Researchers at N.C. State have found, contrary to previous understanding, black sea bass have high survival rates after experiencing the trauma of being brought to the ocean surface too rapidly. This finding has the potential to better inform federal stock assessments that ensure the population of black sea bass stays at a sustainable level.
“We started this research because there was a need for accurate estimates of how many fish die when they are released back into the water after they are caught by either recreational or commercial fishing,” said Jeff Buckel, professor of applied ecology and co-author of the study.
According to Buckel, a stock assessment uses a variety of data to model a population of fish. The National Marine Fisheries Service does stock assessments of black sea bass to determine if any changes are needed, given the size and mortality rate of the fish population, or “stock,” Buckel said.
To collect new data on the black sea bass population, Buckel and his team caught and tagged fish with “spaghetti tags,” which look like pieces of spaghetti. The researchers captured, tagged and released some of the fish on the bottom of the ocean. These fish didn’t experience any sort of trauma, and this group of fish was the control group. The researchers assumed a 100 percent survival rate, Buckel said.
According to Buckel, the researchers caught other fish and brought them to the surface of the ocean before tagging and releasing them.
“One type of trauma associated with being brought to the surface results from the rapid change in pressure,” Buckel said. “During the ascent through the water column, the fish’s swim bladder will expand rapidly and can damage internal organs.”
This pressure trauma, also known as “barotrauma,” can lead to a fish’s stomach sticking out of its mouth, Buckel said.
In addition to barotrauma, researchers tagged fish that suffered from hook trauma, fish with stomach or gill injuries from fishing hooks and fish that were floating.
According to Buckel, during the next year, the researchers caught the tagged black sea bass or received tags from captured tagged fish.
“We compared the tag return rate of fish in compromised conditions to the tag return rate of fish in the control group to estimate survival of fish in compromised conditions,” Buckel said. “Going into this project, we assumed that the fish with barotrauma would have a low survival rate, but it turns out that a majority of those fish lived.”
According to Buckel, the researchers found that approximately 90 percent of the fish in the experimental group with visible barotrauma survived. This was about the same survival rate as for fish that exhibited no visible injury at all. Fish with hook trauma had a survival rate of 36 percent, while floaters had a 16 percent survival rate.
“In previous work, estimates of discard mortality were limited to time periods soon after release,” said Paul Rudershausen, a research associate at N.C. State’s Center for Marine Sciences and Technology and lead author of a paper describing the research. “By tagging a control group, we were able to estimate the long-term effects of injuries associated with fishing.”