ICES Journal of Marine Science, 58: 1053–1062. 2001
doi:10.1006/jmsc.2001.1094, available online at http://www.idealibrary.com on
Distribution and abundance of juvenile Northeast Arctic
Greenland halibut (Reinhardtius hippoglossoides) in relation to
survey coverage and the physical environment
Ole Thomas Albert, Einar M. Nilssen,
Kjell H. Nedreaas, and Agnes C. Gundersen
Albert, O. T., Nilssen, E. M., Nedreaas, K. H., and Gundersen, A. C. 2001.
Distribution and abundance of juvenile Northeast Arctic Greenland halibut (Reinhardtius hippoglossoides) in relation to survey coverage and the physical environment. –
ICES Journal of Marine Science, 58: 1053–1062.
Based on annual bottom-trawl surveys in the Barents Sea and Svalbard area in
1983–2000, variations in distribution and abundance of age 1 Greenland halibut
(Reinhardtius hippoglossoides Walbaum) are described. The surveys showed high
contrasts in abundance during the period, with extremely low abundance in
1990–1995 associated with a northerly displacement of the distribution within the
survey area. A reduced abundance was not reflected in VPA-based estimates of total
abundance of 1-group halibut. We conclude that the survey covered a varying
proportion of the total distribution area. Survey abundance, the range of distribution within the survey area, and the proportion covered by the surveys were all
negatively correlated with temperature in the Atlantic Water of the Spitsbergen
Current. Possible mechanisms linking survey results to the physical environment are
discussed.
2001 International Council for the Exploration of the Sea
Keywords: distribution, Greenland halibut, interannual variation, recruitment, yearclass strength.
Published electronically 15 August 2001.
O. T. Albert: Norwegian Institute of Fisheries and Aquaculture, N-9005 Tromsø,
Norway. E. M. Nilssen: Norwegian College of Fishery Science, University of Tromsø,
N-9037, Tromsø, Norway. K. H. Nedreaas: Institute of Marine Research, PO Box 1870,
Nordnes, N-5024, Bergen, Norway. A. C. Gundersen: Møre Research, Section of
Fisheries, PO Box 5075, N-6021, A
r lesund, Norway. Correspondence to O. T. Albert:
e-mail: [email protected]
Introduction
Greenland halibut (Reinhardtius hippoglossoides) is distributed in Arctic and boreal waters on both sides of the
North Atlantic (Fedorov, 1971). The stocks support
important fisheries in relatively deep waters off Canada,
Greenland, Iceland, Faroe Islands, and Norway (Godø
and Haug, 1989; Bowering and Brodie, 1995). On the
eastern side the distribution is more or less continuous
along the continental slope from Faroe Islands and
Shetland to Svalbard (Whitehead et al., 1986; God and
Haug, 1989). The stock structure of Northeast Atlantic
Greenland halibut has not been studied in detail and for
management purposes a pragmatic definition is used
based on statistical areas. The Northeast Arctic stock
is thus found along the slope off Norway, including
Svalbard, and in the Barents Sea.
1054–3139/01/051053+10 $35.00/0
The stock is commercially exploited using gillnets and
longlines on the spawning grounds and by otter trawls in
the Barents Sea and along the Norwegian slope northwards to Spitsbergen. Based on a decline in estimated
stock size and indications of recruitment failure, the
fishery has been highly regulated since 1992 (Hylen and
Nedreaas, 1995; ICES, 2000). All research vessel surveys
in areas where young fish are normally distributed
indicated a dramatic decline in abundance of younger
age groups during the late 1980s.
Greenland halibut spawn along the continental slope
between Lofoten and Bear Island, and to some extent
south of this area (Godø and Haug, 1989; Albert et al.,
2001). Eggs and larvae drift north and eastwards and
juveniles are generally found in the Barents Sea and in
Svalbard waters (Godø and Haug, 1989). Spawning
peaks in December in the main spawning area, but
2001 International Council for the Exploration of the Sea
1054
O. T. Albert et al.
spawning also occurs in nearby localities during summer
(Albert et al., 2001). Between-year variations in location
and timing of spawning are not well understood. The
drift of eggs and larvae is only inferred from the known
juvenile distribution.
Preliminary modelling of larval drift (A
r dlandsvik
et al., 1999) has shown that both the timing of spawning
and the subsequent bathymetric distribution of eggs and
larvae associated with variations in ocean currents can
have a major impact on the supply of recruits to
different parts of the nursery area. Understanding egg
and larval drift may therefore be a key to understanding
the recruitment process. Our objective is to describe the
geographic distribution and abundance of recruits and
to investigate whether the general decline in juvenile
abundance was associated with changes in the physical
environment or in the distribution of juveniles. We also
evaluate if the surveys covered a consistent proportion
of the total juvenile abundance. The results are discussed
in relation to possible mechanisms of biological–
physical interactions.
