University of Minnesota researchers have created a system that can predict if certain fish species will be endangered in the future, helping fishermen prevent overfishing.

In a two-year study, researchers predicted the threat level of eight marine species based on their current catch and growth rates.

When commercial fishermen want to catch a certain kind of fish, they inevitably catch other unwanted, less profitable types as well.

 Because fishermen want to maintain yellowfin tuna populations, for example, they are careful to not overfish them. But other species caught accidentally can be overfished, because fishermen don’t closely monitor whether they’re at risk. So ecology, evolution and behavior graduate student Matthew Burgess developed a way to measure the effect on those other fish.

Other methods for measuring possible overfishing only identify species that are currently vulnerable. But Burgess’ “eventual threat index” can identify which species will decline in the future based on their vulnerability now.

“The advantage of predicting the decline before it happens is to have time to make small changes instead of having to make a big change after the fact,” Burgess said.

All the data Burgess used — dating back to the 1950s — was publicly available, and anyone can use the index he developed.

The risk for overfishing is most common in the coastal fishing industry, where more than 60 percent of commercial fish are threatened.

Multispecies marine fisheries have the biggest problem with overfishing because their populations decline at different rates, said applied economics professor Stephen Polasky, who advised Burgess on the study.

“If you have multiple fish species and you have a species that is really common and comes back quickly, you can keep fishing that species,” he said. “But you’re catching the other ones and they could go extinct.”

Ocean fisheries manage their populations by using special nets or by shutting down if too many endangered species are caught. Identifying overfishing threats to these species before they occur can help industries prevent closures — resulting in higher profits.

“You … have time to research and develop new technology,” Burgess said, “rather than closing the fisheries.”

Future applications

The index is applicable for any multispecies fishery, Burgess said, but doesn’t yet apply to recreational fishing in Minnesota.

Minnesota Department of Natural Resources senior fisheries specialist Jim Levitt said it’s hard to know the future effect fishing will have on a population.

“It would always be nice to know the fish population when you’re assessing them,” he said. “There’s a lot of variables, so sometimes it’s hard to know until you’re looking backwards what’s going on.”

If a threat index is created specifically for Minnesota lakes, he said, it could be worthwhile. But overfishing isn’t currently a huge problem in the state.

Minnesota commercial fishermen are only licensed to catch invasive species like carp, buffalo and bullhead, said Jeff Riedemann, president of the Minnesota Inland Commercial Fisherman’s Association.

“Basically … they want us to get rid of them,” commercial fisherman Kenneth Seemann said.

Burgess said his index could apply to commercial fishing in the state if they fished more species.

He is also developing a second index that could predict the decline of one species at a time, instead of finding the threat level for all of the fish caught. If he succeeds, the eventual threat index could be useful for a broader range of fisheries, he said.

Currently, Burgess said, his team is calculating and indexing the eventual threats for more than 500 fish species.