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Tr~s paper not to be cited without prior reference to the author

International Council for the Exploration of the Sea

~{erring Conni ttee

NORl'lEGIAlJ TAGGllm EXPERll-1ENTS

nJ

TIE NORTH-EASTERN NORTH SEA AND SYJ:.GERJJ..K,

1964

AND

1965

by

Olav Dragesund ~~d StellLar Haraldsvik Institute of Earine Research, Bergen

IHTRODUCTICH

E:x:cept for the ICES herring tagging experi:-':1ents D""'"l

1957

and

1958

on the Bloden GroLmd (Aasen, Andersen, Gul 1 and , Popp Madsen ~~d S~~hage

1961)

no large scale tagging of nerring with internal metal tags have been carried out in the North Sea. =-Iowever, in view of the rapid developnent of the herring fisheries in the northern ~~d north- eastern North Sea in the recent years, the ~1erring COLIDi ttee of ICES

(Anor,

1965)

^{hl October}

1965

recoI:.1uended that: IIfor a better underst~~dil1.g of the relationship between the herrL~g h~ the north-eastern North Sea and those on the traditional fishing grolli~ds, and also for an estioate of the fishing mortality an D""'"lternational tagging prograL~1e should be laun.ched iI::u:1ediatelyfl. I t was recoLlli1ended to carry out both internal and external taggh~g of overwintering herring L~ the north-easten~

North Sea and tagginE of feeding at""'"ld spmm.ing herring in the -v.restern north Sea. By that time Institute of h:arine Hesearch had already in January

1964

carried out one taggL~g with h""'"lternal tags ll~ the Skagerak area. Since tne reconwendation of the HerrhLg Coa~ittee was given,

attempts have been made by several nations to tag herring, fu1.d Nor,'ray

has carried out three experinents (Noveober

1963.

June

1966

&~d July

1966).

The Dali~ objective of this report is to give a description of the experinents carried out in

1964

a...~d

1965,

and to consider sone preliuinary results that can be dravrn froE the recaptures. The

1966

experiments cfu~

not be dealt wit~ this report due to the short tine between the libera-

t.i.onS ·p.nc.l .tl~.is _.

.

D9Ei

.

t i n0.

- 2 -

THE TAGGINGS

All the herring "'iv-ere tagged "'ivi th internal steel tags and the method applied ",·as briefly the smile as described by Fridriksson and Aasen

( 1950 and 1952). I t should be noted that the herri..t1.g released I'lere measured as to length, and scales were taken from each fish tagged.

The taggings were performed frou a swall tagging craft at drift and the herring secured for tagging, were kept LL a keep net tied to the side

of the tagging craft. Herring were taken individually from the keep net by a dipnet, m~d released directly into the open sea. All the fish tag- ged had been caught by purse-seine. "trJeather conditions were favourable during the tagging operations.

The 1964 experiment (Fig. 1 )

During a cruise 9f R/V lG.H.Dannevig" a total number of 1000 herring - were tagged about 30 nautical miles southwest

of

Lindesnes (Table 1)~

An analysis of a sample taken from the sawe catch as the tagged herring indicated that aut~~ spawners made up about 90.0

%

^{of the herrb~g in}

the sample. Unfortm~ately no otoliths were taken and i t is difficult to give a

cer~in

classification in auturan

m~d

spring spa'imers according to age. However; i t is likely that the 1960 year-class of the auturmrr spawned fish pred01~1ina ted the saDple (Table 2).

More thru~ 50

%

of the herring L1. the sar~ple were in maturity stages VII and VIII (Table J) and consequently these herring are autLrrm spawners.

The mean nunber of vertebrae of the herring in stages VII lli~d VIII was 56.48, al1.d those in stages I a:.ld II 56.51, >'Jhereas the herring ill.

maturity stage IV sho.v-ed a mean n:ut"j.1ber of 57.25. This latter group is certainly spring spawners, and judging froQ the nean number of vertebrae

\,..,Q f herring

Vil'Cl:mturity stages I and II, i t is likely, that most of these herring belong to the autunm spawned fish.

The 1965 experiment (Fig,1)

This tagging tool; place during a cruise of R/V I1Johan Hjortll

(Haraldsvik 1966). The first batch of 1700 herri3.'lg ( liberation 1) ,;ras released 5 November 25 nautical miles south of P,yvingen (Table L).

The herring consisted of 91.2

%

autunm spa-t\'Ilers, a.11.d still the 1960 year-class predominated followed by the 1961 year-class (Table 2). The distribution of the maturity stages of the herring is sho~m in Table

J.

The next batch of 2JOO herring (liberation 2) 1"3.S released ^.-;. I

Hovenber 20 nautical oiles northi;olest of Skagen (Table

1).

The herrit"lg tagged uere alcost en tirely ~utm.'-11. spmnl~c...fis::i

(97 .. 7 jS)

of the 196J year-class (Table 2) • .l'fost of these autumn. spmv:ners were i.n maturity stages I ffi~d I I (Table 3) lli~d the Dean nurrilier of vertebrae was

STATISTICS OF HERRING L.Al\fD~D In NORWAY FROHl JJI..lfUARY

1964

TO

30

JUNE

1966

Before analyS~gthe tag returns i t is nescessary to consider the catch statistics m1.d some biological data of the herrLJ.g collected in the area lliJ.der consideration. This is especially importru1.t in case the recaptures are used for stock size and I:.lortality estimates. For the

present lllvestigation i t is suggested that the catch statistics together with biological data may give valuable inforDation about the overwinterL"lG area for the autumn spavmed stock in the north-eastern :North Sea.

In 196L} the total catch of herring la'lded in Norway from the North Sea and Skagerak amounted to 192,520 tons, being Dore than five times the yield in 1963. This great increase i n the yield is largely due to the purse-seiners participating in the North Sea and Skagerak fishery for the first ti1:.1e. The Elonthly catches landed in the different areas are given in Table

4.

The la.."ldings from Skagerak derive mainly fror;] an area at the entrance of Skagerclc, about 20-40 nautical miles south ahd south-east of LL~desnes. In J~~uary 1964 the fishery nallLly took place in this area, whereas during the follo1ving eight months oast of' the herring were caught at the Egersund Ban .. "tr, ffi1.d Coral Bank. FrOILl nay to July (inclusive) herring were also caught at the Patch and Viking Banks.

Frow October onwards the Skagerak again became the most inportant fishing area.

In

1965

the fishery yieldcd 603,886 tons. During the first two

Donths of the year the oain fishery took place at the entrance of Skagerak:, 1'IThereas fron Harch. througlJ.out the next eight months the

fishery was centered at the ~gerslli1.d Bank.:- Coral Bank, except ll~ July and August, vn~en a good purse-seine fishery cast of Shetlru~d developed for the first tiDe (Table

5).

In Hay also substat"ltial catches were

obtained. at thc Viking BaJ.1.k:. During the last tliJO _ I..lonths of the year the fleet "laS fishing in the Skageral.;: and at the :i:gersund Bank.

Tr~oughout the rest of the period fron ^{< •} Jm~uary

1966

up to 30 J~~e

the fleet shifted betw'een Egersund Batl...lc and Coral Ba..Lk Lloving somevlhat more to-wards '-Jest at the end of the period. The total catch during this period &tiounted to 160,000 tons (Table 6).

