Generation after generation, catch after catch, fishing changes the evolution of fish. This phenomenon, called fisheries-induced evolution, is well-documented but affects myriad fish species differently. Excluded from the pool. This means that fish populations are evolving towards smaller sizes. A recent paper models what it takes to reverse this impact through conservation and what that means economically.
“In general, fisheries are one of the main drivers of change in marine ecosystems,” says Halle Jena, a postdoctoral researcher at the German Integrated Research Center for Biodiversity (iDiv) Leipzig and one of the paper’s authors. Hannah Schenck told Ars.
Fishing increases fish mortality. Larger fish, in particular, are more likely to stay in the net and are therefore more likely to be caught. In turn, this puts selective pressure on the species: fish that mature faster (but stay smaller) have an advantage. , affecting the entire population over time.
“There are trade-offs between the two. [factors], and as cod matures, it grows slower. So when it occurs early, it usually doesn’t grow to a large size as if it hadn’t spawned,” she said.
fish and money
A new study focuses on the well-studied North Sea cod in terms of mortality, growth and more, showing signs of evolution due to fishing. The team began working on his project in 2019 and began integrating evolutionary and economic models. Biological models capture growth, mortality, reproduction, evolutionary change, effects of fishing, and other factors. Economic models work to predict factors such as fishing costs and consumer preferences.
We also fine-tuned various existing algorithms to optimize fish resource management (in this case, North Sea cod) and economic benefits. “We started by developing a model that basically captured all the essential components without being overly complex,” he says.
Data for cod were provided by the International Council for Oceanographic Surveys (ICES), which regularly provides stock assessment data for various species, including cod. For the economic model, the researchers relied on multiple sources, including data from the German Federal Ministry of Food and Agriculture. This provided prices for different sizes and types of fish. More data comes from a report by the Fisheries Scientific, Technical and Economic Commission (STECF) examining the profit margins of fisheries.
The team used the model to optimize evolution and economic health by fine-tuning various parameters that can be controlled by conservation goals and regulations. Management in this case is simply reducing fish catches by having governments set conservation targets. Schenck added that whatever the evolution, the best management plan involves bringing less North Sea cod from the ocean. This is despite the fact that the total allowable catch (commonly he is called the TAC) has already been reduced in recent years.
trade off
By running the model, the researchers showed that management could reverse fisheries-induced evolution when considered over very long timelines (about a century). This is necessary because evolution happens slowly.
A conservation target with a century-long timeline would effectively reverse the evolution induced by the fishery, with a small loss of gains during that time. For example, setting an ambitious conservation target (average fish maturity size of 53 cm compared to 50.6 cm in 2019) for 2050 would result in a 10% surplus loss. The reason this scenario is slightly less profitable is that management may reduce harvests at various points in the future to allow stocks to recover before harvesting begins again.
It’s hard to say whether these findings apply to other fish species, Schenck said. These include historical fishing pressure, rate of evolution, etc. In the future, the team hopes to analyze the types of fishing gear that influence the size of fish caught and the ideal fish size to reverse the evolution induced by fishing. population.
Nature, 2023. DOI: 10.1038/s41893-023-01078-9 (About DOI)