Materials and methods
Surveys and sampling
Greenland halibut data were collected during annual
bottom-trawl surveys designed for estimating shrimp
biomass in the Barents Sea and Svalbard area, 1983–
2000. Two surveys were conducted in each year, one in
the central and western Barents Sea and another from
south of Bear Island and northwards along the western
shelf and inside the Svalbard fjords. The Barents Sea
surveys were conducted over three weeks within the
period 20 April–25 May. The Svalbard surveys were
usually run within the period 15 July–30 August, except
for 1991 (no survey), 1992 (extension to midSeptember), and 1993–1996 (between 20 May and 20
June, as an extension of the Barents Sea survey).
A stratified random survey design has been applied
(Aschan and Sunnanå, 1997). For the analysis of
Greenland halibut data, five new strata were defined a
posteriori (Figure 1), using only hauls within 200–500 m
depth corresponding to the main depth range of 1-group
(Albert et al., 1997). The Barents Sea surveys mainly
sampled areas 1 and 2. The Svalbard surveys mainly
covered areas 3 and 4. Area 5 was sampled only occasionally, partly because in the 1980s 80N was set as the
normal northern limit of the Svalbard surveys. In the
1990s, the intention was to cover the area every year, but
coverage was often restricted owing to dense drift ice.
A Campellen 1800 shrimp trawl was used on all
cruises. No corrections were applied to account for gear
changes throughout the time-series (Table 1). For each
haul, the catch by species in weight and numbers was
recorded. Total length-frequency distributions (to the
nearest cm below) were obtained either by measuring the
entire catch or from a random subsample. All catches of
Greenland halibut without length distribution were
treated as missing observations and not included in the
analyses.
Number of accepted hauls per area varied between
years (Table 2). Only area-year combinations with at
least ten trawls were used in the analysis. There is no
comparable time-series for Greenland halibut from the
slope and basins east and northeast of Svalbard.
Analyses
All length distributions were first converted to logarithmic catch rates of 1-group:
where mi is number of fish of length i in the sample, M
is total number of fish in the sample, C is catch in
number, d is towed distance (nm), and min1 and max1
define the length range of the 1-group. The appropriate
length range could be easily distinguished as a separate
mode in the overall length-frequency distributions by
month (Figure 2). The min1 and max1 were derived
from the aggregated monthly distributions as the smallest length observed and the one with lowest observed
frequency between 14 and 19 cm.
Mean catch rate in year k for the whole survey area,
was calculated as weighted mean of the means within
each area A (j=1–4):
where the weighting factor Aj is the approximate surface
(in nm2; Table 3), Njk is number of hauls, and nk is the
number of areas sampled. Area 5 was excluded because
of lack of time-series data. Thus, nk is 4 for all years
except 1991, when area 4 was not sampled (nk =3).
Another estimate of 1-group abundance (N1vpa) was
calculated from VPA estimates taken from the most
recent assessment (ICES, 2001). Because juvenile age
groups (up to and including ages 5–6) are poorly represented in the assessment, numbers at age 1 were
only calculated for year classes up to 1992, for which
VPA estimates for age 7 were available. When backcalculating from numbers at age 7, we used the catchat-age matrix, natural mortality (M) of 0.15 for all ages,
and the standard VPA equations.
The number at age 1 from VPA is an estimate of
absolute number of fish. For direct comparison, a geometric mean estimate of absolute abundance (N1surv)
within areas 1–4 was calculated as:
Distribution and abundance of juvenile Northeast Arctic Greenland halibut
1055
60°E
85°N
50
0
40
20
10
30
5
80
4
1
500 m
75
3
0
20
m
2
70
Figure 1. Bathymetric map of the Barents Sea. Areas 1–5 are referred to as Hopen Deep, Southern Barents Sea, Bear Island, West
Spitsbergen, and North Spitsbergen, respectively. The South Cape hydrographical transect is located westwards from the southern
tip of Spitsbergen. The archipelago in the northeast is Franz Josefs Land.
N1vpa =[exp(R
z 1k)1] · A/a
(3)
where A is area (nm2) of areas 1–4 combined, and a is
the swept area of a 1-nm haul. The effective fishing width
was set to 25 m, i.e. between the door spread and the
wing spread.
The survey-based and VPA-based estimates of absolute numbers at age 1 are measures of abundance in the
survey area and in the total distribution area, respectively. The ratio may thus be considered as an index of
the part of the stock sampled by the survey. Because the
two estimates depend on widely different assumptions,
they may not be directly comparable. Therefore, the
ratio was only used to consider trends in survey coverage
of the juvenile distribution.
