Black sea bass survive release better than we thought
Black sea bass (Centropristis striata) may not win any beauty awards, but it sure is one of the more popular fishes in school. In 2009, there were 2.72 million of them caught in the US Atlantic. What’s perhaps surprising at first glance is that 89.7% of them – nearly 9 out of every 10 reeled to the surface – were tossed back into the sea.
Why are so many being released? In part, it’s because of ever-tightening restrictions on the capture of reef fishes. The South Atlantic Fishery Management Council imposes strict limits on the size and number of fish that may be taken, it creates open and closed seasons, and it limits fishing to certain geographical areas between North Carolina and Florida. Others are released because some folks enjoy fishing but don’t actually wish to harm the animals, so they simply practice catch-and-release. It’s a popular species, both among commercial and recreational anglers.
The problem is that catch-and-release fishing for black sea bass, even if the more humane barbless hooks are used, still leads to lots of fish mortality. Or, at least, that was the conventional wisdom. A new study by North Carolina State University researchers overturns the conventional wisdom and shows that black sea bass survive catch-and-release much better than most people thought.
Here’s why most anglers thought that releasing black sea bass meant certain doom for most of them. They’re bottom-dwellers and are usually caught at depths greater than 60 feet. As they’re reeled up to the surface, the water pressure around them rapidly changes, making their internal swim bladders expand. As they expand, their internal organs are mixed about, which results in a condition called “barotrauma.” The most obvious sign of barotrauma is seeing the fish’s stomach visibly protruding from its mouth. The new study, published in the Canadian Journal of Fisheries and Aquatic Sciences shows that barotrauma is not the death sentence commonly assumed.
The researchers set out to understand more about “discard mortality” for the fish, which is an important metric in understanding the health of fish stocks and is used in setting fishing restrictions. In other words, how many fish that were thrown back into the water would die anyway? They conducted two clever experiments to find out.
They began by comparing fish that were trapped, tagged, and released on the sea floor over the course of several days by SCUBA divers to fish that were trapped, brought to the surface by the angling researchers, and released. Only the healthiest fish – those who showed no obvious fishing-related trauma – were tagged before release so they could be tracked. They found that 87% of those tagged fish brought to the surface survived, relative to the control group at the sea floor.
That figure served as a baseline for a large-scale study that took place over the course of an entire year. An additional 4,555 black sea bass were caught, tagged, and released from the surface. Later, when commercial or recreational anglers hauled in the fish, they’d see a little tag with a phone number and a message that they would be paid $5 if they returned the tag to the researchers along with some basic information. Nearly a quarter of those tags were sent back to the researchers.
Unlike the fish brought in by trap in the first experiment, the fish in the second experiment were brought in by whatever method the anglers preferred: traps, or hooks and lines. This allowed the researchers to compare the relatively controlled catch and release conditions in their initial, small-scale experiment to the real-world conditions in the larger-scale one.
Ninety-one percent of the bass who had no visible signs of barotrauma or hook trauma appeared to have survived, which is comparable to the 87% from the first study. In addition, an impressive 87% of those with visible barotrauma – their stomachs could be seen pushing out from inside their mouths – also survived. What that means is that those with barotrauma were no less likely to survive than those without. On the other hand, only 36% of those bass with hook trauma survived. Barotrauma is nothing compared to the possible damage a badly-placed hook can do.
Taken together, the study shows that barotrauma is not a good indicator of mortality for reef fishes like the black sea bass, and using barotrauma may considerably skew assessments of the health of various fish stocks. The approach taken in this study, comparing fish released in the best condition to those who were tagged but never brought to the surface, provides empirical support for something that had previously only been assumed to be true. Now, policymakers can begin making more informed decisions about fishing restrictions not just for black sea bass, but for other species found in similar habitats, like the red grouper or the gag grouper. – Jason G. Goldman | 11 April 2014
Source: Rudershausen P.J., Buckel J.A., & Hightower J.E. (2014). Estimating reef fish discard mortality using surface and bottom tagging: effects of hook injury and barotrauma, Canadian Journal of Fisheries and Aquatic Sciences, 71 (4) 514-520. DOI: 10.1139/cjfas-2013-0337
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