Gregory W. Stunz

An Analysis of Artificial Reef Fish Community Structure along the Northwestern Gulf of Mexico Shelf: Potential Impacts of “Rigs-to-Reefs” Programs

Artificial structures are the dominant complex marine habitat type along the northwestern Gulf of Mexico (GOM) shelf. These habitats can consist of a variety of materials, but in this region are primarily comprised of active and reefed oil and gas platforms. Despite being established for several decades, the fish communities inhabiting these structures remain poorly investigated. Between 2012 and 2013 we assessed fish communities at 15 sites using remotely operated vehicles (ROVs). Fish assemblages were quantified from standing platforms and an array of artificial reef types (Liberty Ships and partially removed or toppled platforms) distributed over the Texas continental shelf. The depth gradient covered by the surveys (30–84 m) and variability in structure density and relief also permitted analyses of the effects of these characteristics on fish richness, diversity, and assemblage composition. ROVs captured a variety of species inhabiting these reefs from large transient piscivores to small herbivorous reef fishes. While structure type and relief were shown to influence species richness and community structure, major trends in species composition were largely explained by the bottom depth where these structures occurred. We observed a shift in fish communities and relatively high diversity at approximately 60 m bottom depth, confirming trends observed in previous studies of standing platforms. This depth was also correlated with some of the largest Red Snapper captured on supplementary vertical longline surveys. Our work indicates that managers of artificial reefing programs (e.g., Rigs-to-Reefs) in the GOM should carefully consider the ambient environmental conditions when designing reef sites. For the Texas continental shelf, reefing materials at a 50–60 m bottom depth can serve a dual purpose of enhancing diving experiences and providing the best potential habitat for relatively large Red Snapper.

Evaluation of Visible Implant Elastomer for Marking Juvenile Red Drum

Abstract Visible implant elastomer (VIE) was evaluated for marking juvenile red drum Sciaenops ocellatus in experimental studies. We tested VIE on hatchery-reared red drum (standard length, 29.6–38.7 mm; SE, 0.23) in a laboratory study to examine mortality, tag retention, and growth effects associated with the marking method. We examined two tagging locations and two control treatments in anesthetized and unanesthetized fish. Red drum were tagged below and parallel to the dorsal fin and above and parallel to the anal fin. Five fish were anesthetized, marked, and stocked into replicated tanks and held for 14 d. Tag retention was 100%, and overall mortality was 10%. The mortality of fish tagged below the dorsal fin was 0%, whereas that of fish tagged above the anal fin was 40% (SE, 30.5). No significant difference in growth rates was observed between the marked and unmarked treatment groups. A field study was performed with wild and hatchery-reared red drum marked with VIE and released at three replicate si...

Relative Value of Deep Subtidal Oyster Reefs to Other Estuarine Habitat Types using a Novel Sampling Method

ABSTRACT Subtidal eastern oyster Crassostrea virginica (Gmelin) cover large expanses of many Gulf of Mexico estuaries; however, few researchers have attempted to quantify the value of deep, open-water, subtidal reefs as habitat for fishes and crustaceans as a result of gear limitations. We developed quantitative sampling gear for live oyster reefs by slightly modifying an epibenthic sled. Gear comparison trials showed similar effectiveness among marsh edge, submerged aquatic vegetation, and nonvegetated bottom for both epibenthic sled types. We then quantified the density and community assemblage of nekton and benthic crustaceans on deep subtidal oyster reefs in Lavaca Bay, TX, and compared it with densities found in nearby marsh edge, submerged aquatic vegetation, and nonvegetated bottom habitats. We found significantly fewer nektonic and benthic crustaceans on nonvegetated bottom and oyster reefs than in marsh edge and submerged aquatic vegetation over all seasons and regions, and community analysis revealed similar differences among habitat assemblages. Using gill nets, the greatest catch of transient fishes and crustaceans were collected on oyster reefs and nonvegetated bottom. Although relatively low densities of small juvenile fishes were observed over deep oyster reefs, our community analyses and the high catch-per-unit-effort of large, transient species provide evidence that subtidal reefs are a critical habitat for numerous estuarine fishes and crustaceans.

