While much is known about the fish assemblages, habitats, and ecology of rivers and reservoirs, there has been limited study of the fish assemblages in transitional habitats between these lotic and lentic habitats. Data about these river–reservoir interface (RRI) fish assemblages are needed to guide integrated management efforts of river–reservoir ecosystems. The aim of these efforts is to recommend flows for natural river function, conserve native riverine fish assemblages, and maintain reservoir sport fisheries. We used a multigear approach to assess the fish assemblages of four RRIs in the Colorado River Basin, Texas. In addition to characterizing RRI fish assemblages using species richness and evenness metrics, and habitat‐use guilds, we used a multivariate approach to evaluate intra‐annual shifts in species composition and abundance. All RRIs had high species richness and evenness values and included both macrohabitat generalist and fluvial species. RRIs also contained high proportions of the fish species available within each river–reservoir ecosystem, ranging from 55% to 80%. Observed intra‐annual shifts in RRI fish assemblages resulted from changes in abundance of dominant species rather than changes in species composition, with abundance of most species increasing from early spring to summer. Fish species responsible for intra‐annual shifts included mostly floodplain and migratory species, suggesting that species both used littoral habitats within RRIs and migrated through RRIs to river and reservoir habitats. The diversity of fishes found within RRIs highlights the importance of including these areas in future conservation and management efforts of river–reservoir ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.

We examined the gills of wild fish collected from central Texas for Centrocestus formosanus metacercariae to determine whether this temperature-restricted parasite had invaded the thermally dynamic Guadalupe River via an introduced population in its thermally stable tributary, the Comal River. We collected fish from three sites in the Guadalupe River near its confluence with the Comal River (upstream, at, and downstream) and one site in the Comal River. Centrocestus formosanus infected 14 of the 25 species examined (56.0%) and 171 of the individual fish (27.1%). Several of the infected fish represent new host records for the parasite, and two are listed as species of special concern by the state of Texas. Mean metacercarial intensities varied from 8 to 616 among species, and the highest recorded intensity was greater than 800 in two Guadalupe roundnose minnow Dionda nigrotaeniata. Among the 24 species examined from the Guadalupe River, 11 (45.8%) were infected with C. formosanus. Thorough surveys at the study sites yielded no living specimens of the first obligate intermediate snail host (red-rim melania Melanoides tuberculatus), which must be present to perpetuate the parasite. Thus, the infections were probably due to drifting cercariae that had been shed into the water column upstream of the study area in the Comal River. We therefore investigated spatial patterns in cercarial acquisition using caged fish to determine whether drifting cercariae were present in the water column at the study sites. Of 57 uninfected blacktail shiners Cyprinella venusta exposed to Guadalupe River water downstream from and at the confluence, 52 (91.2%) became infected with C. Formosanus metacercariae at a mean rate of 4 metacercariae/d. This finding extends the known geographic range of this invasive exotic parasite and is the first report of the life cycle being advanced in the fish assemblage of a thermally variable temperate stream in the USA.

Side‐scan sonar (SSS) provides an efficient, nonintrusive sampling tool for many fisheries applications. Professional‐grade systems have proven useful for species‐specific detection of large, distinctive fishes; however, these systems are often cost prohibitive for widespread use. Lower‐cost, consumer‐grade systems are becoming increasingly popular for fisheries applications and have been used extensively to map aquatic habitat. However, these systems often produce lower‐resolution imagery that may limit species‐specific applications. We used experimental ponds stocked with known fish assemblages and a field‐based mark–recapture study to determine the efficacy of a consumer‐grade SSS system in surveying Alligator Gars Atractosteus spatula. Three ponds were stocked with known abundances of Alligator Gars and other sympatric fishes. A fourth pond remained unstocked to assess false positives; a fifth was stocked only with other species to quantify misidentification. Replicate sonar images of each pond were then recorded using a Humminbird 998c system. For the field‐based application, we used gill nets to mark and recapture Alligator Gars and estimate population size within a closed backwater of the Guadalupe River, Texas. Following final recapture, we recorded replicate imagery of the backwater. Imagery from both evaluations was interpreted by three independent readers of varying experience without knowledge of image origin. The results from the ponds indicated a low rate of false detection (7%) and misidentification (4%). The number of Alligator Gars identified was positively related to density; however, the probability of detection varied among readers (range, 0.27–0.71) and was positively related to experience. In contrast, all readers estimated Alligator Gar abundance in the backwater within 10% of the population estimated from the mark–recapture data. Our results suggest that low‐cost SSS can provide an effective, noninvasive alternative to traditional sampling techniques for Alligator Gars.

