YEAR YEAR - - TO TO - - YEAR DYNAMICS OF TROPHIC YEAR DYNAMICS OF TROPHIC LINKS OF THE MAIN COMMERCIAL
LINKS OF THE MAIN COMMERCIAL FISHES IN THE BARENTS SEA AS FISHES IN THE BARENTS SEA AS
INDICATING THE STATE OF ECOSYSTEM INDICATING THE STATE OF ECOSYSTEM
E.L.Orlova
E.L.Orlova, , A.V.Dolgov, A.V.Dolgov , S.V.Belikov S.V.Belikov (PINRO), E.Johannesen (PINRO), E.Johannesen (IMR) (IMR)
The main goals are to investigate the effect of The main goals are to investigate the effect of
climate variation and fishery on structural climate variation and fishery on structural changes in the Barents Sea ecosystem, and changes in the Barents Sea ecosystem, and also influence of these factors on commercial also influence of these factors on commercial
fish populations
fish populations
MATERIALS MATERIALS
There were our own, archive and There were our own, archive and
literature data of feeding, stock dynamic, literature data of feeding, stock dynamic, distribution and fatness of cod and capelin distribution and fatness of cod and capelin
since 70s till nowadays used in this paper
since 70s till nowadays used in this paper
INTRODUCTION INTRODUCTION
The functioning of the Barents Sea ecosystem is based on The functioning of the Barents Sea ecosystem is based on
the energy transformation in phytoplankton
the energy transformation in phytoplankton -zooplankton - zooplankton- - pelagic fishes
pelagic fishes -cod - cod trophic trophic chain. Despite a highly chain. Despite a highly euryphagous
euryphagous character, cod feeding is connected with character, cod feeding is connected with numerous traditional fishes
numerous traditional fishes – – capelin, herring, polar cod, as capelin, herring, polar cod, as well as juvenile fish and crustaceans (
well as juvenile fish and crustaceans ( euphausiids euphausiids , , hyperiids
hyperiids ) forming seasonal concentrations. The effect on ) forming seasonal concentrations. The effect on
commercial fish stocks is also great. The impact of these
commercial fish stocks is also great. The impact of these
factors is often superimposed accompanying by the change
factors is often superimposed accompanying by the change
of dominating species in cod feeding: they were polar cod
of dominating species in cod feeding: they were polar cod
in the 1920s, capelin or herring in the 1930s, capelin in the
in the 1920s, capelin or herring in the 1930s, capelin in the
1970 1970 - - 80s. 80s.
Stocks dynamics of cod, capelin, polar cod and blue Stocks dynamics of cod, capelin, polar cod and blue
whiting in 1980
whiting in 1980 - - 2004. 2004.
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
Year Biomass, 10 3 tones
Cod
Blue whiting Polar cod Capelin
During the last twenty During the last twenty
years, in the Barents years, in the Barents
Sea, the significant Sea, the significant
fluctuations of pelagic fluctuations of pelagic
fish stocks were fish stocks were
registered. They were registered. They were
typical, mainly, for typical, mainly, for
capelin
capelin
Stocks dynamics and cod supply by capelin in different Stocks dynamics and cod supply by capelin in different
time periods in 1978
time periods in 1978- -2000. 2000.
0 200 400 600 800 1000 1200 1400 1600 1800
1978-1984 1985-1989 1990-1992 1993-2000 Period
Abundance,103 ind. (cod), 106 ind.(capelin)
0 500 1000 1500 2000 2500
Number of capelin per a cod.
