INTERNATIONAL COUNCIL FOR TUE
EXPLORATION OF TUE SEA.
C.M. 1973/F : 36.
Demersal Fish (Northem) Committee.
DUTCU INVESTIGATIONS ON TUE DISTRIBUTION OF
PELAGIC O-GROUP GADOIDS IN TUE NORTU SEA 1973
by
Niels Daan
Netherlands Institute for Fishery Investigations,
Haringkade I, IJmuiden (Netherlands)
•
This paper not to be cited without prior reference to the author.
International Council for the
Exploration of the Sea
C.M. 1973/F : 36
Demersal Fish (Northern) Committee
DUTCH INVESTIGATIONS ON THE DISTRIBUTION OF PELAGIC O-GROUP
GADOIDS IN THE NORTH SEA IN 1973.
===========================================================
by
Niels Daan
Netherlands Institute for Fishery Investigations, Haringkade 1,
Ymuiden, The Netherlands_
Introduction
•
During the meeting of the North Sea Roundfish Working Group in Aberdeen in March
1973 the results of the pelagic O-group surveys, carried out in the North Sea
during former years by Scotland, England and the Netherlands (e.ge HISLOP, 1972;
WILLIAMS & MACDONALD, 1972; DAAN, 1972) were discussed and in view of the
promising results detailed directives were put forward for future surveys in
order to assure comparability of the results (ANON, 1973). In June-July 1973
two Dutch research vessels have taken part in these surveys; the "Willem Beukelsz"
fished a number of stations in the southern North Sea in the second half of June,
whereas the "Tridens" worked the northern part in the first half of July. The
fishing methods outlined in the Working Group report were followed except for the
fact that the rigging of the net and the süberkrüb boards used were less heavy
than they should be. During the survey the vertical opening of the net was
measured, which 'generally varied between 7-8 m. Although compnrative fishing trials
with the Scottish and English research vessels were scheduled no contact at sea
could be established.
Results
4t
In fig. 1 the numbers of O-group fish per hours fishing are given for the four
important Gadoid species (Young Saithe was completely absent). In comparison with
the 1972 survey (DAAN, 1972) especially the catches of cod and haddock were
strikingly small. Whiting was caught in significant numbers only to the northeas.t
of the Doggerbank, coinciding with the appear~~ce of jellyfishes (Cyanea capiliata
and Cyanea larmarcki, cf DAHL, 1961) which is in agreement with the results in
1972. Norway Pout was only found along the Norwegian deep, one exceptionally large
haul of 12 000 O-group fish being made at 09 00 AM. However, during this haul
accidentally the bottom was hit and, because the netsonde recording showed fish
schools right on the bottom during this period, it seems likely that Norway Pout
was aggregating very near to the bottom and should not have been caught in these
numbers, when a standard haul had been made. In the same area Norway Pout were
caught in a small beamtrawl at 09 00 PM, whereas large echo's were seen to leave
the bottom at 1000 PM and reach midwater at midnight, suggesting a marked diel
vertical migration in this speciese
Table 1 summarises the length data of the different species and comparison with
last years survey reveals that the fish were generally considerably larger. It
seems possible that the much lower apparent abundance is due to the fact that part·
of the O-group had already ended the pelagic phase.
'
Some more data on condition of these fish are presented in table 2. Generally the
values correspond to last years information, but in Norway Pout the condition was
significantly lower in 1973 th~ in 1972.
The general conclusion seems to b~ justified that there are still big problems
in'the interpretation of these surveys due to the behaviour habits of the O-group
fish and the exact timing of the surveys und there is obviously a need for more
basic information on their behaviour in this respect.
-2-
-2-
REFERENCES
, ANON., 1973.
Report of the Roundfish Working Group 1973
I.C.E.S. C.M. 1973/F
(Mimeo).
DAAN, N., 1972.
Dutch investigations on the distribution of
pelagic O-group gadoids in the Northern North
Sea in 1972. I.C.E.S. C.M. 1972/F : 8 (mimeo).
DAHL, 1961.
The association between young whiting, Gadus
merlangus and the jellyfish, Cyanea capillata.
Sarsia (3): 47-55.
HISLOP, J.R.G., 1972.
Scottish investigations on the distribution of
pelagic O-group gadoids in thc northern North Sea
in 1972. I.C.E.S. C.M. 1972/F : 43 (mimeo).
