Growing seal population isn’t a threat to Baltic fish stocks, study finds

Dec. 10 (UPI) — New research suggests a healthy seal population is not a threat to commercial fish stocks in the Baltic Sea.

Fish stocks in the North Atlantic, including Baltic cod, herring and sprat, have been on the decline for several decades. At the same time, environmental protections and conservation efforts have helped boost the seal population in the Baltic.

Some commercial fishers have suggested the region’s burgeoning seal population is partially to blame for the decline in fish stocks.

But a new study, published this week in the journal Ambio, suggests cod, herring and sprat losses in the region are manmade. In fact, researchers determined the region could host several thousand more seals without harming local fish stocks.

“We currently have 30,000 grey seals in the Baltic Proper, but we can even have more than 100,000 seals and it will still not affect the amount of cod negatively as much as climate change, nutrient load and fisheries,” David Costalago, an ecologist and former postdoctoral researcher at Stockholm University, said in a news release. “The Baltic is very sensitive to human impact.”

Using sophisticated algorithms that account for predator-prey dynamics, as well as the effects of climate and human impacts, scientists modeled the trajectory of cod, herring and sprat stocks in the Baltic through the year 2098.

The simulations showed that while seal population size has little impact on fish stocks, temperature increases and the resulting changes in nutrient load in the Baltic are working to shrink the cod population.

Increases in nutrient load can fuel toxic cyanobacterial blooms, which applies a downward pressure on fish size. Smaller, slender fish are more vulnerable to predators and environmental stress.

The results of the study suggests efforts to conserve the Baltic’s seal population and commercial fish stocks aren’t contradictory.

“We want our insights to affect management and conservation that considers the whole ecosystem and multiple pressures, not only the direct biological interaction between fisheries and seals,” said researcher Monika Winder. “Often debates about the impact of seals arise from poor understanding of the complexity of predator-prey interactions.”