YEARYEAR--TOTO--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.OrlovaE.L.Orlova, , A.V.DolgovA.V.Dolgov, , S.V.BelikovS.V.Belikov (PINRO), (PINRO), E.JohannesenE.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 populationsfish populations

MATERIALSMATERIALS

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

INTRODUCTIONINTRODUCTION

The functioning of the Barents Sea ecosystem is based on The functioning of the Barents Sea ecosystem is based on the energy transformation in phytoplanktonthe energy transformation in phytoplankton--zooplanktonzooplankton--pelagic fishespelagic fishes--cod cod trophictrophic chain. Despite a highly chain. Despite a highly euryphagouseuryphagous 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 (euphausiidseuphausiids, , hyperiidshyperiids) 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 19701970--80s.80s.

Stocks dynamics of cod, capelin, polar cod and blue Stocks dynamics of cod, capelin, polar cod and blue whiting in 1980whiting 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

Biom

ass,

10

3 tone

s

CodBlue whitingPolar codCapelin

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 capelincapelin

Stocks dynamics and cod supply by capelin in different Stocks dynamics and cod supply by capelin in different time periods in 1978time periods in 1978--2000.2000.

0

200

400

600

800

1000

1200

1400

1600

1800

1978-1984 1985-1989 1990-1992 1993-2000Period

Abu

ndan

ce,1

03 in

d. (c

od),

106 in

d.(c

apel

in)

0

500

1000

1500

2000

2500

Num

ber 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 conditionalconditional 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 2,500reaching 2,500--3,400 3,400 indind. . in the early 1980s have in the early 1980s have not exceeded 200not exceeded 200--300 300 indind. recently and was . recently and was minimal in 1995 minimal in 1995

Frequency of occurrence (%) Frequency of occurrence (%) euphausiidseuphausiids in stomachs of in stomachs of capelin by age 2 (a), 3 (b) capelin by age 2 (a), 3 (b) ии 4 (c) in August4 (c) in August--October 1979October 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%10.08100 % 30.09

100 %

03.09.0 %10.10 25% 23.09.

7%25.09. 64%

08.08.11%

23.09. 13%

18.08 75%27.08.

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%

03.09100 %

07.10. 64%

21.09 81%

28.08. 50%

30.08. 60%

30.08. 33%

29.08. 30%

18.08. 73%

14.08. 75%10.08.

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 %

28.08100 %

18.08 85%30.08.

100 %10.10.

0 %

14.08.0 %

10.08100 %

In anomalous 1979, In anomalous 1979, feeding on feeding on euphausiidseuphausiidswas 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 euphausiidseuphausiids and started and started to consume copepodsto consume copepods

Frequency of occurrence (%) Frequency of occurrence (%) euphausiidseuphausiids in stomachs of in stomachs of capelin by age 2 (a), 3 (b) capelin by age 2 (a), 3 (b) ии 4 (c) in August4 (c) in August--November 1980November 1980

In moderate 1980, in In moderate 1980, in AugustAugust--September, September, capelin having migrated capelin having migrated northward to 77northward to 77--78ºN fed 78ºN fed on on euphausiidseuphausiids in the in the large area from the South large area from the South Cape Deep to the Cape Deep to the PerseusPerseusElevation. In 1980, their Elevation. In 1980, their value by weight was very value by weight was very high: 58% in August, 62high: 58% in August, 62--96% in September96% 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%

09.090 %

09.090 %

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%

07.080 %

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%

18.090 %

18.09 50%

21.090 %

21.090 %

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 1980aggregations 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 7067

68

69

70

71

72

73

74

75

76

77

78

79

80

10 20 30 40 50 60 7067

68

69

70

71

72

73

74

75

76

77

78

79

80

10 20 30 40 50 60 7067

68

69

70

71

72

73

74

75

76

77

78

79

80

VIII

IX

X1979

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 (%) euphausiidseuphausiids in cod stomachs in cod stomachs in June (a), July (b), August (c) and September (d) 1998in June (a), July (b), August (c) and September (d) 1998

16 20 24 28 32 36 40 44 4868

70

72

74

76

78

80

16 20 24 28 32 36 40 44 4868

70

72

74

76

78

80

16 20 24 28 32 36 40 44 4868

70

72

74

76

78

80

16 20 24 28 32 36 40 44 4868

70

72

74

76

78

80

In 1996In 1996--1998, cod northeast 1998, cod northeast aggregations distributed more aggregations distributed more southward, than usually, southward, than usually, overlapping the overlapping the euphausiideuphausiid 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 euphausiidseuphausiids

1 to 1011 to 2021 to 4041 to 6061 to 100

Distribution of cod aggregations (red color) in the Barents Distribution of cod aggregations (red color) in the Barents Sea in AugustSea in August--October 1998October 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 northwardmost northwardin 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 SpitsbergenSpitsbergen, 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 AugustSea in August--October 1992October 1992

10 20 30 4 0 50 60 70

68

70

72

74

76

78

8010 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 1990In 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 78ºNreached 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 monthsstomachs in the Barents Sea by months 19991999 (ciphers show (ciphers show

months)months)

10 20 30 40 5068

70

72

74

76

78

12

12

12

98

118 9

117 89 11

12

7 9

7 8

12

37

3 47 8

99

3 67 8 911 12

2 3 45 6

7 1112 6

8

789103 4 5

7 910

1 6

1112

6 8

12

3 4 5 6

7 811

12

4 6

3 4 5

7

10

11 5 6 7

8 10 12

101 5 6

710

1112

5 1011 12

4 5 78

10 11 12

8 9

10

4

5

9

10

7 8

5

3 43

1 2 3

The most favourable The most favourable conditions of cod feeding conditions of cod feeding were in 1999were 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 Mayrecorded in May--June. June. Capelin frequency of Capelin frequency of occurrence reached 65occurrence 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 1984Food consumption of cod in the Barents Sea in 1984--20042004

