3.5 Pelagic fish

Pelagic fish 2016
Typography
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Total biomass

Zero group fish are important consumers on plankton and prey of other predators and therefore an important element in the transfer of energy between trophic levels in the ecosystem. The total biomass of 0-group (cod, haddock, herring, capelin, polar cod, and redfish), was 1.95 million tonnes in August-September 2016, which is slightly above the long-term mean of 1.76 million tonnes (Figure 3.5.1). The biomass was dominated by capelin and herring. Most of the biomass was distributed in the central and northern-central part of the Barents Sea.

Capelin, polar cod and young herring and blue whiting constitute the bulk of pelagic fish biomass in the Barents Sea. The total biomass of the main pelagic species (age 1 and older fish) in the Barents Sea in 1986–2016 has fluctuated between about 0.5 and 9 million tonnes. The main driver of this variation has been fluctuations of the capelin stock. In 2016 the cumulative biomass of capelin, herring and polar cod was below the long-term mean (Figure 3.5.2).

Figure 3.5.1. Biomass of 0-group fish species in the Barents Sea, August-October 1993-2016.Figure 3.5.1. Biomass of 0-group fish species in the Barents Sea, August-October 1993-2016.

Capelin, young herring and polar cod constitute the bulk of pelagic fish biomass in the Barents Sea. In some years (e.g. 2004–2007), blue whiting (Micromesistius poutassou) also has a significant biomass but only in the western, deeper part of the sea. The total biomass of the main pelagic species in the Barents Sea in 1986–2016 has fluctuated between about 0.5 and 9 million tonnes. The main driver of this variation has been fluctuations of the capelin stock. In 2016 the cumulative biomass of capelin, herring, polar cod, and blue whiting was only half of the long-term mean (Figure 3.5.2).

Figure 3.5.2 Biomass of main pelagic fish species (excluding 0-group stage) in the Barents Sea, August-October 1986–2016.Figure 3.5.2 Biomass of main pelagic fish species (excluding 0-group stage) in the Barents Sea, August-October 1986–2016.

Capelin

Young of the year

Figure 3.5.3. 0-group capelin abundance in the Barents Sea 1980-2016. Orange line shows long-term mean for the period 1980-2016, while blue line indicate 0-group abundance fluctuation.Figure 3.5.3. 0-group capelin abundance in the Barents Sea 1980-2016. Orange line shows long-term mean for the period 1980-2016, while blue line indicate 0-group abundance fluctuation.

The 0-group capelin was distributed widely in the Barents Sea with more dense concentrations in the north-central Barents Sea, as in 2016. The area around Svalbard/Spitsbergen Archipelago were covered one month later than the main area and the southern Barents Sea was not completely covered, thus the results should be interpreted as minimum values. Most of the 0-group capelin likely originates from spring-spawning, however some were most likely from summer spawning. The average fish length was 5.6 cm which is larger than in 2013-2015 and close to the long-term mean (5.5 cm). The large size of 0-group capelin may most likely indicate suitable living conditions during summer and increases the chance to survive through winter. The capelin length varied from 1.5 to 7.6 cm, however the length of most of the fish (89%) was between 4.6 and 7 cm. The abundance index of 0-group capelin in 2016 was very high and almost 3 times higher than the long-term mean (Figure 3.5.3).

Older capelin

The total capelin stock in 2016 is estimated at about 0.3 million tonnes, which is the lowest value observed since 2005 and far below the long-term mean level (about 3 million tonnes). The capelin stock is now into its fourth collapse in the last 30 years (Figure 3.5.4).

Figure 3.5.4. Capelin biomass 1973 – 2016. Maturing stock (>14cm) and total.Figure 3.5.4. Capelin biomass 1973 – 2016. Maturing stock (>14cm) and total.

The geographical density distribution of capelin is shown in Figure 3.5.5. The distribution was similar to the one in 2015, but less capelin was found in the eastern areas and very little capelin was found north of King Karls Land. The capelin aggregations were also in general smaller than in 2015. The total stock is estimated at about 0.33 million tonnes, which is well below the long-term mean level of about 3 million tonnes, and about 40% of the stock size estimated for 2015. About 55% (0.18 million tonnes) of the 2016 stock has length above 14 cm and is considered to be maturing. The stock in 2016 was composed of relatively low abundances of all age groups (Figure 3.5.6).

Figure 3.5.5. Estimated total acoustic density distribution of capelin (sA-values), August-October 2016.Figure 3.5.5. Estimated total acoustic density distribution of capelin (sA-values), August-October 2016.

Figure 3.5.6. The capelin stock age composition during 1972-2016.Figure 3.5.6. The capelin stock age composition during 1972-2016.

Herring

Young of the year

0-group herring were wider distributed than previous years and were found in the central, northern and eastern areas area and west of Svalbard/Spitsbergen in 2016. The main dense concentrations of herring were found in the central and eastern areas and west of Svalbard/Spitsbergen. The length of 0-group herring varied between 3.0 and
11.5 cm, and most of the fish (85%) were 7.0–9.5 cm long. In 2016 the mean length of 0-group herring was 8.4 cm and it was the highest since 2000. The 2016 year class of herring was below the long-term mean, and can be characterized as average (Figure 3.5.7).