As a proxy for the influence of the physical environment on the distribution and abundance of juvenile
Greenland halibut, the temperature in the core of
Atlantic Water between 50 and 200 m depth in the South
Cape hydrographical transect was chosen (Aure, 2000;
data for 2000 from Blindheim, pers. comm.). Survey
abundance and distribution were compared with the
temperature in the year prior to the survey (t0; when the
year class was present as 0-group), in the survey year
(t1), and to the mean of these two (t01).
Results
1-group Greenland halibut was caught in all areas
(Table 3), but most frequently and in greatest numbers
in area 4 (West Spitsbergen) and area 1 (Hopen Deep).
In the more southerly areas 3 (Bear Island) and 2
(Southern Barents Sea), 1-group was only caught in 40%
1056
O. T. Albert et al.
Table 1. Ship, trawl equipment and procedures used in each period and survey area (BS: Barents Sea;
Sv: Svalbard).
Survey area/period
Ship
Length (Loa)
Trawl
Ground gear
Mesh size
Wings
Belly and bag
Codend lining
Doors
BS 1983–1991
Sv 1983–1990
MS ‘‘Michael Sars’’
48 m
Campellen 1800
Rubber bobbins (1983–1988)
Rockhopper1 (1989–1996)
BS and Sv
1992
MT ‘‘Gargia’’
47 m
idem
Rockhopper1
BS and Sv
1993–2000
RV ‘‘Jan Mayen’’
64 m
idemidem
80 mm
60 and 40 mm
10 mm (4 m length)
Vaco combination doors,
1500 kg
40 m
Approx. 5 m
60 min (1983–1989)
30 min (1990–1991)
3 knots (1.5 m s 1)
idem
idem
idem
Steinshamn doors,
2050 kg
idem
idem
30 min
idem
idem
20 mm (8 m length)
idem
idem
idem
Sweep length
Vertical opening2
Haul duration3
Towing speed
idem
idem
20 min
1
Engås and Godø (1989).
Measured with SCANMAR wireless gear control system.
3
Standard duration was adjusted depending on bottom area suitable for trawling.
2
and 20% of the surveys, respectively. In years with
positive observations in those areas, the frequency of
occurrence was approximately half of the value in areas
1 and 4. In the far northern area 5 (North Spitsbergen),
young Greenland halibut dominated many of the
catches. The largest catches were found within the small
trench from the continental slope towards the sound
between the two main islands (Figure 1).
Interannual variations in 1-group abundance were
large, apparently with a high degree of autocorrelation
Table 2. Number of trawl hauls by year and area within the
depth range 200–500 m.
Year
1
2
Area
3
4
6
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
28
36
48
54
42
51
46
51
86
44
28
34
42
61
83
42
45
42
44
21
61
63
55
53
57
70
132
70
45
38
53
50
40
42
35
49
17
26
26
29
14
9
35
40
52
41
33
38
28
26
13
36
17
29
40
52
45
68
54
45
50
96
.
80
63
75
102
58
65
91
75
68
1
2
.
7
1
.
2
.
.
8
.
5
.
11
10
12
10
2
in the time-series (Figure 3). Notably, there were two
successive years with particularly high abundance
(1987–1988) and five successive years with very low
abundance (1991–1995). In 1990–1997, mean catch rates
were significantly less than in any of the years 1984–1988
(t-tests, p<0.05). After 1995, catch rates increased
slowly, and in 1999 approached the moderate level
observed in 1984–1986. The temperature in the Atlantic
West-Spitsbergen Current varied during the period
between 2.9 and 5.1C, with a mean of 4.0C (Figure 3).
Mean catch rates were negatively correlated with temperature, especially with the two-years running mean
temperature (t01) during the first two years of life
(Spearman, R= 0.75, n=18, p<0.01; Figure 4). Figure
5 shows estimated numbers at age 1 back-calculated
from numbers at age 7 from the most recent stock
assessment (ICES, 2001). Although these VPA-based
numbers were not correlated with any of the temperature series (t0, t1, or t01; Spearman, p>0.2), there
appears to be a similar periodicity, with increasing
abundance in periods of increasing temperatures.
Catch rates within each area showed the same general
trend as for the weighted mean of areas 1–4 (Figure 6),
with two years of particularly high abundance in most
areas (1987–1988) and five years of extremely low abundance in all areas (1991–1995). The negative correlation
between catch rates and temperature was significant in
all areas, especially with t01 (Spearman, R: 0.49 to
0.75, n=17 or 18, p<0.05).
