© 2005 International Council for the Exploration of the Sea
The relationship between plankton, capelin, and cod under different temperature conditions
Polar Research Institute of Marine Fisheries and Oceanography (PINRO) 6 Knipovich Street, 183763 Murmansk, Russia
*Correspondence to E. L. Orlova: tel: +7 8152 473424; fax: +7 1 78910518. e-mail: orlova{at}pinro.ru.
On the basis of data from cold (1982 and 1987) and warm summers (1983, 1984, 1990, and 1992), we explore the relationship between the phytoplankton bloom and the timing and intensity of the zooplankton bloom. In warm years, there is more overlap in the time between the zooplankton and the phytoplankton bloom. In northern areas (76–78°N) with seasonal ice, the phytoplankton bloom and reproductive processes in Calanus finmarchicus and Calanus glacialis continue well into August, evidenced by the presence of an abundance of nauplii and younger copepodites. We analyse feeding intensity of capelin and its distribution relative to food availability and capelin abundance. The extent to which feeding areas of cod and capelin, its major prey, overlap is subject to the abundance of these species, distribution of zooplankton, and sea temperature in a given year.
Keywords: Barents Sea, capelin, cod, copepods, zooplankton
Received 1 July 2004; accepted 28 May 2005.
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Introduction |
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 Top Introduction Material and methodsResultsDiscussionReferences |
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The central area of the Barents Sea, between the southern extremity of the Spitsbergen Archipelago and northwestern Novaya Zemlya Island, is characterized by high biological productivity. The area has complex bottom topography, with bottom depths of between 100 and >350 m. The main circulation features are the north and central branches of the eastward North Cape Current off northern Norway and Russia and the north-flowing Novaya Zemlya Current. Cold and low salinity Arctic Waters are brought south by the east Spitsbergen Current and southwestward by the Bear Island Current (Tantsura, 1959). Separating the Atlantic and Arctic Waters is the Polar Front. This dynamically active convergence zone extends across the Barents Sea and concentrates different trophic level organisms.
In the 1980s and early 1990s, water temperatures in the Barents Sea varied greatly. Colder-than-normal mean annual temperatures in the 0–200 m layer were recorded in 1980 and 1982, as well as in 1986–1988, resulting in greater quantities of sea ice. In the summers of 1989–1992, Atlantic Waters were warmer than normal, and sea ice coverage was reduced. Such year-to-year variations impact primary production, reproduction, and growth rates of zooplankton and fish species, as well as the over-wintering, feeding, and migration of fish. For example, the ice edge position in June–July determines the onset of primary production in the northern Barents Sea (Rey et al., 1987; Skjoldal et al., 1987; Melle and Skjoldal, 1998). Although the spawning and development of some Arctic copepods (Calanus glacialis, Pseudocalanus minutus) can take place earlier (March–April) under the ice (Hirche and Kosobokova, 2003), the predominant zooplankton species, Calanus finmarchicus and C. glacialis, occur in open waters, and overlap in time with the phytoplankton blooms. The emergence time of new generations of these zooplankton species (eggs, nauplii) varies with the intensity of phytoplankton production (Melle and Skjoldal, 1998). With the seasonal retreat of the ice edge northwards, phytoplankton blooms are initiated in the stratified waters formed by the melting ice. In high latitudes in the zone of floating ice, primary production continues into the autumn (Zernova et al., 2003), when intense blooms of diatoms are observed. The productivity of these areas is higher than that farther south, and approaches that of the coastal areas. The largest biomass of zooplankton in the northern Barents Sea is C. glacialis (Melle and Skjoldal, 1989).
Many commercial fish species feed in the northern Barents Sea during summer–autumn owing to high food concentrations. For example, cod feed at various times on capelin, polar cod, or euphausiids. The temperature range (2–3°C) in the Barents Sea waters occupied by cod is considered optimal. In especially warm (1992) years, cod have been found as far north as 78°30'N and even in relatively cold years (1997) reach 77°30'N (Yaragina et al., 1996).
