CM_1977_H_17.pdf (772.6Kb)

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.=t;,e ~ Y I ++

t:i!~· "·~·"Ii1/~'rl'(I."'/ e ^~ ~z, I~"!'. ^. ,'II . ,. tllt'vilt"?, ^f! ^gJ

:rhis :e~l?~r not to be cited without :erior reference to'JtWei:lut~

International Council for

the Ex;ploration of the Sea c;:.M.1977/B:17

Pdagic~Flsh (North~rn) Committee

Ref. Pelagic Fish (S) CHee

Spawning, egg production and stock size of ma,ckerd (Scombe;r scombru~ L.) in the North S~a 1968-1975,

INTRODU C

TION

By

Svein Arnholt Iv~rsen

Institute of Marine Research Bergen, Norway

c

Mackerel in the North Se;;t st~rts spawninl5 in late May.

Jt

is a so- Falled serial spawner, with continuous development of oocytes through- out the spawning season (MACER 1976), which USQ.a.lly ends in late July.

'rho Institute of Marine Research started a sampling prog:t:'amme for mackerel eggs and larvCl-e in the North Sea in the summ~r 1968 and has been carried out each summer since. T}:le intentions behind this investigation were:

1) To delineate the exact spawning area 2) To see if the nUD;1bers of mackerel eggs

found during a single coverage of the spawning area cO',lld be use~ to give a proper estimate of the parent stock.

IVERSEN (1973) gives the distributions of macl~erel eggs both hori-

~ontally and vertically and an estimate of numbers of mackerel eggs in the North Sea north of 57 oN during the five yeal's frolX'). 1968-1972.

These estimates were based on a single cover<.\.ge of the area. This paper deals with some of those results and in additiqn deals with the years 1973-197r-i.

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lvlA TERIA LS AND METHODS

Fig. 1 shows statiol1 grids and Table 1 gives sampling periods, F'rorn year to year there have been some Inodifieatious of the station gri4s.

From 1968 to 1 CJ72 a J1.1c1ay net (80 ern) was used for sampling in vertical hauls horn 50 m depth to the surface. In 1970-1972 four Clarke Burnpus plankton samplers were used additionally. The sampling depths Were 0, 10, 20 and 30 in. In 1973 the sampling design was changed, anti from this year onwards only Clarke Bumpus plankton samplers were used. The depths were changed to 0, 5, 10 and 15

m.

The l'nesh

size

of the different plankton samplers was 500}l. The plankton samples were preserved in 4'10 formaldehyde.

The volumes of the samples were rneasured in the laboratory after the cruises, and the mackerel eggs were identified and separated into two groups, those in earlY development (no visible larval embryo) and those in later development stages (with visible larval embryo).

In the first gtoup the eggs are less than two days 0ld (DANIELSSEN and IVERS:EN 1977). 'Mackerel eggs were identi:tied from descriptions given by EHlitENBAUM (i905 .. 1909), DANNEVIG (1919) and HIEMSTRA (1962),

The amount of zboplankton and llUmbers of mackerel eggs per square meter were talculated fol' each station. These amou11ts Were srnoothed out in accordanGe with the formula (a

+

2b

+

c)/4 where a, band c are the values from three following stations and b is the value to be smoothed. 'these values were plotted in charts and isolines Were drawn, The amounts 01 plankton and rnackerel eggs were then estimated by integrating the areas within the isolines, This was done by counting squares of 5 :'X .5 rnrtl drawn on a transparent plastic sheet within the lsolines and this was then multiplied with the value of the isoline. The isolines draw11 in these tharts were 5, 10, 30, .50, 60, 70, HO, 100 ilnd 1 '30 ml zooplanktol1 per square meter st11'f.:lce ~l.1·E'a

and S, 10, 26, '30, 501 80, 100, 200, :300, 400, SOO, 600, 700, 800,

1000; 1200, 1400, 16dO, 1800. 2000 mackerel eggs Pt'!' squ~lrr' l1WtVl'

SUrf;'tCI! arell. In the chat'ts presl'lItNi here SOlne isolill(,S an' L1mittt·d

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-

^~

-

;R:g;SU

LTS

A NO

DISC;lJSS~ON

Th~ verti;;:al di$t;db1-J,tiOl1 ~£ Utf'l mack-erel ~~~~ is \i!hpwn in Fig.~.'·

A!i?

