ICES Journal of Marine Science, 53: 1079–1084. 1996
Short communication
Time-series data for a selection of forty fish species caught
during the International Bottom Trawl Survey
Henk J. L. Heessen
Heessen, H. J. L. 1996. Time-series data for a selection of forty fish species caught
during the International Bottom Trawl Survey. – ICES Journal of Marine Science, 53:
1079–1084.
Relative abundance estimates of 40 fish species caught during the ICES coordinated
International Bottom Trawl Survey are presented for the period 1970–1993. Trends in
survey catches for eight commercial species are compared with total stock biomass
estimates derived from stock assessment. In general, there is a remarkably good
correspondence between these two independent parameters, suggesting that the survey
is capable of registering significant changes in abundance. Among the 40 species, there
are many more showing a positive trend during recent years than a negative one.
However, the commercial species are all either declining or are stable. The most
significant changes are observed in ‘‘southern’’ species, which is probably related to a
period of relatively warm winters after 1990. In many resident species, however, that
appear to be increasing over a prolonged period of time, this explanation does not
seem to apply.
? 1996 International Council for the Exploration of the Sea
Key words: fish, long-term trends, North Sea, trawl survey.
Henk J. L. Heessen: Netherlands Institute for Fisheries Research, PO Box 68, 1970 AB
IJmuiden, The Netherlands.
Introduction
Materials and methods
The data from the ICES coordinated International
Bottom Trawl Survey (IBTS) provide one of the longest
time series available for demersal fish species in the
North Sea. The survey has been carried out annually in
February since 1965. Initially, herring (Clupea harengus)
was the target species, and the survey coverage was
restricted to the southern and central North Sea. Since
1969, the Skagerrak and Kattegat have been sampled
and from 1974 onwards the entire North Sea area has
been included in the survey area.
An overview of the distribution of all fish species
caught during the IBTS, based on catches in the years
1985–1987, is given in Knijn et al. (1993). Time series for
10 of the most abundant non-commercial species caught
are presented in Heessen and Daan (1996), and for 6
species of rays in Walker and Heessen (1996). This paper
presents time series of average catch rates for a selection
of 40 other species for the period 1970–1993, including 8
commercially important species. The survey catches of
the latter are compared with estimates of total stock
biomass (TSB) (from ICES, 1995a).
Survey methods are summarized in Heessen and Daan
(1996) and a full description is available in ICES (1992).
All data are stored in the IBTS Database at the ICES
Secretariat in Copenhagen. Data on by-catch species are
incomplete for the period 1970–1982, because not all
data have been computerized. For eight commercial
species the survey catches are complete. Average catch
rates in numbers per hour fishing have been calculated
over all hauls made in the North Sea proper (cf. areas
1–7 in Fig. 1 of Heessen and Daan, 1996).
1054–3139/96/061079+06 $18.00/0
Results
Sharks (Fig. 1)
Except for spurdog (Squalus acanthias) (see Heessen
and Daan, 1996), sharks are caught infrequently. Tope
(Galeorhinus galeus) has only been reported since the
1980s. This species is probably mainly a summer visitor
in the German Bight (Knijn et al., 1993). Smooth hound
(Mustelus mustelus) is caught in very low numbers.
? 1996 International Council for the Exploration of the Sea
1080
H. J. L. Heessen
Scyliorhinus caniculus
N/hr
0.8
8000
0.6
6000
0.4
4000
0.2
2000
0.0
70
75
80
85
90
0
70
75
8000
0.02
6000
85
90
4000
0.01
2000
70
75
80
85
90
0
70
75
80
85
90
Engraulis encrasicolus
Mustelus mustelus
0.05
0.04
0.03
0.02
0.01
0.00
80
5000
4000
3000
2000
35
0
Sprattus sprattus
Galeorhinus galeus
0.05
0.00
TSB
Clupea harengus
3
2
1
70
75
80
85
90
Figure 1. Average catch per one hour fishing for three shark
species, 1970–1993.
