October 13, 2015 | CMAST

“So, a gray triggerfish that’s caught and then thrown back for whatever reason, what sort of shot does that fish have of making it?” This is a question CMAST’s Brendan Runde asked hypothetically as he sat working on dozens of tags spread out in front of him, tags that will end up inside of fish as part of his study. Runde is doing his master’s thesis on the gray triggerfish, one of the most popular recreationally and commercially caught fish from North Carolina to Florida.

The tagging program attempts to test the hypothesis that fish which undergo this barotrauma when caught and then thrown back don’t have as great a chance to survive the experience as if they had not undergone the catch and discard process.

Testing this hypothesis will lead to an expanded understanding of the triggerfish population and is a project that involves extensive surface tagging of fish, deep-sea scuba work, cooperative efforts between CMAST researchers and a local commercial fisherman, and lots and lots of fishing. The approach is to bring these fish up, tag them, throw them back and, in classic message in a bottle fashion, hope they return to researchers with data that leads to answers.

The gray triggerfish lives in water depths of 100 feet or more. When they are brought to the surface by being caught, they typically suffer barotrauma, which is injury due to extreme and rapid pressure changes. In gray triggerfish, common forms of barotrauma include bloating of the abdominal cavity, and intestinal prolapse. If a fish is caught and then discarded, it may have sustained injuries that end its life before it can grow big enough to end up in a fisherman’s cooler another day.

Data on how many of these “catch and discard” specimens grow and thrive to reach legal limits for later catches is critical to setting sustainable catch limits.

Tracking the lives of individual fish would seem at first glance to be a needle-in-a-haystack proposition. However, there are a few factors that make the gray triggerfish a likely candidate for this study. First and foremost, they exhibit what is called “high site fidelity,” which means they tend to live their lives in one spot. Males in particular form a ‘harem’ and then stick close to home. Most fish are recaught in the same spot they were originally tagged, and if not, usually within a one mile radius. This high site fidelity helps ensure that a fish that was not recaptured was lost due to mortality rather than simply migrating from the area.
How the tagging process works

Divers tag fish caught at the bottom for a control group.

Divers tag fish caught at the bottom for a control group.

Researchers use hook and line fishing methods for triggerfish in waters approximately 130 feet deep. When a triggerfish is caught, a small incision is made under the skin and an internal-anchor wire-core tag is inserted. On the tag are the fish ID number and the phone number to call if a tagged fish is caught; anyone catching a tagged fish can contact the researchers for a reward. Once inserted, the tag looks very much like a yellow plastic bread-tie poking a bit outside the fish’s skin.

After tagging, the fish is examined for outward signs of barotrauma. This information is recorded, and the fish is then released. The fish’s response once it hits the water is also carefully recorded. Some take off for the bottom vigorously, apparently none the worse for wear by the experience. Others have more trouble, and, rarely, some die at the surface. The data recorded at the time of catch and tagging will be referenced if the fish is recaught.

However, that’s only half the story. A control group of fish who have not undergone the barotrauma of being caught at the surface are also being tagged and tracked. Tagging these fish is a little trickier. Fish traps are set on the bottom at these same fishing sites where scientists are catching and tagging fish at the surface. Scuba divers, who have only about fifteen minutes of bottom time per session, go down to the traps to perform the incision and tagging procedures on the fish in the traps, which are then released.

With an equal number of surface-caught fish and control group fish tagged, researchers can then develop a formula to calculate how many of the caught and discarded fish died as a result of barotrauma. As a simplified example, if 50% of the control group fish are caught, and there is a 25% return rate for fish caught at the surface, it can be concluded that roughly half of the fish caught at the surface die as a result of barotrauma. Because of the characteristics of the gray triggerfish, the number which simply leave the area is surprisingly small.

A study such as this one is very labor intensive. The tagging process began in May of 2015 and will continue through 2016. There are 1,500 tags to be deployed. That’s a lot of fishing, and a lot of diving, but at the end of the study, there should also be a lot of data, and that’s what it will take to answer questions about what’s happening with this population of fish.

The number of gray triggerfish caught and released every year seems to be on an upward trend. Some states have recently implemented minimum size requirements where there were none before. Other states have put quota systems into effect, so there is more motivation for throwing back a fish under the limit. Catch and discard rates are increasing as a result, and any gray triggerfish released are then subjected to the gauntlet of potential causes of mortality. A tagging study such as this one will help determine how discard rates are affecting the species population as a whole, and may allow scientists to predict how this trend will continue.

This tagging project is funded by a grant from NOAA, under the Cooperative Research Program. It is a yearly grant made available to scientists who want to cooperate with the fishing community to promote knowledge and provide outreach, combining commerce, recreation, and science. The CMAST tagging team is made up of principal investigator Dr. Jeff Buckel, assisted by Paul Rudershausen, and Brendan Runde. Runde will come out the other side of this project with a master’s thesis that will provide important clues to federal agencies who are gathering this and other data to sustainably manage triggerfish.

Local commercial fisherman Tom Burgess of Sneads Ferry is another important participant in this study. He is part of the original grant, and much of the bottom fishing and tagging is done on his vessel. Runde was enthusiastic in discussing the collaborative aspect of the project. “This is the interface between fishermen and scientists, so that everybody understands each other a little bit better. Communicating scientific findings to those outside of the scientific community is such an important part of the big picture.”

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