Sfw

^wnhere only few ~naj.'.;k~r·e1 eggs are fqund pe~QW +5 rn, and

then~ is ~lP s~gni£:i.ca~lt di£f~:rff,IHte ~rl' th~ vt'l:rtiG~l ~H~triqt+tip~ of t;lgglii with

'i-nQ. with<::>ut

embryos. ~n accq:uq~nGe with

this,

tll!;! $~ml?1ing

desigfl was ~hangep, ip 1973 to ~aJmple in

t4f;l

\lprC;l:rmo~t 15 rp of

qle

'fVate:r cohp;nn. Over 900/0 pi the ~gg~ W€1re tp.+<~n in the uppel,1most 121'13 m (Fig. ~).

'J;he you.\1~est eg~s (tho~e wHhQut visible emg1"YQIil) have proPp.bly not drifted £p'r awi,'l;y horn

tll/;!

spaV)'p,:j,ng locatiort.

These

i1g~1:I were

uSE!Q.

to indicate thE! ~Rq..wning al'eft d\lring tlte Cfv,.isea ~968,d~75 as shown in ]figs.

4-11.

The ~Ustributi.ona derp,qnst:t1A-te that int) Nortr Sea stock is

sep<=l-;pated

fro.q'l. th~ st(!H~k west of th~ Bl1iti~h hlel'l q.t

tlw qm.e

of

spawning. Tre most impol.1tan^t sP?lrW.J.1,:j,.qg jil,refl. i~ th!l'l qentral, an~

sQ~thernmp!;)t paJit pf

the

North Sfl~, "rlr~ spawning alon$

the

G9a l't

I

is pmiiLU C;:Qm:pal,"l"I~ ~9 th~ ip.t<;rur;;e

spaw4irg

£U:)fthre1! out

in

the p~PJl'Prl

pallt

of

the

North Sli(a. Th~

Ekonsh

;;qiea se~mfi

t.oqe

M~tY importfi;l..nt as ~ ~pawning locaHty . .As l'~en from th(;j. egg di~~11~b4Uon (fharts, only

the

nQrthern, paxt

at

~h~ ~paw,ning

ftrea

was cov~rep, untU 197~.

F;\.g~.

9,

10

a,nd

11 show that the

area

~Q\,j.th 9£

SrN ilil very

iinpcn:tCJ.nt for Elpawring. lE 1975 t1:).e ~overage of

the

area nO:J,'th of ⁵⁷ON W<;I.S not cqmplete (Fig. 11). T~e distrihution~ of rpfJ.cl}erel egg~

the

\ast two

yep.~l."E/ (Figs. 1 C) p..l1:\.d P) indicate that S9rne s~awntn~ takes r~ace :;>outh of 515

ON. fIowever,

~he rel1!uHs pre!3ented he;r;~

!:'+H4 t,n JOHNSPW

a.n~

DAWSON (1975) show that the ma,.i.l'l filpawning area fOlf mackef e1

19

north pf SII)'N.

The spa.wning in Skagel'ral~ dur\ng thesf;1 yea,rs ip al~o r~la·tiv~l¥ sr-naIl compared t~) the area i't.\rth\H west, Th!':1 cOl)~entllE\tiQl'l pi m a\J1,<e

r

^e1

egg~ in thi s area i$ higrel' along tre ~p'rwegi<\1\ C0a.~t th~qlf:1.~Qn~ ~he DilPish coast.

The distrd)l.ltlon nC I'jQQplnnkton f<H' the yt':/:lt'S ~qGB·rl97~ \l;> shj,)wl) in F'i (.! s , ^l;~, 1 () , Tit ^f·^~j(' d i r.;t rib ^\I^ti () n s n re Oil !:i(;' f,l \t po n pI î\^f)Î~t n Î) ^Sⁱⁿⁿpt (' ^S

t:tl~H\ bv J'l(hy 11ft (HO ern).

Tho

Inp,rl~~'rrl. which is i\ znpp~;)nkt\lll

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feeder, feeds during the spawn~ng p~riod.

The

di~triQl.ltiqn qf mackerel eggs (Figs. 4-8) and the distribuUoJ1 of zooplanktol1 the /3ame y~ars

(Figs. 12-16) demonstrate that th~ mack\"lre1 spawn in areas wh~~e

they can feed.

The mean surface temperature in the spawning area during

the

qiffer~nt

years varies from 11. 3°C in 1971 to 14.5°0 in 1969 (Tap1~

2).

