This paper not to be cited without prior reference to the author.
C.M. 1979 I H: 25
Pelagic Fish Committee
INJ:ERNATIONAL COUNCIL FOR THE
EXPLORATION OF THE SEA.
REPORT ON THE ICES YOUNG FISH SURVEY 1979:
HERRING DATA.
by
A. Corten,
Netherlands Institute for Fishery Investigations,
P.O. Box 68, 1970 AB IJMUIDEN,
The Netherlands.
This paper not to be cited without prior reference to the author.
INTERNATIONAL COUNCIL FOR THE
EXPLORATION OF THE SEA.
C.M. 1979/H:25
Pelagic Fish Committee
Report on the ICES Young Fish Survey 1979:
Herring Data.
by
•
A. Corten,
Netherlands Institute for Fishery Investigations,
P.O. Box 68,
1970 AB IJMUIDEN,
The Netherlands.
Introduction
This paper is one in aseries of yearly reports on the results
of the ICES Young Fish Surveys (formerly called Young Herring
Surveys). These surveys, which are conducted each year during
the ~onth of February are designed to obtain recruitment
estimates for a number of fish species. The area covered by the
survey includes the North Sea, Skagerak and Kattegat.
The surveys were first made in 1960 and 1961. After a break
of 3 years they were resumed in 1965, and from the onward they
have been continued without interruption. At present, 8 countries
participate in this programme. Results from the surveys have been
reported annually to the ICES Statutory Meeting. In addition to
these annual reports, the ICES Working Group on North Sea Young
Herring Surveys has produced several meeting documents in which
the ·survey methods and resul ts have been described and evaluated
(most recent report: ICES 1978).
The abundance of I-group herringand gadoids is estimated by
means of a bot tom trawl which is !ished at random positions
within a statistical rectangle.Most countries participating
in the survey have now adopted the standard GOV-bottom trawl
(ICES 1978). Much of the sampling effort is concentrated in
the southeastern part of the North Sea, in an area designated
as the "herring standard area" (fig. 1).
- 2 -
The squares within this standard area are grouped into
3 different strata;/sampling intensity in eaeh stratum
is proportional to the mean density of juvenile herring
in that stratum during previous years.
In reeent years, the surveys have also been usedto estimate
the abundanee of O-group herring (large herring larvae)
whieh are sampled by means of an Isaaes-Kidd Midwater Trawl
(IKMT). This gear is only fished at night, aeeording to a
standard proeedure deseribed in ICES 1977.
This paper presents the data on 0, 1 and 2 year-old herring
obtained from the survey. Data on gadoids and hydrography,
eolleeted during the survey, are presented to the Statutory
Meeting in seperate doeuments.
•
Partieipation in the 1979 survey •
~~~~!::~
Denmark
~~!E
J.C. Svabo
Franee
Thalassa
Fed.Rep.of German
Solea
Norway
Johan Hjort
The Netherlands
Tridens
Sweden
Argos
United Kingdom
Cirolana
"
"
U.S.S.R.
"
"
Period
~::~j~~!_~~E~::!!~~::
06/02 - 02/03
K. Popp Madsen
A. Maucorps
G. Wagner
------
07/02 - 02/03
01/03
22/03
29/01 J 01/03
05/02
09/03
05/0 3 - 22/03
01/02
28/02
o.
.0stvedt
A. Corten
O. Hagström
W.G. Parnell
A. Saville
Clupea
,13/02 - 07/03.
22/01
09/02
Korifena
01/02 - 01/03
S. , Fiodorov
Explorer
A. Saville
Results from the 1979 survey"
General
Many ships were handieapped by adverse weather eonditions during
the month of February. Extremely low water temperatures, partieularly in the southeastern North Sea, together with strong
gales eaused iee-formation on board some of the research vessels;
whieh then had to go into'port. The inshore area in the southeastern North Sea eould not be sampled beeause of drift iee.
The same applied to the Skagerak and Kattegat whieh were eovered
largely with iee. Sweden had'to postpone the survey by RV "Argos"
until the month of March when fishing in these areas beeame
possible again. It is possible that the abnormally low water
temperatures will have affeeted fish distribution during the
month of February. Herring eatehes were extremely low in the
areas of low watertemperature « 2°C).