In 2003In 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 1999the level of 1999--20012001

ShrimpHerring

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

Con

sum

ed b

iom

ass,

10

3 ton

es

Frequency of occurrence polar cod (red Frequency of occurrence polar cod (red colourcolour) 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

monthsmonths 20012001 (ciphers show months)(ciphers show months)

10 20 30

74

76

78

80

10

2

35

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 1999Since 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 SpitsbergenSpitsbergento the to the PerseusPerseusElevation 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 favourfavour of polar cod.of polar cod.

Frequency of occurrence (red Frequency of occurrence (red colourcolour) blue whiting in ) blue whiting in cod stomachs in the Barents Sea by monthscod stomachs in the Barents Sea by months 20022002 (ciphers (ciphers

show months)show months)

10 20 30 4069

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

88

8

8

9

9

9

9 9

9

10

1010

10

10

10

10

10

11

1111

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 10area (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 colourcolour) herring in cod ) herring in cod stomachs in the Barents Sea by monthsstomachs in the Barents Sea by months 20032003

26 36 46

69

71

73

11

22

2

2

2

2 2

2

22

2

2

2

33

3

3

3

3

44 4

4

4

5

5

66

7

7

8

8

8

88

89

9

9

9

9

9

99

9

9

9

99

9

9

9

10

10

10

10

10

1010

10

11

11

11

1111

11

11

11

1111

1111

11

1212

1212

1212 12

12

1212

12 12

12 12

12

12

1 2 3 4Herring doesn’t play a Herring doesn’t play a considerable part in cod considerable part in cod feeding in the Bear Islandfeeding in the Bear Island--SpitsbergenSpitsbergen area. Due to area. Due to the abovethe 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) (b) ссapelinapelin supplysupply

2

4

6

8

10

Fatn

ess,

%

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, 1990more in the cod diet (1984, 1990--1992, 19981992, 1998--2000). In most cases, 2000). In most cases, after a small reduction in fatness after a small reduction in fatness in Mayin May--July, its abrupt rise (8July, its abrupt rise (8--9%) 9%) was registered in Augustwas 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

Fatn

ess,

%

1986 1988 1993 1994 1995 1996 199

b

Month

CONCLUSIONCONCLUSION•• 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 timeffectiveness 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 consequencbackground 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 commugreat part in ecosystem and cod feeding, from pelagic fish community for nity for a long period (the late 1960sa 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 prGood 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, wpromote 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 favoof main capelin food competitors (juvenile cods) also had a favorable rable effect on capelin feeding condition. As a result, fatness of boteffect 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 consdeficiency resulted low cod feeding and the increase in the consumption of umption of euphausiidseuphausiids 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 wacompensate 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 (1990capelin 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 (1999In 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 northerwell 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 oabundance 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 compcod and blue whiting) that led to the strengthening of food competition, etition, which was indicated by low fatness of these fishes in some caseswhich 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 andpolar 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, andlevel 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 cofeeding, since fish having completely return migration mainly consumed nsumed them (Novemberthem (November--December). December). EuphausiidsEuphausiids, being consumed by cod mainly, , being consumed by cod mainly, were stabilizing as a food supply of planktonwere stabilizing as a food supply of plankton--eaters.eaters.

•• Capelin, with its high accessibility for cod in the conditions oCapelin, with its high accessibility for cod in the conditions of warm years, f 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 consumptiolevel 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 practicIn 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.

YEARYEAR--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 ECOSYSTEMFISHES IN THE BARENTS SEA AS INDICATING THE STATE OF ECOSYSTEM

•• GoalGoal•• Fig. 10. Fig. 10. Frequency of occurrence (%, red Frequency of occurrence (%, red •• IntroductionIntroduction

colourcolour) 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 monthsSea by months 19991999

•• Fig. 11. Fig. 11. Food consumed by cod Food consumed by cod in the in the Barents Sea in 1984Barents 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. Fig. 12. Frequency of occurrence polar cod Frequency of occurrence polar cod euphausiidseuphausiids in stomachs of capelin in stomachs of capelin by age 2 by age 2 (a), 3 (b) (a), 3 (b) ии 4 (c) in August4 (c) in August--OktoberOktober 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 monthsmonths 2001 2001

•• Fig. 13. Fig. 13. Frequency of occurrence (red Frequency of occurrence (red euphausiidseuphausiids in stomachs of capelin in stomachs of capelin by age 2 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 colourcolour) blue whiting in cod stomachs ) blue whiting in cod stomachs in in Barents Sea by monthsBarents 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. Fig. 14. Frequency of occurrence (red Frequency of occurrence (red colourcolour) herring in cod stomachs ) herring in cod stomachs in Barents in Barents Sea by monthsSea by months 20032003

•• Fig. 15. Fig. 15.

euphausiidseuphausiids in cod stomachs in cod stomachs in June (a), 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 Augustcolor) 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 1Distribution of cod aggregations Distribution of cod aggregations (red (red color) in the Barents Sea in Augustcolor) in the Barents Sea in August--October October 1992.1992. •• Conclusion 2Conclusion 2

•• Conclusion 3Conclusion 3•• Conclusion 4Conclusion 4