Between-year variability was much higher in areas 1–3
than in area 4 (CV of mean catch rates areas 1–4: 209,
281, 165, and 82, respectively). This was also reflected in
the number of years with positive catches within each
Distribution and abundance of juvenile Northeast Arctic Greenland halibut
Percentage
4
3
2
1
0
4
3
2
1
0
6
5
4
3
2
1
0
April
n = 4976
10 20 30 40 50 60 70 80 90 100
May
n = 12 910
10 20 30 40 50 60 70 80 90 100
June
n = 600
10 20 30 40 50 60 70 80 90 100
Length (1 cm units)
4
3
2
1
0
5
4
3
2
1
0
7
6
5
4
3
2
1
0
1057
July
n = 6340
10 20 30 40 50 60 70 80 90 100
August
n = 8380
10 20 30 40 50 60 70 80 90 100
September
n = 296
10 20 30 40 50 60 70 80 90 100
Length (1 cm units)
Figure 2. Length-frequency distributions of Greenland halibut by month (all years combined).
6
0.8
5
0.6
4
0.4
3
0.2
1999
1997
1995
1993
1991
1989
1987
2
1985
1983
0
Temperature (°C)
Mean catch rate
1
Year
Figure 3. Catch rate (closed diamonds) of 1-group and
temperature (C; open squares) in the South Cape Transect.
area (Table 3). In some area-year combinations, presence may be based on very few observations. For areas
1–3, Table 4 provides the results of Fisher’s exact test of
significance on pairwise comparisons of years with and
years without catches of 1-group. The presence in area 1
in 1984–1988 and 1999 was significantly different from
the absence in 1992–1995. On the other hand, the
presence in 1983, 1990, 1991, 1998, and 2000 was not
significantly different from the absence in 1992–1995.
The presence in 1984–1987 in area 3 was significantly
different from the absence in 1991–1994, and the presence in 1987–1988 in area 2 was significantly different
from most other years.
The extension of the distribution in each year may be
classified according to the presence or absence in the
survey area from northwest to southeast (Figure 7). In
1992–1995 the distribution was very narrow and
restricted to the northeast (area 4), whereas in 1984–
1990, and particularly in 1987–1988, the distribution
extended much wider southwards. The south-eastwards
extension of distribution was highly positively correlated
with mean catch rate per year (Spearman, R=0.88, n=18,
p<0.01) and consequently negatively correlated with
mean temperature at age 0–1 (Spearman, R=0.67,
n=18, p<0.01). Figure 8 shows the temperature difference between years with different distribution patterns.
Comparable time-series for the occurrence of 1-group
Greenland halibut in areas further away from the
spawning grounds (northeast Greenland, north of the
Hopen Deep and along the slope and trenches between
Spitsbergen and Franz Josefs land) do not exist. North
of Spitsbergen (area 5), high frequencies of occurrence
(>50%) were observed in all four years sampled with at
least ten trawls (Table 3) and juveniles were also
recorded in six out of eight years with one to nine trawls
(Table 2). The swept area estimates of absolute abundance within the survey area were only a small fraction
of the VPA-based estimates, varying from <0.5% in
1990–1993 to 24% in 1988 (Figure 9). Thus, the ratio of
the two increased when the 1-group was widely distributed to the south or southeast, i.e. for year classes that
experienced low temperatures at age 0 and 1 (Figure 10).
Discussion
Distribution and abundance
The main pattern in the abundance of 1-group
Greenland halibut in the survey area during 1983–2000
was a shift from high abundance in 1984–1988 to low
1058
O. T. Albert et al.
Table 3. Total number of hauls and occurrence of 1-group Greenland halibut within each area, all
years combined (only area-year combinations with at least 10 successful hauls within 200–500 m depth
are included).
Area:
Number of hauls
Number of surveys
Number of years with 1-group catches
Frequency of occurrence (%)
All years
Years with 1-group catches
Approx. area (in 1000 nm2)
1
2
3
863
18
14
978
18
4
500
17
7
13.2
15.9
24.3
1.6
7.8
37.3
1127
17
17
3.4
9.1
11.5
17.6
17.6
9.7
5
All
43
4
4
3511
18
18
58.1
58.1
2.5
10.5
16.3
85.3
1200
Percentage of area-mean
0.7
0.6
0.5
0.4
Hopen Deep (1)
Southern Barents Sea (2)
Bear Island (3)
West-Spitsbergen (4)
800
400
0.2
1999
1997
1995
1993
1991
1989
1987
1985
0
0.3
1983
Mean catch rate
4
Year
Figure 6. Catch rate of 1-group by area.
0.1
0
2.5
3.0
3.5
4.0
4.5
5.0
Mean temperature (°C) at age 0–1
40
4
30
20
3
10
1999
1997
1995
1993
1991
1989
1987
1985
1983
2
1981
0
1979
6
5
50
Temperature (°C)
Numbers-at-age 1 (×10 )
Figure 4. Catch rate of 1-group vs. mean temperature at age
0–1.