- 4

Pooling the samples collected during the period frow 1 JruLuary to

30

June

1964

from Skagerak and Egersund Bank - Coral Bank,

85.8 %

^of

the herring examined consisted of' aut"LlIarl spmV"uers (Table

7),

the

1960

year-class predOlainating

(52.9 %),

followed by the

1961

year-class

(34.9 %).

nerring caught at the Egersund Baru~ - Coral Bank from 1 July to

31

October were also predominantly of autuon spawned fish

(81.9 %)

(Table

7).

The

1960

&""1.d

1961

year-classes were the dominant ones in July, irtlhereas the

1962

year-clas s strongly dominated the sanple s froD the end of AU5 ust to October. It should be noted that the ^ad~ixture of spring spa1m.ers in August was relatively high. This is also reasonable since nost of the mature herring at this tillie are more westerly dis- tributed.

The samples taken fro!:l 1 IJover,'1ber

1961.,t

to

30

"Tune

1965

in Skagerak and at the Egersund Bank - Coral Bank consisted of 9^Li,.

9 %

aut1..>1.'!L'1. spavmers, among which the

1960

year-class predominated, followed by the 1961 and

1962

year-classes (Table

7).

North of

59°N

(Patch Bank and Viking Bank)

the autumn spmV"llers contributed only

66.1 %.

In this latter area the older age-groups showed up sonewhat more frequently than further south.

During the sumner and early autunn

1965

the recruits of the autu~""1.

spavmers

(1963

year-class) were predominating at the EgerSlli""1.d Bap~ - Coral Bank. However, off Shetland the sanples sholV"ed a completely diffe- rent age composition. Also in this area the oajority of the fish consis- ted of autur~ spawners

(84.2 %),

but in contrast to the EgerSlli""1.d Bank Coral Bank s&uples the older age groups were more abundant. The

1960

and 1956 year-classes 1'ITere represented y;rith

18.J %

^{and 1L~.3}

%

respectively.

In the samples collected from 1 Noveober 1965 up to JO June 1966 at Egersund BruLk - Coral BruLk and in Skagerak, the

1963

year-class con- stituted !J~1.2

%

of the autUl::ITl spm,mers, whereas thp. :1961- .?,l1:d

126'0

year- classes altogether contributed with only

34.5 %

(Table

7).

Table 8 shows the Belli""1. number of v~rtebrae arranged according to period, area and spavluing group. The menns of the autUlTIL""1. spawners varied between

56.35

and

56.49

indicating that the Bfu"lk herring constituted the Illaia bulk of the autULill spawned fish. During the SUIr.mer and early autunn period

(1

July to

31

October) some of the samples from Skagerak and

Egersund Ba.."'Llc - Coral Bank Sh011T slightly lUvler "leans than in the period 1 November to JO June. I t is likely, therefore, that some adnixture of

, ] .

Kattegat autu~n spaners may take place during sum~er and early autumn.

The spring spavmers appearing in the samples seeB to originate mainly from the northern North Sea.

THE RETURNS

Comparing the biological data of the herring collected from 1 Jal"luary 196L~ up to

JO

June 1966 vIi th those of the herriL~g in the samples fron~ the Saf:le catches as the tagged herring, recaptures from the followir..g periods fu"J.d areas are of special interest: (1) 1 Novewber

to

JO June,

Skagerak and Egersund Bank - Coral

Bruuc

and

(2)

1 July to

JO

October, Viking Bank - Shetland areas.

As i t appears from Tables 4,5 fu"J.d 6 the first area will probably cover the main over~Jinteril1.g grounds for the f:Jature autumn. spawned stock in the north~eastern Horth Sea. According to the biological characteris~

tics of the herring collected in this area i t is likely that no e:;.::ten- sive emigration from and ir:l1nigration to this area takes place from

1

November to

JO

Jlli"J.e the following year.

The second period and area can at present only be dealt with in connection with the 1964 experiment.

Returns from the 1964 Gxperioent (Fig.1)

In Table

9

is given a complete l i s t of all returns during the period from the tagging up to

JO

June 1966. Altogether 17 tags have been recaptured from this experifaent, of 'Vihich 11 are detected at

Norvlegian plants equipped vlith m~gnets. J./lost of the tags were recaptured in the Egersund Bank ~ Coral Bank area. However, i t should be borne in mind that ll"lternal tags recovered at oil ^and meal factories cap~ot be allocated w·ith certaint.y to a particular area fu"'1.d day of la..'1.ding, because

the tag may not reach the magnet and be recovered until some time has passed after the herring have been landed~ NotwithstmLding this disadvan- tage i t is likely that wost of the tags recovered Cru2 be napped out

ly .

correct accordlng to the infon:1ations given by the factories ^t -'1Thich

usually know the tiDe i t takes a tag IrOQ landing fu~til i t passes through the machinery. As the fishing area of the catch (reduced) is l~ovn"l, the area of recapture can be figured out fairly well. I t should be noted that only one tag of the 1964 experi~ent has been recovered in 1965, eventhough the yield froIil the ~Jort:i.1. Sea and Skagerak this year was extremely high coupared to the previous year. In 1966 only 3 tags have been fOLu"ld up to

JO

June.

Returns IrOD the 1965 experiraent (Fig. ~l

Table 10 shows the sRmmary of returns for the two liberations in 1965 up to

JO

Jfu'1.e 1966. A total of

83

recoveries from liberation 1 are returnec., of '1Thich 67 are detected at Nor-"1Tegian plants equipped \v-ith mag- nets. Frow liberation 2, 67 tags are recovered, 36 at Norwegian plants equipped ',-/ith magnets. The tags both from liberations 1 and 2 are mainly recaptured at the Egersund Ba..ll<.: and in the Skagerak. lYlost of the 26

recoveries from Skagerak are froIil Dfu~ish oil ruLe rueal factories.

- 6 -

Returns fror;1 Hor ... egian plants

Only the recoveries froE)' herri:n.g landed in NOr1rlay ,·.rill be den.lt with quantitatively in this report~ and special attention, therefore, will be paid ·to the returns froLl Nortvegian oil an.d neal factories.

However, not all the re:turns fron factories equipped with nagnets Cffil be dealt with qUffiltitatively due to 10 ... efficiency of the magnets and lliLreliable data on the catch reduced.

During the period

15

January to

30

June

1964

all the

6

reooveries

\vere detected at one factory (Table

11),

Out of a total catch of 474828

. ' ! .

tons landed in the sane period, 18,251 tons w'ere reduced to oil and r.1eal at factories equipped i--lith DaGTI.ets~ Unfortunately only four factories 1'>Tith tested ffiagnets ca...'1. be considered. The recapture rate -Vlas estiIJ.ated

to 0.366 per nille returns per 1000 ton$.

