for e ~ t i ~ 2 ~ t i o n of thc spavrrning stock oizc of the blue wliiting was c a r r i c d out under ideal conditions, The fioh wer a mostly conacntratcd i n tvell defined l a y c r s , but a l s o i n cchocslc, i ~ o w e v c r , of low density.
. 6 -.
.
.The n r c a of distribution w n s z l s o r n t h e r w ~ 1 1 ddfinud and whcn c o m p s r c d t 0 th; dislribution a t othvr t i m e s of the y e a r f.~iand t o b2 of mcjderatr:
extention.
T h e c h ~ o o e of t i m e for the ceirv,-y w n s baaed on pi-zviouc invsstigal;ionc (Dragesund and J ~ t k u p ~ ~ L ~ v u 19'91). During s u m r n t s t i m c the f i s h 2 r i
d i s t ~ i b u t e d within wide naioan i n thz Norwegian Sea, while clcnoer conseiltrati2n of postcpawning fish had been l>C.<ted i n the F s e r t ~ e
-
Shetland a r e a i n April
-
X a y (5akupsst:)vu cincl Nc.kkcn 1971).E a r l y Scottish ob~ervat-i.::~no r e p o r t s spawniiig i n the P o r c u p i n e Bank
-
Rockall tJcnnk zrea (Mencl~rson 1959, Baily an6 Seatori 1969). It wao
ther.t:frjre dvcid:?d to unCtcrisi3k~ n s u r v s y i n I'4arc:a this ye?.r, when the fish woixld be on the spawnirig graunds and prscursi.ably wkihiri a welldefined and r e l a t i v e l y rn.odsrate z r z x of distributian. On the f i r s t p a r t of the c r u i s e , during the southward c r o s e i n g , a v e r y open g r i d n;:;; was adopted and the main purpose was to locate a r e a s with c:~nccntrations 2nd. then c a r r y out a m o r e detailed s u r v e y during the northward. c r o ~ s i n g s (Fig. 5).
The rnnp chowing th- distribution of bluu whiting ( F i g , 6) is baced on the densur crossiaigc on the tvay northwardc, Th2 f i s h w c r c located i n t h ~ w e r m high salinc Atlantic wc?tber a t dcpths bctwecn 350 and 550 m e t r e s , but v ~ e l l above the b;tt,rn, The v e r t i c e l e x t ~ n s i o n of thc l s y e r o werc 3 0 to 50 meisres, The fish w e r e i n prcsp?.wninfi stat,.
T h e constant C waa L?und to be 570
-
600 fiah/rnm/prilcs 2.
The calculation gave ri ntack nize of abobout 5x10~' f i s h r r a p p r i z i r n a t e l y 10 mill. tonns.A miire dr.tailcd r e p a r t is given by Jakupsstovu and IvIidttun (1972).
General
Thd absdlutc: abundancc estimate i s dependent .m a rcliable d e t e r m i n a t i m of the factor C. This f a c t l ~ r i s abtained on single fiska r(>cordings, but m u s t bc a s s u m e d t;, be valicd a l s o f ~ r d e n s e r conscn"ia.ti~ns.
The stock s i z e measurcd this year i s somewhat higher than the c o r r c o p s n ~ i n p ; value f r ~ n i 1971. Thc observntic>ns in 1971 did not include any young fich
r d c ~ r d i n g s . But this y c a r m3st of the recordings s,~uth a£ qbout 7 6 " ~ ' c ~ n o i o t of 0- and 1-gr,.up fislz. Omitting t h ~ rec.,rt.l~d vnlqca frarr\ thio
a r e a , the tat21 utclclc s i z c nm..unt t~ 10.5 mill. tann. S h i s i s insignific,?ntly diffsrcnif from the 1971 estimate.
It chauld a l s J bc n\,td,.B tkat the cover-zge in the ~ n s t c r n p a r t of the ar,:?* b ~ t h y e n r s did n n , t incluclv tli., i i i L r l l a r e a ,>f distributil~n.
The f ~ ~ c t j ~ r C f 2 r c a p d i n i s prabably s ~ m a w h a t high sincc the cuunting rnight have included zlso t r n c . 2 ~ f r u m other arna11 organisrns.
Concaauently t h e r e i s a c e r t a i n degree ~f , s v e r c s t i r ~ a t i o n in the t ~ t a l st\ jck s i z e values.
Since the ctsnditions were rmsrs favcsurable f o r the application of the acoustic method in 1971. coropared to this yesrB, the 1971. estirnn,te i s the m o r e reliable of the two. It i s recomrnended tliereforz to c a r r y uut futurc capelin surveys in late Septernbzr when ez)nditi:jns apparently a r e beteer than e a r l i e r i n the sensun.
