David R. Stewart

Verification of Otolith Identity Used by Fisheries Scientists for Aging Channel Catfish

Abstract Previously published studies of the age estimation of channel catfish Ictalurus punctatus based on otoliths have reported using the sagittae, whereas it is likely they were actually using the lapilli. This confusion may have resulted because in catfishes (ostariophyseans) the lapilli are the largest of the three otoliths, whereas in nonostariophysean fish the sagittae are the largest. Based on (1) scanning electron microscope microphotographs of channel catfish otoliths, (2) X-ray computed tomography scans of a channel catfish head, (3) descriptions of techniques used to removed otoliths from channel catfish reported in the literature, and (4) a sample of channel catfish otoliths received from fisheries biologists from around the country, it is clear that lapilli are most often used for channel catfish aging studies, not sagittae, as has been previously reported. Fisheries scientists who obtain otoliths from channel catfish can use the information in this paper to correctly identify otolith age.

Precision of Channel Catfish Catch Estimates Using Hoop Nets in Larger Oklahoma Reservoirs

Abstract Hoop nets are rapidly becoming the preferred gear type used to sample channel catfish Ictalurus punctatus, and many managers have reported that hoop nets effectively sample channel catfish in small impoundments ( 200 ha). Hoop net series were fished once, set for 3 d; then we used Monte Carlo bootstrapping techniques that allowed us to estimate the number of net series required to achieve two levels of precision (relative standard errors [RSEs] of 15 and 25) at two levels of confidence (80% and 95%). Sixteen hoop net series were effective at obtaining an RSE of 25 with 80% and 95% confidence in all but one reservoir. Achieving an RSE of 15 was often less effective and required 18–96 hoop net series given the des...

Using Hierarchical Bayesian Multispecies Mixture Models to Estimate Tandem Hoop-net-Based Habitat Associations and Detection Probabilities of Fishes in Reservoirs

AbstractSpecies distribution models are useful tools to evaluate habitat relationships of fishes. We used hierarchical Bayesian multispecies mixture models to evaluate the relationships of both detection and abundance with habitat of reservoir fishes caught using tandem hoop nets. A total of 7,212 fish from 12 species were captured, and the majority of the catch was composed of Channel Catfish Ictalurus punctatus (46%), Bluegill Lepomis macrochirus (25%), and White Crappie Pomoxis annularis (14%). Detection estimates ranged from 8% to 69%, and modeling results suggested that fishes were primarily influenced by reservoir size and context, water clarity and temperature, and land-use types. Species were differentially abundant within and among habitat types, and some fishes were found to be more abundant in turbid, less impacted (e.g., by urbanization and agriculture) reservoirs with longer shoreline lengths; whereas, other species were found more often in clear, nutrient-rich impoundments that had generally...

Simulation modeling to explore the effects of length-based harvest regulations for Ictalurus fisheries

AbstractManagement of Blue Catfish Ictalurus furcatus and Channel Catfish I. punctatus for trophy production has recently become more common. Typically, trophy management is attempted with length-based regulations that allow for the moderate harvest of small fish but restrict the harvest of larger fish. However, the specific regulations used vary considerably across populations, and no modeling efforts have evaluated their effectiveness. We used simulation modeling to compare total yield, trophy biomass (Btrophy), and sustainability (spawning potential ratio [SPR] > 0.30) of Blue Catfish and Channel Catfish populations under three scenarios: (1) current regulation (typically a length-based trophy regulation), (2) the best-performing minimum length regulation (MLRbest), and (3) the best-performing length-based trophy catfish regulation (LTRbest; “best performing” was defined as the regulation that maximized yield, Btrophy, and sustainability). The Btrophy produced did not differ among the three scenarios. ...

Spatial structuring within a reservoir fish population: implications for management

Spatialstructuringinreservoirfishpopulationscanexistbecauseofenvironmentalgradients,species-specific behaviour or even localised fishing effort. The present study investigated whether white crappie exhibited evidence of improved population structure where the northern more productive half of a lake is closed to fishing to provide waterfowl hunting opportunities. Population response to angling was modelled for each substock of white crappie (north (protected) and south (unprotected) areas), the entire lake (single-stock model) and by combining simulations of the two independent substock models (additive model). White crappie in the protected area were more abundant, consisting of larger, older individuals,andexhibitedalowertotalannualmortalityratethanintheunprotectedarea.Populationmodellingfoundthat fishing mortality rates between 0.1 and 0.3 resulted in sustainable populations (spawning potential ratios (SPR) .0.30). The population in the unprotected area appeared to be more resilient (SPR.0.30) at the higher fishing intensities (0.35-0.55). Considered additively, the whole-lake fishery appeared more resilient than when modelled as a single- panmictic stock. These results provided evidence of spatial structuring in reservoir fish populations, and we recommend model assessments used to guide management decisions should consider those spatial differences in other populations where they exist. Additional keywords: aquatic protected areas, environmental gradients, population dynamics, population model, spatial complexity, sustainability, yield.

