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COOPERATIVE RESEARCH REPORTS
1. Since they were established in 1962, .the Cooperative Research
Reports have been issued in two series, A and B.
Series A contained reports of Working Groups as well as of some
international activities. So far, 30 numbers have been issued.
Series B contained the annual reports of the Council's Liaison
Committee to the North-East Atlantic Fisheries Commission. The
issues were not numbered but were identified by the reporting
year printed on the cover. So far, reports from 1963 to 1971
(inclusive) have been issued.
2. The splitting of these publications in two series is a complicat
ion, both as to distribution and use, and the advantages are
probably not great. The Council's Bureau has, therefore, decided
that the two series will in future be merged into one, which will
be without series designation, and with a consecutive numbering
in continuation of the numbers of Series A. The Liaison Committee
Reports will in future be identified by a red - coloured spine.
3 Accordingly, the present issue, which contains the Report of the
Liaison Committee, 1972, is issued as Cooperative Research
Reports, No. 31.
Charlottenlund, July 1972
Hans Tambs-Llfche
General Secretary
COOPERATIVE RESEARCH REPORTS
No. 31
REPORT OF THE LIAISON COMMITTEE
OF ICES TO THE NORTH-EAST ATLANTIC FISHERIES COMMISSION
1972
Members of the Liaison Committee 1971/72
MrAJLee
Mr J G de Wit
Mr J A Pope
Dr A Meyer
Mr J Da.rdignac
Mr K Popp Madsen
·Prof K Tiews
Dr F A Gibson
Mr K A Pyefinch
Mr A C Burd
Mr J Hamre
Mr Sv A. Horsted
Dr A Schuma.cher
Dr A I Treschev
Mr J M9ller Christensen
Chairman
Chairman, Gea.r and Behaviour Committee
Chairman, Statistics Committee
Chairman, Demersal Fish (Northern) Committee
Chairman, Demersal Fish (Southern) Committee
Chairman, Pel~c Fish (Northern) Committee
Chairman, Pelagic Fish (Southern) Committee
Chairman, Shellfish and Benthos Committee
Chairman, Ana.dromous and Ca. ta.dromous Fish Committee
Coopted Member
Coopted Member
Coopted Member
Coopted Member
Coopted Member
the Council's statistician, Secretary
International Council for the Exploration of the Sea
Cha.rlottenlund Slot, DK-2920 Cha.rlottenlund
Denmark
Augu.st, 1972
https://doi.org/10.17895/ices.pub.5516
ISBN 978-87-7482-523-4ISSN 1017-6195
CONTENTS
A. REVIEW OF NOMINAL CATCHES IN NEAFC AREA 1963-1970 • • • • • • • • 1
B. NOTE ON TEE COMMUNIQuE . FROM TEE SPECIAL MEElriNG OF NEAFC
AT TEE LEVEL OF MINISTERS ................................ 2
C. REGION 1 FISHERIES
C.l North-East Arctic Fisheries 4 C .1.1 Cod •......................... ~ . . . . . . . . . . . . . . 4
C.2
C.3
C.l.2 Haddock ..................................... 0.1.3 Capelin ············•!>••···················· Atlanto-Scandian Herring .•..••.••••.••.••.•••....••
North-West Arctic Fisheries .........................
6
6
7
7
D. REGIONS 2 AND 3 FISHERIES
D.l.l
D.l.2
Herring Fisheries in Region 2
The Bl0den Tagging Experiment 9
12
D.2 North Sea Mackerel Stock and Fishery ••••••••••••••• 12
D. 3 Flatfishes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
North Sea Plaice ........................... 13
The Effect of Shrimp Fisheries on Plaice
a.Ild S·ole • . . . • . . . . • . . . . . . . • . . . . . . • . . . • . . . . • . 15
D.3.3 The Effect of Beam Trawling on Plaice and
Sole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . 15
D.3.4 Irish Sea and Bristol Channel Sole.......... 16
E. NORTH ATLANTIC- SAlMON • • • . • • • • • • • • • • . . . . • • . . • • • . . . • • • • . • • 16
F. EFFECTS OF TRAWLS AND DREDGES ON THE SEAilEID . ............ . 17
G. OTHER ITEMS
G.l Danish Recommendation 6 Whiting Fishery............. 19
G.2 Requirement for Data on North Sea Roundfish •.••••••• 20
G.3 Irish Sea Whiting Investigations •••••••••••••••..•.• 21
G.4 Joint ICES/ICNAF Study of North Atlantic Cod Stocks.. 21
G.5 Assessment of Deep-Water Prawn Fisheries •••••••••••• 22
G.6 Publication of the 1971 Report •.•••••.•••••.•••••••• 22
T.A:BLm 1-4 ••...•••..••.. · • · · · • · · · · · · · · · • • • • . . . . . . . . . • . .. . . . . • 23
MAP OF ICES AND NEAFC FISHING AREAS ......................... 27
· -o-o-o-
- l -
A. REVIEW OF NOMINAL CATCHES IN NEAFC AREA 1963 - 1970
l. A general review of the fish production in the Convention Area from
1963-1970 is given in Tables l-3· The tables, which are based on
statistics published in ICES "Bulletin Statistique" show for each NEAFC
region the nominal catch of all species combined, the catch in the main
fishing areas of (a) demersal species (comprising Pleuronectiformes -
flatfishes; Gadiformes - codfishes; demersal Percomorphs - redfishes,
gurnards, sandeels etc.); (b) pelagic species (all marine fish species
not included in the demersal fish group); (c) each of the main species
within the demersal and pelagic fish groups. Freshwater and anadromous
species, shellfish,and the catches by non-member countries are not ih
cluded in the tables.
?. The main changes in ·the fish production in each region are summarised
below. A map showing the Regions, Subareas and Divisions referred
to is given at the end of the Report.
Region l (Table l)
3. The total production of all species combined increased from 1969 to
1970 by about 600 000 tons to 4 245 000 tons.
4. In Subareas I and II there was a large increase in the c~tch of
capelin which went up by more than 500 000 tons to l 300 000 tons.
Among the demersal species the yield of saithe and of Polar cod in-
creased by about 100 000 tons each. The only species showing a substantial
decline in yield was cod, for which the 1970 catch of about 950 000 tons
was 280 000 tons lower than the catch in 1969.
5. The total catch of all species in Subarea V did not change substan
tially from 1969 to 1970. The catch of capelin and cod continued
to increase.
