Daniel J. Daugherty

Retention of Passive Integrated Transponder Tags in Flathead Catfish

Abstract We evaluated short- and long-term retention of passive integrated transponder (PIT) tags at two anatomical tagging locations in flathead catfish Pylodictis olivaris (n = 72 fish; total length range = 421–854 mm). Tags were injected into the dorsal musculature immediately posterior to the dorsal fin and into the opercular musculature immediately posterior to the left eye. Short-term tag retention evaluated at 1, 3, and 7 d posttagging was 100% at both tagging locations after accounting for one tag failure (at the dorsal musculature site) that occurred during the initial tagging procedure. Long-term (300-d) tag retention was 100% for the dorsal musculature site and 98.5% for the opercular site. Mortality of tagged fish was low (8%); the mortalities that did occur were probably not related to tagging. Our results indicate a high rate of PIT tag retention in flathead catfish at both anatomical locations. Additionally, utilization of the opercular musculature as a PIT tagging location for this species...

Sensitivity of recreational access to reservoir water level variation: an approach to identify future access needs in reservoirs.

Abstract Reservoirs support popular sport fisheries and other forms of water recreation. However, access to these systems is often sensitive to variation in water level. Increasing water demands due to population growth and the effects of climate change suggest that maintaining adequate recreational access to reservoirs will become increasingly difficult. Knowledge of the effects of water level variation on boat and shoreline access is required to identify future needs and to aid in prioritizing improvement efforts that promote participation in fishing and aquatic recreation. To address this need, we developed a geographical information systems-based approach to quantify the effects of reservoir water level variation on recreational access and applied the technique to three Colorado River reservoirs in Texas: Lake Buchanan, Lake Travis, and Lyndon B. Johnson Reservoir. The data were used to identify reservoir-specific water levels (m below full pool) at which the availability of access was adversely affec...

A Strategy for Increasing Gill-Net Catch Rates and Minimizing Sampling Mortality of Alligator Gars

AbstractManagement of the Alligator Gar Atractosteus spatula has been hampered by the lack of sampling methods that can efficiently reveal population characteristics or minimize incidental sampling mortality. In a 3-year evaluation of the Alligator Gar population in Choke Canyon Reservoir, Texas, we documented changes in sampling methodology that produced an eightfold increase in multifilament gill-net catch rates (from 0.66 to 5.10 fish/h). The increased sampling efficiency was attributed to the development of an aggressive-predator sampling strategy over the study period; our highest catch rates were achieved by (1) observing surfacing fish before net deployment and (2) relocating to a new sampling site when catch rates were less than 1 fish/h. This aggressive strategy resulted in shorter net soak times, which reduced incidental net mortalities; nets soaking less than 30 min produced zero mortalities. Our results suggest that the aggressive-predator strategy is suitable for the majority of Alligator Gar...

Population Structure of Alligator Gar in a Gulf Coast River: Insights from Otolith Microchemistry and Genetic Analyses

AbstractGrowing interest in the Alligator Gar Atractosteus spatula among anglers and fishery managers has inspired efforts to better manage populations. Successful management requires identifying population structure and understanding the distribution of stocks and associated differences in life history. This is particularly important in river systems along the coast of the Gulf of Mexico, where transitions from freshwater rivers to saltwater bays provide the potential for life history diversification. We used otolith microchemistry and genetics to assess population structure of Alligator Gars in the Guadalupe River–San Antonio Bay system, Texas. Lifetime Sr:Ca revealed three, distinct life histories that differed in prevalence across the system. River-resident fish (i.e., fish exclusive to freshwater) were present throughout the river but were most common in the uppermost river reach (74% of upper river fish). Transient fish that used both river and bay habitats were also found throughout the river but w...

Effects of Structural and Spatiotemporal Factors on Fish Use of Artificial Habitat in a Texas Reservoir

AbstractWe evaluated fish use of artificial habitat in relation to structure size and shape and the spatiotemporal factors of season, diel period, and reservoir region in Striker Reservoir, Texas. Recycled Christmas trees were used to construct three sizes of cluster- and linear-shaped structures; fish at each were sampled seasonally during the day and night with electrofishing. Largemouth Bass Micropterus salmoides and Bluegill Lepomis macrochirus comprised 57% of the fish collected; other centrarchids comprised an additional 33%. Overall fish assemblages at the habitat structures were not related to the factors we examined. However, species-specific analyses indicated that the percentage of structures occupied, catch per unit effort (CPUE), and mean size of Largemouth Bass and Bluegills were influenced by the factors we examined. Largemouth Bass exhibited a greater percent occupancy of the largest structures and a higher CPUE in small structures; the mean size (TL) of Largemouth Bass was lower in cluste...