Year
Figure 5. VPA-based numbers-at-age 1 (closed diamonds) and
mean temperature (open squares) at age 0–1.
abundance in 1990–1995 coinciding with a gradual
contraction and a north-westerly shift in distribution
(Figure 7). In 1992–1995 1-group Greenland halibut was
only found in the West-Spitsbergen area and (when
sampled) also in North Spitsbergen. The periodic
appearance of recruits in the different areas suggests that
the southern edge of the distribution area pulsated
southwards and northwards. Comparing results from
previous expeditions, Haug and Gulliksen (1982) also
found that juvenile Greenland halibut may only be
present periodically in an area.
The reduced survey abundance in later years was not
reflected in the VPA-based abundance estimates of age
1. On the contrary, the VPA-based estimate was higher
in 1990–1993 than in 1986–1989. Thus, the period of low
abundance and narrow northwesterly distribution in the
surveys was associated with relatively high total abundance. This indicates that the reduced survey abundance
was due to changes in distribution and/or catchability
and not to reduced year-class strength. The higher ratio
of survey abundance to VPA-based estimates in 1984–
1988 than in 1990–1993 suggests that juvenile Greenland
halibut was largely unavailable to the surveys during the
latter years.
The coverage of the distribution by a bottom-trawl
survey has both a horizontal and a vertical component.
Juvenile Greenland halibut is largely a pelagic feeder
(Haug and Gulliksen, 1982; Bowering and Lilly, 1992;
Distribution and abundance of juvenile Northeast Arctic Greenland halibut
1059
Table 4. Tests of significance of presence–absence data for 1-group Greenland halibut per area and year. For each area, each year
of presence was tested against each year of absence by means of Fisher’s exact test (0: not significant; 1–3: significant at 0.1, 0.05
or 0.001 level respectively). Years significant at 0.1 level or better, in at least half of the tests were classified as years of significant
presence (+) or absence ().
Area
Presence
83
84
86
89
90
91
1983
1984
1985
1986
1987
1988
1989
1990
1991
1996
1997
1998
1999
2000
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1
1985
1987
1988
1999
0
3
2
0
0
1
0
0
Significance
3
94
95
96
97
98
00
Significance
0
3
2
3
3
3
1
0
0
2
1
0
3
0
0
3
2
2
3
3
1
0
0
1
0
0
3
0
0
3
2
3
3
3
1
0
0
1
1
0
3
0
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
+
+
+
+
+
+
.
.
+
+
.
+
.
.
+
+
.
0
3
1
2
3
3
0
0
0
0
0
0
3
0
Significance
2
Absence
92
93
1984
1985
1986
1987
1989
1990
1999
0
0
0
0
0
0
0
.
.
.
.
.
.
.
0
3
3
0
0
3
2
0
.
.
.
.
.
.
.
.
.
.
.
.
.
.
0
3
3
0
.
.
.
.
.
.
.
Significance
0
3
3
0
0
3
3
0
0
3
2
0
0
2
2
0
0
3
2
0
0
3
2
0
0
2
2
0
0
3
2
0
0
3
2
0
2
2
2
2
1
0
0
1
2
1
1
1
0
0
1
2
1
1
0
0
0
1
2
1
1
0
0
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
2
1
1
0
0
0
1
2
0
0
0
0
0
+
+
+
+
.
.
.
Area
Distribution pattern
2
–
–
+
–
+
3
–
+
+
+
+
1
+
+
+
+
+
+
+
+
+
+
4
+
–
–
–
–
–
–
–
–
–
–
+
–
4: Wide, Southeast
+
+
–
–
–
–
–
–
–
–
+
–
3: Wide, South
+
+
+
+
–
–
–
–
+
+
+
+
+
2: Narrow, North
+
+
+
+
+
+
+
+
+
+
+
+
1: Narrow, Northwest
83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
Year
Figure 7. Presence (+) and absence () of 1-group by area and year. Hatched squares indicate outcome of significance tests (cf.
Table 4). Empty cells represent missing values. The thick line indicates the extension of 1-group distribution from northwest to
southeast and corresponding distribution patterns are defined in the right column.
Michalsen and Nedreaas, 1998) and its pelagic
distribution may vary with availability of squids and
pelagic fish. Although the extent of vertical distribution
is virtually unknown, it seems unlikely that foraging
mechanisms operating on an hourly or daily time scale
could explain patterns that are consistent over several
1060
O. T. Albert et al.
Physical-biological coupling
Distribution pattern
4
n=4
3
n=4
2
n=6
1
n=4
3
5
4
Mean temperature (°C) at age 0–1
0.3
40
0.2
30
20
0.1
10
1993
1992
1991
1990
1989
1988
1987
1986
1985
0
1984
0
1983
6
50
Ratio
Numbers-at-age 1 (×10 )
Figure 8. Mean temperature at age 0–1 (s.e.) for different
distribution patterns (cf. Figure 7).