Region 2 (Table 2)
6. The total catch in Region 2 was about the same in 1970 as in 1969,
being just above 4 million tons.
- 2 -
7. In Subarea IV and Division IIIathe mackerel catches declined by
400 000 tons to 322 000 tons, whiLe the herring catch remained at the
1969 level. The total catch of demersal species increased by 300 000 tons
reflecting increasing yields of most of the species fished. It should be
noted that the yield of haddock, which from 1968 to 1969 rose substantially,
increased further in 1970. The Norway pout catch went up by 140 000 tons,
and the catch of saithe increased by 60 000 tons.
8. In Subareas VI and VII herring and mackerel catches continued to
increase, and there was a marked increase in the catch of "Other Pelagic
Fish", mainly horse mackerel, to 80 000 tons.
9. A total catch of 255 000 tons has not been specified in the table. ~
85 000 tons of these are non-teleost fishes. 170 000 tons are recorded
as unsorted and unidentified species and 147 000 tons of these were caught
in Subarea IV and Division IIIa,mainly by two countries. At its meeting in
1971 the Council recommended that countries which submit statistics of total
catch (quantity) of unsorted unidentified fishes for publication in "Bulletin
Statistique11 should specify those species of fish which form the main com
ponent of such catches.
Region 3 (Table 3)
10. There have only been slight changes in the yield of the different
species caught in Region 3· The pilchard catches continued to decline,
while the yields of mackerel and horse mackerel were higher than in any
year since 1963.
ll. The figures in Table 3 are only given as an indication of the main
changes in the fish production in Region 3, because of the inade
quacies of the reported statistics mentioned in last yearts Report.
' B. NOTE ON TEE COMMUNIQUE FROM TEE SPEXJIAL MEElriNG AT TEE
LEVEL OF MINISTERS
12. The Liaison Committee has noted that at the NEAFC Special Meeting in
Moscow in December 1971, the Ministers agreed on the importance of:
- 3 -
a. extending the range and scope of fisheries research,
b. increasing cooperation in joint scientific programmes,
c. improving the supply of statistics by Member Countries
to the scientific bodies concerned.
It wishes to draw the attention of the Commission to some important
points which concern ICES in its capacity as the advisory body of
NEAFC and which will be considered by the Council at its next Statutory
Meeting.
13. In order to achieve the necessary improvement of the stock
assessments, it is essential to greatly improve the coverage,
accuracy and speed of reporting of national statistics and to extend
substantially the biological sampling programmes. In this connection
it should be noted that the amount of biological sampling differs con
siderably between countries and is far from propo:+ional to the
quantity of fish caught by the individual countries. Also, the type
of data used up till now in assessments must be augmented by other
information in order to permit more accurate estimation of stock size
and recruitment.
14. With the rapid changes in the fisheries and with the introduction
of catch regulation, the comparability of the present abundance
indices will become less and less precise. They are based on ·long
established national patterns of fishing. Closed seasons, closed areas
or quotas will disrupt these patterns, making it essential to obtain
estimates of stock size independent of catch and effort data, for
example by means of acoustic suxveys and tagging experiments.
15. Another essential requirement for management is a reliable
estimate of future recruitment to the fishery. For some stocks
this is already monitored by means of larval, 0-group and groundfish
suxveys. These suxveys require high investments in time and effort
by research vessels. Provisions must be made for considerable in
crease in such investments and for the expansion of international
cooperation in these types of research activities if scientific manage
ment of the stocks is to become a reality.
- 4-
C. REGION 1 FISHERIES
C.l North-East Arctic Fisheries
C.l.l Cod
16. Nominal catches of cod have fallen from 876 000 tons in 1970 to
617 000 tons in 1971. The catch in 1971 was heavily dependent on
the 1963 and 1964 year classes which, as they matured, led to a big
increase in the proportion of the total catch taken in Division IIa
(Norwegian Sea). The 1965-1968 year classes are very weak and a conse
quent reduction in the abundance of 3-6 year old cod has led to poor
catches and a reduction in fishing effort in the Barents Sea/Bear Island
cod fishery. Fishing mortality on the stock as a whole in 1971 was
close to F = 0.5 on fully recruited age groups. As stated in earlier
reports, this is the level giving the long-term maximum yield per
recruit. Estimates of recruitment in the immediate future remain close
to those given in 1970. The 1970 year class is very rich and the 1971
year class is above average.
17. On the
at the
estimated at
assumption that fishing mortality in 1972 and 1973 remains
1971 level (F = 0.5) catches in these years have been
425 000 tons for 1972 and 380 000 tons for 1973.
18. Although estimates of future catch weight made in earlier years
left room for improvement, the estimates of catch numbers and
stock size are considered reasonably accurate at the present time. The
cod fishery has developed much as expected in the years 1968-1971. The
strong 1963 and 1964 year classes will continue to contribute a major
part of the catch in the Norway Coast fishery in 1972, and to a lesser
extent in 1973, but the Barents Sea/Bear Island fishery will continue
very poor indeed until 1974/75 when the 1970 and 1971 year classes
make a substantial contributj,on to the catches.
19. The following comparison between the estimated average biomass
of different age groups in 1950-1959, and that expected at
the beginning of 1973 shows how the resource has become reduced in
recent years by the combined effects of heavy fishing and poor
recruitment.
•.,;-._-,
- 5-
Weight of the stock in thousand tons
Age Groups 3-4 . 5-7 8+ Total
Average for 1950-59 2 411 2 735 1 350 6 496
1973 2 090 90 614 2 794
The spawning stock will become vexy small indeed by t~e mid-i970's
raising the attendant risks of continuing poor recruitment if the effects
of a stock and recruitment relationship become significant.
20. It is clear that the immediate and perhaps long-tenn future of
the cod resource depends critically on the level of exploitation
of the 1970 year class, especially since it can be expected that the
Barents Sea/Bear Island fisheries will become dominant aga;in ·in 1973/74·
One single year class, even if very rich, cannot 1 " itself rebuild a stock, but it may sustain the resource until the strength of the 1971
and later year classes becomes evident, and the overall risks to the
9ontinuity of the stock as a Whole of heavily exPloiting the 1970 year
class can be properly assessed.
