Steve Rose investigates a catastrophic pollution incident at Furnace Brook, a fishing lake in East Sussex, where thousands of fish suddenly died and the local ecosystem collapsed. Neighbours suspect pollution from nearby Morgans Farm, and Rose examines whether their concerns are justified. In doing so, he uncovers broader national problems with water pollution, illegal waste dumping, and the limited power and resources councils and regulators have to tackle them.

He headed about half a mile up the valley to a tributary joining the stream from a neighbouring property named Morgans Farm. “You could clearly see the water upstream [of the tributary] was totally normal, a sandy colour with clay silt in it, and what was below it had gone a blue-black colour. You could see dead brook trout, wild eels, and there was a dead crow or raven, which may well have eaten something poisonous from the river.” In some places, he says, there was a thick layer of blue-grey scum on the water, which he later learned is sometimes called “bacterial cheese”. “There’s so much nutrient [sic] in the water that it allows for a bacterial colonisation explosion.” The bacteria take up all the oxygen, which causes most of the fish, especially the older, larger ones, to die.

Over recent decades, herrings in the Gulf of Bothnia have grown more slowly. Several factors could be behind these changes, but a clearer understanding of the actual causes is needed. Closing this knowledge gap is the aim of ImproFish.

Every year, scientists carry out research surveys in the Gulf of Bothnia to monitor the status of one of the most valuable fish species in the northern Baltic Sea: herring. Together with sprat, it forms the backbone of the region’s fishing industry, supports coastal communities and provides food for seals, seabirds and predatory fish higher up the food chain.

But despite this close monitoring, several knowledge gaps remain. Over recent decades, herrings in the Gulf of Bothnia have grown more slowly, reached maturity earlier and shown variations in weight and abundance. The research survey struggles with accurately understanding this fluctuation. 

Several factors could be behind these changes, from modifications in the food web to the fishery itself. But without a clearer understanding of the actual causes of these changes, it becomes harder to manage the fishery in a way that the stock becomes and then remains healthy over the long term, and fisheries managers are left trying to steer a stock that keeps changing shape beneath them.

Closing this knowledge gap is the aim of ImproFish. Coordinated by the Natural Resources Institute Finland (Luke) together with the Swedish University of Agricultural Sciences (SLU), and co-funded by the EU through the European Maritime, Fisheries and Aquaculture Fund (EMFAF), the project runs from May 2024 to October 2026. Its goal is to provide a stronger scientific basis for assessing the herring stock in the Gulf of Bothnia, so that fisheries advice can finally catch up with what is actually happening in the sea.

As Laura Uusitalo, the project coordinator from Luke, explained:

“Healthy herring stocks are important for both marine ecosystems and coastal livelihoods. We believe that the new knowledge and methods developed in this project can improve the reliability of stock assessments and support better-informed quota setting for years to come.”

Three scientific advances for a healthier stock

Despite yearly combined acoustic and trawl survey, as well as extensive catch sampling, the assessment of the Gulf of Bothnia herring stock has remained uncertain for a long time. Stock Synthesis 3, a newer stock assessment model used since 2021, has improved stability, but significant gaps remain, especially regarding the abundance of young fish.

 ImproFish addresses this through three recommendations:

• improving the fishery-independent abundance indices by extending the acoustic survey closer to the coast and taking into account oceanographic conditions such as temperature and wind-driven water mixing
• deepening the understanding of what drives the growth and size of fish, in order to sharpen the reference points used in fisheries management 
• identifying potential sub-populations, since early genetic findings point to a more complex population structure than previously assumed, with locally adapted groups 

Together, these improvements would make the stock assessment more biologically realistic and better aligned with ecosystem-based management, while still remaining achievable with a moderate research investment.

EU funding bringing two countries’ science together

Through ImproFish, EU funding is allowing Finland and Sweden to combine their analyses on the acoustic survey, herring catch sampling and genetic analyses across the Gulf of Bothnia, instead of each country conducting research on the shared stock on its own.

For fishing that spans the water of both countries, this joint effort finally makes it possible to study the stock with a more comprehensive data coverage, and bring the assessment and advice closer to ecosystem-based management.

This also contributes to the priority of the European Ocean Pact of protecting and restoring ocean health, while supporting a fishing sector that stays sustainable and economically viable for the communities who depend on it.

A fishery worth understanding better

Reaching this point requires as much work on the water as in the laboratory: acoustic surveys, genetic analyses, catch data from commercial fleets and growth data collected on research vessels like R/V Aranda directly feed into the improvements that ImproFish develops.

Most of these benefits will take shape over the medium and long term, but their reach may extend even further: since herring share many traits with other fish, the methods developed here could help scientists elsewhere in Europe facing similar uncertainties, well beyond the Gulf of Bothnia itself.

If you need further information, check the project website. Project website https://fisheries-rcg.eu/improfish/

Funding

• Funding programme European Maritime, Fisheries and Aquaculture Fund (EMFAF) (2021/2027)

Stakeholders

Coordinators

Natural Resources Institute Finland (LUKE), Finland

Website https://www.luke.fi/en

Participants

Swedish University of Agricultural Sciences / Department of Aquatic Resources (SLU), Sweden

Website https://www.slu.se/en/