Stress Effects of Catch-and-Release Fishing on Tarpon
The catch-and-release tarpon fishery, targeting both adult and subadult fish, generates millions of dollars for the state of Florida each year. To sustain this very important recreational fishery, it is critical to maximize survival after release and minimize the nonlethal stress effects from hook-and-line fishing.
Battling an angler is strenuous exercise for a hooked tarpon. The battle includes heavy pulling by all involved, plus acrobatic leaps and endurance swimming for the tarpon. Once the oxygen supplied to the blood from breathing through the gills runs short, the tarpon has to tap into the energy reserves found in the muscles to fuel the fight. This disrupts internal electrolyte and acid-base balance, builds up lactic acid in the muscles, and dumps lactate into the blood--consequences that could affect the health and survival of a tarpon after release.
Researchers with the FWC's Fish and Wildlife Research Institute (FWRI) used blood chemistry samples to measure stress responses in two size classes of tarpon after the exhaustive exercise of fighting on hook and line. They tested whole blood for hematocrit and hemoglobin levels and blood plasma for glucose, lactate, sodium, potassium, chloride, calcium, phosphorus, magnesium, and cortisol concentrations. The study compared
- angled adults (weighing more than 70 pounds) with adult tarpon not subjected to angling.
- angled subadults (weighing less than 10 pounds) with subadults not subjected to angling.
- adult tarpon with subadults to determine any size-related variation in stress responses after angling.
Because smaller tarpon are easier to handle and anglers may subject them to prolonged air exposure for hook removal or photographs, researchers also evaluated the effect of 60 seconds of air exposure while holding the fish horizontally or vertically out of the water. A third group of angled subadult tarpon were not held in the air before they were bled.
Is there a difference in the stress response of small tarpon based on how an angler holds it in the air for a quick photograph?
FWRI scientists evaluated the blood responses of each tarpon as they related to body size, angling duration, handling, and environmental factors.
Results showed the following:
- Angling events had a significant effect on blood responses of adult tarpon and on select blood responses of subadult tarpon, compared with fish not subjected to fishing.
- Blood responses after angling were more extreme in adult tarpon than in subadults.
- Physiologically, tarpon responded to angling as do other high-energy, powerful fish, such as tunas, sharks, billfishes, and even the smaller species of tarpon found in the Indo-Pacific.
- Angling duration, handling time, and body size significantly influenced the observed physiological responses in blood chemistry.
- No significant difference in the blood responses of angled subadult tarpon resulted from exposing fish to air by holding them horizontally or vertically.
- Environmental variables (air and water temperature, dissolved oxygen, pH, and salinity) played a minimal role.
Scientists also monitored the survival of the subadult tarpon, which they released into a saltwater pond with no natural predators. Out of 28 tarpon, only one died--43 hours later. Furthermore, eight of the sampled subadults were recaptured multiple times, which indicated long-term survival after catch-and-release events.
Applying the Findings
What do these results mean for the recreational Atlantic tarpon fishery?
Anglers can reduce the overall physiological response of most blood parameters measured in this study if they use appropriate tactics to minimize fight time. Handling a hooked tarpon carefully and quickly and releasing it in the absence of large predators will increase its chance of surviving the angler's fight. Also, the results indicate that brief air exposure for a photograph prior to release or minimal handling at the side of the boat to take a DNA sample is probably not too stressful for a tarpon.
Contributions to support this work included Grant F-59 from the Federal Aid in Sport Fish Restoration Act, proceeds from the state of Florida's tarpon tag program, and a private research grant from Bonefish & Tarpon Trust and the Fisheries Conservation Foundation Flats Fishing Alliance. The American Fisheries Society headquarters in Bethesda, Maryland, awarded a Hutton Fisheries Biologist Scholarship for work on this project during an eight-week summer internship.
View the scientific report of this study: Evaluating Lethal and Sub-Lethal Effects of Catch-and-Release Angling in Florida's Central Gulf Coast Recreational Atlantic Tarpon (Megalops atlanticus) Fishery.
Read about DNA testing in tarpon research.