- 3 -
During the weekend of 17-18 February, five of the participating
research vessels met in Esbjerg to compare fishing gear and
discuss survey methods.
'.
•
Distribution and abundance of O-group herring (year-class 1978)
Results of the sampling with Isaacs-Kidd Midwater Trawls are
summarized in figure 2. Also in 1979, there were still some
major gaps in the coverage of the North Sea. This was mainly
caused by one country loosing its entire gear after the 3rd
haul. As only about half the number of participating vessels
are using IKMT' snow, i t is not pos'sible to obtain a double
coverage of the entire sampling area (such as we have for the
bottom trawl), and gaps in the coverage are bound to arise
as soon as any of the IKMT-carrying vessels has problems to
complete its programme. It is therefore very important that
the use of IKMT's is introduced on board all participating
vessels.
The distribution of O-group herring was rather similar to
the one in 1978. The highest numbers of larvae were found
north of 57 ° N, except for so me local patches close to the
English coast south of 57°N.Relatively high catches were
reported from the Moray Firth and from the Orkney-area.
For the first time since 1973 fairly high numbers were also
caught in Skagerak and Kattegat. The southeastern part of the
North Sea contained hardly any larvae at all.
Because of the gaps in coverage of the North Sea in 1978 and
1979, it is not possible to make an exact comparison between
the abundance of O-group herring in both years. The results from
the survey indicate, however, that the abundance of O-group
herring'was probably considerably higher in 1979 than in 1978.
The text table below summarizes the results of the last 3 years •
•
year
number of squares
fished vii th IKMT
in North Sea
mean number
of O-group
herring per
square for
North Sea
1977
68
5.$
0.2
1978
106
0.9
1979
90
3·8
10.5
mean number
of O-group
herringper
square for
Skagerak and .
Kattegat
7.9
Distribution and abundance of 1-ringed herring (year-class 1977).
Figure 3 shows mean numbers/~our/square of 1-ringed herring, and
figure 4 the corresponding mean lengths.
Contrary to the method.of presentation
formeryears, no
distinction has been made between spring and autumn spawners;
all 1-ringed herring have been lumped togather. The reason for .
this new procedure was that considerable confusion in differences
in classification existed for juvenile herring in certain areas.
in
- 4 -
..
•
•
For the Skagerak and Kattegat a:r:.ea, Sweden has not been able
to differentiate between 1-ringed spring and autumn spawners
in recent years. While this area had been causing problems in
this respect far some years already, the situtation in the
North Sea had so far always been fairly straightforward, with
the great majority of the juvenile herring being classified
as autumn spawners, and only an occasional herring (never
more than a few percent) as coastal spring spawners.
In 1979 however, one country (Scotland) reported up to 20%
spring spawners in catches from the southeastern North Sea,
a percentage which had never occurred in that area in the paste
Other countries classified fish with similar otolith types
as autumn spawners (or rather Eastern Channel winter spawners).
Unless the~e problems in identifying spring and autumn spawning
juveniles can be solved, it is not possible to combine data from
different sources into one overall chart giving mean numbers of
autumn spawners per hour.
.
It can be seen from figure 3 that catches of juvenile herring
were extremely low in the eastern part of the.North Sea,the
area which normally contains the largest concentrations of
juveniles, and which therefore ·is sampled most thoroughly.
Very low catches of juvenile herring were also reported from
the Skagerak. and Kattegat, an area where very large numbers of
juveniles were taken during the previous survey in 1978.
In the western part of the North Sea, catches were. slightly
higher tha~ normal. Especially RV "Solea" took considerable
numbers of juveniles off.the Moray Firth, and also between
55°30'Nand 57°00' N. The "Solea" didnot work in this area
until March, a time when most of the other vessels had already
terminated their programme. The findings of the "Solea"were
confirmed by RV "Korifena", which worked the whole of the
western North Sea during March, and which found concentrations
of juvenile herring in the same areas as the "Solea" did •
The mean dens~ty of 1-ringed herring for the herring.standard
area was 139 fish/hour. This is the mean value of all rectangle
means, and it includes a correction for rectangle 38F8, which
was missed in this year's survey. This is by far the lowest
abundance index found during any of the recent surveys (see
table I).
