Thesis (Ph. D.)--Auburn University. / Abstract. Includes bibliographical references.

Thesis (M.S.)--University of North Carolina Wilmington, 2007. / Includes bibliographical references ( Leaves: 77-86)

Thesis (M.S.)--University of North Carolina at Wilmington, 2005. / Includes bibliographical references (leaves: [52]-62)

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references.

Juvenile red snapper are attracted to structure and settle onto low profile reefs, which serve as nursery grounds. Little is known about their life history during this time. However, recent studies from a shell bank in the NW Gulf of Mexico have shown higher growth rates for juveniles located on mud habitats adjacent to low profile reefs, perhaps due to varied prey availability and abundance. To further investigate the habitat needs of juvenile red snapper, individuals were collected from a low profile shell ridge (on-ridge) and adjacent mud areas (off-ridge) on Freeport Rocks, TX, and divided into three size classes (≤3.9 cm SL, 4.0-5.9 cm SL, ≥6 cm SL). Feeding morphology and kinematics were characterized and compared among size classes and between the two habitats. A dynamic jaw lever model was used to make predictions about feeding mechanics, and kinematic profiles obtained from high-speed videos of prey capture events validated the model’s predictive ability. Model output suggested an ontogenetic shift in feeding morphology from a juvenile feeding mode (more suction) to an adult feeding mode (more biting). Stomach contents revealed a concomitant shift in prey composition that coincided with the ontogenetic shift in feeding mode. The model also predicted that on-ridge juveniles would have faster jaw closing velocities compared to off-ridge juveniles, which had slower, stronger jaws. Analysis of prey capture events indicated that on-ridge juveniles demonstrated greater velocities and larger displacements of the jaws than off-ridge juveniles. Shape analysis was used to further investigate habitat effects on morphology. Off-ridge juveniles differed from on-ridge in possessing a deeper head and body. Results from model simulations, kinematic profiles, personal observations, and shape analysis all complement the conclusion that on-ridge juveniles exhibited more suction feeding behavior, whereas off-ridge juveniles used more biting behavior. Stomach contents demonstrated an early switch to piscivory in off-ridge juveniles compared to on-ridge juveniles, which may account for higher off-ridge growth rates. Habitat disparity, perhaps available prey composition, generated variations in juvenile feeding mechanics and consequently feeding behavior. This disparity may ultimately affect the growth rates and recruitment success of juvenile red snapper from different habitats.

Red Snapper, Lutjanus campechanus, are the most economically important reef fish in the Gulf of Mexico. Population assessments that began in the mid-1980’s found red snapper to be severely overfished and lead to extensive regulations and harvest restrictions. As a result of these regulations many fish that are captured must be released and are known as regulatory discards. Red snapper live deep in the water column and when captured and rapidly brought to the surface they often suffer pressure-related injuries collectively known as barotrauma. These injuries include a distended abdomen and stomach eversion from the buccal cavity. High mortality of discards due to barotrauma injuries impedes recovery of the fishery. The purpose of this study was to evaluate the efficacy of two techniques designed to minimize barotrauma-related mortality: venting and rapid recompression. In laboratory experiments using hyperbaric chambers, I assessed sublethal effects of barotrauma and subsequent survival rates of red snapper after single and multiple simulated capture events from pressures corresponding to 30 and 60 m. I evaluated the use of rapid recompression and venting to increase survival and improve recovery indices, including the ability to evade a simulated predator. A condition index of impairment, the barotrauma reflex (BtR) score, was used to assess sublethal external barotrauma injuries, reflex responses, and behavioral responses. Greater capture depths resulted in higher BtR scores (more impairment). Non-vented fish had higher BtR scores than vented fish after both single and multiple decompression events. All fish in vented treatments from 30 and 60 m depths had 100% survival after a single capture event. Non-vented fish had 67% survival after decompression from 30 m and 17% survival from 60 m. Behaviorally, non-vented fish showed greater difficulty achieving an upright orientation upon release and less ability to evade a simulated predator than vented fish. Rapid recompression also greatly improved survival compared to surface-released fish with 96% of all rapidly recompressed fish surviving. These results clearly show that venting or rapid recompression can be effective tools for alleviating barotrauma symptoms, improving predator evasion after a catch-and-release event, and increasing survival. Fisheries managers should encourage the use of either of these two techniques to aid in the recovery of this important fishery.