Abundance of cod Abundance of capelin
Number of capelin per a cod
According to trends of According to trends of capelin stocks, a
capelin stocks, a conditional
conditional index of index of cod food supply (the cod food supply (the number
number
of capelin per a cod) of capelin per a cod) reaching 2,500
reaching 2,500 - - 3,400 3,400 ind. ind .
in the early 1980s have in the early 1980s have not exceeded 200
not exceeded 200- - 300 300 ind ind . recently and was . recently and was minimal in 1995
minimal in 1995
Frequency of occurrence (%)
Frequency of occurrence (%) euphausiids euphausiids in stomachs of in stomachs of capelin by age 2 (a), 3 (b)
capelin by age 2 (a), 3 (b) и и 4 (c) in August- 4 (c) in August -October 1979 October 1979
74°
75°
76°
77°
78°
79°
80°
10° 15° 20° 25° 30° 35° 40° 45° 50° 55° 60°
74°
75°
76°
77°
78°
79°
80°
10° 15° 20° 25° 30° 35° 40° 45° 50° 55° 60°
74°
75°
76°
77°
78°
79°
80°
10° 15° 20° 25° 30° 35° 40° 45° 50° 55° 60°
a
b
c
21.09.
0 %
09.09.
13% 03.09 83%
10.08 100 %30.09
100 % 03.09.
0 % 10.10
25% 23.09.
7% 25.09.
64%
08.08.
11%
23.09.
13%
18.08 27.08. 75%
17%
30.08 24%
14.08 40%
08.08.
68%
29.10.
50%
25.09.
65%
23.09.
29%
12.08 24%
09.09.
13%
03.09.
33%
03.09 100 % 07.10.
64%
21.09 81%
28.08.
50%
30.08.
60%
30.08.
33%
29.08.
30%
18.08.
73%
14.08.
10.08. 75%
96%
09.09.
100 % 12.08.
33%
08.08.
0 % 25.09 85%
07.10.
100 % 15.09.
70%
04.09.
50%
21.09.
100 % 03.09.
100 % 28.08 100 %
18.08 85%
30.08.
100 % 10.10.
0 % 14.08.
0 % 10.08 100 %
In anomalous 1979, In anomalous 1979, feeding on
feeding on euphausiids euphausiids was the most prolonged was the most prolonged in the Hope Area. To the in the Hope Area. To the north of 77ºN, capelin north of 77ºN, capelin did not feed on
did not feed on euphausiids
euphausiids and started and started
to consume copepods
to consume copepods
Frequency of occurrence (%)
Frequency of occurrence (%) euphausiids euphausiids in stomachs of in stomachs of capelin by age 2 (a), 3 (b)
capelin by age 2 (a), 3 (b) и и 4 (c) in August 4 (c) in August - - November 1980 November 1980 In moderate 1980, in
In moderate 1980, in August
August - - September, September,
capelin having migrated capelin having migrated
northward to 77
northward to 77- -78ºN fed 78ºN fed on euphausiids on euphausiids in the in the
large area from the South large area from the South
Cape Deep to the
Cape Deep to the Perseus Perseus Elevation. In 1980, their Elevation. In 1980, their
value by weight was very value by weight was very
high: 58% in August, 62 high: 58% in August, 62 - -
96% in September 96% in September - -
October, 89% in October, 89% in
November.
74°
75°
76°
77°
78°
79°
80°
10° 15° 20° 25° 30° 35° 40° 45° 50° 55° 60°
74°
75°
76°
77°
78°
79°
80°
10° 15° 20° 25° 30° 35° 40° 45° 50° 55° 60°
74°
75°
76°
77°
78°
79°
80°
10° 15° 20° 25° 30° 35° 40° 45° 50° 55° 60°
a
b
c
07.09.
62%
07.09 58%
07.09 78%
09.09 0 %
09.09 0 % 09.09.
2%
10.09 42%
10.09.
35%
10.09 78%
10.09.
71%
10.09.
87%
07.08.
11%.
07.08.
32%
07.08.
32%
27.09 25%
27.09 23%
27.09.
37%
28.09.
100 %
28.09.
94%
28.09 75%
05.10.
100 %
05.10.
83%
13.10.
65%
13.10.
100 %
04.08.
33%
04.08.