It should be noted that even this extremely low abundance
figure in 1979 contains a positive bias because of the incluiion'
of a certain percentage spring spawners. As mentioned above,
spring spawners have always been excluded in calculating the
mean density during previous years.
- 5 The 90% confidence limits for the mean were calculated according
to the procedure used in previous reports (ICES 1975). For this
purpose, the hauls are grouped by strata, and the stratified mean
and variance for the whole standard area are calculated. The
results of this calculation are summarized below.
stratum
•
number of rectangles
number of hauls
stratum mean
stratum variance
stratified mean whole standard area
variancestratified mean
standard error
90% confidence limits
I
II
III
37
81
136
335- 356
15
84
91
46 942
5
24
301
397 336
139
.1910
44
139 + 72
Because cf the abnormal distribution of the juvenile herring in
1979, the application of stratified sampling·was of little use;
the mean density in stratum II was even lower than the one in
stratum I.
, 0:"
In order to estimate the strength of the year class in absolute
numbers on the basis of the abundance index from the Young Fish
Surveys, the following regression formula has been used in
recent years· (ICES 1978):
.
•
y
= 0.0031:X - 0.21
where y is the absolute size of the yearclass in numbers x 10 9 ,
and xisthe mean catch of I-group herring per hour for the
herring standard area.
During the latest meetin~ of the Herring Assessment Working Group
for the area south of 62 N, it was decided that a regression line
through the origin would be more appropriate w~en dealing with
extremely low year class sizes (ICES 1979). This Working Group
therefore used the formula
y
= 0.0031
X
to calculate the strength of year-class 1977 on the basis of
preliminaryresults from the Young Fish Survey in 1979.
The preliminary abundanc·e index for year- class 1977, used by the
Herring Assessment Working Group was 144 fish/hour. This corresponded to an absolute year-class size of 0.45 x 109. Substituting
the final figure of 139 fish/hour, given in this report, the
absolute size of the year-class is estimated ht 0.43 x 109. The
preliminary figure used by the Working Group thus appears to have
been a very good approximation of the final out~ome of the survey.
- 6 -
,'.'-
It was mentioned earlier that the exceptionally low water
temperatures during February may have affected the distribution
of juvenile herring, and thereby the abundance estimate derived
from the Young Fish Survey. The relatively'high catches in the
northwestern North Sea would suggest a shift of the distribution
area towards deeper and less cold water. If this were true, the
juvenile herring in 1979 would not have been sampled as effectively as in normal years. At the present moment, however,
there is no way to verify this hypothesis, and for the time
being thefigure of 0.43 x 109 I-ringers should be accepted
as the best estimate of year class 1977.
Distribution and abundance of 2-ringed herring.
Mean numbers per square of 2-ringed,herring and their mean
lengths are shown in figure 5-6. Also this age group was
extremely scarce in the southeastern North Sea. Slightly
higher catches were obtained in the western half of the
North Sea, particularly north of 58°N. Reasonable numbers
were alsp taken in the Kattegat; }an area where this yearclass had been very abundant in 1978 as 1-ringers.
References.
Corten, A., 1978
Report on the lCES Young Herring
Survey in the North Sea in 1978.
lCES CM 1978/H:6~
lCES 1975
Report of the Working Group on North
Sea Young Herring Surveys.
lCES 1977
Report of the Working Group on North
Sea Herring Larval Surveys.
lCES Coop. Res. Rep. No. 68 ••
lCES 1978
Report of the Working Group on North
Sea Young Herring Surveys, 1977.
lCES Coop. Res. Rep. No. 81.
lCES 1979
Report of the Herring Assessment
Working Group for the area south of
62°N.
lCES CM 1979/H:6.
Table I - Mean abundance indices of 1-ringed herring for the
__________ ~~~~~~~_~~~~~~~~_~~~~_~!_~Z_~g~~~~~~
survey year
I
e
•
1970
1971
1972
1973
1974
1975 .
1976
1977
1978
1979
year class
No/hour
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
822
2647
1629
827
1195
1529
452
342
575
139
_
ES
E6
E7
E8
E9
FO
F1
F2
F3
F4
F5
F6
F7
F8
F9
GO
G1
G2
jt-
52
.~
51
50
49
48
47
46
•
45
44
43
35
34
33
32
31
30
29
28
.
