CM_1970_H_05.pdf (467.2Kb)

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International Council for the

TIb:;:plor"d.tion o,r the Sea ^CoN" 1970/H:5

Pelagic Fish (NorthelY!) C~ittee

Age, Growth, Reproduction,and Feeding of Eenthosema glaciale (YJyctophid.ae) from '\oJestern Norway

by

Jakob Gj0s@terx)

Introduc:.li.2.u

Benthosema ^gla~ial~ (Reinhardt,

1837)

is the most common member of the Myctophidae in the North Atlantic and the Norwegian Sea. It is mesopelagic, and most records are from areas outside the 400 m depth contour, or from fjords where the depth is 300 - 500 m or more (Johnsen,

1922).

A diurnal vertical migration is shown to occur ( Halli day,

1970)"

This paper gives some preliminary results from an investigation on Benthose~a glaciaJ,e from Byfjorden in the Bergen area, western Norway.

Material and methoq§

The main part of the material was collected in 1969 by R/V ttFri tjof Nansen" of the Biological Station,

University 'of Bergen. A collection of ~ glaciale

taken during investigations on euphausiids in 1967 and

1968

was also placed at my disposal by Dr. Kr.Fr.Wiborg.

:z:) Institute of JvIarine Research, Eergen, and

Biological Station, University of Bergen.

11

..

I"lost of the fish were collected bymlsaacs-Kidd three-foot midwater trawl, but a Beyer low speed midwater trawl with an

opening about 1 m2 was also used.

standard length was measured to the nearest 0.5 mm.

The fish collected in 1969 were measured immediately after captures and then preserved in about 4

%

formalin. The otoliths were removed within a few hours. Fish from 1967 and 1968 were preserved in formalin and measured in this condition. To make these length measurements comparable, the formula lfresh= 1.050 lpres.- 0.574 was used.

otoliths were used for aging. They were placed in absolute alcohol, transfered to creosote, mounted in

Canadabalsam or Eukitt, and viewed by binocular microscope using reflected light. Age w,as determined by counting the hyaline zones.

To confirm the assumption that the zones were laid down annually, record was kept of the seasonal formation of the

edge zones. On some otoliths a gradual transition from opaque to hyaline zones and vice versa was observed. In these

cases the character of the rand zone was often difficult to claSSify, and they were noted as ttundetermined^tf•

The hyaline zones were mainly laid down in summer and the opaque in winter. (Fig. 1)

As an additional check on the age determination, the age groups were compared to the peaks in the length-frequency distribution, and a good correspondence was fQund.

The material from, 1967 and 1968 was preserved in formalin, and the otoliths were partly dissolved.

Therefore, only the 0- and I-groups which could be aged from their lengths, were used in the growth calculation.

I I I

In Fig. 2 is shown the age distribution of ].! .£~ial~

collected in 1969. Calculated from these data, the

estimated average annual mortality in the 1-, 11-, III-, and IV-groups are about 70%. But as the number of specimens included in the calculation is small, and little is known about the selectivity of the gear, this estimate is

probahly not vf$ry reliable.

Fig.

3

showa the mean length and standard deviation for the months when data were available. Data from 1967, 1968, and 1969 are combined, as the difference in growth between years seemsto be small. Halliday (1970) showed that there. is no sexual dimorphism in growth, both sexes are therefore combined.

The constants of the von Bertalanffy growth equation were determined by graphical methods (Ricker, 1958). To make the results easily comparable to those of Halliday (1970), age was calculated from 1 April.

The resulting equation was:

It ^=: 74.0 (1 - exp[-0.46(t + O.(5)J) This is shown graphically on Fig. 3.

In the Nova Scotia area Halliday (1970), who also used otoliths for age determination, found:

It = 68.28 (1 - exp[ -0.36(t + 0.49)] ) based on measurements from preserved specimens.

L~ may be converted to fresh length by using the formula

lfr~sh= 1.050 lpres. - 0.574. This gives L~ ^=: 71.14 while K and to are not altered.

This indicate that ~ glacial~ grows faster and att8~ns a slightly greater size in the Bergen area than off Nova

Scotia. The latter conclu~ion is also supported by the fact

IV

that the largest specimens in Hallidayt s material w¹ere

67

and

68

mm (converted to fresh length

69.8

^&~d

70.8

mm)"

Iv-hile the largest in my collection were 72 and 77 rom.