Fron July to October (lllclusive) i t is likely that DoSt of the herring tagged 'were out of' the area .·,here the HOr1rlegian fleet operated, and judging :from Table

7

the catches ,·.ere also strongly dominated by recruits. The 101'J ITunber of returns

(1

tag)~ therefore, is reasonable during this period~ H01'TeVer ~ f'roD 1 Eovenber 196^Lt- up to 30 June 1965 only one tag was recovered (Table 12). This low figure is strange taking into aCCOlli""lt the relatively good fisl1.ery that took place in this period

(Tables

5

^aJ.1.d

6)

and bearing in r;.;.:in.d that the SaL18 year-classes predoni-:- nated the catches as the year before. (The per nille returns per 1000

tons was only O~008)~

During the sumner/autnnn period fron 1 July to 31 October 1965 ne herrit"l.g were recaptued fro:r:1 Skagerak a...'1.d Egersund Bar-lIe - Coral Ban.k.

This is also reasonable SDLce the

1962

fuLC 1963 yeaf-classes made up r~ore than 60

%

of the herri...Lg caught (autUl:1n spa .... mers). Off ShetlC"L.'ld:

however, t,he purse-seiners exploited the same year-classes as those tagged. Out of a catch of 187l81.~2 tons from this area only one tag 1'1aS recovered (Table 9)~

Turning to the returns of the 1965 experinent (Table 10) i t wi~l be seen that almost all the tags were recovered ~ the Skagerak m~d Egers~'1.d

BruLk - Coral Bank area~ Tru<i~ng into account the recoveries otily from this area and pooling the nULmer of returns from liberations 1 and 2 a total nunber of

99

tags ,v-ere detected at 10 factories (Table 13) '- giving

· . l

a per mille returns of O~239 per 1000 tons.

FACTORS AFFECTHm THE RETURNS OF TAGS

The percentages of returns of tags nay be influenced by several factors, ru~ong which the following are the BOSt i~portfuLt:

(1)

WLeven dispersal of the tagged fish a...'1.d the fishing effort in the area llilder

consideration~ (2) non-returns of tags recovered and losses of tags not boL~g detected, (3) mortalities due to tagging, h~Ldllllg and bad condi-

tiorff the fish tagge6,

(4)

losses of tags from the fish by shedding lliLd (5) losses of tags through nigration.

Uneven dispersal of the tagged fish and the fishing effort

I t is striking that only one factory (Ho.2) has detected all the tags fron the

1964

experiment (Tables 11 ru."'!.d 12). I t should be noted tha t during the first

6

El0nths of 1964 the herring l~J.ded 1-,rere reduced a t only a few factories compared 1'li th the period from 1 November 196L~

to

30

June 1965. Nevertheless, i t is expected to find tags at all facto- ries listed ^D'l Tables 11 and 12. The explanation for this bias in returns must be the failure of the tagged herring to disperse ra...."J.domly. Since

also the fleet obviously did not fish at random, such lli'l uneven distri- bution of the returns -~.8.y- occur.

Nor did the herring tagged in 1965 Seelti to mix evenly during the first 8 Donths after release (Table 13). By using the mean number of tags per 1000 tons of reduced herring as the expected nUL1ber and compa- ring i t 1vi th the actual nUDber of returns per 1 ^COO tons in each reduc- tion plant, i t proved possible to carry out a;(2_ test. The;(2_ values obtained

(p<O.05)

indicate that the tags are not randoLlly distributed bet,,,,eon reduction plants, both 1'17"11.en considering the returns from libera-

tions 1 and 2 separate and pooling them. Also when excluding the recap- tures during tile first three months after the release the distribution of the tag returns was biased CP·..:! 0.05).

Non-return of tags recovered and losses of tags not being detected Not all the tags froc recaptured fish are returned, some tags are not sent to the Institute of Marine Research, SODe fish are processed at factories not equipped with magne~s, and SODe tags are not detected by the nagnets.

The non-returning rate of recovered tags of cod, coalfisn, haddocl~,

halibut and catfish in Norway was estimated to be at least 4-6 C;~ (:aylen

19 63).

HOvlever, i t should be noted tl1.at the revlard fur each of these tags

is 5 N.kr., ",vhereus the rei-vard for a herring tag is 10 IT. kr. Almost all the recoveries of in.ternal tags come from oil and weal factories and in these plfu"'!.ts there are only a fe,",r workers 1"11-10 attend to that part of the ruachinery 1'17"here the magnets are placed. Thus, only a fairly limited

nUBber of people are dealt with, ili~d in all the plants there are placed posters with detailed instructions of uhat to do with the recovered tags.

Due to this circuri1stances and a '"Jorth while reward, the loss in ]\for1vegian plants due to non-returns of tags recovered is probably negligible.

The returns from factories vd thout magnets and vd th r;lagnets of especially low efficiency are rejected for further quantitative treat- ment in this report. To test the efficiency (e) of the magnets the returns from a b"J.own lluober of tagged fish introduced into each factory is measu- red. The figures for e at the different plants are listed ill Table 11, 12 ru1.d 13. The efficiency (e) at each factory multiplied by the qu~~tity (p) give the effective quantity of herring reduced (e

x p)

in Tables 11, 12 and 13.

- 8 -

IV;orta 1 i ty due to taggL~g 7 handling unci bad conGi ti:)l1. of the fish

Ne specilll. test· 't\Tas carcl"eeL. out to inv.estiG:?t' .... · the taggib,g' L.ortalityi....'1. cOIll1.ec'ticm vJi th. tile present tuegD"1.G oxper.i.wGl1.ts.

HOv;Tever, several atteI:1pts have been done to study this problem on Norv-regifuJ. spring spq:~m.ers (Fridriksson and Aasen

1950, 1952).

These experiI:lents indicate that the tagging mortality can be regarded as alnost i....~signific~~t.

During the sur-rr.:er

1966

^El. tank experiDent ".ras curried out at Institute of l·larine Research, Bergen, to test the Dortality of inter- nal tagged herring. In August

1965

herrh'1.g 1\Tere brought to the Insti-

tute from a purse-seine catch near Bergen. The herrL'1.g were kept under observation by Haraldsvik for gro1rJth studies (these experiLi0nts are not yet fL1'1.ish.ed), aD.d on

17

JUl1.e

1966

1 OL~ of these ilerring (Table

14)

v/ere taken froD one of the ta.'1.ks al"ld tagged with i:n ternal steel tags lli1.d transferred into a tank of the SaL.le size (6x]X1.80)n

3 :

close by.

The herring SWlli~ restless arolli1.d without foroing a shoal just after the tagging and did not eat the f i r s t t'l'JO days. (-[hen the experi- ment was finished

9

Septeober

1966}

unfortw1.utely

25

of the tagged

1 " ~1.err~ng were 1 ac lng, k' tl _1.ose f " " lsn pro ab_y calign b - ¹ bein!? t ¹ Dy b' Jr·:cs. ¹ A t t -^-0 a.L ^0"': .(:' 8 herring • ..rere picked up as dead, of which [J. cied during the f i r s t three days of the experiment. 1vllen exar;.lining the dead herring a."1.d the position of the tag, i t seeGS likely that non of the herring had been directly hurt by the tag i t s e l f . A Dore likely reason for the t:lortality is the tagging operation, D"1.cluding cutc~h~g ~"1.d. hm~dlll1.6 of the fish.

Excluding the loss ef the

25

herring the tagging mortality is

Gsti.D.ated to 10.1 per cent, whereas including these herrL'1.g the Llortali- ty anounts to

7.7

per cent. For calculating the effective nuober of herrD~g tagged the mean value of these two figclres:

(8.90 %.)