57%
04.08.
77%
07.08.
13%. 07.08.
19%
07.08 0 %
13.08 40%
13.08.
36%
13.08.
30%
18.08.
18%
18.08.
20%
04.11.
14%.
04.11.
33%
23.08 49%
23.08.
55%
23.08.
80%
13.09.
74%
13.09.
83%
13.09.
86%
18.09 0 %
18.09 50%
21.09 0 %
21.09 0 % 21.09.
13%
29.09.
29%
16.11.
100 %
16.11.
100 %
16.11.
100 %
November.
Distribution of cod (red color) and capelin (shading) Distribution of cod (red color) and capelin (shading)
aggregations in the Barents Sea in 1979 and 1980 aggregations in the Barents Sea in 1979 and 1980
10 20 30 40 50 60 70
68 70 72 74 76 78 80
10 20 30 40 50 60 70
68 70 72 74 76 78 80
10 20 30 40 50 60 70
68 70 72 74 76 78 80
1980
VIII
IX
X
10 20 30 40 50 60 70
67 68 69 70 71 72 73 74 75 76 77 78 79 80
10 20 30 40 50 60 70
67 68 69 70 71 72 73 74 75 76 77 78 79 80
10 20 30 40 50 60 70
67 68 69 70 71 72 73 74 75 76 77 78 79 80
VIII
IX
1979 X
In 1979 and 1980, cod In 1979 and 1980, cod distribution was, to a distribution was, to a minor extent, connected minor extent, connected with capelin. Alongside with capelin. Alongside with this, taking into with this, taking into consideration that cod consideration that cod small concentration small concentration overlapped the capelin overlapped the capelin ones feeding one can ones feeding one can assume that the reason assume that the reason of the limited
of the limited
consumption of capelin consumption of capelin was not only
was not only
inaccessibility for cod inaccessibility for cod because of low
because of low temperature.
temperature.
Frequency of occurrence (%)
Frequency of occurrence (%) euphausiids euphausiids in cod stomachs in cod stomachs in June (a), July (b), August (c) and September (d) 1998 in June (a), July (b), August (c) and September (d) 1998
16 20 24 28 32 36 40 44 48
68 70 72 74 76 78 80
16 20 24 28 32 36 40 44 48
68 70 72 74 76 78 80
16 20 24 28 32 36 40 44 48
68 70 72 74 76 78 80
16 20 24 28 32 36 40 44 48
68 70 72 74 76 78 80
In 1996
In 1996- - 1998, cod northeast 1998, cod northeast aggregations distributed more aggregations distributed more southward, than usually,
southward, than usually, overlapping the
overlapping the euphausiid euphausiid ones. ones.
In those years, a small increase in In those years, a small increase in capelin abundance was being
capelin abundance was being noticed, however, till August, noticed, however, till August, capelin seldom occurred
capelin seldom occurred
in the cod diet, in the cod diet,
and cod and cod regularly regularly
(from April to (from April to
July) July)
fed on fed on
euphausiids euphausiids
1 to 10 11 to 20 21 to 40 41 to 60 61 to 100
Distribution of cod aggregations (red color) in the Barents Distribution of cod aggregations (red color) in the Barents
Sea in August
Sea in August - - October 1998 October 1998
10 20 30 40 5 0 6 0 70
68 70 72 74 76 78 80
1 0 2 0 30 40 50 60 70
6 8 7 0 7 2 7 4 7 6 7 8 8 0
10 20 30 40 50 6 0 7 0
68 70 72 74 76 78 80
VIII
IX
X
1998
The distribution of cod was the The distribution of cod was the most northward
most northward
in 1998, when its schools in 1998, when its schools reached 77ºN
reached 77ºN
in the area of the West in the area of the West Spitsbergen
Spitsbergen, the southern , the southern
extremely of the Edge Island, extremely of the Edge Island, in the South Cape Deep and in the South Cape Deep and Hope Area partly overlapping Hope Area partly overlapping aggregations of feeding capelin aggregations of feeding capelin which distributed to 79ºN.
which distributed to 79ºN.