An equally high or higher maximum length is , recorded froG other Norwegian fjords (Bernhoft--Osa, 1935 ; Lid, 1967 ; Gj0Sffiter, unpubl.).

Reproductiog

The maturity of the gonads was classified according to a scale from

1

to

5,

where,1 is immature and

5

spent.

The scale is based on macroscopic characters, and for the females also on egg-diameter measurements. The resulting figures are presented in Table 1.

(p.

VIII).

The spawning probably occur between f;lay and July.

Juveniles were found from September, when they had reached a length of ,15 - 16 mm. Smaller specimens \.>lere not found, probably because they were not caught by the net.

Specimens 9.5 - 14.0 mm in length have previously been caught in the Bergen area

m

September (Johnsen,

1944).

Off Nova Scotia post-larvae are found in Nay and July (Halliday,

1970),

and off Icela~d larvae and post-larvae are talcen i Nay, June, and August (Hagnusson, Magnusson and Halgrimsson, 1965; Hagnusson, 1966).

This may indicate a somewhat later spawning period in western 1:Torway than in the other areas.

A part of the population in Byfjorden spawns at age 2 and probably all at age 3 and subsequent ages. The same is found by Ha11iday

(1970)

off NOva Scotia.

Eggs were counted in 19 specimens. The results are shown in Fig.

4.

From these data the regression line

19 N = 3.18 Ig 1 - 2.74

was calculated (N is number of eggs and 1 standard length in mm.)

v

~.

The stomach contents were studied in about 400 specimens ..

The fullness was classified according to the following scale (Lie~ 1961):

o

^empty

1 very little contents 2 some contents

3 full

4 expanded stomach

The mean fullness in the different seasons were:

spring (March - May) summer (June - Aug.) autumn (Sept.- Nov.) winter (Des.- Febr.)

2.35

2.16 1.69 1.68

15

%

of the fishes had empty stomacbs~ Thi s may in part be due to a regurgitation of the food as they were

captured. Therefore, the figures indicating mea~ fullness are minimum values only.

The degree of fullness through the year is gmven in Fig. 5~

showing that B. Elg£iale feed all the year, but most through spring and summer.

Fish with food in their stomachs were found both day and night, but the highest values for mean fullness occ'l.lXTed in the first hours after sunset. The contents were also least digested in fishes taken at this time.

In the stomachs Copepoda and Euphausiacea were found.

Representati ves of other groups ,,'ere not found, but many stomachs had conten~ too much digested for identification.

Euphausiacea were most common in fish· of age 3 and 4.

Table 2 gives the frequency of occurrence. of the main food groups. (Table 2. see page VIII).

VI

Su~ar:z::

Ben!hose~ ~le from western Norway attains a maximum age of at least five years and a maximum length of about 75 mm. The grovrth is a little faster than in the north- western Atlantic.

Spawning occurs between May and July. Part of the popula.tion spawns for the first time a.t age 2 and all at subsequent ages. f.1ean egg count is about 800.

~hosema feed all the year, but most through spring

and summer. The main food is copepods, but much euphausiid3 are also eaten.

VII I:@ference§.

Bernhoft - Osa, A. 1935. Bidrag til Rogalands fiskefauna.

Stave .Nus .. Arb. l2.22~

:

75 - 109

Halliday, R. G. 1970. Growth and vertical distribution of glacier lanternfish, Benthosema£laciale, in the northwestern Atlantic. J. Fish. Res. ^Bd~~

:a.. :

^{105 - 116}

Johnsen, S.; 1923. Remarks on ·the distribution and the biologi of MyctoEhum, glaciale (Reinh.). Berge~

JIus • ..lrb. 1921 -22 (6): 1 - 50, 1 pI.

1944. Studies on variation in fish in North - EUropean waters. I. Variation in size. Bergen

!:ills

Ar~ 1244 (4): 1 - 129

Lid, G. 1967. Fiskeobservasjoner fra rekefeltene i Oslofjordens indre del. Fauna~~

gQ :

96 - 106

Lie, U. 1961. On the growth and food of 0 - group coalfish,

£Ql!achius ~!!§. in Norwegian 'Iw.ters. Sarsia

2:

^{1 -} 36 Magnusson, J. 1966. On capelin larvae (Mallotus villosus

O.F.Muller) in Icelandic waters during the years 1960 - 1964, with some notes on other fish larvae.