Effect of bait and gear type on channel catfish catch and turtle bycatch in a reservoir

Hoop nets have become the preferred gear choice to sample channel catfish Ictalurus punctatus but the degree of bycatch can be high, especially due to the incidental capture of aquatic turtles. While exclusion and escapement devices have been developed and evaluated, few have examined bait choice as a method to reduce turtle bycatch. The use of Zote™ soap has shown considerable promise to reduce bycatch of aquatic turtles when used with trotlines but its effectiveness in hoop nets has not been evaluated. We sought to determine the effectiveness of hoop nets baited with cheese bait or Zote™ soap and trotlines baited with shad or Zote™ soap as a way to sample channel catfish and prevent capture of aquatic turtles. We used a repeated-measures experimental design and treatment combinations were randomly assigned using a Latin-square arrangement. Eight sampling locations were systematically selected and then sampled with either hoop nets or trotlines using Zote™ soap (both gears), waste cheese (hoop nets), or cut shad (trotlines). Catch rates did not statistically differ among the gear–bait-type combinations. Size bias was evident with trotlines consistently capturing larger sized channel catfish compared to hoop nets. Results from a Monte Carlo bootstrapping procedure estimated the number of samples needed to reach predetermined levels of sampling precision to be lowest for trotlines baited with soap. Moreover, trotlines baited with soap caught no aquatic turtles, while hoop nets captured many turtles and had high mortality rates. We suggest that Zote™ soap used in combination with multiple hook sizes on trotlines may be a viable alternative to sample channel catfish and reduce bycatch of aquatic turtles.

Estimating the Effects of Environmental Variables and Gear Type on the Detection and Occupancy of Large-River Fishes in a Standardized Sampling Program Using Multiseason Bayesian Mixture Models

AbstractSampling in non-wadeable rivers presents methodological challenges for monitoring fish species. Changing environmental conditions may affect the ability to accurately capture species (i.e., detection) and consequently may lead to inappropriate inferences on occupancy rates. We used hierarchical Bayesian multiseason mixture models to estimate occupancy and detection of 41 of 52 fish species in the Kankakee River, Illinois, by using data from a standardized monitoring program. Fish were sampled with AC boat electrofishing and shoreline seining over 7 years. Some centrarchids (e.g., Smallmouth Bass Micropterus dolomieu) were efficiently sampled by boat electrofishing, whereas most other species had low detection probabilities. Moderate changes in environmental conditions, such as water velocity and temperature, produced moderate changes in detection and occupancy. Generally, when species had high detection probabilities, changes in environmental conditions produced relatively small changes in the est...

Using an experimental manipulation to determine the effectiveness of a stock enhancement program

We used an experimental manipulation to determine the impact of stocking 178 mm channel catfish Ictalurus punctatus in six impoundments. The study design consisted of equal numbers (two) of control, ceased-stock, and stocked treatments that were sampled one year before and two years after stocking. Relative abundance, growth, size structure, and average weight significantly changed over time based on samples collected with hoop nets. Catch rates decreased at both ceased-stock lakes and increased for one stocked lake, while growth rates changed for at least one ceased-stock and stocked lake. The average weight of channel catfish in the ceased-stock treatment increased by 6% and 25%, whereas weight decreased by 28% and 78% in both stocked lakes. The variability in observed responses between lakes in both ceased-stock and stocked treatments indicates that a one-size-fits-all stocking agenda is impractical, suggesting lake specific and density-dependent mechanisms affect channel catfish population dynamics.

Synthesizing models useful for ecohydrology and ecohydraulic approaches: An emphasis on integrating models to address complex research questions

U.S. Geological Survey, Oklahoma Cooperative Fish and Wildlife Research Unit, 007 Agricultural Hall, Stillwater, OK 74078, USA Oklahoma Cooperative Fish and Wildlife Research Unit, Oklahoma State University, Stillwater, OK, USA Division of Biological Sciences, U.S. Fish and Wildlife Service, Albuquerque, NM, USA Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Department of Biological and Agricultural Engineering, North Carolina State University, Raleigh, NC, USA Correspondence Shannon K. Brewer, U.S. Geological Survey, Oklahoma Cooperative Fish and Wildlife Research Unit, 007 Agricultural Hall, Stillwater, Oklahoma 74078, USA. Email: shannon.brewer@okstate.edu Present Address Thomas A. Worthington, Conservation Science Group, Department of Zoology, University of Cambridge, Cambridge, UK

An Invertebrate Ecosystem Engineer Under the Umbrella of Sage-Grouse Conservation

Abstract. Conservation practitioners often rely on areas designed to protect species of greatest conservation priority to also conserve co-occurring species (i.e., the umbrella species concept). The extent to which vertebrate species may serve as suitable umbrellas for invertebrate species, however, has rarely been explored. Sage-grouse (Centrocercus spp.) have high conservation priority throughout much of the rangelands of western North America and are considered an umbrella species through which the conservation of entire rangeland ecosystems can be accomplished. Harvester ants are ecosystem engineers and play important roles in the maintenance and function of rangeland ecosystems. We compared indices of the abundance of western harvester ants (Pogonomyrmex occidentalis) and Greater Sage-Grouse (Centrocercus urophasianus) at 72 sites in central Wyoming, USA, in 2012. The abundance of harvester ant mounds was best predicted by a regression model that included a combination of local habitat characteristics and the abundance of sage-grouse. When controlling for habitat-related factors, areas with higher abundances of sage-grouse pellets (an index of sage-grouse abundance and/or habitat use) had higher abundances of ant mounds than areas with lower abundances of sage-grouse pellets. The causal mechanism underlying this positive relationship between sage-grouse and ant mound abundance at the fine scale could be indirect (e.g., both species prefer similar environmental conditions) or direct (e.g., sage-grouse prefer areas with a high abundance of ant mounds because ants are an important prey item during certain life stages). We observed no relationship between a broad-scale index of breeding sage-grouse density and the abundance of ant mounds. We suspect that consideration of the nonbreeding habitat of sage-grouse and finer-scale measures of sagegrouse abundance are critical to the utility of sage-grouse as an umbrella species for the conservation of harvester ants and their important role in rangeland ecosystems.