Distribution of cod aggregations (red color) in the Barents Distribution of cod aggregations (red color) in the Barents
Sea in August
Sea in August- - October 1992 October 1992
10 20 30 4 0 50 60 70
68 70 72 74 76 78
80 10 20 30 4 0 50 60 70
68 70 72 74 76 78 80
1 0 2 0 30 40 50 6 0 7 0
6 8 7 0 7 2 7 4 7 6 7 8 8 0
VIII
IX
X 1992
In 1990
In 1990- -1992 cod was 1992 cod was characterized by the north characterized by the north distribution. In the Hope Area and distribution. In the Hope Area and Perseus Elevation, large fish Perseus Elevation, large fish reached 78ºN
reached 78ºN - - 78º30’N. There, 78º30’N. There, feeding areas of cod and capelin feeding areas of cod and capelin overlapped that conditioned a overlapped that conditioned a high consumption level of the high consumption level of the latter.
latter.
Frequency of occurrence (%, red color) capelin in cod Frequency of occurrence (%, red color) capelin in cod stomachs in the Barents Sea by months
stomachs in the Barents Sea by months 1999 1999 (ciphers show (ciphers show months)
months)
10 20 30 40 50
68 70 72 74 76 78
12
12 12
8 9 11
8 9
11 7 8 911 12
7 9
7 8
12
3 7
3 4 7 8
9 9 3 6
7 8 9 11 12 2 3 4
5 6 7 11
12 6
8 7 8 9 3 4 5 10
7 9 10
1 6
11 12
6 8 12
3 4 5 6
7 8 11
12
4 6
3 4 5
7
10
11 5 6 7
8 10 12
1 5 6 10 7
10 11 12
5 10
11 12
4 5 7
8 10 11
12
8 9
10
4 5
9 10
7 8
5
3 4 3
1 2 3
The most favourable The most favourable
conditions of cod feeding conditions of cod feeding
were in 1999
were in 1999 -2001, when - 2001, when
capelin abundance increased.
capelin abundance increased.
The year of 1999, when cod The year of 1999, when cod
fed on capelin already in fed on capelin already in
January, was noted in the January, was noted in the
northwestern wintering years.
northwestern wintering years.
Intensive capelin feeding was Intensive capelin feeding was
recorded in May
recorded in May - - June. June.
Capelin frequency of Capelin frequency of
occurrence reached 65
occurrence reached 65 -90% - 90%
that conditioned its maximal that conditioned its maximal
value in the annual feeding value in the annual feeding – –
about 60% by weight.
about 60% by weight.
Food consumption of cod in the Barents Sea in 1984
Food consumption of cod in the Barents Sea in 1984 - - 2004 2004
In 2003
In 2003- -2004, 2004, despite the usual despite the usual
reduction in capelin reduction in capelin
stock, the fish stock, the fish
consumption by cod consumption by cod
in absolute figures in absolute figures
was extremely high was extremely high
in 2003 and 2004 in 2003 and 2004
(1263 t and 1101 t, (1263 t and 1101 t,
respectively) and respectively) and
was approaching to was approaching to
the level of 1999 the level of 1999 - - 2001 2001
Shrimp Herring
Capelin Polar
cod
Cod
Haddoc
Sebastes
Others
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
Year Consumed biomass, 103 tones
Frequency of occurrence polar cod (red
Frequency of occurrence polar cod (red colour colour ) and young ) and young polar cod (shading) in cod stomachs in the Barents Sea by polar cod (shading) in cod stomachs in the Barents Sea by
months
months 2001 2001 (ciphers show months) (ciphers show months)
10 20 30
74 76 78 80
10
2 3
5 6
6 7
7
7 8
8
8
9
9
9
9
9
10
10
10
10
10 11
11
11
11 11
11
11
11
12
12 12
12
1 2 3 4
Since 1999
Since 1999- -2000, 2000, the area of cod the area of cod feeding on polar feeding on polar cod widened and cod widened and the adult fish
the adult fish started to be started to be
consumed by the consumed by the cod from the
cod from the West
West Spitsbergen Spitsbergen to the
to the Perseus Perseus
Elevation and the Elevation and the Franz Josef Land. In Franz Josef Land. In 2004 polar cod practically substituted capelin in the food of 2004 polar cod practically substituted capelin in the food of cod. In its turn, that might be indicative of food competition cod. In its turn, that might be indicative of food competition strengthening between them in
strengthening between them in favour favour of polar cod. of polar cod.