Capelin feeding depends upon the stock size, age composition, and planktonic prey. In the 1970s, with greater abundance and more older fish (10–15%), capelin were distributed more to the northeast (Rettingen and Dommasnes, 1985). The feeding efficiency of capelin was high and their fatness reached 15–18% by September of those years. In the mid-1980s and early 1990s, with a more southward and westward distribution, capelin fatness was 8.6–10.8% and, in some years (1985 and 1992) when feeding conditions were unfavourable, it was not higher than 5.7%.
The purpose of this paper is to consider further plankton–capelin–cod interactions in the Barents Sea under different temperature regimes.
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Material and methods |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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Hydrographic, plankton, and fish data were obtained during August surveys in the central latitudinal zone of the Barents Sea during cold (1982 and 1987) and warm years (1983, 1984, 1990, and 1992). The hydrographic data were collected at standard depths (0, 10, 30, 50, 75, 100, 150, 200, 250, 300 m) and near the seabed on a regular grid with an interval of approximately 30' latitudinally and 2° longitudinally (Figure 1). Average temperatures at these depths were also available. We calculated average temperatures in the central latitudinal zone of the Barents Sea. The thermal condition of waters each year was defined as a deviation from the average temperature on standard sections of the Barents Sea. Additional zooplankton data were obtained in July.
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The position of the ice edge in June–July, as well as phytoplankton and zooplankton data, was obtained from the Russian Federal Hydrometeorology and Environment Monitoring Service. Phytoplankton data were obtained at the same time as the zooplankton in a Juday net (37-mm open diameter, 180-µm mesh sieve). In all, 600 samples were taken. Estimates of microalga concentration were recorded, based on the frequency of cell occurrence using a five-unit scale ranging from a single cell (1) to a large mass of cells (5). Phytoplankton composition was determined to genus. Zooplankton density was expressed in individuals m–3 and biomass in wet weight in mg m–3. In total, 6000 cod and 9800 capelin stomachs were analysed. Prey were identified by species, and their weight and frequency of occurrence were recorded. Feeding intensity (condition factor) was determined from stomach fullness indices (in % body weight), and for capelin using a five-unit relative scale increasing with better condition. The latter was estimated in the field. Cod and capelin distributions were based on survey catches in the different fishing areas.
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Results |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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Cold years
1982
In 1982, the central Barents Sea was colder than average, and production processes were delayed. Copepod spawning was late, and the peak of the phytoplankton bloom at 76°N did not occur until mid-June, by which time, the majority of the copepodites in the region 74–76°N and 30–35°E had only reached Stage II (Skjoldal et al., 1987). By late August in the same area, we observed that most copepods in the south had reached Stages IV–V, but in the higher latitudes, C. finmarchicus nauplii and copepodites at Stages I–III were still found. Farther north (76°44' N) in the Arctic Water mass, C. glacialis dominated with equal numbers at all stages. Production was also delayed farther west. Other copepods included Metridia (mainly, in the lower layers), Oithona similis, and Pseudocalanus minutus (Table 1).
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The mean zooplankton biomass in August was 227 mg m–3 at 72–75°N and 203 mg m–3 at 76–78°N. It consisted mostly of small and large copepod species, but in some cases, the percentage of chaetognaths, euphausiids, hyperiids, and others was high. In the southern regions of the study area, biomass measurements in the upper 50 m varied from 20–40 mg m–3 at night to 890–960 mg m–3 during the day, and from 20–50 mg m–3 at dawn to 300–420 mg m–3 at twilight. Less daily variation occurred farther north.
The main capelin concentrations in the northwest of the study area overlapped with high zooplankton biomass. During August–September when they fed predominantly on copepods, the condition of two- and three-year-old capelin was low. Conditions only improved for these and older fish with intensive feeding on euphausiids. The switch in prey became obvious in September, but did not occur synchronously (Figure 2). Capelin of all sizes in the South Cape Deep were feeding intensively on copepods, while on the Persey Elevation and in the Hopen area, there was a drop in feeding intensity. Small capelin in the Central Elevation area fed on copepods, and the large ones on hyperiids.
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With high capelin abundance and low cod abundance, cod were well supplied with food. Cod fatness was not lower than 6–7% and, in October, reached 8.4% (Yaragina, 1992). The cod did migrate eastwards to feed, but did move northwestwards occasionally in the second half of the year when food availability there was high.