4
fig. 1.
.
10
Herring standard area of 57 rectangles, and allocation
of rectangles to different strata.
27
12
E5
E6
E7
E8
E9
FO
F1
F2
F3
F4
F5
F6
F7
F8
F9
GO
G1
G2
52
51
50
49
48
47
I.
46
45
44
43
57
•
34
33
32
31
'It:r-~O~
. [,r-4-rJ
30
!,
r-..
29
50 H - - + - - - - T - - 4 - - - + - - - ! - - l - /
...
Ir-
"i'l-J
1I---V=
H--+--+--:~-H
u
~ \
o·
28
.
2
...
27
o
10
12•
g.
fig. 2.
Results of IKMT ..sampling in Feb~uary 1979.
Middle figures in heavy print represent mean catches
of O-group herring (year class 1978 autumn spawners).
Top figure : number of tows.
Bottom figure : mean length of larvae.
E5
E6
E7
E8
E9
FO
F1
F2
F3
F4
F5F6
F7
F8
F9
GO
G1
G2
i~
.~
o
61
0
0
0
0
0
1
1
2
2
1
0
.n ~~
1
1
0
0
0
0
3
1
1
1
'7
O'.f
r
0
59
•
1
2
~~ 0
0
i'~ 1
~r26
~
~
3
3
1
0
2
. 2
0
0
1
1
0
0
2
1
2
0
0
0
3
1
2
_..
3
0
0
1
7 10.186 172 ' 0
0
3
I
2
1
~65 >- 81 ''1 60
223
1
J
0
57
26
R'1
°t
0
3
0
1
1
2
406 253 1.636
-..,
3
2
29
5
2
5
2
13 2.498
\
76
3
2
2
5
4
4
17
1
2
2
2
6
~
142
6
6
5
1
37
30
73
251
736
736 290
33
74
129 307
41
192 464
62
5
18
5
109
.12
2 .
1~3ß
3
6
2
2
16
3
2
3
2
2
6
5
5
6
2
6
6
~9
0
Y
(J
145 123 "'\ 42
1
3
149 2
K:'}
72~
1
~
1
"-'-J.-Lc\~
')
t::
0
2
~~
37
32
rd. '!i{'
",-"1r--~
31
(
30
.
Ir),-___.P'"
0
38
33
2
i'
o
39
34
29
28
1)-'")
u
40
35
144 372
2
41
36
2~0~
0
s:
I5-")J~
!-r- l'2.Ih
1?1
6
-{
-;L 'b
43
1
t~\ ~~~< ~
6
6
3
~
I ~~
44
~; ~2
7
0
1
6
10-
lIfh(
1
65
6 .
2
1
0
6
2
-~
.
5
2
2
2
..../""
3
2
1
79
~
)
:Jf
~rJ
10
0
2
4
2
~
50
1
2
I
45
4 •
0
31
2
24
2
)
0
1
46
'I
3
0
3
1
\ 1366 120
~ y~~~~
fig. 3.
1
2
12
3
~-<\
0
1427
53
3
520 /
4
6
1
1
1
3
~ '---.1
349
~~~
o
0
5
11
p-
o
51
2
31
2
~
54
6 II 18
~a r~
1
1
47
~
1
3
1
29
20
~1"{("
0
2
48
,.,)I.'i!'t
lf~~~
0
2
1
~qv
~~V
,
3
50
~r7
3
49
!?
:'f"
1
1
11
Ov
1
12
3
3
0
•
2
3
" 2
~2
56
55
O'
2
~
~1.61-
0
1
13
~
~
1
0
1
3
11
0
58
0
~
0
51
ii't..b
j
0
11/J
0
.. F
0
0
52
27
0
2
4
0
6
0
0
8
Mean numbers/square of 1-ringed herring (mainly year
class 1977 autumn spawners) in February 1979.
Bottom figure :. number of hauls.