^{is used.}

Differences in percentages of returns of herriIlg tagged by various taggers have been denonstrated by Aasen et al.

(1961).

In the present investigation a l l the ~1.erring tagged in.

1964

.·rere tagged by the sane tag-ger, vlhereas the

1965

experir;1ent 'was perforI:led by tr-..ree different persons. Judging fron Table 15 no special trend is noticed, a."1.d i t seehlS likely ( p > 0.01) that the herrir..g have been subjected te the si@ilar handling by the different tag-Gers.

Especially in open sea taggi..."1.gs, where herring have to be provided by purse-seiners lli1.d transferred L'1.to a keep net before the tagging Cfu~

start, sonetiEGS in ~mfayourable weather, the herring way soon be descaled and the condition of the fish 1-rill becoL1e reduced.

I f this ·was the case in the present experi.Qent one I:light expect to

find I:iOre returns frora fish tagged early in each liberation ( f i r s t half of release) thfu"1. those froe the second half cf release. In two cases

(Table

16)

the rate of recaptures is sliGhtly higher for the f i r s t half of release, ·whereas i t is l01'.Ter in one. Testing the 1: 1 ratio by applyi..."lg aY -test no significal1.t differences could be fOl.m.d 2

(p>

0.01).

The extreDely favourable "lea th8r during all the taggin.g operations may explain this close agreenent i..."'1. returns.

Shedding of tags

The present tank experinent showed that

4

tags were lost by shedding.

Con trol sa;"'":lplil'1.g the tagged herrL'lg i t "!as revealed that t;he ,;,roUJ."1.d had

caused by the insertion of the tag healed after 9 weeks, ru1.d loss of tags due to shedding will not tru~e place after this tiDe.

Tests have also been made on No r;,ie gial1. spring spav-mers by DragesU!"'1.d (lli'1.published data), and accordh"1.g to these experinents special atten~

tioD. should be given to herring tagged in prespavming al"1d spalnll'lil1.g stages. Tags ·were frequently found in one or both gonads, alJ.d these tags will be subjected to a pressure during the spa~mliJ.g process.

Consequoil tly the shedding Tdill be rela t i vely l"-igh ·w::'"len fish are tagged in these stages. Since the herrhLb tagged in the present experi~ents

1rlGre a l l L"1. post spawning stages or iDnature, the shedding rate should be cowpaJ..~eable with tho se of the herring in the tat"1.k experiElen t , giving an average 72..1uo of

A.4.s

:;;Jar cent.

Variations assosiated t'lith the size of fish and losses frof.J. wigratiol1.

Alraost a l l the herrll1.g (98

%)

landed frora the North Sea and

Skagerak have been caught by purse-seine, and i t is unlikely, thereforeJ

to expect a~y selection effect due to fishing on the nULIDer of returns.

Eow'ever, the oortality of the tagged herring Day be associated with the size of the fish sO that the larger fish survive botter than the smaller ones, or vice versa.

In Table 17 is given the length distributions ~I ·-t~1G 'tG.':"';';":<' QHd

recaptured fish, together vIi th the means and variances. The differences between the weans are snall and far from being significfuLt both separa-

tely a..t"1.d combined.

Losses of tags Day also talce place by segregation. Fror.1 Table

7

i t will be see:::l that mai..."1.1y old herring 1-J'ere caught off Shetland by the purse-seiners in the surLier

1965.

I t could be that the older age- groups of the tagged herring reoained in this area and. did not return to the Skagercl~ a"1.d 2gerSlli1.d Ba;~ - Coral Bank after spa~ming to the sane extent as the y01 .. u~ger mature fish. HOvlever, this possibility Cfu"J.

10 -

hardly ex.plain. the 10"1111 rate of recapture of the

1964

experiment during the period fron 1 November

1964

to

30

June

1965,

since the sace year- classes occurred in the catches fro8 Skagerci< fu~d Egersund Bank - Coral Bank as of the tagged fish (Table 2)"

conCLUDING REI-jIARKS

The present results are not sufficient to give a description of the Dovewent of the herrL~g fron the overwintering area in the north- eastern North Sea to the feed;ng and spawtiing area in the northern and western Nort~l Sea. I t should be pointed out that for Dore detailed a...TJ.d reliable analysis of the migration pattern as li~dicated by tagging experi- ments, external as well as double tagging should be carried out.

Even though not all the requirel:1ents for an unbiased stock size estinate are fulfilled a tentative estimate for tile overwintering stock in the north-eastern :North Sea is given. For fu"'l ideal experiment of this kind i t is necessary that: (1) the tagged fish or the fishing effort is evenly dispersed throughout the area Q~der consideration, (2) data for adjustsent for losses of tags in reduction plants ffiLd

tagging mortality, hfu~dlll~g of the fish illLd shedding of tags is available, (3) there is no recruitment durL""lg the period in question and

(L!-)

no

Digration of fish into or out of the tagging and recapture areas truces place.

DefinL"I'lg the overTtvinterL"lg area as the Skagerak fu"'ld Egersun.d Bank Coral Bank and considering the returns of the

1965

experiuent during the period from tagging to 30 JU11.e

1966,

the requirenent (1) is not fulfilled. This is shmm. by the results :from the i - t e s t cODpariug the expected nuober with actual number of returns in the reduction plants.

I t should be noted that not the whole qUfu"'ltity reduced in the plfu"'lts COlle from the overwinterine area. However, making correction for the

amount caught outside this area would hardly influence the test.

The further analysis of the results would be Dore reliable i f the local fishing intensity ^OiL each liberation could be calculated. This requires detailed effort statistics by areas and some asslli~ptions about the move- ments and dispersal of the tagged fish. Unfortlli~ately no e:ffort statistics is available at present fu"'ld consequently the figure of the stock size

,viII be biased.

To adjust for losses of tags mentioned under require:oent (2) the data presented L""l Table 13 and the results of the tank experi:oent are

tl1.e

used. ApplyL~g figures obtaL~ed for taggL"'lg Llortality and sheddll'lg of tags in the tfu~k experiDen~, the effective nuober of tagged herring is calculated to be

3465.

The third and fourth requirements are difficult to judge thoroughly from the present material. I t is likely that recruits were present

t~~oughout the period in question although the sawples collected indicate that the

1963

year-class is less abundant froD March onwards (Table

18).

The rate of mixture bet-:;veen the spring Cl.J."'ld autunm spawners w·e-re alnost the same during the period Q~der consideration.

The 1'ITestward miGration from the over,,,rintering area to the feeding and spmming groun.ds in northern an.a vlestern North Sea usually starts in June and i t is reasonable therefore/to assw~e that the do@inant part of the autUM~ spaWl~ers is co~centrated in the Skagerak fu~d north-eastern North Sea during the period from November to June (inclusive).

On the other h~~d i t should be noted that the fis~ery off Shetland star~

ted sODe,ti~at earlier llL

1966

than in

1965

^Cl.J.~d the first catches from this area 1:lere caught in the niddle of June. However, only a few herring have been recaptured in this area up to the end of June

1966.