1987
In 1987, abnormally cold conditions resulted in delayed ice clearance, with more than 50% of the Barents Sea covered with ice in May–July (Figure 3). In August, the temperature of the surface layer in the south of the central Barents Sea was 1–3°C lower than the long-term mean, although at 50-m depth, it was near average (Figure 4A, B). The phytoplankton bloom was late (beginning of August), with simultaneous blooms of Chrysophyta, Diatomea, and Peridinea algae and the highest concentrations in the east (Figure 4). Total zooplankton biomass (mostly copepods) was quite high, and in the northeast of the central zone, their greatest concentrations in the 0–50 m layer coincided with intensive blooms (Figure 4C). Among the copepods, C. finmarchicus dominated, but in the Spitsbergen Bank, South Cape Deep, and Novaya Zemlya Shallows areas, C. glacialis accounted for 20–30% of the zooplankton biomass. By August, spawning of calanoids was complete except in the northeast, where eggs were still observed at some stations and the abundance of nauplii exceeded 500 individuals m–3. In the west, approximately 50% had reached Stage III, while in the centre they made up not more than 20–25%. C. glacialis regularly occurred in all layers in small numbers, but being mainly Stage Vs, they contributed significantly to the biomass. Younger copepodites of C. glacialis were found in considerable quantities (Stage I, 110 individuals m–3; Stages II–III, 60 individuals m–3) only in the northeast (77°N 54°E).
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Zooplankton biomass in the 0–100 m layer was highest (500–900 mg m–3) in the north (76–77°N) of the eastern and central latitudinal zone; below this layer, the biomass did not exceed 100–160 mg m–3. In the south (74–75°N), where plankton development was more rapid, the biomass was 130–140 mg m–3 in the 0–100 m layer, but higher (230–370 mg m–3) in lower layers. The highest biomass of C. finmarchicus generally occurred in the west (the South Cape Deep, the eastern slope of Bear Island Bank, and the Central Elevation), where it often coincided with similarly high concentrations of C. glacialis, and more rarely with Calanus hyperboreus. Farther east, C. hyperboreus became relatively more important. The biomass concentration of M. longa was usually much lower than the Calanus species (Table 2).
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Owing to delayed warming, capelin started feeding late, and owing to their low abundance, had a more limited geographical distribution. They fed in western Spitsbergen, the eastern slope of Bear Island Bank, and the Central Elevation during early September, then later that month spread into Hopen. In the first two areas, copepods were the dominant prey, but since the copepod biomass was low, the condition factor of the capelin did not exceed 2. Prey was more diverse in western Spitsbergen, while in Hopen capelin fed intensively on euphausiids. Euphausiids made up a high proportion of the capelin ration in the Central Elevation area as well.
With an increase in the abundance of cod and the decline of capelin, there was an abrupt drop in the food supply for cod. Cod over-wintered in the northwest, where near-bottom water temperatures were well below average (the Bear Island Bank, the West Deep, and the north of the Kopytov area). Cod fed mostly on redfish juveniles, amounting to 80% by weight. On the whole, cod feeding was poor due to slow digestion under low temperature conditions and poor food rations. As a result, cod fatness was <3% during the first half of the year. By June some of the cod had left the over-wintering areas while the remaining cod fed on Themisto, most intensively in the South Cape Deep (August) and the western slope of the Bear Island Bank (September). Cod fatness remained <4% for an extended period, but rose slightly (5–6%) in September.
Warm years
1983
In 1983, to the west of 45°E, the ice edge in June–July was located along 77°N (Figure 3A). With its rapid retreat north, an intense bloom followed, and there was a change of dominating species of diatoms as well as a short-term appearance of Phaeocystis. The latter was observed on the Spitsbergen Bank in early to mid-July with a relative intensity of 2 and 4, in west Spitsbergen (3–5) and the South Cape Deep (3–4) on 13–16 July, and in Hopen at the ice edge (2) in late July. An intense short-lived Phaeocystis bloom (5) was also registered in Persey Elevation (77°N 33°E) on 22 July.
