Ecosystem survey in Norwegian Sea reports low mackerel catches, strong blue whiting signals, high salmon presence and killer whale activity. Photo: Leif Nøttestad/Havforskningsinstituttet
Ecosystem Cruise Reports Sparse Mackerel, Abundant Salmon and Active Killer Whales
A wide-ranging pelagic ecosystem cruise across the Norwegian Sea has recorded unusually low mackerel concentrations but high acoustic detections of juvenile blue whiting and significant salmon trawl catches. The joint survey, involving the chartered vessels Eros and Vendla, has now completed 62 research stations in cooperation with other Nordic and EU research partners.
The survey aims to provide a quantitative foundation for mackerel stock assessments across 2.5 million square kilometres of the Northeast Atlantic. It also contributes broader ecosystem data on key pelagic species and oceanographic conditions.
“We’ve had mainly low catches of mackerel in most stations, especially north of Bodø,” reported researchers Leif Nøttestad and Hector Peña. “The few larger catches were centred in the eastern and central Norwegian Sea, with one haul yielding 3.5 tonnes.”
Half of all sampled stations reported mackerel catches under 50 kg, with average individual weights ranging from 81 to 631 grams. Most of the heavier mackerel, above 500 grams, were found north of 66°N, in waters near Jan Mayen.
Herring, Blue Whiting and Post-Smolts Prominent
Norwegian spring-spawning herring were caught primarily in the west of Vesterålen, east of Jan Mayen, and northwest of Tromsø. Catches ranged from zero to over six tonnes. Echo sounder detections were inconsistent, particularly because some shoals remained near the surface, beyond the reach of keel-mounted transducers.
Average herring weights varied from 18 to 419 grams, with younger cohorts dominating the northeastern areas. The presence of juveniles highlights an ongoing recruitment pattern, but overall acoustic density was described as “low”.
In contrast, blue whiting — especially younger age classes — showed strong acoustic signatures between 50 and 400 metres deep. These fish were concentrated along the continental shelf, decreasing in numbers further offshore.
The final stock index for blue whiting will be calculated once data are pooled across all participating research vessels.
High Salmon Numbers Raise Genetic Questions
Trawl catches of salmon have been frequent, with post-smolt individuals (100–200 grams) caught along multiple transects stretching from Lofoten westward to southeast of Jan Mayen. Larger salmon, weighing up to 2.6 kg, were also recorded further north by Eros.
Genetic analyses are being undertaken to determine whether all post-smolts are Atlantic salmon, or whether they include juvenile pink salmon, which are known to migrate from rivers into the Norwegian Sea during summer.
Zero-Group Fish and Marine Mammal Activity
Trawl hauls north of 73°N and west of Bjørnøya recorded up to 17 kg of 0-group fish per tow. Species included cod, haddock, capelin, saithe, polar cod, plaice and whiting, suggesting the area remains a key nursery zone.
Marine mammal sightings have been particularly strong. Both vessels carried dedicated whale observers, who recorded numerous killer whale pods, as well as minke whales, fin whales, sperm whales, humpbacks, porpoises, and dolphins. Notably, killer whales were observed following trawlers and hunting mackerel close to the surface.
“The overlap in time and space between killer whale activity and mackerel shoals is striking,” the observers noted.
Calm Conditions and Ocean Data
Weather conditions have remained exceptionally good, with mild temperatures and clear visibility aiding survey efforts. The cruise has also conducted plankton sampling (0–200 m) and oceanographic CTD profiling (0–500 m) at each station.
Preliminary satellite data suggest sea surface temperatures are 1–3°C above the long-term average for July. These results will be verified against in-situ measurements collected during the cruise.
Final findings from the marine mammal survey component will be published by the North Atlantic Marine Mammal Commission (NAMMCO). Oceanographic and biological data will inform forthcoming stock assessments and ecosystem management recommendations.