Year
Rank of ratio
Figure 9. Survey-based (closed diamonds) and VPA-based
(open circles) numbers-at-age 1 and the ratio (broken line)
between the two.
12
12
10
10
8
8
6
6
4
4
2
2
0
1
2
3
4
Index of distribution
0
2.5
3
3.5
4
4.5
5
Mean temperature (°C)
Figure 10. Rank order of the ratio of survey-based and
VPA-based numbers-at-age 1 compared vs. (left panel) distribution pattern (cf. Figure 7) and (right panel) temperature at
age 0–1.
years. The most likely explanation for the observed
changes is thus that the 1-group is largely distributed
outside the geographical area covered by the surveys,
and more so during the first half of the 1990s.
The Northeast Atlantic Current that transports the
spawning products of Greenland halibut splits into
three major branches on its way northward (Dragesund
and Gjøsæter, 1988; Blindheim, 1989; Loeng, 1989). One
branch enters into the Barents Sea south of Bear
Island, while the other continues northwards as the
Spitsbergen Current. The water on the western side of
the Spitsbergen Current leaves off into the Norwegian
Sea directing towards Greenland. The remaining current
follows the continental slope north of Spitsbergen and
may enter the Barents Sea from the north. The relative
volume transport in each branch is highly variable
and depends on the weather conditions (A
r dlandsvik and
Loeng, 1991).
Survey abundance, extent of distribution in the survey
area and the ratio of survey abundance to VPA abundance were all negatively correlated with the mean
temperature in the Spitsbergen Current at the South
Cape transect experienced during the first two years
of life. Haug and Gulliksen (1982) surveyed West
Spitsbergen waters in 1979–1981 and found much higher
1-group abundance in 1979 than in the two succeeding
years. This difference also coincides with a distinctly
lower mean temperature (at age 0 and 1) in 1979 (Figure
5). The temperature in the Spitsbergen Current may
reflect the temperature in the Northeast Atlantic Current
or may be an indication of the volume transport in the
current. The mechanisms linking the distribution of
juvenile Greenland halibut to temperature in the
Spitsbergen Current may thus be related to the flux (as
affecting drift of spawning products), to temperature (as
affecting thermotactic migration towards more favourable temperatures), or indirectly to other factors that
may be influenced by these factors (such as spawning
location and abundance of predators and prey).
A
r dandsvik et al. (1999) simulated egg and larval drift
of Greenland halibut by way of a numerical model of
current fields. They observed considerable interannual
variability in the distribution of larvae between the
branch south of Bear Island and the one along West
Spitsbergen caused by variation in the relative volume
transport in the two branches. In all simulations, the
Spitsbergen Current was the most important transport
route, whereas the branch south of Bear Island was
more variable. This corroborates our finding of higher
variability of 1-group abundance in the Hopen Deep
than along West Spitsbergen. The presence of pelagic
0-group in the international 0-group surveys in autumn
was also much more variable in the Barents Sea than
along West Spitsbergen (Albert et al., 1997; e.g. ICES,
1996).
Along western Spitsbergen, 0-group was distributed
close to the coast in some years and extending west of
5E in others (e.g. 1978–1987 and 1993–1994; Albert
Distribution and abundance of juvenile Northeast Arctic Greenland halibut
et al., 1997). Such westerly distributions may result in
part of the 3–8 cm long 0-groups being carried further
away from the coast with the Northern Norwegian Sea
circulation. The extent of this leakage and the fate of the
individuals involved are largely unknown, but should be
expected to vary between years. However, A
r dlandsvik
et al. (1999) observed that only a minor fraction of the
larvae has been caught in this westerly current.
Haug et al. (1989) found that some recruits would end
their drift migration and settle in the slope and on
coastal banks along the west coast of Spitsbergen.
Others may continue eastwards, north of the archipelago. These may spread out along the deep trenches
of the northern Barents Sea and along the slope of
the Arctic Ocean. Although these areas have only
been sampled sporadically, Bowering and Nedreaas
(2000) showed that areas east of Svalbard and around
Franz Josefs Land may be important nursery areas for
Greenland halibut, at least periodically.
Greenland halibut may thus be transported along
three main routes corresponding to the three branches of
the North Atlantic Current. The relative importance of
each route, and the main settlement areas along the
routes, may vary between years. Variation in volume
transport is just one potential factor. Others include
variations in areas where spawning is most intense, and
differential survival of young fish between areas.
Kovtsova et al. (1987) showed that the latitudinal
distribution of spawners varied between years, and
A
r dlandsvik et al. (1999) showed that such variation
would greatly influence the distribution of larvae
between southern and northern regions. Godø and
Haug (1987) noted the possible impact of predation
from cod and of by-catch in the shrimp fishery.