Although the majority of calanoids spawning finished, eggs and Stages I–II nauplii of Calanus still were observed on 22 July. Owing in part to the prolonged period of spawning, growth rates differed significantly between areas. During July, the relative abundance of Stage III Calanus (both C. finmarchicus and C. glacialis) in Atlantic Waters (the Spitsbergen Bank and the South Cape Deep) fluctuated between 40% and 55% of the total copepod abundance, while it was not until August in the Arctic Waters (Persey Elevation) that copepods at this stage made up 30–50%. Increased abundances of Stages IV–V copepodites appeared in the South Cape Deep, the Persey Elevation, western Spitsbergen, and the Hopen areas in July–August. The highest abundance of these late stages of C. finmarchicus was recorded in the first two areas in July (up to 500–700 individuals m–3) and mature females were also found (100–230 individuals m–3). The maximum concentration of older C. glacialis copepodites and females was much less (150–250 and 20–50 individuals m–3, respectively) in the Spitsbergen Bank, the South Cape Deep, and the Admiralty Peninsula areas. Plankton biomass concentrations in 0–50 m during July did not exceed 100–200 mg m–3, nauplii and juveniles being dominant, while higher biomasses (500 mg m–3 and more) formed owing to older copepodites in the above-mentioned areas (Table 3). In some cases, the lower layer biomass concentrations were 100–300 mg m–3. In August, the main variations in zooplankton biomass resulted from mass maturation, descent, and probably predation. In the 0–50 m layer, concentrations usually did not exceed 50–75 mg m–3. In the deeper layers, they fluctuated, and in the area 76°N and farther north, reached 200–540 individuals m–3.
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Capelin began feeding in July (western Spitsbergen and the West Deep), but many stomachs were empty, and those that were feeding had a large variety of prey. Four-year-old capelin fed on older copepodites only in western Spitsbergen. In August, feeding was primarily limited to copepods. In August–September, the areas of maximum feeding were in the Central Elevation, the Persey Elevation, and Hopen areas (Figures 5 and 6), with older copepodites of C. finmarchicus, C. glacialis, and C. hyperboreus the preferred prey of three- to four-year-old capelin.
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Owing to the low abundance of cod in 1983, their distribution was confined to the western fishing areas and reduced, compared with capelin. In the north, cod were distributed in the area bounded by the South Cape Deep and the Bear Island Bank slopes (July–October), where they fed on capelin. On the southern and eastern slopes of the Bear Island Bank and in the Hopen Island area, capelin were also being consumed. Cod fatness index was 8–9% (Yaragina, 1992).
1984
In 1984, with high temperatures in the upper 50 m and a rapid retreat of the ice edge (Figure 3B), the main bloom in the Barents Sea was over by the end of July. However, during mid-August in the central region, primarily north of 76°N, large concentrations of Peridinea were observed (bloom intensity of 3). Based on the stages of C. finmarchicus (I–III) in mid-August and the estimated time from hatching (Østvedt, 1955; Runge et al., 1985), spawning took place in early July roughly coinciding with the intensive phytoplankton bloom.
The distribution of C. finmarchicus Stages I–II was limited to 0–100 m, with the largest concentrations in the Persey Elevation, the Novaya Zemlya Shallows, and the Admiralty Peninsula areas reaching 1000–4000 individuals m–3 at some stations. Maximum abundance (7680 individuals m–3) occurred on the Persey Elevation on 17 August (76°50'N 44°E) at a time when Stage IIIs at the southern stations were increasing (often to 1000–2000 individuals m–3). The abundance of older copepodites varied greatly, but there was a clearly increasing trend in their numbers at depth. Cold-water species at all stages were found in great numbers, with C. glacialis Stages IV–V dominating. Their concentrations were considerably less than those of C. finmarchicus, with maximal values of 350 individuals m–3 in the north of the Novaya Zemlya Shallows and 80–95 individuals m–3 in the Hopen and Persey Elevation areas. Further, C. hyperboreus Stages II–IV were present with maximum concentrations of 190 individuals m–3 in the Admiralty Peninsula area and 110 individuals m–3 in the Novaya Zemlya Shallows. The concentration of Metridia longa was in hundreds of individuals m–3 with the younger copepodites prevailing, and was highest in the area from the Persey Elevation to the Admiralty Peninsula.