In the absence of reliable effort statistics and data on local fishing L~tensity a reasonable estimate of the stock size in the over- wintering area can be obtaineQ frow the

1965

experiment using a nodifi- cation of the sisple Petersen method (Aasen et al.

1961).

In Fi6 ure 2, the nur:.lber of tags returned eacl). l.i.lOn tb by factories equipped ·wi th tested magnets have been plotted agall~st the weight of herring reduced at the

same factories in that Qonth. These data have been fitted by a simple proportional line, givllLg

9.7

tags per

10

000 tons landed.

The individual fish Bay have grovID since the tiDe of tagging, so that the

10

000 tons of fish L'1. Hay/June represented less than

10

000 tons at the tine of taggllLg. However, durh~g the tiDe in question the nUL1ber of tagged herrL~g has decreased due to fish~~g fu~d natural Dortality and this "tvill to sone degree balfu"""1.ce the increase both in the length ffiLd fatness. For t~e present calculations therefore, no correction has been wade for these factors influencL~g the nunber of returns in relation.

to the qumLtity landed.

The nllil1ber of herring effectively taggod vms 3

u ..

65 and the estinated stock at the tiDe of tagging is calculated to

3465

x 10~OOO/9.7=

J!572

lJ.lill. tons.

Onitting liberation 2 and only taking into aCCOlli"""1.t the herring tagged in liberation 1, the estiQated stock size is calculated to

1473

x

10,000/6.2= 2.376

l:.1ill. tons. The cause of this difference in

stock size is probably that the herring tagged in the eastern part of Skagerak (liberation 2) lvore L'lainly recruits and did not appear in. the main fishery area fortft'6rwegian fleet to the sane extent as the herring

tagged further to the "t'rest (liberation 1). From Table 10 i t vIill be seen that a difference in pattern of returns exists between the two

liberations as

80.7 %

of the returns fron liberation

1

and

53.7 %

^{of the}

returns in liberation 2 are recovered by Horvlegian plants equipped w·ith r..1agnets respectively. The rest of the tags :;'"l.ot returned frOG Uor"V>Tegian plan ts, are recaptured by foreiGTI vessels, hlainly Danish a:n.d Gerl:J.an.

- 12 -

At present no further steps can be take:;:l to estiDute the total catch/stock size relationship in the overvvintering area as the catch statistics for the other nations fishing in the suoe area are not yet available. HOvJever, the catch taken by tl'le HOT1;·,regia:.'l fleet from 1 Nover:l- ber 1965 to 30 June 1966 expressed as percentage of the stock present at the tiDe of tagging is 5.29 per cent ill~d 7.96 per cent respectively.

Further experinents are needed to confiro the validity of the results obta:L""led from the present investigation. HUt'lever, the tagging experiruents have already shovm some reasonable estimates of the stock size in the north-eastern North Sea, 8..l"1.cl further tagging 1<'lill be of great importill1.ce

to solve some of the urgent problens in. the Eorth Sea.

Anon. 1965.

REFZRENCES

Resolutions passed by the 53rd Statutory r!ieeting.

Proces-Verbal de la Reunion 1965. ICES meeting, 1965: 110- 121. (Kimeo.).

Aasen, 0., Andersen,K.P., Gull8..l"1.cl, J . , Po pp 1J.:udsen,K. a."ld SahrhageJ D.

1961. ICES aerring Tagging Experiments in 1957 and 1958.

Haraldsvik, Sildei..L'l1.derS0kelser i Nordsj0en og Skagerak med F/F "Johan Hjorttl 18. oktober - 10. nover:1ber 1965.

Fiskets Gang, 52: 813-817.

Hylen, A. 1963. The non-returning of fish tags recovered by HOTtlTegifu"'l fishermen. FiskDi r. Skr. Ser. :;:{av illders.,

..!1 (6): 80-87.

Fridriksson, A. and Aasen₁ O. 1950. The NOr1'\Tegian - Icelandic herring

11 1952.

tagg:L""lg eXperiI:lents. Report No. 1. FiskDir. Skr. Ser.

HavtPders., 9(11)= 1-43.

The Norwegia...""l - IcelfuLdic h3rring tagging experiments Report No. 2. Rit. Fiskid.,

l(1): 1-54.

Sea and Skagera~, 1964 and 1965

I I I \

Date

,

Position Mode of

f

Lib' Type of Serial ¹ Total

i _{I • :} j

IN

^{E catch IlIo. tag nUtlbers}

i

_!

,

I

1 I

1964 17 Jan.j5737' ^{i 0} 06°35' Purse- 1 Internal N 240501-241500¹1000

seine

1965 ^I °

07°20¹

5 Nov.157 30' Purse- 1 Internal N 255501-256900 1400

r seine

\ ^{f I}

11 It 11

_"_

^{_ I f -}

-

¹¹

-

¹¹

-

ⁿ

-

^N 257001-2573001 300

11 7 Nov. 58°12' 10°53' Purse- 2 Internal; IT 256901-257000\ 100

seine ⁱ , _,

!

"

^{!l 11}

-"-

^_tI_

...

^II

- _" -

^If

^-

^{: N} 257301-259500 2200

t

Total _{••••••••}

.l500o~

,

I

Table 2. Age composition of autuon and spring spavmers in samples

taken froQ the same catches as tIle tagged herring

*

, r 19p4, ..

LOb _~

•

1

vTinter- rings

o

1 2

3 4 5 6 7

8 8+

Total

NI

1 lYear-

[

r:p

_blass

-j

1962

28 30.

4 11

⁹⁶¹

53 51 •6 \ 1960

1959

2 2.2 ^I1

II 1958

2 2.2 1957

: ::~ ^I ::~:

1 ^I

1.1 I

¹

I I

92 )100.0)

[

1 _I

• p

1965

!1. t

",u ^,UIilll spawners

I

Lib. 1 _j ^! Lib. 2

N

4 13 23

33

2 1

7

83

!

₁

_% t 4.81

15.71 i

! 2

7 •7 \

39~81

2.4\

1.2I _i

8.4!

i

i

%

:N ^I

I

91

I

-I 2\

96.8 2.1 1 \ 1.1

-\ -I

=1

!

I

.j

I

,100.01 94 ,100.0

I i

!

!

\

\

\

_I

i

\

t

S ^pr~nK spawners

year .... Lj.b.

class J:J

1964 !

1'

1963 1

19621

3

1961 \

3

1960 1 1

1959

I -

1958 [ 1956 \ - 1955 \

1 I

8

1 Lib.

IT 1 1

2

2

*

8 herrL~g from liberation 1 (1964) did not fit for age deteroination,

nor did

9

herring froo liberation 1 (1965) and from liberation 2

(1965) fit for age and type deterninations.

s

Table

J.

The naturity stages of the herring in samples tclcen fron the same catches as the tagged herring

1964

! Liberation 1

J

Liberation 1 Liberation 2

I

I ^I

^~

^{. .}

aturity

I

Aut"LU14""JL ¹ Spring AutULuJL

I

I

^0pr:Lng

f

s;eavmers I sEawners s;!2a\.\71'lers spavmers

%

¹

P

^{I !}

I _~ ^I

tage l'T ^I If _i ^I t IT !

N.