It is known that the mackerel spawns in wqters w~th teFPpelf'fl:t\.J.re S 12⁰-13 ⁰~

and higher (OR TON 1920). JOHANSEN (925) £o\l.Qd that the spawning in the middle ar)'d noxthern pp-,rt of the North

Sea

t90k pla<;e ~t 11 ^p- 14°C in June and at 13°-17°C in July. As shown in Table :3 the quantity of zooplankton in 1969 was the Mghest d,q.ring the period 1968-1972. The 1969 year-class of

the

North SeC\. mackerel il:1 very strong, in fact the best in several ye;;tl.'sr Thl,3 yearT"Cla~S~R from th~

following years are pool!'. The tot:;l..1 .\J.'Ilmper qf mackerel eggs found dl.,lring cruises in the different years ('l'able4) shqw~ ~h/il.t ~he l1uml;>~H

foun4 in 1969 was not pal'ticul<p1y high. Un£ortq.nf;l.tely, ol'l.ly the

northern part of the spawning areC). was ![;Qver~d Q.uring the H:rE1t years, including 1969. If eggs found north of SrN are UIHHl al'i an index; fof' the total egg production, the proportion of the tpi;:tf;::k;~:t;'~l

atoek

spawning here m\;l.st be constant every year. A. .p;l.Ore $o-y.thern spavyning one

yea;r among the otherfi will l1esult i.p. an '\,lnqer\::lf;!Umaf~d tnde::x:: The spawning activity at the time of the Cove;r;;;tge of the sl?awning ;:l.l;ea will also affect this estimate. The i~1de4: m:J.I:p.bel' of e~gs without visible larval embryos/m,lmber of eggs with and withq~t vj,s~bl~

larval embryos (Taple 4) can be u$ed al;)

an

indiGation of spawn~ng

activity;, a low index ;means that the investiga,.tiQn

that

particular year has been carried out 1a,.te in the spawning season. 'rhi13 w~F,I the caSf;:l in 1968 al'ld 1969 (Table 4).

A ccording to data collected QY the Instit\,l.te of Marine Re/3earch (unpublished)' the mackerel spawning set;lrns to la~t for 30 ~ay~, and the spawning activity seems to be more or le~s the same all thuough this period.

If the rlf<lckerel eggs without vifli1:;>le amPl'YQI3 are, on a,.vfl:rilgl'l, pne day old, tllf~n the estimated amount of eggs without viliible empl'Yps

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- 5 -

in the covered area is 1/30 of total production of nlacl,erel egg~

during the spawning period. In 1974 55% of the total egg aQ'lQunt was found south of 57°N (Table 4). In 1972, according to data in;

Table 4 and JOHNSON and DAWSON (1975), this proporti9n Wl'l-S

again 550/0. In general, 500/0 of the eggs seexn to be spawned south and 500/0 north of 57 oN. The total estimated amQun,t of eggs produced in the North Sea <;luring the spawnhlg season (30 <;lq,ys) is showp. in 'Table 5. An estin'late of the size of the spawning stock c<:l.n be made from data on weight and fecundity. Two estimates welie made, the first by using the mean length and weight of rnCl-ckerel three year!'!

of age and older caught in the Norwegian purse seine fishery in the autumn of the years referred to. This data, however, do not give a

<::orrect fish size at spawning because a large increase i~, weight is gained in the early autumn (CASTELLO and HAMRE 1969). In the other estimate therefore, the mean weight of the fish the qutumn ' before the spawning has been used, The feoundities \.).sed are thosE1

estimated by the formula y

=

^{7.602 x} ^~45510given by MACER (1976) where y is the fecundity and x iE! the cube of the length. The results are shown in Table 5. DA NIELSSEN and IVE;R$EN (1977) observed an average mortality of about 100/0 in mackerel eggf? the Hrst day after spawning at 12 ° C. The size of the spawn~ng ptock (T;;tb~e 5) has been raised accordingly.

The stock as estimated from egg observations in 1968, 19\59 ;;l.nd 1970 is much lower than the size the sto<::k estil'l,'lq..ted by tagging

experiments.

.,

Years 1968 1969 1970 1971 1972 1973 1974 Size of tagging

1. 50 1.20 0.51 0.41 1. 25 1. 30 1.

00

spawning experiments

stock egg data

x10 -6 tons (Table 5)

O.

39 O. 17 0.18 0.62 1.51 1. 44 0.94

1975 0.80

1. 32

The stock estimates from tagging include mackerd two years of agl"

and older. and give the size at the beginning of the year (ANON lQ77).