In early July, zooplankton biomass reached maximum concentrations (900–1300 mg m–3) in the north, compared with 200–400 mg m–3 in mid-July. They were slightly lower in August (Orlova et al., 2002a), with high biomass concentrations (up to 300–500 mg m–3) primarily limited to the 0–50 m layer in more southern and eastern areas. A significant portion of the copepods remained in lower layers (80–280 mg m–3 in 75–76°N, 140–300 mg m–3 in 76–77°N, and 230–680 mg m–3 above 78°N). Note that the biomass consisted of copepods and other groups, except above 78°N where there were only copepods. C. finmarchicus peaked in the Novaya Zemlya Shallows (about 150 mg m–3) and in the Hopen area (68 mg m–3) and contributed the most to the plankton biomass. C. glacialis (35–55 mg m–3) and C. hyperboreus in the east (72–82 mg m–3) also contributed significantly.
Capelin abundance was relatively low, and its distribution overlapped with the zooplankton. Intensive feeding was observed already in early July in western Spitsbergen, the eastern slope of the Bear Island Bank, and the Central Elevation areas (Orlova et al., 2002b). Besides copepods, capelin fed on euphausiids, the maximal numbers being consumed by older fish. In the first two areas, copepods were the main prey only for young fish, and in the Central Elevation, copepods only made up 16% of capelin food weight, while euphausiids (about 56% by weight) were the primary food source. In most other areas, the diet was mixed. The areas of the most intensive capelin feeding were the Persey Elevation (August–September), the Central Elevation (August), Hopen (September), and the Novaya Zemlya Shallows (August). Capelin were generally characterized by a high condition factor (2.3–3.4) except in the Hopen and Persey Elevation areas where, by the first days of September, feeding intensity was greatly curtailed (condition factor of 2).
Cod distribution only partly coincided with that of capelin, owing to migration of cod farther to the east. To the northwest in the areas affected by Atlantic Waters, cod also formed concentrations where feeding capelin were abundant (July–August).
1990
The Barents Sea was warmer than normal again in 1990. The ice edge in early July was at 78°N (Figure 7A), and with the rapid ice retreat, the phytoplankton bloom was completed in July. By the end of July, copepod spawning had finished, except at the northernmost stations. The rapid zooplankton development was similar to that in 1983. Owing to a rather extended spawning period of Calanus, their biomass values in different areas differed greatly.
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Capelin abundance was high, with the bulk of the population made up from the 1989 year class. They were distributed over a vast area (from the western Spitsbergen area to the Novaya Zemlya Shallows), with the highest concentrations (100–200 t nautical mile–2) in western Spitsbergen, Hopen, and Persey Elevation areas, corresponding to the regions of high zooplankton (mainly copepod) concentrations.
Cod fed mainly on capelin in August on the south and eastern slopes of the Bear Island Bank and in the Central Elevation area, which corresponded to the time and location of feeding capelin concentrations. In the Hopen area, cod continued feeding on capelin into October–November, and as a result the fatness index was high.
1992
In June 1992, to the east of 35°E, the ice in the Barents Sea was located 65–90 km north of its long-term mean position, resulting in the smallest ice coverage in 30 years (Figure 7B). By August, the phytoplankton biomass was low except in a few small areas where Rhizosolenia and Ceratium dominated.
High temperatures contributed to early copepod spawning and fast growth. By mid-August, copepods occurred in all areas in relatively large concentrations, except in the northern section of the Persey Elevation where concentrations were much reduced (maximum 400 individuals m–3). C. finmarchicus Stages II–III dominated, although in the east, the number of Stage IVs increased, and in the Novaya Zemlya Shallows, mature females were found. In the deep layers, the concentrations of zooplankton were primarily C. finmarchicus Stages III–IV. Arctic copepod species were less numerous except for Pseudocalanus minutus and M. longa, which occurred throughout. In some eastern areas, high concentrations of C. glacialis were observed in the upper layers and, while all stages of development were present, IV–V dominated (up to 700 individuals m–3 in the area of the Admiralty Peninsula and 50 individuals m–3 in the Novaya Zemlya Shallows and the Persey Elevation). In the southern areas (74–75°N) during August, biomass concentrations (copepods only) in the upper layer were 100–400 mg m–3, with the means in the east slightly higher than those in the west (206 vs. 180 individuals m–3). Those in the north were somewhat lower (188 and 155 mg m–3 in the east and west, respectively).
