Graduation Year

2011

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Marine Science

Major Professor

David A. Mann

Keywords

air exposure, mortality, physiology, stress, tarpon, telemetry

Abstract

Atlantic tarpon are sought after because of their fighting ability on various tackle and support a popular, lucrative and predominantly catch-and-release recreational fishery in Florida. They are not commercially harvested or consumed by the general public, therefore assessing effects of catch-and-release angling on tarpon survival is critical to a sustainable fishery. Tarpon caught on artificial breakaway jig and traditional live bait fishing charters in Boca Grande Pass (n=42) and trips from the recreational fishery of Tampa Bay (n=40) were tagged with ultrasonic transmitters and tracked up to 6 hours immediately following release to estimate post-release mortality. Of the 82 tagged tarpon, 11 suffered mortality as inferred from movement patterns (or lack thereof) or visual confirmation (i.e. shark attacks) which yields a combined total estimated catch-and-release mortality rate of 13% (95% confidence interval: 6-21%). There was no significant difference in mortality between the two estuarine systems. Associations between tarpon mortality and angling duration, handling time, fish length, bait type (artificial versus natural), and hook type (circle versus "J") were not significant. Hook location (foul-hooking) and swimming condition at release were significant factors on tarpon mortality (P<0.05). Shark predation was the primary cause of post-release mortality (64%). Excluding predation, the overall mortality rate was estimated at 5% and attributed to poor handling and irreparable physiological damage from angling.

Angling events will cause anaerobic activity resulting in physiological disruptions that may have consequences compromising the health and survival of tarpon. Both adult (mature, >70 pounds, 31.8 kg) and sub-adult (sexually immature, <20 pounds, 9 kg) tarpon support Florida's recreational fishery, so maximizing post-release survival and minimizing sub-lethal stress effects of both size classes are critical to their sustainability. In this study, stress responses after exhaustive exercise (angling) were measured using an array of blood chemistry parameters, including hematocrit, hemoglobin, and plasma glucose, lactate, sodium, potassium, chloride, calcium, phosphorus, magnesium and cortisol. Angled, adults (n=45) were compared to large tarpon in a resting state (controls, n=6). Angled, sub-adults (n=28) were compared to those in a resting state (n=9). Adult tarpon were then compared to sub-adults to determine any size-related, intra-species variation in stress responses after angling. Finally, because smaller tarpon are logistically easier to handle and may be subjected to prolonged air exposure by anglers for hook removal or photographs, we evaluated the effect of 60 seconds of air exposure with horizontal (n=9) or vertical (n=9) handling out of the water relative to non-air exposed (n=10) fish in angled sub-adult tarpon. Associations and interactions among the blood chemistry responses of tarpon from each treatment to angling duration, handling time, body size and environmental factors related to each capture event were evaluated using a non-parametric, multivariate redundancy analysis. The duration of the angling event had a positive effect on responses of some parameters, and responses were more extreme in adult tarpon than sub-adults. The exception was cortisol which was significantly higher in sub-adults. Environmental parameters were less influential than angling and handling on observed physiological responses. Sub-adults showed no difference in physiological responses among handling treatments with and without air exposure and exhibited no short term mortality. Using appropriate tackle and gear to reduce fight times and handling should help minimize metabolic and acid-base imbalances.

Tagging studies coupled with physiology can be a valuable tool for estimating post-release mortality and secondary stress responses of game fish, especially for large species that might be difficult to maintain in floating pens or tanks. Yet adverse effects of catch-and-release angling could also have population level consequences. Future studies should integrate biology and fish physiology to evaluate post-release recovery windows and establish lethal thresholds to provide potential predictive capability of mortality. In general, it appears that sub-adult and adult Atlantic tarpon along the Gulf coast of Florida can recover from physiological disturbances incurred during routine catch-and-release angling events in the recreational fishery when they are released in the absence of large predators. The anglers themselves can play a key role in tarpon conservation.

Share

COinS