0
10
0
12
E5
E6
E7
E8
E9
FO
F1
F2
F3
F4
F5
F6
F7
F8
F9
GO
G1
G2
52
H---+------t---t----- -----+----+-- - -
51
50
49
48
47
•
46
45
o
58
44
43
o
57
_
I
13.60
16.25
16.78
19.75
17.75
17.65
17.29
') "
• 15.04
o~
"~
16.55
16.54
'- 17.04
16.68
16.59
18.15
17.05
15.43
16.13
17.42
17.06
l6.56
17.63
16.16
15.50
"'"\
55°~7
W
r
oH-=-IY+-~.!I
54
o
•
~
H-----j-----l:'
n
53
o
34
.J
33
52/"
~
32
31
30
29
')-")
u
4
0
t:: \
0
2
Ir-
28
)r---..~
0
0
27
0
2
4
0
0
6
0
8
0
10
0
12
1/
fig.
4.
Mean length/square cf 1-ringed herring (mainly year
class 1977 autumn spawners) in February 1979.
. E5
E6
E7
E8
E9
FO
F1
F2
F3
F4· F5
F6
F7
F8
F9
GO
G1
G2
52
51
50
49
48
47
•
46
45
o
58
44
6
2
o
57
41
o~
"7
0
55
•
~:r
38
~
54H--+--~
34
33
32
31
30
29
28
27
o.
4
fig •. 5.
o
4
Mean numbers/square of 2-ringed herring (mainly year
class 1976 autumn spawners) in February 1979.
Bottom figure : number of hauls.
o
10
o
12
I
E5
E6
E7
E8
E9
FO
F1
F2
F3
F4
F5
F6
F7
F8
F9
GO
G1
G2
52
51
50
60 H---+----+----+--~·-+-25.-5-0-r24.00 24.37
•
~.~
24.92
21.63 I
-t---+- - -
23.33
49
r-----+--J,.~~~rF.~F
48
+----I-f~~: rL
21.2-5
I
'1
47
'iiJ'ff;:
46
26.25
58
23.25
21.75
20.88
--_·-+--f--~N.
22.76
tvn
/
o
57
LJ
1
23.75
21.48
56.~
2175
19.56
19.75
{I}~r
18.65
21.32
la25
26.25
21.00
2Q25
~ ~3.22
21.46
23.25
Ii
(\
~
\
54H--+--B'
r.
pr
I+---+--J,
o_~
53~
2275
~ 23.06
)
22.42
21.92
22.80
22.05
2048
2Q25
20.87
21.35
19.11
19.53
21.25
20.82
20.32
2Q55
~
27.75
22.36
22D7
23.25
23.00
_.--
~
\
21.03
22.27
)
2095
•
~-t-
\,..
~) ~-~ I~
I'
o~rJ
40
39
38
36
35
34
33
~
32
~~:-+--I+------jf---(.~ ;r
-~
...... 1t"' '"
~ y~~;>~'V--------~
41
. ~ 37
la25
~
42
o
"H--1_-t-2-11.75~
q7
.J
~
ht
20.05 2053
2Q7~ p7-I-t.c\~
la75
V
52/
r?_ 1'2.,
2075
t~
43
~\j---+--=",IH
23.12
"T-I--_l--_j--_+--_+--_+-_+-_+-_+-_ _+_~~(J.
55°~r7
o
22.75
1
~
(JuI
~~
~
~=+-25-.16-+-23-.25--+-19.-.7.-:s-+-2-2.53-t-20-.97--+---+'2-3.-25-+-2-2A5-f-2-1.2-9-+---+l rt-\ .
23.75
l
~
2Q5O 2275
.....
24.00
5t
44
2175 :
25.75 27.13
22.63
~9.93-.. 19.15 "\.24.16
1l---+--+--t---t----+---+---+---+---+----1--.JI----r'- ....-I----T
21.25
18.68
22.63 "'2123
24.15 24.35
/
~~~~--+---+~
J"~'---+---+---+---+---+---+--+--+---+---+---H
o
45
Q
./-~-+----+--+--+--+---+-,----+-----1-+---=1
~~tLL:t--+- - t - - - - 1 f - - ' V)
o
31
(
30
r
29
50 H--_+_-_+_-+--+--+--+7"'"
IrI + - - t - - t - :",--H
Q'I~
1 },t,,----v----
28
u
o
4
27
o
2
4
o
o
10
o
12
/3
. fig. 6.
Mean length/square of 2-ringed herring (mainly year
class 1976 and spawners) in February. 1979.