In mid-September, in the most northern stations off Novaya Zemlya and Franz Joseph Land (77–79°N), where intensive blooming of phytoplankton was registered, zooplankton concentrations ranged between 30 and 700 mg m–3, with a mean of 228 mg m–3. At depth, concentrations were 50–260 mg m–3 in the northern areas and 10–170 mg m–3 in the south, with the highest values above 77°N (110–380 mg m–3). Concentrations near-bottom were lower (15–250 mg m–3 in the east and 5–85 mg m–3 in the west). Overall zooplankton biomass was not high in 1992. Finally, we note that C. finmarchicus concentrations in the eastern areas (the Admiralty Peninsula and the Novaya Zemlya Shallows) were about 145 and 130 mg m–3, respectively, while C. glacialis were 234 and 83 mg m–3, respectively.
One of the possible reasons for the low copepod biomass was consumption by capelin and cod. According to the data from the international survey (Orlova et al., 2001), in 1992, cod abundance grew by a factor of 6 compared with 1990, and amounted to 38 x 109 individuals. Juveniles were distributed farther north, typical of warm years. Capelin, with a relatively high abundance and two- and three-year-olds dominating the population, were distributed from the western Spitsbergen area to Sukhoi Nos. The overlapping distribution of capelin and cod feeding areas covered a large territory. Feeding conditions for capelin were favourable in the west during August, but in September when the capelin migrated eastwards and had to compete with cod, capelin feeding conditions became worse (Orlova et al., 2002b).
In 1992, cod and capelin distributions overlapped, and cod fed primarily on capelin during August on the eastern slope of the Bear Island Bank and in the Hopen and Persey Elevation areas. However, in the Hopen Island area during August–September, up to 50–70% of cod stomachs were empty. In the Hopen and Persey Elevation areas, cod were distributed extremely far north (up to 78°30'N). Cod fatness increased from only 4–5% in July to 9–10% by October.
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Discussion |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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Investigations of zooplankton, capelin, and cod were carried out in the Barents Sea during cold (1982 and 1987) and warm (1983–1984, 1990, and 1992) years. In all years, phytoplankton blooms and copepod reproduction were observed with seasonal changes in the microalgae species diversity, and a high abundance of nauplii and younger copepodites by August. There was intensive growth of copepods with new year-class individuals reaching Stage III and their transition to Stages IV–V. Relatively high zooplankton biomass was observed where capelin fed. The zooplankton abundance and biomass depended upon copepod species composition and their reproduction and growth rates, all of which varied spatially. The increase in biomass of the dominant Atlantic species, C. finmarchicus, is connected to the availability of mature females and to copepod growth rates. In the warmer southern waters, events occur earlier and, in warmer-than-normal years, the organisms descended to diapause by August and upper layers become depleted. In the north (above 76°N), these processes are delayed until September, which results in a potentially longer feeding time. The biomass of the Arctic species C. glacialis, whose distribution is connected with ice melting, increased in warm years. This species has a one- or two-year life cycle, and a large biomass can be mainly older copepodites stages (IV–V) composed of individuals that over-wintered.
In the summer and autumn of warm years, there tends to be greater synchrony of phytoplankton and zooplankton peaks, and the capelin and cod are located in the central latitudinal zone. However, in some years, there was only partial overlap in the distribution of capelin and cod, believed to be caused by a combination of rapid sinking of zooplankton, predation by fish, or poor feeding migration of cod. The latter was not related to the sea temperature as it was observed both in cold (1982) and warm (1983) years.
In the abnormally cold year of 1987, the feeding areas of capelin and cod did not overlap. Because of its small abundance, capelin could not cover northern areas rich in food, but stayed mainly in areas with poor availability of plankton. There was also a reduced feeding area for cod, probably a result of the limiting effect of low temperatures. Under such circumstances, availability of food for capelin was not a decisive factor.
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Acknowledgements |
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We thank two reviewers for constructive comments on the draft manuscript, and Andrew Payne (Cefas, Lowestoft) for helping us improve the English language and other valued suggestions.