Frequency of occurrence (red
Frequency of occurrence (red colour colour ) blue whiting in ) blue whiting in cod stomachs in the Barents Sea by months
cod stomachs in the Barents Sea by months 2002 2002 (ciphers (ciphers show months)
show months)
10 20 30 40
69 71 73 75 77 79
2 2
2
3
3 3
3
3 4
4
4
5 5 5
5
5
5
6 6
6
6
7 7
7
7
7
8 8
8
8 8
8
8
9 9
9
9 9
9
10
10 10
10
10 10
10
10
11 11
11 11 11
11
11
11
12 12
12
12
12
1 2 3
• •
A wide distribution of blue whiting A wide distribution of blue whiting in warm years favours growth of in warm years favours growth of food competition between fish food competition between fish species. In the Bear Islandspecies. In the Bear Island--
Spitsbergen area, where to large Spitsbergen area, where to large fish migrate, they, alongside with fish migrate, they, alongside with euphausiids and hyperiids, feed on euphausiids and hyperiids, feed on capelin, polar cod, juvenile cods.
capelin, polar cod, juvenile cods.
• •
The blue whiting itself also started The blue whiting itself also started to occur significantly more often in to occur significantly more often in cod feeding. The largest area of cod feeding. The largest area of blue whiting consumption was blue whiting consumption was recorded in 2002, that coincided recorded in 2002, that coincided with the maximal biomass of this with the maximal biomass of this fish in the Bear Islandfish in the Bear Island--Spitsbergen Spitsbergen area (around 145 x 10
area (around 145 x 1033t) and made t) and made up about 10% by weight in the
up about 10% by weight in the annual diet of cod.
annual diet of cod.
Frequency of occurrence (red
Frequency of occurrence (red colour colour) herring in cod ) herring in cod stomachs in the Barents Sea by months
stomachs in the Barents Sea by months 2003 2003
26 36 46
69 71 73
1 1
2 2
2
2
2
2 2
2 2
2
2 2
2
3 3
3 3
3 3
4
4 4
4 4
5
5 6 6
7
7
8 8
8
8 8
8
9 9
9
9 9
9
9 9
9 9
9 9
9
9
9 9
10 10
10 10 10
10 10
10
11
11 11
11 11
11 11
11
11 11
11
11 11
12 12
12 12
12
12 12
12 12
12
12 12
12 12
12
12
1 2 3 4
Herring doesn’t play a Herring doesn’t play a considerable part in cod considerable part in cod feeding in the Bear Island feeding in the Bear Island - - Spitsbergen
Spitsbergen area. Due to area. Due to the above
the above - - mentioned mentioned shift of cod wintering shift of cod wintering borders eastwards, its borders eastwards, its influence on
influence on
concentrations of herring concentrations of herring wintering in the central, wintering in the central, coastal southeastern and coastal southeastern and even eastern areas
even eastern areas strengthened. In the strengthened. In the
highest degree, it showed highest degree, it showed itself in 2003
itself in 2003
Seasonal changes in cod fatness with high (a) and low Seasonal changes in cod fatness with high (a) and low
(b) с (b) сapelin apelin supply supply
2 4 6 8 10
Fatness, %
1984 1990 1991 1992 2000
а
Capelin was characterized by Capelin was characterized by
higher calorie content (2 kkal/g in higher calorie content (2 kkal/g in raw weight). According to the
raw weight). According to the significance of capelin in annual significance of capelin in annual dynamics of cod feeding, the two dynamics of cod feeding, the two groups of years. The first group groups of years. The first group included the years with the
included the years with the
capelin significance of 15% and capelin significance of 15% and more in the cod diet (1984, 1990 more in the cod diet (1984, 1990-- 1992, 1998
1992, 1998--2000). In most cases, 2000). In most cases, after a small reduction in fatness after a small reduction in fatness in May
in May--July, its abrupt rise (8July, its abrupt rise (8--9%) 9%) was registered in August