Estimated predation on Greenland halibut increased
from near zero in 1984–1990 to a few thousand tonnes
annually in 1991–1995 (ICES, 1997). Accounting for
increased natural mortality would tend to increase VPAbased estimates of total abundance of 1-group for the
first part of the 1990s, resulting in an even lower ratio of
survey abundance to VPA abundance for those years.
However, the data on predation by cod are limited.
Among 80 000 cod stomachs examined, 1–3-year-old
Greenland halibut were recovered from just 27 stomachs
(S. Mehl, pers. comm.).
Bowering and Nedreaas (2000) report that Greenland
halibut in the Barents Sea and Svalbard area is most
abundant at temperatures below 3C. In our surveys,
high abundance and a wide southerly distribution were
observed at temperatures in the South Cape Transect
around 3C, whereas low abundance and a narrow
northerly distribution were associated with temperatures
above 4.5C. If Greenland halibut exhibit thermotactic
migrations after settlement, these would probably be
towards colder water. There are areas of cold Arctic
Water in the trench between Spitsbergen and Bear
1061
Island (Dragesund and Gjøsæter, 1988). This area was
included in the surveys but did not show any concentrations of juveniles. Cold water (down to 1C) is also
found along the slope at depths below 600–1000 m.
Although several hauls were taken at these depths, no
1-group was recorded (Albert et al., 1997). Thus, any
thermotactic migration after settlement would probably
go in the same direction as the drift migration, i.e.
northwards out of the survey area.
Implications
A central question of interest for the management of
Northeast Arctic Greenland halibut is how to obtain
reliable recruitment estimates. Currents, temperature
gradients, or other physical factors are apparently
important for understanding how survey results relate to
recruitment and our analysis suggests that the ‘‘recruitment failure’’ reported in previous assessments (ICES,
1998) is an artefact caused by a decreasing proportion of
the year classes at younger ages being present in the
survey area.
It is obviously essential that surveys used for tuning
VPA or otherwise in stock assessment, sample a consistent proportion of the juvenile population. In polar
regions, frequently covered by ice for the whole or major
parts of the year, this is not always possible. Both
northwest Greenland waters and the waters along the
slope and deep basins between Svalbard and Franz
Josefs Land are frequently ice-covered the whole year.
The problem could be partly circumvented if the proportion of the population covered by the survey can be
linked to some measurable factor, particularly if the
mechanisms are understood. Although this still may
not allow reliable predictions of abundance in areas
not surveyed, at least an assessment of the level and
direction of the bias might be achieved.
Acknowledgements
Dr Michael Fogarty, Professor Niels Daan, and
two anonymous referees are thanked for valuable
suggestions for improving the manuscript.
References
A
r dlandsvik, B., and Loeng, H. 1991. A study of the Barents Sea
Climate System. Polar Research, 10: 45–49.
A
r dlandsvik, B., Gundersen, A. C., Nedreaas, K. H., Stene, A.,
and Albert, O. T. 1999. Modelling the advection and diffusion of eggs and larvae of northeast Arctic Greenland
halibut. ICES 1999/K: 03, 20 pp.
Albert, O. T., Nilssen, E. M., Nedreaas, K. H., and Gundersen,
A. C. 1997. Recent variations in recruitment of Northeast
Atlantic Greenland halibut (Reinhardtius hippoglossoides) in
relation to physical factors. ICES 1997/EE: 06, 22 pp.
1062
O. T. Albert et al.
Albert, O. T., Nilssen, E. M., Stene, A., Gundersen, A. C., and
Nedreaas, K. H. 2001. Maturity classes and spawning behaviour of Greenland halibut (Reinhardtius hippoglossoides).
Fisheries Research, 51: 217–228.
Aschan, M., and Sunnanå, K. 1997. Evaluation of the
Norwegian Shrimp Survey conducted in the Barents Sea and
the Svalbard area 1980–1997. ICES 1997/Y: 07, 22 pp.
Aure, J. 2000. Havets miljø. Fisken og Havet, særnummer 2.
Institute of Marine Research, Bergen, Norway. 138 pp.
Blindheim, J. 1989. Ecological features of the Norwegian Sea.
In The Proceedings of the Sixth Conference of the Comité
Arctique International, pp. 266–288. Ed. by L. Rey, and
V. Alexander. Fairbanks, Alaska. 13–15 May 1985.
Bowering, W. R., and Brodie, W. B. 1995. Greenland halibut
(Reinhardtius hippoglossoides). A review of the dynamics
of its distribution and fisheries off Eastern Canada and
Greenland. In Deep-Water Fisheries of the North Atlantic
Oceanic Slope, pp. 113–160. Ed. by A. G. Hopper. Kluwer
Academic Publishers, The Netherlands.