Figure 3.5.7. 0-group herring abundance in the Barents Sea 1980-2016. Orange line shows long-term mean for the period 1980-2016, while the blue line indicates 0-group abundance fluctuation.Figure 3.5.7. 0-group herring abundance in the Barents Sea 1980-2016. Orange line shows long-term mean for the period 1980-2016, while the blue line indicates 0-group abundance fluctuation.

Herring age 1, 2, and 3

From 2013-2016 the abundance of young herring found in the ecosystem survey has been relatively stable. Figure 3.5.8 shows the biomass of age 1 and 2 herring in the Barents Sea, calculated based on the last ICES assessment for age 2+ and assuming M=0.9 for age 1. In 2016 herring were found in patchy distributions in the southern Barents Sea (Figure 3.5.9).

Figure 3.5.8. Age 1 and 2 herring in the Barents Sea – based on WGWIDE VPA estimates (ICES 2016b)Figure 3.5.8. Age 1 and 2 herring in the Barents Sea – based on WGWIDE VPA estimates (ICES 2016b)

Figure 3.5.9. Estimated total density distribution of herring (t/nautical mile2). August-October 2016. Note that the survey coverage in the south central area was not complete.Figure 3.5.9. Estimated total density distribution of herring (t/nautical mile2). August-October 2016. Note that the survey coverage in the south central area was not complete.

Polar cod

Polar cod is a true Arctic species found in the whole circumpolar region. Traditionally, the world’s largest population(s) of this species has been found in the Barents Sea.

Young of the year

Figure 3.5.10. 0-group polar cod abundance in the Barents Sea 1980–2016. Red line shows long-term mean for the period 1980–2016, while the blue line indicates 0-group abundance fluctuation.Figure 3.5.10. 0-group polar cod abundance in the Barents Sea 1980–2016. Red line shows long-term mean for the period 1980–2016, while the blue line indicates 0-group abundance fluctuation.

As in previous years, the distribution of 0-group polar cod in 2016 was split into two components: western (around the Svalbard/Spitsbergen Archipelago) and eastern (off the west coast of Novaya Zemlya). Polar cod of the eastern component distributes usually along the west coast of Novaya Zemlya, however in 2016 only few registrations were found there. The length of polar cod varied between 1.5 and 8.0 cm, and most of the fish were between 2.0 and 5.0 cm long. The mean length of 0-group polar cod (4.2 cm) was close to the long-term mean of 4.1 cm. The abundance of the western component was only approximately 1/7 of the long-term mean. The abundance index of the eastern component was very low and only 0.8% of the long-term mean. The 2016 year class of polar cod was very weak at 0-group stage. (Figure 3.5.10). The abundance indices of 0-group polar cod have been extremely low for several years, indicating lack of spawning success and/or that a large proportion of the polar cod 0-group are distributed outside the standard survey area.

Older polar cod

In 2016 there was a significant increase in polar cod biomass, and it was mainly driven by a very high abundance of 1-year-olds. The biomass level was the highest since 2010, and the abundance of 1-year-olds the second highest on record. This marks a break in a long lasting trend of decreasing abundance of polar cod in the Barents Sea. The distribution was concentrated in the northeast (Figure 3.5.12), and polar cod typically occurred in dense and large pelagic schools. The total stock in 2016 amounted to 0.9 million tonnes (Figure 3.5.11).

Two reason are possible for good recruitment of polar cod in 2016. A lot of the 0-group polar cod are distributed outside the standard survey area, so the indices are more uncertain than for other species. In addition, survival of 0-group is very fluctuating and strongly depends from environment, cannibalism, consumption by other predators etc. Most probably from 2015 to 2016 there were very good conditions for survival of polar cod from age 0 to 1.

Figure 3.5.11. Total abundance in billions (coloured bars and left axis), and biomass (turquoise line and right axis) of polar cod in the Barents Sea (acoustic survey and BESS data), August-September 1986–2016. (2003 numbers based on VPA due to poor coverage in survey).Figure 3.5.11. Total abundance in billions (coloured bars and left axis), and biomass (turquoise line and right axis) of polar cod in the Barents Sea (acoustic survey and BESS data), August-September 1986–2016. (2003 numbers based on VPA due to poor coverage in survey).

Figure 3.5.12. Estimated total density distribution of polar cod (t/sq nautical mile), August-October 2016.Figure 3.5.12. Estimated total density distribution of polar cod (t/sq nautical mile), August-October 2016.

Blue whiting

Acoustic estimates of blue whiting in the Barents Sea have been made since 2004. In 2004–2005 estimated biomass of blue whiting in the Barents Sea was higher than 1 million tonnes (Figure 3.5.13). The estimate dropped abruptly in 2008. In 2016 blue whiting biomass was about 397 000 tonnes which is a slight decrease from last year (Figure 3.5.13). Blue whiting migrate from the Norwegian Sea into the deeper parts of the Barents Sea (Figure 3.5.14) when the stock is large and when sea temperatures are high.

Figure 3.5.13. Total abundance in billions (coloured bars and left axis), and biomass (turquoise line and right axis) of blue whiting in the Barents Sea (BESS data), August-September 2004–2016.Figure 3.5.13. Total abundance in billions (coloured bars and left axis), and biomass (turquoise line and right axis) of blue whiting in the Barents Sea (BESS data), August-September 2004–2016.

Figure 3.5.14. Estimated distribution of blue whiting (t/nautical mile2) based on acoustic recordings. August-October 2016.Figure 3.5.14. Estimated distribution of blue whiting (t/nautical mile2) based on acoustic recordings. August-October 2016.

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