WILLIAMS, T.. , &
MACDONALD, 1972.
English investigations on the distribution of
pelagic O-group gadoids in the central North Sea
in 1972. I.C.E.S. C.M. 1972/F : 23. (mimeo).
ti.
ds
•
TABLE 1 Mean length of pelagic O-group gadoids in July 1973.
11
11
11
Range 1111 N
11
COD
SPECIES
L
S
Area.
N
all stations
combined
1972
21 3.5 1.8
1048 3.4 1.1
"11
HADDOCK
NOR\'IAY
11
11
11
11
S
Range 1111 N
S
L
L
Range 111I N
11
11
1.4 1.7-9.211 13 6.2 1.7 3.5-9.21111 807 4.3
11
11
11
1.1 1.2-7. 0 :1 966 3.0 0.9 1.4-6.6 :: 804 3.3
"11
\'lHITING
L
1.6-7.51 469
11
11
1.6-7. 8:l 565
4.9
3.1
POUT
S
Range
0.8
2.1-6.7
cm
0.8
1.6-5.8
cm
===========~==========================Ik=======================~=======================~========================
N
= number
= mean length; S = Standard deviation
measured; L
TABLE 2 Weight/Length relationshipl and conditionfactors in O-group gadoids in 1973.
11
11
11"
W
K 1111 N
L
11
11
11
11 10
11 25
1I
11 25
11
11
11 25
4.05 0.39 0.59 1111 25
11
11 25
11 25
0.6811
1.17
25
5.55
6.35 1.88 0.7311 25
11
11 25
0.8611
7.45 3.56
11 15
11
9
11
I1
5
11
1
11
11
1
H
length
class
N
2.0-2.5
2.• 5:-3.0'
3.0-3.5
3.5-4.0
4.0-4.5
4.5-5.0
5.0-5.5
5.5-6.0
6.0-6.5
6.5":7.0
7.0-7.5
7.5-8.0
8.0-8.5
8.5-9.0
9.0-9.5
1
1
2
1
TOTAL ... , .. 5.
Values
1972
N
197
I
I
I
•
I
,
f
•
I
I
.Q~7?11.?99.
1
0.68 "1 190
11
11I1
-
-
HADDOCK
H
11
11
11 N
11
11
11
2.25 0.060 0.5311
2.75 0.124 0.60 ii'
3·25 0.31 0.61 ::
3.75 0.37 0.6911
1
4,25 0.61 0.79 1111
4.75 0.83 0.77 1111
5.25 1.14 0.791111
2
5.75 1.59 0.84
1
6.. 25 1.99 0.82
1
6.75 2.53 0.82
2
0.89
3.38
7.25
0.80
7.73 3.70
8.21 4.53 0.82
8.95 5.79 0.81
1
9.25 6.06 0.77
L
11
I
11
vlHITING
COD
SPECIES
\1
. .
,
.,
,
I
I
I
I' I' .•
K
Q~75li., .~ .
11
0.781111 161
1111
'w
L
K
N
1
"
I
I
•
I
t
I
•
I
POUT
L
W
.' I
•
,.,
,
I·
K
2.75 0.121 0.58
3.25 0.182 0.53
3.75 0.28 0.54
4.25 0.46 0.60
4.75 0.60 0.56
5.25 0.80 0.55
5.75 0.96 0.51
6.25 1.30 0.53
9
25
25
25
25
25
28
7
11
4.05 0.45 0.68::
11
11
11
5.75 1.62 0.8611
6.25 2.00 0.8211
6.95 3.24 0.7911
7.25 4.12 1. 01 11
11
1I
11
11
11
11
0.9311
7.35
9·25
"1111 '169
. ,."
. 0'89 u.'
, ..
•
_.
NOR\'IAY
,
"
I
I
I
I
I
'.
I
'
•
I
I
•
Q~55"
"
11
0.911111 156
1111
~ number in samplej L = mean length in cm; W= mean wet weight in grams; K = 100 W/L 3
0.63
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RELATIVE ABUllDh1~CE OF PEL'\GIC O-GROUP GADOIDS IH ..m NE/JULY 1S§73,
CATCH PER HOUR FISHING.
Southern stations: ":lILIJEN BEUKELSZ" t 14-22 june.
Northern stations: "TRIDEriS" t 2-11 july.
.'