For a truly sustainable fishery, more needs to be considered than just the abundance of the harvested species. Harvesting even abundant species can create indirect extinction cascades down the food web that can harm the long-term economic and ecological sustainability of a fishery. 

That is according to a study from the University of California, Davis, published today in the journal Science Advances. 

For the study, scientists incorporated the economic drivers of fishing into models of food-web networks to evaluate thousands of single-species fisheries across hundreds of simulated food webs. They compared those efforts under a “fixed effort” — in which there is a steady, fixed amount of harvestable fish allowed — and a profit-driven, “open-access” strategy, in which price fluctuates with market demand.

They found that harvesting under an open-access strategy helps keep abundant species in the market, with little threat to that specific species’ existence. However, a fixed-effort strategy is better for the ecosystem as a whole. This is because when an abundant species is harvested, cascading effects can impact other species throughout the food web. Those oscillations may trigger secondary extinctions. 

“If you fish abundant species, it’s less likely that species itself will go extinct but more likely the fishing effort will make other species go extinct,” said co-leading author Fernanda Valdovinos, an assistant professor with the UC Davis Department of Environmental Science and Policy. “You wouldn’t see that unless you’re studying the whole food web.”

Humans as part of the ecosystem

The models used in the study enable scientists to study thousands of individual species, not just a handful — and their food-web and human interactions. This helps fisheries managers balance both ecological and economic needs. 

Valdovinos said the research opens a new avenue for research in ecological networks.

“We need to understand ecosystems not just by themselves as isolated from humans, but as another element in the ecosystem,” Valdovinos said. 

The study also points to the importance of both theoretical and empirical research. The theoretical models allow scientists and resource managers to understand interactions among thousands of species anywhere in the world, and more quickly than field work alone could accomplish. 

“We need empirical data to test predictions of the models, but at the scale of our current environmental issues, we cannot wait 500 years to understand the fate of large ecosystems,” Valdovinos said.

Postdoctoral researcher Paul Glaum of UC Davis and the University of Michigan, Ann Arbor, at the beginning of the study, shares co-leading authorship with Valdovinos. Additional co-authors include Valentin Cocco of École Normale Supérieure, Biology Department PSL Université Paris, France.