Lesser-spotted dogfish (Scyliorhinus caniculus) is slightly
more abundant, particularly in the north-western
parts. Since the early 1980s the catches have been fairly
stable.
Pelagic species (Fig. 2)
Both the survey catches and TSB clearly show the
reduction in herring abundance in the late 1970s, and the
recovery of the stock in the following 10 years. Catches
of sprat (Sprattus sprattus) are rather variable. Anchovy
(Engraulis encrasicolus), a southern species, was regularly caught in the 1970s. Over recent years numbers
have been slightly increasing (see also Boddeke, 1996).
The lesser argentine (Argentina sphyraena) dominate
over the greater argentine (A. silus) in the catches, but
both species appear to have increased over the last
decade.
Gadoids (Fig. 3)
The gadoid catch is largely dominated by the four
commercial species cod (Gadus morhua), haddock
(Melanogrammus aeglefinus), whiting (Merlangius
merlangus), and Norway pout (Trisopterus esmarki).
After a number of strong year classes in the 1970s the
abundance of cod gradually decreased. Since around
1975, both survey catches and TSB show the same
downward trend. Catches of haddock and whiting
0
70
75
80
85
90
Argentina sphyraena
50
40
30
20
10
0
70
75
80
85
90
Argentina silus
0.4
0.3
0.2
0.1
0.0
70
75
80
85
90
Figure 2. Average catch per one hour fishing for five pelagic
species. For herring, the drawn line represents estimated TSB
(Total Stock Biomass in ’000 t; right-hand axis; Anon., 1995a).
varied considerably over the 24-year period, but recent
numbers per hour were at the same level as in the 1970s.
For haddock, survey catches and TSB follow the same
pattern. For whiting, however, there is no agreement
between the two. Since the mid-1980s, the IBTS data
show a gradual increase, whereas according to the
assessment TSB remains stable (ICES, 1995b). For both
saithe (Pollachius virens) and Norway pout (Trisopterus
esmarki) there is little resemblance between the
survey catches and TSB. Pollack (Pollachius pollachius),
tusk (Brosme brosme), ling (Molva molva), and hake
(Merluccius merluccius) are caught irregularly without
clear trends.
Time-series data for a selection of forty fish species
Gadus morhua
250
200
150
100
50
0
Trisopterus esmarki
1200 12 000
1600
800
8000
1200
400
4000
800
70
75
80
85
90
0
0
400
70
75
Melanogrammus aeglefinus
2000
1500
1000
500
0
70
75
80
85
90
3000
2000
1000
70
75
80
85
90
0.3
85
90
0
1200
3
800
2
400
1
0
0
0.2
0.1
0.0
70
75
80
85
90
Molva molva
70
Pollachius virens
75
80
85
90
Merluccius merluccius
100
1500
75
1000
50
2.0
1.5
1.0
500
25
0
80
Brosme brosme
2500
2000
1500
1000
500
0
Merlangius merlangus
4000
0
1081
70
75
80
85
90
0
0.5
0.0
70
75
80
85
90
Pollachius pollachius
4
3
2
1
0
70
75
80
85
90
Figure 3. Average catch per one hour fishing for nine gadoid species. For cod, haddock, whiting, saithe, and Norway pout, see also
legend to Figure 2.
‘‘Southern’’ species (Fig. 4)
Flatfishes (Fig. 5)
The four ‘‘southern’’ species presented here show a
remarkable increase in the most recent period (see also
Corten and van de Kamp, 1996). Lesser weever
(Echiichthys vipera) is a resident species on sandy
bottoms. John Dory (Zeus faber) and mullet (Mullus
surmuletus) have been caught incidentally in earlier
years, whereas boar-fish (Capros aper) and blue-mouth
(Helicolenus dactylopterus) are newcomers. The catches
of blue-mouth, a deep-sea species, have been traced to
one single year class that invaded the northern North
Sea in the winter of 1990/1991 (Heessen et al., 1996).