A s mentioned earlier the estimation of the egg nprpbers in 19q8 and 1969 W<lS carried out too late in the spawning seaapn to give a propel'

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estimate. The estlrnate in 1970 is probably underestirpated because of the coverage of the spawning area. This year there was lesser 2;OO~

planl~ton north of SrN (Table 4) than the other years, and maybec~ this independent types of estimates a·re in relatively good aCGor<;J,ance with each other. The best years are 1972, 1973 and 1974. By including data for 1972 from JOHNSON and DAWSQN (1975) these c;tve the thr.ee years with the most comprehensive covel'c;tge of the spawning area.

SUMMARY

1. This paper deals with mackerel eggs and zpoplankton data in the North Sea and some years in Skagerrak in 1968-1975 during the summer.

2. The mackerel eggs are distributed in the upper layer of the water column. Over 90% of the eggs are found in the upper

12~13

m.

3. The most important spawning area is located in the c€lntra1 part of the North Sea. The spawning along the coasts both in Skagerrak and the North Sea is scarce. GeneraUy it seems in normal years that about 50% of the spawning takes place north and 5010 south of 57°N.

4:.

The mean temperature in the covered part of the spawning area varies between 11. 3°C in 1971 and 14.5^QC in 1969.

5. The 1969 mackerel year - class is a very strong one, and this is a favourable year both in zoopla.t;lkton- and temperature conditions.

6.

The estimates of the size of the spawning stock by ~gg prod\.lction and tagging experiments give more or less the same results. This is true when there is a prope r coverage of the spawning a rea and the investigations is not carried out too late in the spawning

period.

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~ 7 -

REFERENCES

ANON. 1977. Ressursoversikt for 1977. Fisken og Havet, saernummer 1977. 97 pp.

GASTELLO, J. P. and HAMRE, J. 1969. Age and growth of

mackerel from Skagerak and the nQ:rthe~'n North Sea.

Coun. Meet. into Coun. Explor. Sea, 1969 (H:7): 1-12,

.

^.

4 tabs., 4 figs. [Mimeo] .

DANIELSSEN, D. S. and IVERSEN, S. A. 1977. Tem:per<;l.turens innvirkning pa utviklingen av naturlig og :klln~tig

befruktete makrellegg (Scomber scombrus L.)

, , i

Fisken og Havet Ser. B, 1977 (2): 1-17

Et!RENBAUM, E. 1905-09. Eier und Larven von Fischen des Nordischen Planktons. Nord. Plankton, 1: 1-396.

BIEMSTRA, W. H. 1962. A correlation table as an aid for i<;len~i

fying pelagic fish eggs in plankton sampll'ls. J. cons.

perm. into Explor. Mer. 27: 100-108.

IVERSEN, S. A. 1973. Utbredelse og mengde av makrellegg ($cor,nber

i " ,

scombrus L.) og zooplankton i Skagel,'rak og fl,ordlige del av Nordsj~en i arene 1968 .... 1972. The~is, Un~v.

i i f

Bergen. 71

FP.

[Mimeo].

JOHANSEN,

A.

C. 19,25. On the influence of the currentli! upop the frequency of the mackerel in the Kattegat and in

adjacent parts of the Skagerak. Medd. Kornrn, Havu~1<;le:r s.

i ' i

Ser. Fisk. 7(8): 1-26.

JOHNSON, P. O. and DAWSON, W.A. 1975. The di$tril;>ut~op of eggs and larvae of some pelagic fish species il~ the central and southern North Sea during June 1974,. COUD. Meet,

if"

int.Coun.Exp1or.Sea. i975 (BD): 1-23.2 tabs, l2 figs.

l

^Mimeo^'.1

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MACER, C. T. 1976. Observations On the maturity and fecundity of Iuackere1 (Scomber scombrus L.). Coun. MeGt. int.

Coun. Explor. Sea, 1976 (H 6): 1-7, 1 tab., 3 figs.,;

[Mimeo

J .

OR TON, J. H. 1920. Sea temperature, breeding and distribl,ltions in marine animals. Mar. Biol.Ass. J. n. s. ~2(~):

339-366.

i

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Table 1 Time and area investigated the different years.

THE NOR TH SEA S:KAGERRAI\

Year Time 57°N-60045'N 56°-5rN 55°_56°N

1968 17 June - 5 July Yes No No

1971 6 June - 25 June Yes No No

1973 30 May - 18 June Yes Yes No

1974 25 May - 11 July Yes Yes Yes

1975 1 1 J un e - 1 1 J ul y Yes Yes Yes

Table 2 The estimated numbers of mackerel eggs (including both the developmental stages) in the area the different years.

"-.