^IT

i : ^I

i

ⁱ

I

I ^!

¹

I

I

27 27.0 4 ! ^4.7

^{! 1}

⁵⁷

^{I 60.6 1}

! ^j

1

I

I I 14 14.0 4 ^{I t} 4,.7

I

^{1 ../-':l"S I I}

37.2 -

I

^I

3 3.0

^!

I ²

I I I

- -

^!

-

^{1 1 .1}

IV 4

4.0

-

I ^- I

^{J ~}

^{I - - -}

V

I ⁴

- -

!

I ^{- - - -} -

VI - -

_I

- -

^I

^- - - ^-

VII .5

5.0

I ^{7 8.2} _t

I ¹

-

^{1 1 • 1}

-

VIII

46

46.0

I

₁

_{70 82.4} I

¹

- - -

t ^{I t}

^{1 00. 0}

I ^• 1 ⁹⁴

^\

Total 100 I 100.0

f

⁸⁵ , ^{10 100.0}

³

Approx, rect.ref.

Tabl.e 4. Landings of herring in Norway _(

in

tons) from the

i:-~orth

Sea and Skagevak arranged according to month and fishing area, 1964 to in(Stat,Fishin g area Month Newsletter) Jan. Febr. I>1arch April May J1..ll'le JUlY Aug, Sept. Oct. Nov. Dec. Total 18 E Bressay shoal 2.D -186.5 11'7.0 54.2 299.7 719.4 15 E Fladen Ground _ 17_,7 .25.1 182,3 372.0 1222.4 68.2 1892ft7 "Hest of 02

0

E 17.7 25.1

2~0

186.5 359.3 431.2 1522.1 68.2 2612.j 20 H Viking Bank 71.4 162.1 2.1 1562.3 2140.1 155.6 2.8 4096

e

4 17 G Patch Bank 281.0 358;9 231.8 26.9 9343.1 1226,6144.8 527 •. 9 82_.7 . ___ 4.4

12~28~

1 North of 59°N 352.4 521,0 233.9

1589~2

11483.2 1382.2 147.6 527.9 82.7 4.4

16324Q~

16 G Coral

Bfu~l:

1306.7 6201,4 54.0 836,1 199.8 8598.0 15 G Ling Bank

207~9

299.8 174.3 682.0 15 J-K Egersund Bank 123.2 1602.7 399.5 936.6

62~0

27.4 7989.6 22968.0 8265.3 4235.5 46609.8 14 G West Bank 87.2 87.2 14J-K Jaeren Riff 346

i

6 1582_5 649.2 1107.1 1343,2 598.7 1086.9 1796.2 11846.1 87.8 20462.3 Bladen Ground

H

Danish Coast 3883.9 Dogger Bank Sum area IV b 3883. 118,9 15 N Skagerak

Coast22$7~";5

19.8 3.3 2391.1 ·16869,·119438;4 20503.1 14 0 Halse Bank 119.2 2190.2 1072.3 13 N Hanstholmen 14 P Skaa:en 45.1 Grand Total 23588,8 3620.2 1598.1 2297.0 3001.8 * tons landed by foreign vessels in Norway

r

Approx.

Taple.5. Landings of herring in Norway (in tons) from the North Sea and Skagerak arranged according to month and fishing area, 1965 rect.ref.

F'

h'

M

th to in( Sta t. loS long area l'.lOn __ Newsletter) Jan. Febr. March April May June July Aug, Sept. Oct. Nov. Dec. Total 20 G Tampen 34.,4 1.7 - -

.~

- .. 36.1 19-20 D Shetland 2693.6 158.8 83781:6 91563.0 12497.3 190694.3 18

E

Bressay shoal 93.2 1~5 - 94.7 15

E

Fladen G.!:9 und 8.5 ':"_____ 47.0 1846.312.34.4 155,2 30.2 JJ21,6 West of 02

0

E 42.9 2788., 1,8.8 83830.1 93409.3

13731~7

15.5.2

JO.2 194146.7

20

H

Viking Bank 7.2

3()iJljlj 25!32~.s'

172.53.1 1.7 1647,2 1 • .5 21463.5 17 G Patoh Bank 1.33., 406.1 .3478.9 1291 •. 8 921.3 3.1 128.1 180.5 • .5 8.5.8 0.8 82.57.8 17 H Sirahola - 71 • .3

39~8

77.7 .54208 North of .59

0 N

140.5 _-207.8 639,.2 18622.6 221.3

J.1

1 2 2. 8 3452,7

87'J

0,8

J0246.1

16 G Coral Bank 3.514.4

79874~.5

41884.0 246.9 1047.2 126.567.0 1.5 G Ling Bank 4.7 193.9 1089.9 147.3 143.5.8 1.5 J-K Egersund Bank 381.3 478.6 2256.0 1139.6 807.7 121.54.8 17993.7 20786.4 18159.3 3.55.53.4 134.9 1.52.5.7 111370,8 14 J-K Jaeren Riff 2.8 74.8 833.3 .5066.6 7619.0 1186,2 815.9 1645.4 24.5.9 833.2 18323.1 14

L-M __

List2-_,__ ... ,9991.0 6328.1 18157.9 1540.3 2J3.8 36251.1

o

South of 59 N 384.1 545,9 3089.3 6210.9 1213.5.0 9430.5.4 60840.3 32669.7 25780.5 54544.5 1675.2 1759.5 293947.8 Sum area IV a 384.1 722'J 3597.1 12606.1

.3~'46.1

2.5J85,.5 144673.5 126208.8 42964.9 ,4787.0 1706.2 1759 • .5 518358.6 11 L Bleden Ground 130.4 130.4 9 G Dogger Bank 122.2 788.6 910.8 Sum area IV

b __ ~ ___ ~_ _-:' __ _ _

122 .2 788.6 130. 4

_~-_

1041 .2 15 N Skagerak Coast24122.420790.9 340.4 3282.8 2435.7 6300.8 24.594.7 988.3 828.56.0 14 0 Halse Bank 1046.3 430,7 78.3 15.55.3 13

N

Hanstholmen ... 44.6 44.6 Sum area III a 24122.Ag9790.9 340.4 1090.9 3713.5 2435.7 6300.8 24673.0 988.3

8445~

Not specified 29,9 29.9 Grand Total 24506.521227.6 3937'2 12606.1 3 J 668.3 96174.1 145764.4 130022.7 45400.661087.8 26379.2 2747,8 603882.6 * 1668.3 tons landed by foreign vessels in Norway *

Table

6.

Landings of' herring in N-orway (in. tons) f'rom the North Sea end Skagerak arranged according to month and f'i.shing area,

1

January to

30

.J:u.;ne

1966

.J ..-~-~~-: -"" Approx.r~ct . Month ref'. to ~n F~shing area .... "'::""'_-. ... -....-...._-....,.,....--:":'. ~_.-:-__ -:--_"""":~ __ ~ ___ ~ _____ -:::-_-:-___ (Stat. tll:(",sletter

..Lan.'· '

Febr.·'March April Hay June Total ? .~;~ ~ 'I'~~;~

20

G Tampen "...

12.3 12.3 19-20

D Shetland

·'!.l9.3 66.5 30083.0 30198.8

1

2

E c.. ".I<~ladEm G:r,'oUl'ld...