E!1_fiskideildar~

(4):

1 ~ 35

Magnusson, J., J. r1agnusson and J. Hallgrimsson. 1965. The ItEgir" redfish larvae expedition to the Irminger Sea in May 1961. Rit fiskideildar

1

(2): 1 - 86 Ricker,

w.

E. 1958. Handbook of computation for bi21.Q.gi.£gl

statistics of f~sh populations. Bull. Fish. Res.

Bd. Canada 119. 300 pp.

VIII

Table 1 - - -

fiTaturity of Benthos~ of age

2, 3,

and

4.

r,laturi ty Janl' Oct"

stage Febr. March April May July Sept. Nov.

Des.

1 9

3

1 5

2 10

3

2

3

5 7

3

15 6 5 ¹

3

4 2

10

5 ¹

3

19 1

Total

34

¹² 9 15

3

25 16

;Iallu

stomach contents.. Frequency of occurrence.

Spring Summer Autumn Winter Total

Copepods 59

72 32

19 182

Euphausiids

3

⁰

18

12

33

Undetermined

21 7

55

30 113

No. of stom.

examined

I

91

86

119

80 376

% tOO 90 80 70 60 50 40 30 20 10 3 5 AND 6 MONTH

7 FIGURE 1. DISTRIBUTION OF THE MARGINAL CHAHACTER OF THE OTOLITHS. 1: HYALINE 2: UNDErERMINED 3: OPAQUE

9

0

1

~2

3 10 11 12

250

200

150

J-

:r

100

(!)

:>

«

u

d z

50

o

11 III IV

v

AGE GROUP

FIGURE 2. AGE DISTRIJ3UTION OF BENTHOSEMA. COLL:EDTED IN 1969.

MM 70 60 50 ~40 ~ ~ 20-1 10J

+

1

0

t 1X

1 I I 12 1 6 12 1

GROWTH CURVE OF lIENTl!osmA. HORIZONTAL IIAI1XS I OBSERVED MEAl! IJlNGIl.'JIS VERTICAL LINES I TIIO STAIIDAlU> DEVIATIONS. AGE GROUP 11 I III IV I I • I 6 12 1 6 1'2 1 6 12 MONTH

2000 1500 1200

fII

1000 .. 900

(J)

800

(!)

ill 700

LL

600

0

d z 500 400

FIGURE 4. RELATION BEIl'WEEN STANDARD LENGTH AND EXm eoUNI'. It

300 45 50 55 50 55 70 75

80 LENGTH IN MM

0/0 100

90 ..,

111 ~ !) Q

III e Q Q G /i:I ~ G

& '0 VI Il ^{: : : 0 :}

80 -1

^{" ,,01 Cl}

0. ( i I " il

..

~ er. III I)

1!1 0 , e

" • G a " Co 0. !) ^{' G e "}

" Cl I) G

I) 0 c (\'

, '

.

" 0 Qt. Oi) , a c 0-

I) Q ~ ;"

...

. : : : I

^{Cl '}

^..

^{Cl 0.}

^·

^{I) GC! & 01).}

D

70 i

~

... .

^{, ' ' 1:1 S I) 0 G}

⁰

I' ...

^{G " {I G} 0<: , . 0.

t/O 00 (l • , c e 0 ^l1li 41

c.

^III

• Q G 0 D (I e e ' 38 11 11 I)

£I <$ e Q " " 0 0

·

^{G Cl Cl (I 0 ~ " .. 0 0.}

e " I l l I)

10'1 G G €I

r' '.

^{(I I)} & l1li

@ t. G : • o • •

'I r' . ·

50 -i

~

r:: :

^: ®e : : : I ^{• 0 e la}

I ₁

e • " et 01 eo C IJ

• Q 1/1 oC 0: 1/1 e Cl

I ill ~ " ID

Cl " "Ill '&

.. 0 11 C!I

I) G • 11 0

·

G C III 11 0

Q "1/1 .. I) Qel! fb

Cl """ 0 • III I) 0 0

111 0 " G o e III 11 If

~

q " . III

50 1 ^§

• Q \tI '!J •

2

~

^{l1li et (\' Cl tI." e " 0}

40 1 a ^B

^IW'~ I'l"/~

§ ³

- ^{~ § 11}

30 -i

~

I 4

i I

>---'

I,

!---!J

20 -1 l::I±tt1 ~

_{i ' -} "---,1 _"

10

s ^su

FIGURE

5.

DEGREE OF FULLNESS OF STOMACHS.

SP: SPRING SU: Stl]\WlER A: AUTUM1T W: WINTER