21. Of the estimated yield of 380 000 tons in 1973, 80 000 tons is
expected to be taken from this 1970 year class if, in the absence
of abundant older age groups, fishing concentrates in areas Where it is
most numerous. If the capture of 3 year olds in 1973 could be·prevented,
this would decrease the yield by 80 000 tons in that year and it would
increase the expected number of 4 year olds by some 150 million fish,
representing.a potential yield nf 170 000 tons (equivalent to that of
the total recruitment of 4 year olds in the 1965-1969 year classes).
22. In order to rebuild the spawning stock it is advisable that the
1970 year class should not be heavily exploited when it reaches
fishable size. This could be achieved by:
a) a regulation of the age at first capture, combined with
b) an overall regulation of fishing mortality.
In the absence of overall regulation of fishing mortality, the year
class would still be vulnerable to heavy exploitation whenever the fish
- 6 -
become liable to capture and this might nullify any benefits that had
been achieved by a) above. If it is considered that protection of
the 1970 year class and of the stock as a whole could best be ensured by
the regulation of the allowable catch, then so far as possible this
should be allocated to regi0ns of the fishery according to the relative
abundance of different parts of the stock.
C .1. 2 Haddock
23. Contrary to expectation, haddock landings increased in 1971 to
113 000 tons. The fishery on fully recruited age groups followed
the expected trend, but catches of 4 year old haddock from the newly
recruited 1967 year class were greater than expected. This year class
is stronger than previously estimated, but also fishing is believed to
have concentrated upon haddock to a greater extent in 1971. As a
result, fishing mortality on haddock may not have declined mach. Estimates
of recruitment in the immediate fUture remain close to those given in
1970. The 1969 year class is rich and both the 1970 and 1971 year
classes are above average.
24. On the assumption that fishing mortality in 1972 and 1973 remains
at the 1971 level (F = 0.6) catches in these years have been
estimated as .127 000 tons for 1972 and 122 000 tons for 1973. An
additional estimate has been made by assuming that F is reduced to a
level giving the long-term maximum yield per recruit, viz. F = 0.3. If
this level is reached in 1972, the corresponding catch will be 59 000
tons in 1972 and 80 000 tons in 1973· If the mortality rate remains
at 0.6_in 1972, but is reduced to 0.3 in 1973, the catch in 1973
will be 62 000 tons.
C.l.3
25.
Capelin
There has been a dramatic increase in the capelin landings in
the north-east Arctic fishing areas from about 0.7 million tons
in 1969 to 1.3 million tons in 1970 and 1.6 million tons in 1971. By far
the main part of these catches is taken by Norwegian purse seiners, when
the capelin concentrate for spawning. Up till 15 February 1972 the
Norwegian landings were 600 000 tons, which is about 200 000 tons more
than the catch obtained by the same date in 1971.*)
*) According to information from Norway, landings from the spawning fishery in January-April 1972 off the Norwegian coast were approx. 1.2 million tons. The fishery was closed for abt. 2 months during that period for regulation purposes. (Added May 1972).
- 7 -
26. Norwegian acoustic surveys show that the stock size in 1971 was
about half the stock size in 1970. Preliminary estimates for
1972 show that the spawning stock is now considerably smaller than in
1971, being about 1.9- 3.7 million tons. Larval surveys show that
great fluctuations in year class strength occur within the capelin
stock.
C.2 Atlanto-Scandian Herring
27. The Liaison Committee has noted that .negotiations conQerning
regulation of the fishery on the Atlanto-Scandian herring stock
have taken place outside the framework of NEAFC. In this connection
the Committee wishes to inform the Commission that the statement conce~
ning Norwegian spring spawners in the Report presented at the Ninth
Meeting of the Commission is still valid, viz.:
"In view of the present critical state of the stock, it is
concluded that in order to increase recruitment to the adult
fisheries and to allow the recovery of the Norwegian spring
spawning stock as a whole, it would be advisable to reduce
the exploitation rate of immature herring to the lowest
practicable level, much lower than has been the case in
recent years. The adjustment of this exploitation rate
should be made relative to the estimates of year class strength
derived from the international 0-group surveys rather than by
arbitrary catch adjustments".
It should be added that the most recent surveys indicate that the stocks
still show no signs of recovery.
c.3 North-West Arctic Fisheries
28. At the Commission's Ninth Meeting the Liaison Committee reported
on the results of an assessment of Icelandic cod and haddock
stocks carried out by the Council's North-Western Working Group. Following
the objections of the Icelandic Delegate to some of the conclusions·of the
Report being based only on trawling effort data when other gears were
also in use, the Chairman of the Liaison Committee invited the Icelandic
scientists to submit more detailed data on these other fisheries for con
sideration by the Liaison Committee. This has been done.
I· I
I:
- 8 -
29. In the Report to the Ninth Meeting it was stated that the totalcatch of cod had increased from 1967 to 1969, in spite of a reduc
tion in fishing effort. The Working Group had no data which allowed it
to. make a precise estimate of" the actual fishing effort in terms of ·a standard unit. The total internationa� fishing effort for each year up to 1969 was therefore estimated by raising the English effort data by the
ratio between the English catch and the total international catch. The
estimate so derived is nothing but an index which give� the total effort in terms of the English trawler ton hours necessary to account.for the total catch in each year. It was on the basis of this index that a decrease
in total effort of about 35% was regarded as "having taken place between
1966 and 1969.
30. This technique, which is .commonly used to obtain an index of the
total effort, was chosen because:
a) the English data were the only ones which were comparable
between years for a long time period,
b) effort data were not available for all countries and
fisheries,
c) the available effort data were not comparable betweencountries and gear.
31. National effort data for certain years for the United Kingdom,Germany and Iceland were available to the Working Group. From 1966
to 1969 the English effort had decreased.by about 50%, and the German
effort pad de_creased by about 10%, while the Icelandic estimates of their
trawl effort showed an increase of about 6()%.
32. The new Icelandic effort data submitted to the Liaison Committee are
based on a conversion of effort by trawl, gill-net and long-line and
by size category of vessels into a standard unit which expresses the effort
as days fishing. These data show an increase in the total Icelandic effort
of about 50% from 1966 to 1969. The details of the method of conversion
have.not been examined by the Liaison Committee.
33. It should be noted that the main conclusions of the Report of the
North-Western Working Group are based on assessments which are completely independent of effort data. In the tabulation of changes in yield
for different levels of "effort" in the Working Group's Report and in· the
Report of the Liaison Committee to the Ninth Meeting of NEAFC, the term "effort" refers to the fishing mortality rate.
