Article by Capt. Mark Sampson
Most anglers are familiar with the term “post release mortality” (PRM) which is used to describe a fish that dies after it has been released. While weak or erratic swimming actions will sometimes clue anglers to the fact that a particular fish they just released probably isn’t going to make it, it’s impossible to tell for certain what the fate of any fish is just by watching it swim away. Even if a fish appears healthy when it swims away from the angler who caught it, factors such as strength, stress, internal and external damage from the catch and release process, as well as predation for other fish (like sharks) all play a part in whether or not a particular fish will be able to fully recover from being caught and released.
Researchers, however, have certain tools and techniques that allow them to more accurately determine PRM in certain fisheries. One tool in particular is the pop-up satellite archival tag (PSAT). The PSAT is a device that can measure water temperature, depth, light, location and other environmental factors. These external tags are attached to the fish by a small dart that is planted just under the skin. Usually about the size of a large cigar, these tags are typically reserved for use on larger species of fish that can carry them without complications. PSATs are programmed to release from the fish after a specific number of days and then float to the surface where they can upload their archived data to a satellite. When they can be used, PSATs are great tools for determining PRM because they will very accurately show when and where a fish has quit swimming.
A couple weeks ago at a National Marine Fisheries Service Highly Migratory Species Advisory Panel meeting in Silver Spring, MD, I was in the audience for a presentation by Dr. John Graves from the Virginia Institute of Marine Science about a study he and his team conducted to determine the post release mortality of white marlin in the recreational fishery. While trolling from sport fishing boats out of the Virginia Beach area, the researchers caught 20 white marlin on J-hooks and 59 on circle hooks. All the marlin were tagged with PSATs and released without bringing them out of the water. After 30-days, the tags released and the data showed that 7 of the 20 marlin caught on J-hooks had died, resulting in a PRM of 35%. Of the 59 circle hook caught fish, only one died for a PRM of only 1.7%.
Most will agree that a 35% mortality rate for such a valuable fish as a white marlin is way too high and should not be tolerated. On the other hand, the 1.7% PRM for circle hook caught fish is very acceptable and a good testament on why anglers using dead bait for billfish should always use circle hooks.
Taking his studies one step further, Dr. Graves then tried to determine the effects of air exposure on PRM when white marlin are not released in the water, but are brought out of the water as anglers sometimes do in order to have a photograph taken of them with their catch. In this study, 18 white marlin were caught while trolling ballyhoo on circle hooks and all were fitted PSATs. Six marlin were brought out of the water for 1-minute, five came out for 3-minutes, and seven were out for 5-minutes. All of the marlin were laid on a wet deck with a wet towel over their head to help calm them and prevent injury while aboard. After the prescribed time, all the marlin were promptly released.
The results of this study, combined with the previous study where the marlin were released in the water, are both eye opening and somewhat frightening. Comparing the time out of the water to the mortality rate, they observed the following:
0-minutes out, 59 tagged, 1 died, PRM = 1.7%
1-minute out, 6 tagged, 1 died, PRM = 16.7%
3-minutes out , 5 tagged, 2 died, PRM = 40%
5-minutes out, 7 tagged, 3 died, PRM = 42.9%
Even though all of these fish were caught on circle hooks and, therefore, the mortality should have been very low, 33% of them died within the first 30-hours! The simple conclusion of this study is that air exposure dramatically increases the likelihood of PRM. Dr. Graves gave an interesting analogy of why a white marlin might so often succumb to being pulled out of the water, even for a short time, when he asked us to imagine running as fast as we could for a long time and then have someone hold our heads underwater for a minute or so. We’d be deprived of oxygen at a critical time when our bodies needed it the most. If this study is accurate, it could be that one out of every three marlin plucked out of the water for a photo-shoot ends up dying.
What does all this mean to us fishermen? We’ll, there’s a lot of evidence, both online and in printed media, that not all marlin are being released in the water. Many anglers might not be aware of the federal regulation requiring all HMS species (billfish, tuna, sharks, swordfish) not be pulled from the water prior to their release. Obviously, by the amount of photos that show up everywhere with HMS fish out of the water, this is not a regulation the NMFS has strived to enforce, but with this new evidence of white marlin PRM, the regulation could become more of a priority. At the very least, fishermen who are now aware of the high risk to white marlin from air exposure should think twice before plucking their catch out of the water and opt instead for a picture of the fish in the water with the proud angler leaning over the gunwale above it.
Capt. Mark Sampson is an outdoor writer and captain of the charter boat, “Fish Finder”, docked at the Ocean City Fishing Center.
