Age-Selective Fishing Causes Major Change in Norwegian Spring-Spawning Herring Migration
A groundbreaking study published in Nature reveals that Norwegian spring-spawning herring (NSS herring) have shifted their spawning grounds 800 km northward, from Møre to Lofoten. This major change is linked to a loss of collective migration memory among older fish, primarily caused by age-selective fishing practices.
The findings raise critical concerns for fisheries management, marine biodiversity, and coastal food web stability.
What Is Collective Memory in Fish Migration?
In schooling fish like herring, migration routes are passed from older to younger individuals through social learning—a process known as entrainment. Older, experienced fish traditionally lead migrations, guiding recruits along established spawning paths.
However, targeted fishing of older herring has disrupted this natural process, resulting in fragmented migratory routes and a loss of cultural transmission.
From Møre to Lofoten: A Shift in Spawning Grounds
Historically, NSS herring migrated up to 1,300 km south from their wintering areas to spawn along the Møre coastline. This long-distance migration was energetically costly but crucial for larval survival in warmer southern waters.
Now, due to reduced guidance from older fish, newer generations have established a new spawning route further north—with the spawning center moving to Lofoten, approximately 800 km away.
Key Research Insights from 1995–2024
The study, titled “Herring spawned poleward following fishery-induced collective memory loss”, was led by researchers at Norway’s Institute of Marine Research. It combined:
- Fisheries records (Norway, Iceland, Faroe Islands)
- Scientific acoustic-trawl surveys (2018–2024)
- Tagging data from over 200,000 herring (2016–2023)
These datasets covered nearly 80% of the global herring catch as reported to the International Council for the Exploration of the Sea (ICES).
Tagging and Tracking: How the Shift Was Discovered
Between 2016 and 2023, researchers tagged 202,155 herring using Passive Integrated Transponder (PIT) tags in northern Norwegian fjords. When these tagged fish were later recaptured in processing facilities, their migration paths and spawning locations were cross-referenced with survey data.
Results confirmed that the 2016 herring cohort was the first to abandon the traditional Møre route and establish the new northern route to Lofoten. This change became dominant by 2021, as younger fish followed the same pattern.
Alarming Decline in Older Spawners
Acoustic-trawl surveys during peak spawning seasons revealed a 68% decline in older spawners—from 4.0 million metric tons in 2019 to just 1.3 million tons in 2023.
By 2021, the 2016 cohort made up more than 50% of the spawning population, effectively reshaping the species’ migration behavior.
Long-Term Impacts on Marine Ecosystems
The loss of social learning and reduced interaction between age groups means that newer generations no longer learn traditional routes. This shift may lead to:
- Altered food web dynamics
- Reduced nutrient fluxes in southern spawning areas
- Challenges in ecosystem-based fisheries management
- Potential decline in prey availability for dependent species
Once a new collective memory is formed, reverting to historical migration patterns may become impossible.
Final Thoughts
This dramatic poleward migration shift of NSS herring highlights the profound ecological consequences of selective fishing practices. The research emphasizes the importance of protecting older, experienced fish to maintain migration culture and ecosystem stability.
As climate change and overfishing continue to reshape marine habitats, understanding the social dynamics of fish migration becomes crucial for sustainable fisheries management.
Reference
Aril Slotte et al. (2025). Herring spawned poleward following fishery-induced collective memory loss. Nature. DOI: 10.1038/s41586-025-08983-3