.:; 9 -
34. When reporting on the effect of the proposed closure to trawling of
an area off the north-east coast or Iceland, the Working Group
estimated the proportion of fishing in that area on the basis of trawl
catches and concluded that, in terms of the average for the 1965-1969 period, this fishery accounted for 6.1% of the total landings in the non
spawning fishery, the Icelandic share being 0. fJ!o. The new information
from Iceland indicates that in recent years the Icelandic catch figures
for that area are larger than the figures presented by' Iceland at the
Working Group meeting. In the absence of concrete, detailed Icelandic
data the Liaison Committee is not able to reassess the effect of a closure.
D. REX;IONS 2 AND 3 FISHERIES
D.l.l Herring fisheries in Region 2
35. At NEAFC 1 s Special Meeting on Herring hel~ ~n Moscow in December
1971 the Liaison Committee presented a new assessment of the North
Sea herring fisheries including a prognosis of the development in catch
and stock size for the period 1972-1975· The prognosis provided answers
to some of the questions on which NEAFC asked for advice at its Ninth
Meeting.
36. Due to the very restricted facilities and time available to the
North Sea Herring Asse_ssment Working Group at the meeting held
immediately prior to the 1971 Statutory Meeting of ICES, it was necessary
for the Group to meet at the end of January 1972 in order to make a cri
tical review of its previous work, to make further considerations of the
NEAFC questionnaire,and to collect preliminary catch statistics for 1971.
37· The Liaison Committee has appraised the recent report of the
Working Group, and accordingly submits the following statement to
the Commission:
Total Catch Limits
38. The previous prognosis was based on certain as·sumptions and esti-
mates of the population parameters. In the present prognosis
these parameters have been updated, e.g. the recruitment strength of the
1969 year class, which earlier was set at average (as are all subsequent
year classes), was now assessed as being 5o% above average.
- 10 -
39. From catch and effort data it was thought to be more realistic
to use an adult fishing mortality ofF = 1.0 in 1970 rather than
F = 0.7 as used in the previous prognosis. Minor corrections to growth
parameters and national catch figures were also introduced.
40. , The present prognosis of the development in catch and biomass
at different sets of values of fishing mortalities of juvenile
and adult herring (Table 4) does not differ markedly from the one
presented at the NEAFC Special Meeting on Herring.
41. In Table 4 the columns refer to specific fishing mortalities of
juvenile,(i.e. 1-ringed) herring from F = 0.0 to F = 0.7. Each
row refers to a fishing mortality of adult herring from F = 0.0 to
F =' 1.5. At each intersection of rows and columns three figures are
given. The upper figure is the expected catch in 1972, the middle
figure gives the percentage change of the 1975 catch as compared with
1972, and the lower figure is the biomass of the stock in weight as
at 31 December 1975 expressed as a percentage of the biomass as at
1 January 1972.
42. Entering the table at the calculated 1970 values of fishing mor-
talities (F = 1.0 for adults and F = 0.5 for juveniles) the
expected total catch in 1972 is 638 thousand tons. If that level of
fishing intensity is sustained, the catch in 1975 should decline by 14%,
i.e. to about 550 thousand tons, and the biomass of the herring stock
would be reduced by 8% over the 4 year period, all assuming average
recruitment.
43· The new prognosis is thus compatible with the Committee's state
ment at the Moscow meeting: ''Without a reduction in fishing
effort'it,is expected that the stock will not recover and that catch
as well as stock size may continue to decline".
~!£!~=~~!!~!_2~!~~-~!~!~_Er_2~!~g~~
44· The fisheries for juvenile herring (15-22 em) are mainly exploiting
the 1-ringers (2 year old herring). Estimates of the effects of
differential catch limits for this category can therefore be obtained
from the table.
I
- 11 -
45. At constant average recruitment the upper row of Table 4,
corresponding to an adult F = 0.0, indicates the catch of 1-ringed
herring at different juvenile fishing mortalities in anyone year. They
represent at the same time the yearly catch quotas to be applied in order
to achieve the corres}>onding fishing mortalities.
46. As an example, a Go% reduction in juvenile morta1ity, e.g. from ,'
0.5 to 0.2 could be achieved by a reduction of catch from
111 thousand tons to 51 thousand tons. With a sustained level of fishing
mortality of 1.0 for the adults, the total catch in 1972 would be
578 thousand tons including 51 thousand tons of juvenile herring. In
1975 the predicted total catch would be lo% higher, i.e. about
636 thousand tons. This total would still only include 51 thousand tons
of juvenile herring so the entire increase would benefit the adult
fisheries.
47· If fishing on herring is confined to the second half of the year,
there will be an increase in average weight of the individual
fish caught. If a catch quota in weight was enforced, then the con
servation effect would be greater in the first half' of the year than
in the second.
48. AssUJI!ing that the same number of herring is caught in the sec~md
half of the year as would otherwise have been taken over the
whole year, it has been estimated that, in the current range of fishing
mortalities, the gain in weight could be of the order of 20-3o%· How
ever, if, as seems likely, closure of the fishery during the first
half of the year would result in a decrease in the number of 1-ringers
caught, there would be an additional increase in the subsequent gain
in weight of the overall catch.
The Development of the Fishery in 1971 ----------------~---------------------
49· The preliminary catch figures for 1971 show an overall reduction
of 100 000 tons compared with 1970. It should, however, be
noted that past experience indicates that preliminary catch figures tend
- 12 --
to be too low. The catch of juvenile herring increased by about 100 000 tons,
due to the entry of the comparatively good 1969 year class, while the catch
of adult herring was reduced by about 200 000 tons.
50. The westward change in distribution of the fisheries, apparent in
1970, was continued in 1971 when a high proportion of the Norwegian,
Faroese and Icelandic catches derived from west of 4~·
51. It is too early to assess the effect of the closed periods in 1971.
This will be considered by'the Working Group when. more detailed
information is available.
D.l.2 The Bl~den Tagging Experiment
52. As reported to the Commission in 1971 the ICES .Working Group on the
Bl~den Herring· Tagging Experiment met in 1971 to make a first assess
ment of the tagging data and to prepare the timetable for the remaining·
studies.
