Graduation Year

2014

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Philip J. Motta

Keywords

acoustic telemetry, animal movement, artificial reef, barotrauma, catch and release

Abstract

Groupers (Epinephelidae: Epinephelinae) are apex predators within many reef communities worldwide. Grouper landings contribute significantly to global fisheries, and many populations are suffering from unsustainable levels of exploitation. The large size, site specificity and catchability of most groupers increase susceptibility to fishing pressure, and a large number of grouper species throughout the world are currently overfished. Multiple species are listed as endangered or threatened, and many have suffered local extirpations across their range. Removal of these upper level predators can significantly alter community structure and result in second order effects that may have critical ecological implications. The economic and ecological value of groupers is significant, and data regarding the abundance, habitat and behavior of these exploited species are necessary in order to implement realistic and effective management strategies.

Atlantic Goliath Grouper (Epinephelus itajara) historically occurred in tropical and subtropical waters from the west coast of Africa to the east coast of Florida, south to Brazil, and throughout the Caribbean Sea and Gulf of Mexico. As one of the world's largest groupers, individuals are known to reach at least 37 years of age, and may grow to sizes exceeding 2.5 meters and 400 kilograms. The life history and behavioral characteristics of this species amplify vulnerability to exploitation, and Atlantic Goliath Grouper harvest was banned in U.S. waters in 1990 after a noted sharp decline in population numbers. The species has responded encouragingly to protective measures; however, the population's recovery and present status with U.S. waters should be thoroughly evaluated before altering regulatory guidelines. Traditional fishery-dependent data are not available (i.e., landings data); thus estimates of population demographics and recovery are dependent upon directed, fishery independent research efforts. It was the goal of this project to provide information regarding demographics, movement patterns, effects of catch and release angling, and feeding behavior of Atlantic Goliath Grouper within the central eastern Gulf of Mexico.

The majority of research involving Atlantic Goliath Grouper began after the stock was already overfished, resulting in the absence of an existing "baseline" with which to compare current population parameters. Replication of visual surveys over a range of depths and habitat types provided an index of abundance for specific sites, and allowed for quantification of the size distribution of individuals. Atlantic Goliath Grouper were most abundant at high relief, high volume artificial reefs within the study area, and the majority of individuals observed were 80 - 160 cm in total length. Knowledge of fish movement, behavior and habitat associations has been used to exploit many species of fish; thus, this knowledge is critical for the creation of regulatory guidelines regarding conservation.

Protection from harvest does not immediately imply that fishing mortality is negligible. As opportunistic ambush predators, Atlantic Goliath Grouper are relatively easy to catch on hook and line, and the species is often targeted for sport or caught incidentally during angling efforts for other reef fish species. Acoustic tracking allowed for continuous monitoring of individuals for several years after catch and release events. Barotrauma severity increased with capture depth, but immediate mortality was not observed during this study. Additionally, the length of total monitoring period was not affected by the severity of barotrauma, which suggests that with proper handling, Atlantic Goliath Grouper are not subject to high levels of release mortality in the study area (at depths < 40 m). However, strong site fidelity of Atlantic Goliath Grouper to artificial reefs increases susceptibility to fishing pressure and amplifies interactions with anglers, so the chronic effects of repeated capture remain unclear.

Description and quantification of goliath grouper feeding behavior may allow for innovative suggestions to decrease the probability of catch and release mortality, and potentially offer new tactics to reduce opportunistic predation upon hooked fish. Kinematic analysis of Atlantic Goliath Grouper feeding sequences demonstrated that they are capable of modulating feeding behavior based upon prey activity level and position within the water column. Individuals exhibited larger maximum gapes and more rapid feeding sequences when presented with mobile live food. Immobile (dead) food was primarily consumed through suction, and strikes upon these items were characterized by slower, closer approaches, smaller maximum gapes and longer bite durations. It is hopeful that the information presented herein will provide insight regarding the ecology of Atlantic Goliath Grouper and can be applied to future management efforts involving this protected species.

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