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Tord S. Østervold in full swing at
The first part of the mackerel ecosystem tour is now coming to an end
(NORWAY, 7/26/2023)
Mackerel
The center of gravity of the mackerel has been relatively far east in the Norwegian Sea into the Norwegian economic zone. Closer to the coast, there have been smaller quantities.
Map of the Norwegian coast showing the catches of mackerel using red dots. The map shows that most mackerel have been caught relatively far east in the Norwegian Sea, and less along the coast.
Figure 1. Provisional distribution of mackerel catches (kg).
The preliminary picture is that the mackerel stay off the edge of the shelf in deeper water, probably due to better grazing conditions in this area. The short distance to the Norwegian coast can lead to more mackerel close to the coast if it migrates east during the late summer.
In the area south of Jan Mayen, which was the most northwestern coverage area so far in the voyage, there were few mackerel.
The examined mackerel samples have so far had approx. 30% with 3-year-olds, which makes the 2020 class the dominant one in the population. It corresponds to the results from last year when the same year class was the most common cohort, then as 2-year-olds. The 3-year-old mackerel is now mainly 300-380 grams.
The map of the Norwegian coast shows the average weight of mackerel using blue dots.
Figure 2. Average weight (kg) of the mackerel in the catches.
Otherwise, there is a relatively spread age distribution in the mackerel population, with 15% being 10 years or older, so far. The next part of the cruise will cover the northern Norwegian Sea where the larger and older mackerel traditionally dominate.
Herring
At the start of the cruise there were records of North Sea herring both on the sonar and in the trawl catches. These were herring of ~160–200 grams. The North Sea herring also spread partially into the southern Norwegian Sea north to approx. 63˚N.
Towards the Norwegian coast north of the North Sea, some Norwegian summer-spawning herring (nvg) have been recorded, while there have been few herring in the central Norwegian Sea. The nvg herring move further west, and so far no significant nvg herring have been recorded on the trip.
Sonar image showing small schools of herring.
When there were little waves, it was possible to register small schools of herring standing close to the surface with the sonar.
It is likely that the next part of the cruise, which will cover the area around Jan Mayen, will record a greater proportion of nvg herring in that area.
Blue whiting
As usual, the gray tern is spread out over large parts of the Norwegian Sea, as this is an important grazing and rearing area for this species. The char is scattered in the water column at a depth of 100–500 m, but sometimes moves all the way to the surface at night. In the Norwegian Sea, the 2-year-olds from the 2021 year-class now dominate, in a similar way to how this year-class dominated as 1-year-olds last year.
Four people stand on the deck of a research tool. In the foreground, a man is holding on to a lifting hook, and a woman is squatting to fix one of the instruments they are trying out. At all predetermined stations, we take a plankton sample. Ivar Magne Østervold and Aina Bruvik have here got the plankton rake on board again on "Vendla". Photographer: Erling Boge/HI
Salmon
Salmon from a number of different European countries graze in the Norwegian Sea and occasional salmon are caught together with other pelagic fish in the trawl. The cruise is probably the most important cruise in the Atlantic Ocean to gain better knowledge of the salmon's migration in the sea, and how changes in the marine environment affect the salmon.
A large humpback salmon lies on an electronic board that measures the length and weight of the fish. Below the humpback salmon lie four small fish, in a row. Among the catches for the mackerel ecosystem tour are also humpback salmon. Here with other fish.Photographer: Institute of Marine Research
Most of the individuals that are caught have recently migrated out of the rivers and are 20–25 cm long, but some larger individuals that have been in the sea for one or two years are also caught. So far, more than 30 individuals have been caught, and it is expected that the next part of the trip will catch more salmon.
Authors/Source: Kjell Rong Utne and Hector Peña / Norwegian Institute of Marine Research
[email protected]
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