Depredation, the partial or complete removal of a captured fish by a non-target species, is one of the most pressing issues facing Gulf fishermen of all sectors – recreational, commercial and charter-for-hire.
Most fishermen and fisheries scientists agree that depredation is escalating throughout the Gulf. However, the specific aspects and trends vary over time and by location, making it difficult to understand and address the problem. Furthermore, depredation does not only impact the “catch” side of the equation – for example, the fishing strategies used by fishermen and the quantity of fish caught – it is also affecting the “release” side of the equation, when fishermen must discard fishes due to size limits, bag limits, seasons and other regulations.
In the Gulf, reef fish (snappers, groupers and triggerfish, to name a few) are often caught and released due to the reasons listed above. These fishes are primarily caught on structured habitat at depths of 30+ feet, making them susceptible to pressure-related injuries collectively referred to as “barotrauma.” In these situations, trapped gas may injure a fish’s internal organs and, in cases of catch-and-release, can prevent the fish from swimming to the seafloor and ultimately result in death.
Until recently, a technique called “venting” – piercing an expanded swim bladder to release trapped gas – was the main method for combating barotrauma. However, about a decade ago, the SeaQualizer entered the picture. This descender device, which returns fishes to the depth of capture, is relatively inexpensive and easy to use. As such, it is a great alternative to venting, especially among recreational fishermen who are not sure how to vent correctly (venting incorrectly can cause more harm than good). Most importantly, descender devices like SeaQualizers are a critically important tool for increasing post-release survival of reef fish.
Despite the benefits associated with descender devices, recreational fishermen are apprehensive about the effectiveness of these devices in the face of depredation. Specifically, some anglers have expressed concern that even if they are able to avoid depredation while catching a fish, using a descender device to release the fish simply provides an additional chance for depredation, as predators could pull a descending fish straight from the device.
Notably, the use of descender devices by anglers, and the resulting impact on post-release survival of reef fish, rely heavily on angler buy-in. In other words, if anglers do not believe that descender devices increase post-release survival, they are less likely to use these devices.
Consequently, Mississippi-Alabama Sea Grant Consortium Marine Fisheries Specialist Marcus Drymon and I initiated a project to examine the prevalence of depredation on reef fish released using descender devices and identify the species responsible for depredation. This work, which is funded by the Gulf States Marine Fisheries Commission and spans the U.S. Gulf, is being conducted in partnership with charter-for-hire captains. The concept is simple: captains use downward-facing GoFish Cams to film reef fish descents on SeaQualizers and return full memory cards and completed datasheets to us for data analysis and interpretation (Figure 1). We then disburse a stipend for each trip completed.
So far, one season of data collection has been completed (spring through fall 2022), with another season beginning shortly. During the first data collection season, 7 captains documented 464 descents: 233 off Florida, 184 off Alabama, 31 off Louisiana, and 16 off Texas (Figure 2). The depth at the descent locations ranged from 56 to 287 feet, with an average of 114 feet. The most common species released were red snapper (207) and red grouper (191), but 15 species were represented: 7 groupers, 4 snappers, 2 grunts, greater amberjack, and gray triggerfish.
Over the past several months, graduate students Alena Anderson and Danielle McAree have been entering the data and watching the video footage from the first data collection season. Although they are not finished yet, most of the videos analyzed so far have shown successful releases (see 0:00 – 1:51 below)! A few successful releases even occurred despite potential predators appearing in the frame (see 1:52 – 3:07 below). This suggests that predators may react differently to descending fishes (i.e., fishes being released) compared to ascending fishes (i.e., fishes being caught) – a rationale presented in a preliminary opportunistic study off the coast of Alabama in 2020 by Marcus Drymon, me and others. Most importantly, only one depredation event has been noted thus far (see 3:53 below), although one instance of post-release predation by dolphins has been documented (see 3:08 below).
Ultimately, the results of this project will build upon the preliminary findings from the Drymon et al. (2020) study by providing a complete picture of depredation on descender devices across the U.S. Gulf. Upon completion of the project, we will share our conclusions with the scientific community and the fishing public. If the data indicate that depredation rarely occurs on fishes released using descender devices, it is our hope that anglers will embrace the use of descender devices whenever they release reef fish, thereby increasing the sustainability of their fishing practices.
Meet the author
Amanda Jargowsky
Marine Fisheries Specialist
Amanda Jargowsky is a marine fisheries specialist with the MASGC-supported Marine Fisheries Ecology Program at the Mississippi State University Coastal Research and Extension Center. She conducted... Read more
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