Black Sea Bass Can Withstand Trauma Surprisingly Well

Black sea bass exhibit an unusual resilience to trauma, according to researchers.

In a broader study assessing mortality rates in fisheries and what can be done to make them sustainable operations, a team of North Carolina State University fisheries researchers found that black sea bass can survive the physical trauma from being hauled up from more than 60 feet of water then released at the surface.

When fish are hauled up form deep water, the water pressure changes rapidly, causing the fishes' swim bladder to expand. When this happens, pressure is placed on other organs inside the fish, sometimes forcing them out of order. In some cases of so-called barotrauma, a fish's stomach can be partially forced out of its mouth.

The long standing belief on this sort of barotrauma was that the fish would die when thrown back in the water, but the NC State researchers report this is not the case.

They came to this conclusion through testing what's known as the "discard mortality rate" for black sea bass. An understanding of the percentage of fish the die after being harvested form the deep and thrown back in the water is useful for fisheries managers making accurate stock assessments.

Scuba-diving researchers tagged black sea bass in deep water, establishing a control group. On the same day, they then caught, tagged and released the same number of sea bass in a traditional fishing method. Over the next year, the tagged fish were caught by the researchers or other anglers and the tags were returned to the researchers.

The discard mortality rate was calculated by comparing the number of tags returned from the experimental group tagged on the surface to the control group tagged below the water.

It turned out that 90 percent of the fish in the experimental group with visible barotrauma survived, much to the researcher's surprise.

"In previous work, estimates of discard mortality were limited to time periods soon after release," said Paul Rudershausen, a research associate at NC State's Center for Marine Sciences and Technology. "By tagging a control group, we were able to estimate the long-term effects of injuries associated with fishing."

Rudershausen and his colleagues reported their findings in the Canadian Journal of Fisheries and Aquatic Sciences.