53· Two meetings were held in the spring and autumn of 1971. A first
assessment of the data revealed that a marked migration of herring
from the central to the north-western North Sea had taken place in the
course of the experiment. Due to this complication, it was decided to
apply a newly developed mathematical model which embraces parameters
representing migration and dispersion. It was also realised that.with the
relatively large number of tags returned from the north-western North Sea,
the scope and outcome of the experiment could possibly be enlarged to
determine. the fishing rate and size of that part of the adult stock.
54· The amount of data and the complexity of the calculations involved
have necessitated the use of a computer with a large capacity, which
has been made available by the Marine Laboratory, Aberdeen. The computer
analysis is being carried out during 1972 and the Working Group will meet
as soon as possible after it has been completed.
D~2 North Sea Mackerel Stock and Fishery
55. In the last Report of the Liaison Committee, recent information on
the state of the mackerel stock and fishery was presented to the
Commission according to its request at the Eighth Meeting. From data
- 13 -
placed at the Committee's disposal by Mr J Hamre, last years information
can be updated as follows:
56. The total catch declined from 740 000 tons in 1969 to 320 000 tons
in 1970 and approximately 250 000 tons in 1971. According to
Norwegian tagging experiments the stock of mackerel in the north-eastern
Nbrth Sea and Skagerrak declined from 4.3 million tons ~n 1964 to
550 000 tons in 1970. New data indicate that a further decrease took
place in 1971 when the stock size was estimated at about 460 000 tons.
The 1969 year class constitutes atpresent about 8o% of the stock in
weight and the older year classes amount to less than 100 000 tons.
57. The younger year classes, 1970 and l971, appear to be below average
strength and there are reasons to believe that no substantial
recruitment to the spawning stock will take place en 1973 and 1974. Under
these circumstances a further depletion of the stock could take place
unless the fishery is kept under strict control.
58. Calculations made from Norwegian data indicate that yield per
recruit will not increase appreciably when fishing mortality
exceeds 0.4. At this value the sustained annual yield is estimated to
be about 400 000 tons under average recruitment. The corresponding
stock size under these conditions would be about 1.1 million tons or
more than twice the present level.
59. Norwegian tagging experiments have also yielded new information
concerning the division of stocks in the northern part of Area rv. They show that the fishery around Shetland exploits both the stock of
the North Sea and that spawning to the west of the British Isles. On
the basis of tag releases in 1970 it is found that about 2Q% of the
Shetland catch originates from the North Sea stock.
D.3 Flatfishes
D.3.1 North Sea Plaice
60. The total North Sea landings of plaice have increased continuously
from 96 000 tons in l965 to 129 000 tons in 1970. This increase is
- 14-
partly due to the recruitment to the fishery of the strong 1963 year class
and partly due to a gradual increase in the fishing capacity of the Dutch
fleet by replacing the otter trawl with the beam trawl and improving the
efficiency of the beam trawl. The Dutch share of the increase in the
total landings is more than two-thirds.
61. The landings of plaice in recent years differ substantially from the
actual catch. This is particularly true for the Dutch fishery,
where in 1969 and 1970 an average of 40% of the catch in numbers and 23%
in weight were discarded. This is a consequence of the fact that a con
siderable part of the Dutch plaice catch is a by-catch from the sole
fishery. As the discarded fish are believed to have only poor chances of
surviving, these large catches of undersized plaice may have a con
siderable influence on the level of recruitment to the adult fisheries.
This problem is being studied by the Council.
Immediate prospects
62~• Between 1965 and 1970, after several years of average recruitment,
the fishery benefitted from the presence of the very abundant 1963
year class. The importance of this strong year class is now declining
and in general succeeding year classes are only of average abundance, but
with the 1966 year class of somewhat above average and the 1968 year class
of below average strength. The immediate prospects up to 1974 must there
fore be a fall in the catch rate towards the 1960-65 level with catches
of about 90 000 to 100 000 metric tons at the present level of fishing
effort.
Long:term prospects
63. The high catch per unit effort for the North Sea plaice since 1960
reflects the value of keeping fishing effort low, especially on
small plaice. However, if beam trawling for dwindling sole catches should
become uneconomic, or if diversion of fishing effort into the North Sea
from other areas increases the competition for roundfish, plaice fishing
~ intensify thereby raising the mortality rate so that catch per unit
effort will fall. Further, if the increasing market preference for
small plaice for fillets leads to a substantial increase in the mortality
rate on the younger age groups, the total catches may also fall. In
- 15 -
view of this it might be desirable to consider safeguaxding the
stocks of small plaice and to give thought to the possibility of
stabilising fishing mortality by means of effort regulations or by
catch quotas.
Do'3.2 The Effect of Shr:i,mp Fisheries on Plaice and Sole
64. In the triennial review of mixed fisheries reported to the
Commission in 1971, attention was drawn to the large by-catches
of protected species in the Dutch and German shrimp fisheries. The
Council's North Sea Flatfish Working Group. has carried out a study of
the effect of shrimp fisheries on plaice and sole.
65. While it has been possible to make an estimate of the number of
juvenile plaice and sole destroyed in the shrimp, fishery, the
effect of this destruction on the adult stocks could not be assessed
because the data available are insufficient. Much more research will be
required before this can be achieved.
D. 3· 3 The Effect of Beam Trawling on Plaice and Sole
66. At its meeting in 1971 the Commission requested ICES to investigate
the effects of beam trawls with chains on the sole and plaice
stocks.
67. In a Dutch study, the numbers of undersize'd discarded sole and
plaice in the Dutch sole fishery from October 1969 to October
1970 were estimated to be 65.7 million and 131.6 million respectively,
that is about half the number of adult sole and plaice caught in the
same period by the same fishery. As it is believed that discarded fish
have only poor chances of surviving, these catches may have a consider
able influence on the level of recruitment to the adult fisheries.
68. The main reason for the high discard rate of small flatfish is
the tendency of part of the Dutch fleet to fish in inshore waters
for soles amidst large quantities of undersized fish. The major part
- 16 -
of the discard is caused by the beam trawl fisheries but there would also
be a large amount from the use of otter trawls in inshore waters.
D.3.4 Irish Sea and Bristol Channel Sole
69. After 1964 the catch of sole in the Irish Sea and the·Bristol Channel
increased substantially due to recruitment of the strong 1963 year
class to the stock~ and to a diversion of Belgian, Dutch and. French effort
into the areas. Before 1964 the average annual catch was about 1 000 tons.