11

8 • 8

.5 • 4124. 2

'IIest of'

02°:8) 49.3 185.3 17.7 30083.0, .30315.3

76~3

109.9 50.9 1327.0 154.5 1718.6 2.6 165.4 263.3 431.3 20 H 17

G

____ 17

H

Vi.king Bank Patch Bank Sirahola

:.:24§3.7 3201.7...

J'+.,~6~_

_ 55i_8_0 .•

~L

°

North of

59

N

16

G Coral Bank

15

G Ling Bank

15

J-K Egersund Bank

14

J-K Jaeren Riff'

14

L Lista

7166.4

8~·.3

7 8 .9 10909 2680.0 4528.7 432.4 7829.9 292.7 14.3 254.9 108

02

422.1 2933.0 49888.6 446.4 99.6 3113.1 54509.9 159.5

3535.2 115045.5 912.3

Lindesnes

1917.8 - 1917.8 §..2.£!h

0vf

59

0 N

9168.6 ,301.'1

...;~61.1 J§Ol·'C.s-49988.~

;;:'7782.5

121l~10.8 Sum area IV a

9168.6 435.2 658.3 6499.2 54516.9 88297.9 159.576.0 15

N Skagerak Coast

419.8 3.B 423.6

~3um area III a L~19.B 3~8

423.6

Sum r.£'otnl 9588.h

432-.2 658.3 6.503.0 54516.9 88297.9 159999

0

6 * 360.7

tons landed by f'oreign vessels in Norway

*

Table 7. Age composition of herring from 3kagerak and northern North Sea arranged according to period, area and type (the figures in b·rackets,

%) ---,---1---·--- I i

T~,)e · ___ ·-_______ A ___________________ ·_· ___ ~~~:t:._~}ass .. -.--- Area

.I~;~~~~~~:~ 1~:~--1-;631~96:!::f.:0~~~~~~56 ~411;63119~ilis:::

,Q' suawner1L-_

-- I .- 1960 1959 1958 1957 19561<19 :9~!n. ~ ~~:~~ra~38 r:- I ~ 14 1173 9J 1· 41 221 4.1 I 31 43 30

Jun.

~~~~ BB: I (85.8) I (14.2) 1 r

34•

91(52.9) (2. 71 (0.3)(

I.

2) 1(6.

8) ( I.

2] ( 5.3)1(16.

8

1964

Eger..

I 506 !

112

I I 2181\ 971143 I 91 6 I 4 I 91 1 ;IJ~~;, ~~~lBB: \(81.9) (18.1) !~4.8) (19.9)

(l9.4)!(1.

8) (1.2)1(0.8)\(1.8) (0.2) 11 31 71

( 1.. 0) .(~.

11 (7

3 • 2

1964/65

Zkagerak,

1

Nov.'· Eger-.

I 460 I 25 30

Jun. sundB.,

(94.9) (5,1)

Coral B.

1965

Skagerak,

1

Jul... Eger-

I 465 I 74 31

Oct. sundB.,

(86.3) (13.7)

Coral B,

- " .

I Shetland

I

358

67 (84.2) (15.8)

78 J 134 l197 I 41 4\ 3 I 18 I 1 31 16 (17.

8~ (30.5)~44.9)

(0.

9~

(0.9) (0, 7) (4"

1)

1{12 .. 0M64.0) I I 212

I

58 I 16

k'

90

I

71 61 13

1

29

1

1

I 5 /.,

7 j 31 35

~9.1)(13.4)K3,7)

10.8) (1.6)1

(1.

4 )(3.0) (6.7) (0.2) (7.1)(10.0) (4.

3

:)(50.0' 25160168 5 10 12

47

1 21.48 (7.6) (18.3)

(5I.~)(1.5)

(3.1) (3.7) (14.3) (0.3) (3,,1)1(73.8' 1

Nov. -Eger-902 87 2

365 160 98 207 5 5 7 36 1

29

15 1:6

:12 Coral Bo. I .

7 (12.5)

8

(8.2) 5

(l0.0)

6 (8.6) 4 (6.2) 3 (3. 5) 1965/66

3kag erak'l

'_1 J I j 30

Jun, Bund B.,

(91.2) (8.5) (0.2) (1.l,Z)/(18

fl) (11.1)

(23.4) (0.5) (0.5) (0.8)/(4.1) (0.1)

(3-3~7) (17.4)<1~{))r14~0 • ______ ~_4._._... __ • __ • __ • ____ ._~. ...-_. __ ... ___ • _____ ~ .. __ _ _______ ... __ ._ _ ___ ._ _ ----~---. --•• _-

---

;. ...

-.:..

3 (5.3) 9

4

9.

3)

(4. 1) (1

1

(4.0) 12 1

1

(17.1) (1.4)

(1.4) 11

(16.9 8 1 1 1 (9.2) (1.2) ( 1.2)

(1"

2)

1----". 1--

56

1

.0)

Table 8. Mean number of vertebrae of herring from Skagerak and northern Sea arranged according to period, area and type (figures in brackets, number)

---. -.. _---.---- -r---.--- ---,-_._.---_

..

-

Table

9.

Summary of returns from the 1964 experiment arranged according to area and month after release. The figures in brackets are number of tags recovered at Norwegian plants equip~ed with magnets ,--'~---t---'---.---.---.

I

Month after release

r=---

1964 1965 1966 Un-

--.

-- car-

I

Dn--- eer- Area 1 2 3

"*

5 6 7 8 9 1 0 11 12 tain 13 14 15 16 17 18 19 20 2.1 22 23 24 25 26 27 28 29 30 tain T otal . .----~--- Skagerak 1 1 (1) .

-

Egersund B'I 3 1 1 1 1 Coral B. (3)(1)(1)(1) (1) Shetland Uncertain 3 1

- - ----.-- -

Total 3 1 1 4 1 1 2 (3)(1)(1)(1) (1) (1)

-

~~~.~-~---.~--~~.-.~--~----.. -~---~.~---~~.--..

.'~,"-

-_

....

_---_._--- --- . -

.. 1 (1)

- ----

1 (1)

-

2 (2) 1

-

~~"- 2 1

(2) -

1---'

-

^{2 (1)}

⁹ (9)

1 (1) ( f" ::> f-,._ 1 (1 7 1)

Liberation

1

11

11

11

I1

2

!I

!I

JI

11

1 and 2

arranged according to area and month after release.

The figures in brackets ar.e number of tags re- covered at Norwegian plants equipped with magnets

! I

Area ^t 1965

I

t

¹

!

Skagerak

jll

i (6) Egersund B.J

I

Coral B. ¹ !

i i

j

!

I

^{Shetland I !}

I ,

i

Uncertain ⁱ 3

I

1

(1)

Total

\14

(7)

I

^Skagerak

I ~

! I

I

^Egersund

B·,I

t Coral B.

I

I

^Shetland

^I

Uncertain

I

⁴

f I

I ^Total

11:

I

t

^{Gr~:d total} 125

_I

(7)

2

1

-

1

(1)

2 (l)

3 (1)

1 (1)

1

....

:>

(2) 7 (3)

Month after release

I

_I

I !