'.~rea 55- 56- S7-

"'{e3.r ~, 56 ; :\~ 57' ~r S8 ~N

:963 591

1969 643

1970 156

1 en ¹ ⁴⁷⁸

1 'j72 1121

1973

-

¹¹⁹⁹ ¹⁰⁷⁷

1174 516 H7 1:i41

1 rJ I~ ~ 422 456 930

Numbers og egg x 10 -10

THE NORTH SEA

58- 59- 60-

59'01 60':-1 60'45 ':-I

139 I I I 27

51 9 0

53 14 1

139 56 4

170 31 4

S9 20 17

181 16 3

J 10 18 9

SKAOERRAI<

55- 56- 57-

60'45'N 60'45'N 60'45'N

- -

⁸⁶⁸

^-

-

^- ⁷⁰³ ⁹³

- ^-

²²⁴ ¹⁴

- ^-

⁶⁷⁷ ¹⁰

- -

¹³²⁶ ¹⁸

-

²³⁷² ¹¹⁷³ ¹³

2306 1788 1041 58

2491 2069 J 113

-

No Yes Yes Yes Yes Yes Yes No

index 01 spa\vning_

activIty 0.21 0.11 0, ,10

0, .H

0, :; 3 0,:;';

0, ·13 0.37

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Table 3 The rnean surface temperature in the n1.ackerel spawning area.

Year

11968~~_

¹⁹⁷¹ ¹⁹⁷²

~

¹⁹⁷⁴ ¹⁹⁷⁵

Toe

~114.

⁵

r~-

^{11. 3} 12.8 /12.3 14.0 liT 7

Table 4 The estimated biomass of ZiQoplankton in

.rp~

x 10- 3 based on a single covel'age of the area.

THE NORTH SEA

Year 57-58°N 58-59 oN 59-60 oN 60-60⁰45'N 57-60⁰45'N

1968 640 360 310 230 1540

1969 2730 1660 1310 510 8210

1970 660 230 270 120 1280

1971 740 830 300 180 2050

1972 970 450 790 330 2540

___ ~_·T

S;KAGERRAK

-

23 27 6 12

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Year 1%8 1 <:16-9 1970 1971 1972 1913 1974 1975

Table 5. The estimated total production of mackerel eggs in the North Sea and the size of the spawning sto,ck from 1968 to 1975. 1 1 1 !Total number Mean length of Total number Adjusted for Spawning stock of male and fe-Size 6f 10';1aegg from tagging I of eggs spawning fish Mean weight Fecundity male spawners spawning stock mortality experiments ! j x IO-ID kg x10-1D x10-6 -6 xlO-"6 tons xH)-6 cm xlO tons I

j

1) 28-0. D j 35.2 D.41 8413.8 0.35 O. 313 12 152 1.5

1

' 2) 37~ 1 0.48 342.6 709.4 0.34 0.38 1) 38.3 0.52 386. :() 266.9 0.14 0.16 5 152 1.2 2) 35.2 "0.41 28o.D 3{,O.3 D.15 0.17 1 1) 39.5 0.56 4~3. 0 28-2.4 D.lo 0.18 , 5 972 0.51 2) 38.3 D.52 386. €I 309.4 Q.16 0.18 ] I) 35.9 0.45 3:0"6.2 1 297.1 0.58 0.64 19 85S 0.41 2) 3<:1.5 0.5-6 423. {) 93S.~ 0.53 11.59 . 1) 35.0 0.4"0 280.4 3 341. 5 1. 34 1. 49 46848 1. 25 2) 35.9 0.45 300.2 3 DbO.O 1.38 1. 51 - 1j 36.1 0.45 312.1 29D6.0 1.31 1.45 45 348 1. 30 2} 35.0 -0.40 28:0.4 3 234.5 1.29 1. 43 1j 36.7 0.46 33D.2 1 S07. 2 0.-83 D.92 -29 837 1.D 2) 36.1 0.45 3-12.1 1 <:I12.Q ~ 0.86 '0_ 95 1) -37.4 a.50 352.1 2 402.1 L26 1. 33 42 289 -O. SD 2) 3-6_ 7 0.46 33-D.2 2-561. 4 1.17 1. 30 2) Data from the autumn the previous year

-- -

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The main station grids, From. y~a1" t(!) year there has bee.Q, slight rr).odifj,Gat i9ns.

2

The vertical q}stribution p£ mackerel eggs .0 the upper 35 m of the water column,

1) Eggs with put visible larval ernbrYQ$

2) E;ggs with vl.sibl~~ larval embryos.

(13)

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7.5

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vertical diatdbuti<;>n

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