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References |
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TopIntroductionMaterial and methodsResultsDiscussionReferences |
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Hirche H-J. and Kosobokova K. (2003) Early reproduction and development of dominant calanoid copepods in the sea ice zone of the Barents Sea – need for a change of paradigms? Journal of Marine Biology 143:769–781.[CrossRef]
Melle W. and Skjoldal H-R. (1989) Zooplankton reproduction in the Barents Sea vertical distribution of eggs and nauplii of Calanus finmarchicus in relation to spring phytoplankton development. In Ryland J.S. and Tyler P.A. (Eds.). Reproduction, Genetics and Distribution of Marine Organisms(Olsen and Olsen, Fredensborg, Denmark) pp. 137–146.
Melle W. and Skjoldal H-R. (1998) Reproduction and development of Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus in the Barents Sea. Marine Ecology Progress Series 169:211–228.[Web of Science]
Orlova E.L., Boitsov V.D., Nesterova V.N., Oganin I.A., Ushakov Y.U., Konstantinova L.L., Antsiferov M.Yu. (2001) Food supply forming specificity and feeding conditions of capelin in 1992–1993(PINRO Press, Murmansk) pp. 134–136 Abstracts of papers of the Eighth All-Russian Conference on Fisheries Forecasts Problems (in Russian).
Orlova E.L., Boitsov V.D., Nesterova V.N., Ushakov N.G. (2002) Composition and distribution of copepods, a major prey of capelin in the central Barents Sea, in moderate and warm years. ICES Journal of Marine Science 59:1053–1061.
Orlova E.L., Ushakov N.G., Nesterova V.N., Boitsov V.D. (2002) Food supply and feeding of capelin (Mallotus villosus) of different size in the central latitudinal zone of the Barents Sea during intermediate and warm years. ICES Journal of Marine Science 59:968–975.
Østvedt O.J. (1955) Zooplankton investigation from weather ship M in the Norwegian Sea, 1948–49. Hvalrädets skrifter. Scientific Results of Marine Biological Research 40:1–93.
Rettingen I. and Dommasnes A. (1985) Acoustic estimation of the Barents Sea capelin stocks in 1972–1984. The Barents Sea capelin biology and fishing, Proceedings of the 2nd Soviet-Norwegian SymposiumMurmansk pp. 49–123 (in Russian).
Rey F., Skjoldal H-R., Slagstad D. (1987) Primary productivity in connection with climatic changes in the Barents Sea. The effect of climatic conditions on distribution and populational dynamics of the Barents Sea commercial fishes. Proceedings of III Soviet-Norwegian SymposiumMurmansk pp. 28–55 1987 (in Russian).
Runge J.A., McLaren I.A., Corckett C.J., Bohrer R.N., Koslow J.A. (1985) Molting rates and cohort development of Calanus finmarchicus and Calanus glacialis in the sea off southwest Nova Scotia. Marine Biology 86:241–246.[CrossRef]
Skjoldal H.R., Hassel A., Rey F., Loeng H. (1987) Spring phytoplankton development and zooplankton reproduction in the central Barents Sea in the period 1979–1984. The Effect of Oceanographic Condition and Population Dynamics of Commercial Fish Stocks in the Barents Sea(Institute for Marine Research, Bergen) pp. 59–89.
Tantsura A.I. (1959) On the currents of the Barents Sea. Trudy PINRO XI:35–53 (in Russian).
Yaragina N.A. (1992) Fatness dynamics of Arcto-Norwegian cod. Ecological Problems of the Barents Sea(PINRO Press, Murmansk) pp. 3–35 (in Russian).
Yaragina N.A., Albikovskaya L.K., Lebed N.I., Lukmanov E.G. (1996) Peculiarities of cod distribution in the Barents Sea and the main tendencies of dynamics of Russian fishery in 1989–1994. Atlantic Cod. Biology, Ecology and Fishery(Nauka Publishing, St-Petersburg) pp. 164–181 (in Russian).
Zernova V.V., Shevchenko V.P., Politova N.V. (2003) Peculiarities of the Barents Sea phytocene structure on the meridional section by 37–40°E (September 1997). Okeanologiya 43:419–427 (in Russian).
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