I

I

I

I

3

2

(2)

2

-

4

(2)

3 (3)

1 -1 (3)

!

8

!

⁽⁵⁾

4 5

1 2

(1) -

1 2

(1)

-

1 1

1 8

2 9

3 11

(1)

1966

6

7

6 8

(6) (7)

6 8

(6) (7)

2

1 14

Cl) (14)

1 1

4 15

(1) (14)

10 23

(7) (21)

8

I

_Total

12

(6)

32 49

(30) (46)

8 8

(7) (7)

6

14

( 6) (8)

L16

I

⁸³

(in)

I

^{( 67)}

!

₁₄

(1)

16 35

(16) (35)

1

_- I

I ¹⁸

17

I

⁶⁷

(16) (36)

63

150

(62) (103)

Factory No.

---.J..-

2

12 16 31

Total Jan.

5125.0 233,7 56.4 21. 3 5436.4

Table 11. 'Quantity of herring (in tons) processed and number of returns from the

1964

experiment at Norwegian plants equipped with magnets,

15

January to

30

June

1964

Month Quantity

--- - -

Febr. March April May June (p) --_ ... 89E.5

391.5 343.1 61. 5 282.6 7102.2 567.6 199.6 546.9 27.4 534.7 2109.9 502.6 189.8 170.2 - 2346.7 3265.7 172.7 146.9 424.0 203'-2,. 8 2973.9 5773.6 --- ---- 2141.

4

927.8 1484.2 2123.7 6137.9 18251.

4

-

i~

953.7

tons derive from landings of foreign fishing boats in Norway.

r-- Et f iciency

- --

(e)

o o o o ^{.95 .94 .93} ,80

Corrected 1uantity e x p)

6747.1 * 1983.3 3037.1 4618.9 16386.4

Ret urns

6 ---

6

\--- Factory N>. Nov.

2

5439.2 3 7 12 480.8 16 618.5 18 20 31 631.4 42 Total 7169.9

Table 12.

~uantity

of herring (in tons) processed and number of returns from the 1964 experiment at Norwegian plants equipped with magnets, 1 November 1964 to 30 June 1965 --- Month ---- Dec. Jan. Febr. March April May June

-'~"'\-_---'-'

----._.,,--- ---

41L1,6. Z

6517.0 570.6 678.0 337.3 4482.3 11531. 5 2725.1 351.0 268.3 5969.8 5269.9 4671.1 680.0 300.4 1011.4 15546.3 473.5 436.0 741.5 156.8 77.2 527.2 2263.2 1249.Z 650.5 807,0 24.2 1556.9 3603.5 6127.5 511.5 511. 5 182.4 692.2 2396.2 6632.3 1062.8 2042.7 131.3 295.2 1701. 3 6043.5 1222.7 1082.0 2109.7 166.5 2641.6 12686.3 10662.7 834.4 ,---, 7091.6 18255.2 11454.1 2019.2 6251.8 26676.5 65611.2 *1602.2 tons derive from landings of foreign fishing boats in Norway.

Quan

(p)

,---- 3370 93 274 515 146 1092

112

3120 83 14452 9.5

---

- Effici - Corrected ency quantity Returns (e) exp ---- --

'---~

0.95 32017.0* 1 0.81 7544.5 - 0.80 21983.3 - 0.94 4846.8 - 0.93 13612.7 - 0.87 9506.1 - 0.86 9698.0 - 0.80 2496.2. 3 - 0.72 600.8

~ -

124771.5 1 - .. -

___ J.i[ Faot _, EfLI Corr No _ (e) Quan 1

1 0.93

2 I

0.95 3 0,81 7 0.80 12 0.94 16 0.93 18 1 0.87 20 1 0.86

31

J

0.80

42 0.72 --- -_.

(exp

255 418 142 204 43 57 49 58 179 11 - ---

{Lye m b~ _______

•

Heturns

t. m-;

Lib~ ) 1

2 ._._- _._-_.- --- 7.0 7.0 3 2.1 9.1 2.4 3.1

1

2.6

1

2.3 6.3 1 5.8

1 ---_.

---

Total

1420 7.7 7

Table

13.

Quantity of herring (in tons) prooessed and number of returns from the

1965

experiment at Norwegian plants equipped with magnets1 1 November

1965

to

,..---_.-...-

__ Dj3oem er _. __ Corr. Returns Quant. Lib. IJi b. (exp)

1 2

(---i---

---- 130.6

1 2

375.2 6.8

~---,.. ...

-

'"

512.6

1

2

30

June

1966

---~--- _<L.§"ll1!.fgJL ___ . __ orr. Returns uant. Lib.

hlb;

exp) 1 2

Februar Corr. Returns Quant. Lib. L~

b

(exp) 1 2

- ... ---.----1----1---- 534.71 1 3 116.41 2 34.0 326.0 198.2 165.3 47.8 26.2 79.2 5.3

1 .---~-"-_l----__+__---.

446.0 12

3

87.1 1 1

-,---_

..

_---_._-

Maroh .

--- ---.----

Corr. Returns Quant. Ili b, Lib. (exp)

1 2

1---(----

124.8 129,5

9~0 -

-- 263.3 ---

_ " ______ L _____ .L.-___ L ~ ____ " _

- _._'----

---....---~---.

--

... ~ __ Ap~il __ ~_ay __ _ orr'l Returns' Corr. returns uant. Lib.

J.Jib,"'

Quant. Lib~ltib. exp) 1 2 (exp) 1 2 ,--

--

51. 911

31.4 5 62 •

.8

210.5 38.1 33.2 23.3

1

4066.1

I

3 4781.611 941.5 4498,61

1

962.9 3030,31 2 1914.7 2898,0 4407.4

3

5 4

I June Corr. Qua.nt, (exp)

Returns Llb'l Lib. 1 2 4---+----

7816.3 9 9279.7 6 1590.1 2 5852,

~

3

1361.9

3713

.1

2 2873.7 2 44·53,4 4 6629.1 4 1621,21 2 I

⁶

⁵

¹

2 235.7 ---1----1--- .. -

_""'--" ___ -..-.w __

51 .2

!

6

1

27736.8

1 7 2

44726.6 1 34 14

L ____ ' ___ _

Dimension of

tag

(mm)

15x2xO.5 20x3xl Total

Liberation 1

11

2

11

11

Experiment

1964 (lib. 1) 1965 (lib. 1)

11 (lib.

2)

internal steel tags in the tank experiment

Length in cm

I _,

l~Total

13 .5 14 .5 15 .5 16 .5 17 .5 18 .5

1 5 10 6 14 4 40

1 3 17 14 15 4 3 2 2 2

I _.

^{, 63}

1 5 10 7 17 21 14 15 4 3 2 2 2 1103

!

Table 15. Number of herring tagged and tags returned separated according to taggers (1965 experiment)

Tagger 1 2 1 2 3

Number tagged 850

850 750 750 300

Returns

I

Rate of recapture

(<7;)

46

39 20 18 7

5.41 4.59 2.67 2.40 2.33

Table 16. Number of returns from the first and second half of the tagged batch of each liberation

N~unber of returns Number of returns

from the first half troIn the second half Total of the tagged batch of t..he tagged batch

9 6 15

42 43 85

35 32 67