Seventeen flatfish species have been reported in the
IBTS (see also Heessen and Daan, 1996), of which 11
are shown here. Compared to many other species,
catches of most flatfish species are remarkably stable.
Although the gear used in the survey is certainly not
very efficient for catching flatfish, the trends in catch
rates in numbers and in TSB (weights) from stock
assessment for plaice and sole are in remarkably
good agreement, indicating both decreases in plaice
(Pleuronectes platessa) in recent years and recent
maxima in sole (Solea solea). Turbot (Psetta maxima),
1082
H. J. L. Heessen
Echilichthys vipera
8
6
4
2
0
70
75
80
85
90
recently increased. The tub gurnard (Trigla lucerna)
shows no clear picture. The dragonet (Callionymus lyra)
had a much higher abundance in the 1970s than in recent
years. The spotted dragonet (C. maculata) is caught in
low numbers, but recent catch rates have been relatively
high. Catfish (Anarhichas lupus) and lumpsucker
(Cyclopterus lumpus) show similar patterns with highest
catches in the mid-1980s.
Zeus faber
0.06
Discussion
0.04
0.02
0.00
70
75
80
85
90
Capros aper
0. 03
0.02
0.01
0.00
70
75
80
85
90
Helicolenus dactylopterus
8
6
4
2
0
70
75
80
85
90
Mullus surmuletus
0.08
0.06
0.04
0.02
0.00
70
75
80
85
90
Figure 4. Average catch per one hour fishing, for five southern
species.
brill (Scophthalmus rhombus), witch (Glyptocephalus
cynoglossus), and solenette (Buglossidium luteum) show
similar patterns with a maximum in the late 1970s and
an increase in recent years. Scaldfish (Arnoglossus
laterna) and Norwegian topknot (Phrynorhombus
norvegicus) have also increased. Flounder (Platichthys
flesus), halibut (Hippoglossus hippoglossus), and megrim
(Lepidorhombus whiffiagonis) appear to have remained
stable over most of the period.
The IBTS data represent a valuable source of information for studying changes in the North Sea fish fauna.
Unfortunately, computerized data for the years prior to
1983 are still incomplete, and more data do exist in paper
format in different laboratories that have participated in
the past. The interpretation of the time-series data for
the earlier years (1970–1973) is also hampered by the
gradual increase of the survey area during that period. A
more detailed analysis might show which effect the expansion has had on the time series, but such analyses
must wait until all data hae been made available.
The catch rates in numbers show close agreement
with the estimated trends in stock biomass based upon
stock assessment for many of the commercial species,
including flatfish. This seems remarkable, because the
survey has been primarily aimed at estimating recruitment and the youngest year class makes up a much
larger proportion of the total population in numbers
than in weights. The agreement for flatfish is also not
expected because the survey is not geared to these
species. The conclusion might be drawn that the survey
is well capable of registering changes in stock abundance
in general.
The data show that, on a total North Sea scale, many
of the southern species have done relatively well in
recent years, corroborating the findings of Corten and
van de Kamp (1996) that relative warm winters may
have been a critical factor for this group. However, also
many of the resident species appear to have become
gradually more abundant over much longer periods,
suggesting that another factor is involved. Relatively few
species have decreased in abundance, but among these
the commercially important species are noteworthy,
suggesting effects of the fisheries. In general, a better
understanding of the biology of the by-catch species
appears to be a prerequisite for understanding what has
caused all the observed changes in the North Sea fish
fauna.
Acknowledgements
Mixed demersal species (Fig. 6)
The catches of angler (Lophius piscatorius) and red
gurnard (Aspitrigla cuculus), a southern species, have
All data have been retrieved from the IBTS Database at
ICES Headquarters in Copenhagen. The assistance of
the ICES Secretariat is greatly appreciated.