was registered in August--October October and the level was high till
and the level was high till
December. The second group December. The second group involved the years with the involved the years with the significance of less than 15%
significance of less than 15%
(1986
(1986--1988, 19931988, 1993-1997)-1997)
2 4 6 8 10
1 2 3 4 5 6 7 8 9 10 11 12
Fatness, %
1986 1988 1993 1994 1995 1996 199
b
Month
CONCLUSION CONCLUSION
• •
Structural changes in pelagic (plankton, nekton) communities andStructural changes in pelagic (plankton, nekton) communities and interspecificinterspecific relations of the main commercial fishes determined the relations of the main commercial fishes determined the effectiveness of the Barents Sea ecosystem functioning. From tim
effectiveness of the Barents Sea ecosystem functioning. From time to time e to time fishery made a significant contribution to the
fishery made a significant contribution to the trophodynamicstrophodynamics that, on the that, on the background of climatic variations led to catastrophic consequenc
background of climatic variations led to catastrophic consequences. It is es. It is exemplified by the falling out of the
exemplified by the falling out of the AtlantoAtlanto--ScandianScandian herring, playing a herring, playing a great part in ecosystem and cod feeding, from pelagic fish commu
great part in ecosystem and cod feeding, from pelagic fish community for nity for a long period (the late 1960s
a long period (the late 1960s--early 1980). early 1980).
• •
The situation with capelin also turned out dramatically. Cold yeThe situation with capelin also turned out dramatically. Cold years (midars (mid-- 1970s1970s-- the early 1980s) conditions were the most favorable for capelinthe early 1980s) conditions were the most favorable for capelin. . Good feeding conditions, a high growth and reproduction rates pr
Good feeding conditions, a high growth and reproduction rates provided ovided big size of capelin stock.
big size of capelin stock.
• •
Cod was provided well with the main food (capelin) and didn’t maCod was provided well with the main food (capelin) and didn’t make ke stretched migrations, concentrated in the western areas. These fstretched migrations, concentrated in the western areas. These factors actors promote the disconnection of feeding areas of cod and capelin, w
promote the disconnection of feeding areas of cod and capelin, which feed hich feed in the north waters, that conditioned a week press of predators.
in the north waters, that conditioned a week press of predators. The lack The lack of main capelin food competitors (juvenile cods) also had a favo
of main capelin food competitors (juvenile cods) also had a favorable rable effect on capelin feeding condition. As a result, fatness of bot
effect on capelin feeding condition. As a result, fatness of both capelin and h capelin and cod was high.
cod was high.
• •
Capelin was fished intensively that led to the collapse of its sCapelin was fished intensively that led to the collapse of its stocks in the tocks in the midmid--1980s. With a low abundance and abrupt reduction of older fish i1980s. With a low abundance and abrupt reduction of older fish in n population, capelin didn’t use feeding resources of northern arepopulation, capelin didn’t use feeding resources of northern areas. Capelin as. Capelin deficiency resulted low cod feeding and the increase in the cons
deficiency resulted low cod feeding and the increase in the consumption of umption of euphausiids
euphausiids and and hyperiidshyperiids, i.e. cod and capelin became food competitors., i.e. cod and capelin became food competitors.