Bluc whiting
.
Even though the behavisur .3f the blue whiting by fariming well defined s c a t t e r i n g l a y e r U i.,%r'er.;d cxcellent conditiuns f :jr the a s e of: a c a u s t i c techniyue, the reccjrdingn vmre .jften di s t u r b e d by noiae f m r n s h i p r,Aline;
and f r o m ghost bottom. vciio;=s. T h i s will c a u s e n mi*n;>r v a r i a n c e to t h z a s t i m a t e .
R CKNOWLEDGMENT
W e will lik* t o e x p r e s s our gratitude: t o t h ~ s e of sur c3llecigues at th-.
Institute of M a r i n e R e s e a r c h who have participcltcd i n the col1ecti:)n and a n a l y s i s of the m a t e r i a l .
REFERENCES
F ~ i l e y , R. S and S2,2t ,n, C , C. 1969. Q b s e r v n t i , ~ n s un the spawning and d i ~ t r i b u t i ~ n c ~ f spawning p r ~ d u c t s 2f the bluc whiting at
Rockzll. Coun. Meet. int. Coun. E x p l x . Sea,1969.
( F 31): 1
-
5 , 3 fig.,
2 tab, (Mirneo).Blindheim, J. Jaktapset-~vu, H. , Midttun T,.
,
and Vestnes G, 1971:Kolmuleunders@kelser med
F/F
"G. O. S a r s " t i lNarskehavet 12.
-
29, juni 1970 F i s l t r t s Gang 57: 26-
29Blindheim, J. and Ndcken, 0, 1971. Abund2ncc e . ~ t i r n a t i o n cf the spatvnine Lofoten cod 1971. Coun. M e c t , ini. Coun. Explar. Sza 1971.
(B:15) : 1
-
5 , 3 t a b s ,,
2 fig.
(hfiri-ici~).Dragcsund, 0 . and Jakupast NU, S, H. 1971, Bbserv;?tians on distribution and migration af Micri>mesitius pc,ut,?oslr>u (RISSO, 1U10) i n the n,jrtheclst Atlantic.
-
Coun. Mett. int. Coun. E x p l s r Sea 1931. (1-1 26) : 1-
7, 5 fig;. (l\lIirnc~).Drag2sund, 0. and ~Monotr,d, T. 1972; Obscrv?.tiona on Capelin
(.Mzllotus Villasus) i n New Foundland Viraters, Coun. ~Mcet.
int. Explor. Sea, 1972 (H: 12) : 1
-
8, 9. tab. 11 fig ( . ~ i m e d )Hendercon, G.
T.
63. 1957. C ~ n t i n ~ u o u s plankton r u c o r d s . The d i s t r i b u t i a n of y:jung Gadus p 2 u t a s s ~ > u (RISSO). Bull m a r . E c a l . 4:179
-
202.Jakupsstovu, S , H. and Midttun, L. 1972: K c l m u l e ~ n d ~ ~ r s ~ k e l s e r n ~ r c l v e s t f o r
Dc
B r i t i s k e Øyer i f e b r u a r - m a r s 1972. F i s k c t s CaneJakupsstovu, S, H. and lVakken, 0. 1971: Kolmuleunclursøkelser i Nc;rslrehavct i a p r i l
-
m a i 1971. F i s k e t s Gang 57:605
-
607.Midttun, L. and Nakkeil, 0. 1971. On acaustic identification, sizing and c'bundanct estimation of fiah, FiczkDir. Skr. Ser..
H a v Undcrs., 16: 36
-
48,Fig. 1 . Survey route and grid of stations 12-29 September 1971.
1 ) Hydrographic stations with TSD sonde,
2) hydrographic stations with water bottles, 3 ) pelagic trawl stations,
4) bottom trawl stations.
Fig. 2. Integrated echo intensity (mm deflection) of capelin 12-29 September 1971.
F i g . 3. Survey route and grid of stations 5-20 August 1972.
1 ) Hydrographic station with TSD sonde, 2) hydrographic station with water bottles, 3 ) pelagic trawl station,
4) bottom trawl station, 5) bathy station, 6 ) purse net station.
F i g . 4 . Integrated echo intensity ( m m deflection) of capelin 5-20 August 1972.
IS' 8' I - . . , , O' 5' E
. , l . . . . , . ,
5'W
r u*,
F i g . 5 . Survey route and grid of stations 28 February - 26 March 1972.
1) Hydrographic station with TSD sonde, 2) hydrographic station with water bottles,
3 ) pelagic trawl station,
4) bottom trawl station,
5 ) plankton station,
F i g . 6 . Integrated echo intensity ( c m deflection) of blue whiting 12 - 26 March 1972