Venting or Rapid Recompression Increase Survival and Improve Recovery of Red Snapper with Barotrauma

Abstract Red Snapper Lutjanus campechanus are the most economically important reef fish in the Gulf of Mexico and a heavily targeted fishery. When brought to the surface from deep water, this species often suffers pressure-related injuries collectively known as barotrauma. This trauma results in high discard mortality and has affected recovery of the fishery. In laboratory experiments using hyperbaric chambers, we assessed sublethal effects of barotrauma and subsequent survival rates of Red Snapper after capture events from pressures corresponding to 30 and 60 m deep. We then evaluated the use of rapid recompression and venting to increase survival and improve recovery after release in this controlled environment. Vented fish in simulated surface release and rapid-recompression treatments had 100% survival. Fish released at the surface that were not vented had 67% survival after decompression from 30 m but only 17% survival from 60 m, while nonvented rapidly recompressed fish had 100% survival from 30 m and 83% survival from 60 m. Fish that were vented upon release at the surface showed significantly better ability to achieve an upright orientation and evade a simulated predator. Results showed clear benefits of venting or recompression. Our data also show strong depth effects resulting in increased barotrauma injuries, more impaired reflexes, and greater mortality as depth increases. Overall, our data support venting or rapid recompression as effective tools for alleviating barotrauma symptoms, improving predator evasion, and increasing overall survival.

Catch-and-Release Mortality of Spotted Seatrout in Texas: Effects of Tournaments, Seasonality, and Anatomical Hooking Location

Abstract The purpose of this study was to assess initial and delayed mortality of spotted seatrout Cynoscion nebulosus captured during live-release tournaments. Additionally, we examined spotted seatrout mortality as a function of season and anatomical hooking location. We assessed tournament-related mortality at 10 live-release fishing tournaments held in four Texas bays—Galveston, Matagorda, Aransas, and Upper Laguna Madre—from February 2004 to April 2006. Combined overall mean mortality was 22.9%, mean initial mortality (percent of dead fish brought to weigh-in) was 10.4%, mean delayed mortality (percent of fish that died in tournament holding tanks) was 14.1%, and delayed short-term mortality (percent of fish that died during a 14-d observation period in laboratory tanks) was 1.9%. To assess seasonal mortality, we examined a total of 364 spotted seatrout captured by hook and line from July 2004 to June 2005 using replicated 3.5-m3 field enclosures for 72 h. Overall mortality for the seasonal study was...

Catch-and-Release Mortality of Spotted Seatrout in Texas

Abstract Catch and release is becoming more common as a management tool in marine recreational fisheries. Clearly, a critical factor in determining different management scenarios that use this strategy is postcapture survival. We investigated the mortality associated with catch and release in the fishery for spotted seatrout Cynoscion nebulosus in south Texas. Specifically, this study investigated the mortality for hook-and-line-captured spotted seatrout as a function of bait type, hook type, angler skill level, and fish size. Using a variety of angling techniques, we captured 448 spotted seatrout ranging from 250 to 760 mm total length (TL) and assessed mortality in replicate field enclosures. The overall short-term mortality for all treatments was relatively low (11%); the majority of fish survived. The exception was angler skill level. Angling by novices produced a significantly higher mortality rate than angling by skilled anglers; however, mortality averaged only 18% even for inexperienced anglers. T...

Gulf-Wide Decreases in the Size of Large Coastal Sharks Documented by Generations of Fishermen

Abstract Large sharks are top predators in most coastal and marine ecosystems throughout the world, and evidence of their reduced prominence in marine ecosystems has been a serious concern for fisheries and ecosystem management. Unfortunately, quantitative data to document the extent, timing, and consequences of changes in shark populations are scarce, thwarting examination of long-term (decadal, century) trends, and reconstructions based on incomplete data sets have been the subject of debate. Absence of quantitative descriptors of past ecological conditions is a generic problem facing many fields of science but is particularly troublesome for fisheries scientists who must develop specific targets for restoration. We were able to use quantitative measurements of shark sizes collected annually and independently of any scientific survey by thousands of recreational fishermen over the last century to document decreases in the size of large sharks from the northern Gulf of Mexico. Based on records from fishing rodeos in three U.S. coastal states, the size (weight or length) of large sharks captured by fishermen decreased by 50–70% during the 20 years after the 1980s. The pattern is largely driven by reductions in the occurrence and sizes of Tiger Sharks Galeocerdo cuvier and Bull Sharks Carcharhinus leucas and to a lesser extent Hammerheads Sphyrna spp. This decrease occurred despite increasing fishing effort and advances in technology, but it is coincident with the capitalization of the U.S. commercial shark long-line fishery in the GOM.

