Warmer seas bring more species to the trawl but threaten local fish communities

Marine scientists have investigated how coastal fish communities are changing with climate change and higher temperatures along the Norwegian coast.

Over the past 30 years, several fish species along the Norwegian coast have migrated further north, as both climate and seas have become warmer.

“The number of different fish species yielded in a trawl catch from northern Norway has increased from 6-7 species in the past to up to 15 different species today,” says researcher Anna Siwertsson.

In a new study, scientists from the Fram Centre project CLEAN show changes in fish populations along the Norwegian coast because of climate change.

More species in the north

The researchers have analysed data from coastal surveys done by the Institute of Marine Research over a 25-year period. The goal is to find out how fish communities have changed over time due to a warmer climate and ocean.

“The north has seen a clear increase in species richness. Warmer ocean temperatures allow warm-adapted species to expand their range into northern waters, leading to new arrivals like silvery pout and mackerel,” says Siwertsson. 

When new species enter a coastal ecosystem, it can lead to changes in the food chain.

“When fish migrate, it changes the composition of species along the coast. If there are major changes in the ecosystem, one consequence may be that fisheries are affected,” says Ulf Lindstrøm, another of the scientists behinds the study.

Changes local ecosystems

When migratory fish settle in a new area, it changes the interaction in fish communities. This can create problems for local fish populations that are already established.

“If local fish populations such as coastal cod face challenges, this can affect fisheries and coastal communities. With both sea temperatures and human activity along the coast increasing, the effects of climate change on biodiversity must be considered in future management decisions,” says Lindstrøm.

An example of when such a decision went wrong is the collapse of the cod population in the Gulf of Maine 15 years ago. At that time, those in charge did not consider that a warmer climate would affect the fish, and the cod was overfished.

Arrival of new species may also benefit the fishing industry.

“New resources will become available for the fishing industry, which can be a good thing,” Lindstrøm says.

Threatened from different angles

But it is not only migratory fish species that are a danger to coastal ecosystems. Along the coast we also find aquaculture, pollution from land, tourism and other human activities.

The scientists in the research project CLEAN put all factors that may affect ecosystems together to manage them in more holistic way.

“We lack this knowledge today. The sectors work separately, and the impacts are studied separately. It is very rare that we put it all together, says Raul Primicerio,” associate professor at UiT and leader of the CLEAN project.

Primicerio explains that if we know how the various hazards affect the ecosystem, we can use this knowledge to get an overall risk assessment. This way, we can make decisions that take the best possible account of our species and ecosystems, also in light of climate change.

Making the best choices

CLEAN also examines how management is carried out now, how it may be improved, and which tools can be useful.

“The aquaculture industry and local coastal fisheries operate in some of the same areas, and now we also have new species entering. How do we make management choices in the best possible way? At present we lack good tools that enable us to consider multiple challenges simultaneously,” says Primicerio.

In addition, some factors have greater impact together than they do individually. So, it is not always useful to simply add up the effects, because the effect can be greater when hazards interact.

“What we ultimately want to achieve with CLEAN is a comprehensive risk assessment that can inform management and form a better basis for decision-making,” says the project leader.