Bowering, W. R., and Lilly, G. R. 1992. Greenland halibut
(Reinhardtius hippoglossoides) off southern Labrador and
northeastern Newfoundland (Northwest Atlantic) feed primarily on capelin (Mallotus villosus). Netherlands Journal of
Sea Research, 29: 211–222.
Bowering, W. R., and Nedreaas, K. H. 2000. A comparison of
Greenland halibut (Reinhardtius hippoglossoides Walbaum)
fisheries and distribution in the Northwest and Northeast
Atlantic. Sarsia, 85: 61–76.
Dragesund, O., and Gjøsæter, J. 1988. The Barents Sea. In
Continental Shelves, pp. 339–361. Ed. by H. Postma, and
J. J. Zijlstra. Ecosystems of the World, vol. 27. Elsevier,
Amsterdam.
Engs, A., and Godø, O. R. 1989. Escape of fish under the
fishing line of a Norwegian sampling trawl and its influence
on survey results. Journal du Conseil International pour
l’Exploration de la Mer, 45: 269–276.
Fedorov, K. Y. 1971. Zoogeographic characteristics of the
Greenland halibut (Reinhardtius hippoglossoides (Walbaum)).
Journal of Ichthyology, 11: 971–976.
God, O. R., and Haug, T. 1987. A preliminary report on the
recruitment variation in Greenland halibut (Reinhardtius
hippoglossoides (Walbaum)) in the Svalbard area. NAFO
SCR Doc. 87/83 (Ser. no. N1386). 14 pp.
Godø, O. R., and Haug, T. 1989. A review of the natural
history, fisheries, and management of Greenland halibut
(Reinhardtius hippoglossoides) in the eastern Norwegian and
Barents Seas. Journal du Conseil International pour
l’Exploration de la Mer, 46: 62–75.
Haug, T., Bjørke, H., and Falk-Petersen, I.-B. 1989. The
distribution, size composition, and feeding of larval
Greenland halibut (Reinhardtius hippoglossoides Walbaum)
in the eastern Norwegian and Barents Seas. Rapports et
Procès-Verbaux des Réunions du Conseil International pour
l’Exploration de la Mer, 191: 226–232.
Haug, T., and Gulliksen, B. 1982. Size, age, occurrence,
growth, and food of Greenland halibut (Reinhardtius hippoglossoides Walbaum) in coastal waters of western
Spitsbergen. Sarsia, 68: 293–297.
Hylen, A., and Nedreaas, K. H. 1995. Pre-recruit studies of the
north-east arctic Greenland halibut stock. In Precision and
Relevance of Pre-recruit Studies for Fishery Management
Related to Fish Stocks in the Barents Sea and Adjacent
Waters. Proceedings of the Sixth IMR-PINRO Symposium,
Bergen, 14–17 June 1994, pp. 229–238. Ed. by A. Hylen.
Institute of Marine Research, Bergen.
ICES. 1996. Preliminary Report of the International 0-Group
Fish Survey in the Barents Sea and Adjacent Waters in
August-September 1996. ICES 1996/G: 31, 37 pp.
ICES. 1997. Report of the Arctic Fisheries Working Group.
ICES 1998/Assess: 4, 318 pp.
ICES. 1998. Report of the Arctic Fisheries Working Group.
ICES 1998/Assess: 2, 366 pp.
ICES. 2000. Report of the Arctic Fisheries Working Group.
ICES 2000/ACFM: 3, 312 pp.
ICES. 2001. Report of the Arctic Fisheries Working Group.
ICES 2001/ACFM: 2, 340 pp.
Kovtsova, M. V., Nizovtsev, G. P., and Tereshchenko, V. V.
1987. Conditions for the formation of prespawning and
spawning Greenland halibut concentrations of the
Norwegian–Barents Sea stock. In The Effect of Oceanographic Conditions on Distribution and Population
Dynamics of Commercial Fish Stocks in the Barents Sea,
pp. 199–211. Ed. by H. Loeng. Proceedings of the Third
Soviet–Norwegian symposium, Murmansk, 26–28 May 1986.
Institute of Marine Research, Bergen, Norway.
Loeng, H. 1989. Ecological features of the Barents Sea. In The
Proceedings of the Sixth Conference of the Comité Arctique
International, pp. 328–365. Ed. by L. Rey, and V. Alexander.
Fairbanks, Alaska. 13–15 May 1985.
Michalsen, K., and Nedreaas, K. H. 1998. Food and feeding of
Greenland halibut (Reinhardtius hippoglossoides Walbaum)
in the Barents Sea and East Greenland waters. Sarsia, 83:
401–407.
Whitehead, P. J. P., Bauchot, M.-L., Hureau, J.-C., Nielsen, J.,
and Tortonese, E. 1986. Fishes of the North-eastern Atlantic
and the Mediterranean. UNESCO, Paris. 1473 pp.