• •
Despite of mass cod feeding on Despite of mass cod feeding on macroplanktonmacroplankton, food chain was shortest , food chain was shortest then usually; the low calorie content of those crustaceans did nthen usually; the low calorie content of those crustaceans did not ot compensate fish energy consumption. As a result, cod fatness wa
compensate fish energy consumption. As a result, cod fatness was low s low (less then 3%). Only in some periods, with a short
(less then 3%). Only in some periods, with a short--term recovery of term recovery of capelin abundance, ecosystem came to a normal condition (1990
capelin abundance, ecosystem came to a normal condition (1990--1992) 1992) based on interaction of the key species:
based on interaction of the key species: euphausiidseuphausiids, copepods , copepods –– capelin capelin –– cod.
cod.
• •
In the warm period (1999-In the warm period (1999-2004) plankton2004) plankton--eater feeding base stabilized eater feeding base stabilized due to strengthening the transport of warmdue to strengthening the transport of warm-water species -water species euphausiidseuphausiids (and copepods, probably) and their wide distribution in the Bare
(and copepods, probably) and their wide distribution in the Barents Sea, as nts Sea, as well as the opportunity of fish to use food resources of norther
well as the opportunity of fish to use food resources of northern areas.n areas.
• •
Plankton abundance conducted migrations and wide distribution ofPlankton abundance conducted migrations and wide distribution of blue blue whiting from Norwegian Sea and polar cod from Kara Sea. As a reswhiting from Norwegian Sea and polar cod from Kara Sea. As a result, ult, abundance of these fishes in the Barents Sea increased. On the o
abundance of these fishes in the Barents Sea increased. On the other hand ther hand in some local areas their feeding areas overlapped (capelin and
in some local areas their feeding areas overlapped (capelin and polar cod, polar cod, cod and blue whiting) that led to the strengthening of food comp
cod and blue whiting) that led to the strengthening of food competition, etition, which was indicated by low fatness of these fishes in some cases
which was indicated by low fatness of these fishes in some cases..
• •
Negative consequences of food competition for cod were leveled bNegative consequences of food competition for cod were leveled by its y its wide distribution in the warm years and high accessibility of cawide distribution in the warm years and high accessibility of capelin and pelin and polar cod, as well as of herring, wintering in the southeast and
polar cod, as well as of herring, wintering in the southeast and east. The east. The level of consumption of these fishes by cod was rather high, and
level of consumption of these fishes by cod was rather high, and cod cod fatness increased. Blue whiting didn’t play a significant part
fatness increased. Blue whiting didn’t play a significant part in cod in cod feeding, since fish having completely return migration mainly co
feeding, since fish having completely return migration mainly consumed nsumed them (November
them (November--December). December). EuphausiidsEuphausiids, being consumed by cod mainly, , being consumed by cod mainly, were stabilizing as a food supply of plankton
were stabilizing as a food supply of plankton-eaters.-eaters.
• •
Capelin, with its high accessibility for cod in the conditions of warm years, Capelin, with its high accessibility for cod in the conditions of warm years, it was under a great predation press, which might be confirmed bit was under a great predation press, which might be confirmed by the y the level of the fish consumption in that period. Capelin consumptio
level of the fish consumption in that period. Capelin consumption by n by predators was intensified by fishery that resembled that one in
predators was intensified by fishery that resembled that one in 19931993-1995. -1995.
In contrast with the 1970s, when the predation press was practic
In contrast with the 1970s, when the predation press was practically ally absent. At present the influence of predators (of cod, only) is
absent. At present the influence of predators (of cod, only) is greater than greater than the effect of fishery.
the effect of fishery.