The 1970 catch was 2 600 tons. British, Dutch and Belgian scientists are
preparing an assessment of the stocks and fisheries. This is to be pre
sented at the next Statutory Meeting of the Council.
E. NORTH ATLANTIC SALMON
70. At its meeting in March 1971, the Joint ICES/ICNAF Working Party
on North Atlantic Salmon reviewed the latest info~tion available
about the long-line fishery for salmon in the Norwegian·Sea and made
further assessment of the effects of this fishery.
71. In 1970 the total catch of the long-line fishery was 964 metric tons,
which.is slightly greater than the catch for 1969 (918 tons), and
substantially greater than that for 1968 (408 tons). The further increases
in total catch were mainly due to an increase in the number of Danish and
Norwegian vessels which, as in previous years, took almost the Whole of
the catch. The area of the fishery during 1970 did not differ significantly
from that during 1969.
72. In 1970 about 9ofo of the salmon caught between February and mid-
May had already spent two or more winters in the sea, but from
mid-May onwards, an increasing proportion of the catch consisted of one
sea-winter fish. T.be Condition Factor of the two-sea-winter fish varied
widely, but was, on average, low. Evidence concerning the. destination of
salmon in the Norwegian Sea, from tagging experiments, clearly indicated
that most of the fish in this fishery migrate to Norwegian home waters,
mainly as two-sea-winter fish.
73· An assessment of the effect of the Norwegian Sea fishery on
the total yield (Norwegian Sea plus home ·waters) indicated that
this fishery had resulted in an overall increase in the.total catch
by weight. It was pointed out,1 however, that the overall average 'quality•
of the total yield would be lower in the presence of an offshore
fishery because of the low ayerage Condition Factor of the fish taken
offshore. A separate assessment of the effects of the Norwegian Sea
fishery on home-water· catches indicated that, for a long-line
catch of l 000 tons, the losses to home-water catches would be
Within the range 500 - l 040 tons.
74· The Working Party also reviewed the information available on
the fishery conducted by Faroese lo~liners in the vicinity
of the Faroe Islands. -The catch from this fishery,which had been
conducted during the spring of 1968, 1969 and 1970, had never excee~ed
10 tons', and to judge by the catch made from a research vessel, con
sisted mainly of one-sea-winter fish. _The recapture in home waters
of fish tagged in the vicinity of the Faroese suggest that Faroese
waters are a feeding and/or transition area of salmon originating
from and returning to north European rivers.
75· The Working Party also discussed the preliminary plans for a
Salmon Tagging Experiment to be conducted by member countries
of ICES and ICNAF at West Greenland in 1972. An Expert Planning Group
has met twice and has worked out detailed plans for this experiment,
which will be considered finally at the meeting of the Joint Working
Party in March 1972.
F. EFJ!'JOOT OF TRAWLS AN1l DREDGES ON THE SEABED
76. Member countries of ICES have been requested to investigate the
·effects" of trawls and dredges, and especially of heavy chained
trawls, on the seabed and on fish and bottom-living organisms; The
following statement is a summary of the studies so far reported to the
Council.
I
- 18-
7• Direct obsorvation indicates that otter-boards, beam·trawl
heads and tickler chains on beam and otter trawls, all
penetrate the bottom to extents varying very much with the nature of
the substrate; for example, they dig deeper into soft ground than
into hard compacted sand. Sector-scanning sonar readily detects the
tracks made by otter-boards on some grounds but not on others.
78. The skimming action of tickler chains is the same whether.
used on a beam trawl or on an otter trawl. Each tickler
chain "skims off" a thin layer (a few mm on sand) of the seabed. No
direct observations have been made of h"!avy trawls on mud grounds.
Tickler chains, chain on the groundrope, and chain lower legs of a·
trawl dislodge some stones from certain types of bottom. Dislodged
stones are more likely to be caught in a trawl than are partially
embedded stones. A tentative estimate based on direct observations
is that an array of fifteen tickler chains might disturb a muddy-sand
bottom to a depth of about 100 mm; another lik~wise tentative estimate,
based on observation of invertebrates caught, puts the figure at
100 - 200 mm.
79. Tickler chains are at present an essential part of efficient
flatfish trawling gear - whether beam or otter trawling. The
beam trawl allows more tickler chains to be used than does an otter
trawl. Other than this ability of the beam trawl to carry more
ticklers, there is no technical reason for considering the destructive
effect of beam trawls separately from that of otter trawls and dredges·.
The multi-chained beam trawl is a very efficient gear for catching
soles, for instance a double beam trawler with seventeen ticklers
heavily outfished on the same grounds otter trawlers without ticklers,
both on soles and on invertebrate benthos (especially those species
burying in the seabed). Damags to soles in the beam trawl catch was
probably asbociated more with benthos caught than with the action of
the gear, and damaged fish picked up by an otter trawl on a beam
trawled ground were evidently discards from the beam trawlers.
~L------------------------------------------------------~
L
- 19 -
80. First results of an investigation of the effects of varying the
number of tickler chains in a beam trawl indicate increased
digging, and thus increased catches of burying benthos, with increased
number of ticklers; more of the benthos was damaged as the number of
chains was increased.
81. The Liaison Committee notes that, although research in this
field has4Deen started, conclusive results have not yet been
obtained. To some extent this is due to the fact that it has taken
time to incorporate the subject into laboratories' research programmes.
The Committee stresses the need to continue investigations of the
effects of trawls and dredges on the seabed.
G. OTHER ITEMS
G.l Danish Recommendation 6 Whiting Fishery
82. The following data on whiting caught by Danish vessels in the
Skage=ak and Kattegat comprise catches from the Danish Recommen
dation 2 (mixed) fishery as well as from its Danish.Recommendation 6
(special whiting) fishery.
Landings (in metric tons) of whiting for industrial purposes
Year Skage=ak Kattegat Total
1966 13 561 5 755 19 316
1967 13 643 15 719 29 362
1968 19 155 9 863 29 018
1969 11 335 4 247 15 528
1970 6 545 6 315 12 860
1971 5 688x) 5 834x) 11 522x)
x) Preliminary figures extrapolated from the landings in the first ten months of the year.
83. The percentage composition of species,in samples containing
more than lofo whiting, taken from landings in one Danish port
during the period January-March 1971 ]s shown on top of next page,
together with corresponding figures for previous years:
- 20 -
.. , .. .. ··-.. -_.