Time-series data for a selection of forty fish species
100
75
50
35
0
70
75
80
85
800
600
400
200
0
90
4
3
2
1
0
70
150
100
50
70
75
80
85
0
90
4
3
2
1
0
70
70
75
80
85
90
5
4
3
2
1
0
70
75
80
85
85
90
75
80
85
90
70
90
75
80
85
90
Lepidorhombus whiffiagonis
1.0
0.8
0.6
0.4
0.2
0.0
70
75
80
85
90
Phrynorhombus norvegicus
0.12
0.08
0.04
70
75
80
85
90
0.00
70
75
80
85
90
Arnoglossus laterna
Scophthalmus rhombus
0.20
0.15
0.10
0.05
0.00
80
Platichthys flesus
Psetta maxima
0.25
0.20
0.15
0.10
0.05
0.00
75
0.05
0.04
0.03
0.02
0.01
0.00
Buglossidium luteum
Solea solea
2.0
1.5
1.0
0.5
0.0
Hippoglossus hippoglossus
Glyptocephalus cynoglossus
Pleuronectes platessa
1083
1.0
0.8
0.6
0.4
0.2
0.0
70
75
80
85
90
Figure 5. Average catch per one hour fishing, for 11 flatfish species. For plaice and sole, see also legend to Figure 2.
References
Boddeke, R. 1996. Changes in the brown shrimp (Crangon
crangon L.) population off the Dutch coast in relation to
fisheries and phosphate discharge. ICES Journal of Marine
Science, 53: 995–1002.
Corten, A., and van de Kamp, G. 1996. Variation in the
abundance of southern fish species in the southern North Sea
in relation to hydrography and wind. ICES Journal of
Marine Science, 53: 1113–1119.
Heessen, H. J. L., and Daan, N. 1996. Long-term trends in ten
non-target North Sea fish species. ICES Journal of Marine
Science, 53: 1063–1078.
Heessen, H. J. L., Hislop, J. R. G., and Boon, T. W. 1996. An
invasion of the North Sea by blue-mouth, Helicolenus dactylopterus (Pisces, Scorpaenidae). ICES Journal of Marine
Science, 53: 874–877.
Please note Figure 6 is on the following page.
ICES. 1992. Manual for International Bottom Trawl Surveys.
Revision IV. ICES CM 1992/H: 3/Addendum.
ICES. 1995a. Report of the ICES Advisory Committee on
Fishery Management, 1994. ICES Cooperative Research
Report No. 210.
ICES. 1995b. Report of the Working Group on the assessment
of demersal stocks in the North Sea and Skagerrak. ICES
CM 1995/Assess: 8.
Knijn, R. J., Boon, T. W., Heessen, H. J. L., and Hislop, J. R.
G. 1993. Atlas of North Sea fishes. ICES Cooperative
Research Report No. 194. 268 pp.
Walker, P., and Heessen, H. J. L. 1996. Long-term changes in
ray populations in the North Sea. ICES Journal of Marine
Science, 53: 1085–1093.
1084
H. J. L. Heessen
Callionymus lyra
Lophius piscatorius
1.5
30
1.0
20
0.5
10
0.0
70
75
80
85
90
0
70
Anarhichas lupus
75
80
85
90
Callionymus maculatus
0.6
0.8
0.6
0.4
0.4
0.2
0.0
0.2
70
75
80
85
90
0.0
70
Trigla lucerna
0.3
0.2
0.1
70
75
80
85
80
85
90
Cyclopterus lumpus
0.4
0.0
75
90
0.05
0.04
0.03
0.02
0.01
0.00
70
75
80
85
90
Aspitrigla cuculus
0.8
0.6
0.4
0.2
0.0
70
75
80
85
90
Figure 6. Time series, as average catch per one hour fishing, for a mixture of seven demersal species. Data from the ICES IBTS
Database.