YEAR-YEAR-TOTO--YEAR DYNAMICS OF TROPHIC LINKS OF THE MAIN YEAR DYNAMICS OF TROPHIC LINKS OF THE MAIN COMMERCIAL
COMMERCIAL
FISHES IN THE BARENTS SEA AS INDICATING THE STATE OF ECOSYSTEM FISHES IN THE BARENTS SEA AS INDICATING THE STATE OF ECOSYSTEM
•• GoalGoal
•• Fig. 10. Frequency of occurrence (%, red Fig. 10. Frequency of occurrence (%, red
•• IntroductionIntroduction
colour
colour) capelin in cod stomachs ) capelin in cod stomachs
•• Fig 1. Fig 1. Stocks dynamics of cod, capelin, polar Stocks dynamics of cod, capelin, polar cod and blue whiting
cod and blue whiting in 1980in 1980--2004.2004.
•• Fig. 2. Fig. 2. Stocks Stocks dynamicsdynamics and cod supply by and cod supply by
in Barents in Barents Sea by months
Sea by months 19991999
•• Fig. 11. Food consumed by cod Fig. 11. Food consumed by cod in the in the Barents Sea in 1984
Barents Sea in 1984--20042004
••
capelin
capelin in different time periods in 1978in different time periods in 1978-- 2000.
2000.
•• Fig. 3. Fig. 3. Frequency of occurrence (%) Frequency of occurrence (%) Fig. 12. Frequency of occurrence polar cod Fig. 12. Frequency of occurrence polar cod euphausiids
euphausiids in stomachs of capelin by age 2 in stomachs of capelin by age 2 (a), 3 (b)
(a), 3 (b) ии 4 (c) in August4 (c) in August-Oktober-Oktober 1979.1979.
•• Fig. 4. Fig. 4. Frequency of occurrence (%) Frequency of occurrence (%)
(red
(red colourcolour) and young polar cod (shading) ) and young polar cod (shading) in cod stomachs
in cod stomachs in Barents Sea by in Barents Sea by months
months 2001 2001
•• Fig. 13. Frequency of occurrence (red Fig. 13. Frequency of occurrence (red euphausiids
euphausiids in stomachs of capelin by age 2 in stomachs of capelin by age 2 (a), 3 (b)
(a), 3 (b) ии 4 (c) in August4 (c) in August-November 1980.-November 1980.
•• Fig.5. Fig.5. Distribution of cod (red color) and Distribution of cod (red color) and colour) blue whiting in cod stomachs colour) blue whiting in cod stomachs in in Barents Sea by months
Barents Sea by months 20022002
••
capelin (shading) aggregations
capelin (shading) aggregations in the in the Barents Sea in 1979.
Barents Sea in 1979.
•• Fig. 7. Fig. 7. Frequency of occurrence (%) Frequency of occurrence (%) Fig. 14. Frequency of occurrence (red Fig. 14. Frequency of occurrence (red colour
colour) herring in cod stomachs ) herring in cod stomachs in Barents in Barents Sea by months
Sea by months 20032003
•• Fig. 15. Fig. 15.
euphausiids
euphausiids in cod stomachs in June (a), in cod stomachs in June (a), July (b), August (c) and September (d) July (b), August (c) and September (d) 1998.
1998.
•• Fig. 8. Fig. 8. Distribution of cod aggregations Distribution of cod aggregations Seasonal changes in cod fatness Seasonal changes in cod fatness (red
(red color) in the Barents Sea in August
color) in the Barents Sea in August--October October 1998.
1998.
•• Fig.9. Fig.9.
with high (a) and low (b) capelin supply.
with high (a) and low (b) capelin supply.
1998.
1998.
•• Conclusion 1Conclusion 1 Distribution of cod aggregations
Distribution of cod aggregations (red (red color) in the Barents Sea in August
color) in the Barents Sea in August--October October 1992.
1992. •• Conclusion 2Conclusion 2
•• Conclusion 3Conclusion 3
•• Conclusion 4Conclusion 4