Juvenile red snapper are attracted to structure and settle onto low profile reefs, which serve as nursery grounds. Little is known about their life history during this time. However, recent studies from a shell bank in the NW Gulf of Mexico have shown higher growth rates for juveniles located on mud habitats adjacent to low profile reefs, perhaps due to varied prey availability and abundance. To further investigate the habitat needs of juvenile red snapper, individuals were collected from a low profile shell ridge (on-ridge) and adjacent mud areas (off-ridge) on Freeport Rocks, TX, and divided into three size classes (≤3.9 cm SL, 4.0-5.9 cm SL, ≥6 cm SL). Feeding morphology and kinematics were characterized and compared among size classes and between the two habitats. A dynamic jaw lever model was used to make predictions about feeding mechanics, and kinematic profiles obtained from high-speed videos of prey capture events validated the model’s predictive ability. Model output suggested an ontogenetic shift in feeding morphology from a juvenile feeding mode (more suction) to an adult feeding mode (more biting). Stomach contents revealed a concomitant shift in prey composition that coincided with the ontogenetic shift in feeding mode. The model also predicted that on-ridge juveniles would have faster jaw closing velocities compared to off-ridge juveniles, which had slower, stronger jaws. Analysis of prey capture events indicated that on-ridge juveniles demonstrated greater velocities and larger displacements of the jaws than off-ridge juveniles. Shape analysis was used to further investigate habitat effects on morphology. Off-ridge juveniles differed from on-ridge in possessing a deeper head and body. Results from model simulations, kinematic profiles, personal observations, and shape analysis all complement the conclusion that on-ridge juveniles exhibited more suction feeding behavior, whereas off-ridge juveniles used more biting behavior. Stomach contents demonstrated an early switch to piscivory in off-ridge juveniles compared to on-ridge juveniles, which may account for higher off-ridge growth rates. Habitat disparity, perhaps available prey composition, generated variations in juvenile feeding mechanics and consequently feeding behavior. This disparity may ultimately affect the growth rates and recruitment success of juvenile red snapper from different habitats.

Three low-relief banks (Heald Bank, Sabine Bank, Freeport Rocks) in the northwestern Gulf of Mexico were evaluated as lane snapper (Lutjanus synagris Linnaeus, 1758) nursery habitat. Trawl surveys were conducted in three habitat types (inshore mud, shell ridge, offshore mud), designated by side-scan sonar surveys, to determine patterns of distribution and abundance. Heald Bank and Sabine Bank were trawled in 2003 while Freeport Rocks was trawled in 2000 (Freeport A) and 2004 (Freeport B). Density of lane snapper was higher on Sabine Bank (20.8 ± 2.8 ind ha-1) than on Heald Bank (1.1 ± 0.4 ind ha-1), Freeport A (12.7 ± 2.3 ind ha-1) or Freeport B (3.0 ± 1.0 ind ha-1). Habitat-specific differences in density were observed, although patterns were not consistent among banks. Highest densities of lane snapper were found on Heald Bank’s offshore habitat (1.7 ± 1.0 ind ha-1), Sabine Bank’s ridge habitat (26.5 ± 6.9 ind ha-1), and on the inshore habitat of Freeport A and B (17.6 ± 4.9 ind ha-1 and 4.8 ± 3.6, respectively). Otolith microstructure analysis was performed on lane snapper collected in trawl surveys to determine age, hatch-date distribution, growth and mortality of new recruits. Hatch dates ranged from May 1 to August 31, peaking in June for Freeport (A and B) and in July for Heald Bank and Sabine Bank. Growth rates varied from 0.90 mm d-1 at Heald Bank to 1.27 mm d-1 at Sabine Bank, and rates were highest on the ridge habitat of Sabine Bank (1.31 mm d-1). Mortality of post-settlement lane snapper was higher on Sabine Bank (15.2% d-1; Z = 0.165), than on Freeport A (9.2% d- 1; Z = 0.097), and was greatest on the ridge habitat of Sabine Bank (24 % d-1; Z = 0.275). Recruitment potential (G : Z), evaluated on habitats at Sabine Bank, was highest on the offshore habitat, with a value greater than 1.0, indicating higher potential contribution to the adult population. Results indicate Heald Bank, Sabine Bank, and Freeport Rocks all serve as settlement habitat of lane snapper, which appear to be capable of successful settlement across a variety of habitats and banks.

Thesis (M.S.)--Auburn University, 2008. / Abstract. Includes bibliographical references (p. 31-38).

Thesis (Ph. D.)--Auburn University, 2008. / Abstract. Includes bibliographical references.