Hierarchical and interactive habitat selection in response to abiotic and biotic factors: The effect of hypoxia on habitat selection of juvenile estuarine fishes

Habitat selection is a shared process among animals where individuals choose areas that differ in biotic and abiotic characteristics to maximize individual fitness. We used manipulative laboratory mesocosm choice experiments to examine hierarchical and interactive relationships influencing this habitat selection process of estuarine fishes. We assessed selection among substrate, dissolved oxygen (DO) concentration, food availability, and predation risk using two common juvenile estuarine fish species, pinfish (Lagodon rhomboides) and Atlantic croaker (Micropogonias undulatus). For both species oxygen concentration greatly influenced selection patterns; fishes strongly avoided low DO conditions, while in higher levels of DO factors such as substrate or food influenced selection patterns. However, both species strongly avoided predators even when alternative habitat was severely oxygen limited. These results suggest that predation risk may be the greatest determinant of habitat selection of the factors considered. Expansion of low DO areas in the world’s oceans is a major anthropogenic disturbance and is rapidly increasing. Assessing impacts of hypoxia on habitat usage of mobile organisms is critical as changes in environmental metrics including predator distribution and DO levels may alter habitat selection patterns disrupting critical ecosystem processes and trophic interactions. Our results indicate that juvenile fishes may forgo emigration from hypoxia due to predation risk. If similar patterns occur for juvenile fishes in estuaries they may potentially suffer from reduced growth, reproductive output, and survivorship.

The Effects of Boat Propeller Scarring on Nekton Growth in Subtropical Seagrass Meadows

Abstract An increasing boating population has led to extensive propeller scarring in many shallow seagrass meadows, and research has focused on relating scarring to nekton abundance; however, little information exists on the impacts on habitat functionality. In this study we moved beyond simple measures of faunal density as an indicator of habitat quality by comparing the growth rates of common estuarine nekton in different levels of propeller scarring in Redfish Bay, Texas. Growth rates of selected fauna were examined by using field enclosures and otolith microstructure analysis. Otolith microstructure analysis on pinfish Lagodon rhomboides indicated no difference in growth rates at various scarring intensities. We conducted field growth enclosure experiments on a common decapod crustacean, the white shrimp Litopenaeus setiferus. White shrimp showed significantly lower growth in highly scarred areas than in reference sites. These results suggest that regions of low-level propeller scarring (less than 15%...

Quantifying delayed mortality from barotrauma impairment in discarded red snapper using acoustic telemetry

Abstract Red Snapper Lutjanus campechanus is the most economically important reef fish in the Gulf of Mexico, and despite being intensively managed, the stock remains overfished. These fish are susceptible to pressure-related injuries (i.e., barotrauma) during fishing that compromise survival after catch and release. Barotrauma-afflicted fish may not only experience immediate mortality but also delayed mortality after returning to depth. This variability and unknown fate leads to uncertainty in stock assessment models and rebuilding plans. To generate better estimates of immediate and delayed mortality and postrelease behavior, Red Snapper were tagged with ultrasonic acoustic transmitters fitted with acceleration and depth sensors. Unique behavior profiles were generated for each fish using these sensor data that allowed the classification of survival and delayed mortality events. Using this information, we compared the survival of Red Snapper released using venting, nonventing, and descending treatments over three seasons and two depths. Red Snapper survival was highest at cooler temperatures and shallower depths. Fish released using venting and descender tools had similar survival, and both these groups of fish had higher survival than nonvented surface-released fish. Overall, Red Snapper had 72% survival, 15% immediate mortality, and 13% delayed mortality, and all fish suffering from delayed mortality perished within a 72-h period after release. Results from these field studies enhance the understanding of the delayed mortality and postrelease fate of Red Snapper regulatory discards. Moreover, these data support the practice of using venting or descender devices to increase the survival of discarded Red Snapper in the recreational fishery and show that acoustic telemetry can be a valuable tool in estimating delayed mortality.