. 1968 1969 1970 1971 Percentage of samples containing
more than lcrfo whiting (Rec.6
fishery) 98 81 92 76
Average percentage in these
samples of:
(a) Whiting 60.0 · .. 59.8 26.2 29.2
(b) Rec.2 Species, mainly he=ing, sprat and No~ pout 31.4 27.4 42.3 47.0
(c) Rec.4 Species, mainly cod, haddock and dab 5·7 7·7 24.2 12.0
(d) Other Species, mainly long rough dab 3.0 5.0 7.0 11.8
. 84. The total Danish catch of whiting from the Skage=ak and Kattegat has
decreased continuously during the last four years. The share of the
·catch taken by the special Recommendation 6 fishery decreased from 92% in
1970 to 7&/o in 1971. During the last two years whiting has constituted a ..
lesser part of the total catch than previously, while Recommendation 4
(protected) species have constituted a larger part.
G.2 Requirement for Data on North Sea Roundfish
85. In 1971 the Commission was informed about a study undertaken to
evaluate the effect of Recommendation 2 (mixed) fisheries on the
gadoid stocks in the North Sea. The Liaison Committee drew the attention
of the"Commissioners to the fact that without adequate data on the com
position of catches from Recommendation 2 fisheries, a proper assessment of
the effect of those fisheries on the Recommendation 4 (protected species)
fishery could not be made.
86. When considering the Report on the above-mentioned study in
September 1971, the Council's Demersal Fish .(Northern) Committee
noted that the Working Group had been unable to complete its task satis
factorily because of laok of data on.the species composition of landings
from Recommendation 2 (mixed) fisheries.
.
1·~
- 21 -
87. All ICES member cuuntries have been requested to collect and ·
report such ?ata in order to enable the Council's North Sea Round
fish Working Group to carry out a new assessment when sufficient data
become available.
G.3 Irish Sea Whiting Investigations
88. At its 1971 meeting the Commission requested ICES to investigate
the Irish Sea whiting stocks. The Council has requested its
member countries e~ed in fishi~ for whiting in the Irish Sea to
collect up-to-date data on the fisher,y, the stock composition, and the
mesh sizes in use, with a view to setting up a Working Group at the
1972 Council Meeting.
G.4 Joint ICES/ICNAF Study of the North Atlantic Cod Stocks
89. At its Statutor,y Meeting in 1971 the Council decided, that:
"the joint ICES/ICNAF Working Group on Cod Stocks in the North
Atlantic meet in Copenhagen for one week in March 1972 to summarise
existing assessments concerning cod stocks in the North-East Arctic,
Icelandic and East Greenland Waters, as well as the West Greenland,
Labrador and Newfoundland cod stocks, and to examine in general terms
the effects of possible regulator,y measures, with particular emphasis
on the interaction.between fisheries on different stocks".
90. It is expected that the various scientific and statistical
problems concerned with the diversion of effort from one fisher,y
to another will be examined by the Working Group.
91. The Liaison Committee notes the need for studies of the effects
of the redeployment of fishing effort in other regions and
fisheries in the NEAFC area and hopes that the Joint ICES/ICNAF Study
of the North Atlantic Cod Stocks will provide guidance as to best to
proceed with these.
- 22 -
G. 5 Assessment of Deep-Water Prawn .. Fisheries
92. At its last Statutor,iMeeting the Council decided to set up a
Working Group to assess the stocks of deep-water prawns in the
ICES area and the effect of fishing upon them. This Working Group will
meet in May 1972.
G.6 Publication of the 1971 Report
93. The Report of the Liaise~ Committee for 1971 has been published
as an ICES Cooperative Research Report, Series B.
- 23 -
Table 1. Nominal catch (in OOOts metric tons) by Subareas
and main species in NEAFC Region 1.
1'163 1964
Total NominaJ Catch in Region 1x·
3 403 3 42'1
Subareas I and II (North-East Arctic)
Pel!'£;iC Fish
Herring 716 870 Cape lin 35 20 Others 4 4
Total Pelagic Fish 755 8'14
Demersal Fish
Cod 805 468 Haddock 145 87 Polar Cod . . . . . . Saithe 149 1'18 Redfish 42 66 Flatfish 28 53 Others 52 64
Total Demersal Fish 1 221 '136
Total Catch of all Species ._ .......... 1 976 1 830
~ubarea v (Iceland and Faroe)
Pel!'£;iC Fish
He=ing 531 640 Cape lin 1 9 Others 1 1
Total Pelagic·Fish 533 650
Demersal Fish
Cod 433 460 Haddock 131 ll8 Saithe 61 82 Redfish 93 103 Flatfish 24 23 Others 64 55
Total Demersal Fish 806 841
Total Catch of all Species .......... 1 33'1 1 4'11
Subarea XIV (East Greenland)
Total Catch of all Species .......... 63 81
x)Including non-teleost fish, unsorted and unidentified species.
1965 1966 1967 1968
3 '100 4 386 4 125 3 679
1 169 1 520 1 627 700 222 389 408 538
9 7 6 8 1 400 1 '116 2 041 1 246
480 557 619 1 102 106 130 '15 156 . . . ... . .. . .. 186 203 181 llO
40 .,- 24 18 /.
43 ,~
/I 33 32 5'1 56 52 56
914 1 018 1 004 1 474
2 314 2 '134 3 045 2 720
628 492 145 37 50 125 97 78 - 1 1 1
678 618 243 ll6
421 381 371 414 ll7 79 73 69 82 78 '17 98
120 llO 100 103 28 26 41 33 58 47 53 61
826 721 735 778
1 504 1 339 '178 894
58 80 60 40
1'169 1970
3 677 4 245
62 62 680 1 314
4 4 746 1 380
1 224 944 146 85 140 243 133 236
30 29 52 83 60 74
1 78"> 1 6'14
2 531 3 074
30 1'1 171 192 - -
201 211
443 503 70 66
144 142 88 80 38 33 6'1 53
852 877
1 053 1 088
50 40
- 24-Table 2. Nominal catch (in ODD's metric tons) by Subareas and
main species in NEAFC Region 2.