Natural Hybridization of Lepisosteids: Implications for Managing the Alligator Gar

AbstractThe Alligator Gar Atractosteus spatula has become a focal species of management and conservation due to declining populations and growing popularity among anglers. The Alligator Gar is sympatric with the Longnose Gar Lepisosteus osseus and Spotted Gar L. oculatus throughout much of its range, providing the potential for hybridization that can complicate conservation efforts. Hybridization between gars has been documented in captivity; however, natural (i.e., wild) hybridization has not been formally assessed. Population sampling and genetic analyses of Alligator Gars in Texas provided an opportunity to examine hybridization among gars and to assess the potential implications for Alligator Gar management. Specifically, we (1) developed markers to distinguish lepisosteid species and their hybrids, (2) characterized hybridization between species, and (3) assessed our ability to differentiate hybrids from parent species via field evaluation of snout morphology. Fin tissue samples from Alligator Gars a...

Size Selectivity of Multifilament Gill Nets for Sampling Alligator Gar: Modeling the Effects on Population Metrics

AbstractGill nets are commonly used to sample Alligator Gar Atractosteus spatula; however, gill nets are size selective. We used five common multifilament gill-net meshes (88.9-, 101.6-, 114.3-, 127.0-, and 139.7-mm bar measure) to collect 477 gar between 1,000 and 2,300mm TL. We fit size-selectivity functions for these meshes for a net in which each mesh was fished equally, i.e., equal-effort net design (EEND), and found selectivity was best described by a binormal distribution in which the assumption of geometric similarity had been relaxed (i.e., binormal with deviations). Overall relative retention was about 30% for fish at 1,200 mm, increased to 100% for fish at 1,670 mm, then declined to 50% when fish were 2,100 mm. To reduce size selectivity, we used an optimization to create a net that minimized bias over the greatest TL range of fish sampled, i.e., weighted-effort net design (WEND). We compared the WEND to the EEND via simulation to estimate the effects of selectivity bias on population metrics. ...

Efficacy of a Light Attractant for Increasing Trap Net Catches of White Crappies

Abstract We evaluated the efficacy of trap nets fitted with a battery-operated, submersible light in the net mouth in increasing the catch rates of white crappies Pomoxis annularis by comparing the catch rate and size structure of white crappies collected by these nets with those of fish collected by standard (i.e., unlighted) trap nets in six Texas reservoirs. The catch rates of standard (mean = 16.3/net-night) and lighted trap nets (12.1/net-night) did not differ significantly. We found no significant difference in the catch of stock-size white crappies (≥130 mm total length [TL]) by standard (12.7 fish/net-night) versus lighted trap nets (9.9 fish/net-night); however, significantly fewer preferred sizes (≥250 mm TL) were taken by lighted (1.9 fish/net-night) than by standard sets (2.9 fish/net-night). The length-frequency distributions of the white crappies collected by each trap net treatment were similar and did not significantly differ in four of the five lakes tested. Our results suggest that trap ...

Modeling the Responses of Alligator Gar Populations to Harvest Under Various Length-based Regulations: Implications for Conservation and Management

AbstractInterest in managing Alligator Gar Atractosteus spatula populations as a unique sport fishery has increased over the past decade, but despite this interest, population responses to harvest are poorly understood. Fishing regulations for Alligator Gar vary throughout their distribution; however, to date most regulations have focused on a daily creel limit. We developed an age-structured dynamic-pool model in R to, (1) quantify population level effects of exploitation, and (2) evaluate how these effects were altered under a suite of length-based fishing regulations. The model was parameterized based primarily on empirically estimated dynamic rates for Texas Alligator Gar populations. For each model scenario, we calculated the mean and variance of the number of trophy fish in the population, the population size, Spawning Potential Ratio (SPR), and the fishery yield over a 100-year chronology. Alligator Gar populations were highly sensitive to exploitation in our model simulations. An exploitation rate...