1963 1964 1965 1966 1967 1968
Total Nominal)Catch in Region 2 x 2 571 3 005 3 471 3 638 3 912 4 262
Subarea IV and Div. Ilia (North Sea and Skagerrak)
Pelagic Fish Herring 965 1 206 1 469 1 191 1 069 1139 Mackerel 73 115 208 530 931 821 Sprat 78 76 79 111 76 70 Others 10 7 14 9 10 7
Total Pelagic Fish 1 126 1 404 1 770 1 841 2 086 2 037 Demersal Fish Cod 129 136 194 235 270 303 Haddock 65 199 223 270 169 140 Whiting 117 113 125 175 122 174 Norvncy- Pout 180 97 68 65 194 486 Saithe 30 58 73 90 76 102 Sandeel 184 132 141 180 209 201 Plaice 125 133 110 109 115 126 Other Flatfish 49 36 43 58 66 61 Others 34 46 53 42 39 33
Total Demersal Fish 913 950 1 030 1 224 1 260. 1 626
Total Catch of all Species .......... 2 039 2 354 2 800 3 065 3 346 3 663 Subareas VI and VII (west and south of British Isles)
Pelagic Fish He=ing 83 90 90 131 143 142 Mackerel 27 27 22 46 39 40 Sprat 4 7 8 5 4 8 Others 12 14 7 6 6 5
Total Pelagic Fish 126 138 127 188 192 195 I Demersal Fish
·Cod 20 35 41 41 48 45 Haddock 10 44 43 41 29 25 Whiti 36 39 47 45 53 44 HakeXX, 25 20 42 15 17 18 Flatfish 23 29 32 37 33 30 Others 48 48 74 40 50 60
Total Demersal Fish 162 215 279 219 230 222
Total Catch of all Species •········•· 288 353 406 407 422 417
x). Including non-teleost fish, unsorted and unidentified species.
xx) The hake· statistics are unreliable. Part of the catch is reported by landing port and not by fishing area.
1969
4 043
838 739
69 9
1 655
212 640 216 151 109 115 135
49 35
1 662
3 317
192 45 8
21 266
46 33 39 13 32 86
249
515
1970
4 071
834 322 58 19
1 233
239 673 195 290 172 195 145
38 27
1 974
3 207
230 65 14 80
389
29 41 28 14 31 77
220
609
- 25-
Table 3. Nominal catch (in 000 1 s mstric tons) by main
species in NEAFC Region 3·
1963 1964 1965 1966 1967 1968
Total NominaJ Catch in Region 3x 794 890 899 811 824 780
Pelagic Fish
Pilchard 220 252 225 215 199 164 Mackerel -27 29 56 44 56 43 Horse Mackerel 117 125 116 100 116 138 Others 148 181 226 162 162 126
Total Pelagic Fish 512 587 623 521 533 471
Demersal Fish
Hake=) 102 105 75 89 98 89 Others 93 98 108 108 111 118 Total. Demersal Fish 195 203 183 197 209 207
Grand Total 707 790 806 718 742 678
1969
766
151 49
136 117 453
83 111 194·
647
x) Including non-teleost fish, unsorted and unidentified species.
=) The hake statistics are unreliable. Part of the catch is reported by landing port and not by fishing area.
1970
785
136 82
163 107 488
100 108 208
696
- 26-Table 4· Prognosis for North Sea Herring. - Initial catch levels (1972) and
percentage increase in catch and biomass 1972-75·
~~~~~!~-~~~!~!!!!~~~{!:~!~~~~2 F .o .1 .2 ·3 ·4 .5 .6 ·1
0 27 :)1 73 93 111 127 142 .o 0 0 0 0 0 0 0
392 359 329 302 277 255 235 217
79 105 130 152 172 190 206 221 .1 243 164 120 90 73 59 49 41
300 272 247 224 203 184 167 152 150 177 201 223 243 261 277 292
.2 196 148 115 92 74 61 50 41 231 208 186 166 149 i33 118 105 215 242 266 288 308 326 342 357
·3 158 123 97 77 62 50 40 32 180 159 141 124 109 95 82 71 273 300 324 346 366 384 401 416
·4 128 100 78 61 48 37 28 21 r;:;1 141 123 107 92 79 67 56 46
<DI 327 353 378 400 419 438 453 469 '1:11 r-11
·5 103 80 62 47 35 25 17 10 01 I 110 95 80 68 56 45 36 27 '1:11
til: 375 406 426 448 468 486 502 517 I OJI .6 83 63 47 34 24 15 7 1 f.< I
~: 87 73 60 49 38 29 21 13 I'll ·rll 419 445 470 492 511 529 546 561 f.< I I I ·1 67 50 35 24 14 6 -1 -7 ''" ~ 68 56 44 34 25 16 9 2 I
OJI <DI 458 485 509 531 551 569 586 600 ·rll .PI .8 54 38 25 15 6 -2 -8 -14 •rll r-11
54 42 32 23 14 7 0 -7 all .PI 1-<1
494 521 545 567 587 605 622 636 01 S1
·9 43 29 17 7 -1 -8 -14 -19 I .PI 42 31 22 13 6 -1 -8 -13 r-11 ::<I
'1:11 527 554 578 600 620 638 654 669 «<I 1.0 34 21 10 1 -7 -14 -19 -24
32 22 14 6 -1 -8 -13 -19 556 583 607 629 649 667 684 699
1.1 26 14 4 -5 -12 -18 -23 -28 24 15 7 0 -7 -13 -18 -23
583 610 634 656 676 694 711 725 1.2 20 8 -1 -9 -16 -22 -27 -31
17 9 2 -5 -11 -17 -22 -27 608 634 659 681 701 719 735 750
1.3 14 3 -6 -13 -20 -25 -30 -34 12 4 -3 -9 -15 -20 -25 -29
630 657 681 703 723 741 757 772 1.4 10 -1 -9 -16 -23 -28 -33 -36
7 0 -7 -13 -18 -23 -28 -32 650 677 701 723 743 761 777 792
1.5 6 -4 -12 -19 -25 -30 -35 -39 3 -4 -10 -16 -21 -26 -30 -34
Upper figure: catch 1972 (1 000 tons) Middle figure: increase in catch 1972-75 (%)
I
-•
ICES and NEAFC
- 27 -
Fishing Areas
October 1970
UU.l SUl£
' ' I I I 1 I I I I w---:----:----r---:----1 I I t I I I I
' ' 100000 SQUAll£
IUUTICAl llllU
IIUit lllt(U SCAL[
0 100 tOO SOO 400 lllUTICAt llllES
• " • ,,.lO'• I
"'
"·