Physical and hydrologic connectivity among river-reservoir ecosystem (RRE) segments, including the river, riverreservoir interface (RRI), and reservoir, requires consideration of management at larger spatial scales. Multiple objectives (e.g., ecosystem function, sport fisheries, and maximizing fish diversity) seem well suited to this broad spatial scale; however, data limitations regarding the distribution of taxa within RREs currently hamper such an approach. We quantified the fish assemblage of the Trinity River-Lake Livingston ecosystem in Texas, USA, using a stratified approach to determine the contribution of individual segments to the overall fish assemblage. In general, fish assemblages varied along a continuum from the river to the reservoir; however, fish assemblages in several river backwaters did not follow this gradient, thus adding diversity to the overall RRE. Variability in fish assemblages among ecosystem segments was the result of both species composition and relative abundance. Species richness (N = 58 total) was highest in the river segment (N = 49) followed by the RRI (N = 46) and was much lower in the reservoir (N = 36). In contrast, average catch per standardized unit of sampling effort (all species combined) was greatest in the RRI, about 25% lower in the reservoir, and about 50% lower in the river. Across the ecosystem, 26 species (45%) were considered common, while 32 species (55%) were considered rare. Notably, species of conservation need were not always most abundant in river habitats, and species supporting recreational fisheries were not always most dominant in the reservoir. These findings suggest that the RRE can serve as an appropriate spatial scale for both conservation and recreational fishery management actions.Regulation of rivers through impoundment provides many benefits to humans (e.g., water supply, electricity, and recreation); however, alteration of these ecosystems has been detrimental to many native fish species, especially fluvial specialists (e.g.,

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Attaching telemetry transmitters to catfishes (family Ictaluridae) has historically been problematic. Current attachment techniques produce low retention rates or high mortality, or cause altered physiological or behavioral effects. We investigated an alternative attachment technique during three experiments in which external transmitters were fastened to the supraoccipital bone of Blue Catfish Ictalurus furcatus. We hypothesized that attaching a transmitter to the skeletal structure would improve retention rates and minimize negative health effects. In a 2‐month pilot study, retention was 100% (N = 20; TL range = 435–638 mm) and fish appeared to be in excellent condition. However, in a subsequent laboratory experiment, retention was poor (41.7% at 2 months and 0% at 6 months; N = 24, TL range = 600–995 mm), which may be attributed to excessive handling during the experiment. The attachment technique was also field tested as part of a larger telemetry study. Fifty Blue Catfish (TL range = 600–995 mm) were tagged and monitored for up to 17 months in Lake Buchanan, Texas. Retention in the field was 40% at 6 months and 19% at 12 months, which was comparable to current free‐floating internal transmitter retention rates. Although our procedure produces lower retention than internal transmitters fastened to the pectoral girdle (60–93% annual retention), we believe this modified attachment procedure has future utility despite our mixed results. Our procedure avoids negative health effects (i.e., transmitters absorbed in the intestine or stomach or passed through the body wall) associated with internal tags fixed to the pectoral girdle and has retention rates similar to free‐floating internal tags without the need for surgical implantation. Our work demonstrates an alternative transmitter attachment method and suggests future direction (i.e., attaching transmitters to the skeletal structure) in further improving attachment procedures for Blue Catfish. Received March 12, 2013; accepted June 20, 2013

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Consumer-grade side-scan sonar has become a versatile fisheries management tool.  First applied to assess habitat, its use has expanded to surveying fishes in recent years.  However, an important consideration is the skill and experience of users, which can impact both the accuracy and comparability of surveys.  To this end, we characterized the ability of a small sample of novice users (N = 8) to identify alligator gar Atractosteus spatula in imagery, as well as the effect of a two-hour training exercise on user performance.  Prior to training, mean accuracy (expressed as the difference between observed and expected counts) among participants ranged from -2.6 to 1.3 fish and precision ranged from ± 1.2 to 2.4 fish, with the majority of participants underestimating the number of alligator gar present in the imagery.  False positives (i.e., identifying alligator gar in imagery when none were present) were common among participants.  Post-training mean accuracy ranged from -3.1 to 0 among participants and precision ranged from ± 1.6 to 3.2 fish.  The frequency of false positives was significantly reduced following training, and participants reported significant increases in confidence associated with image interpretation.  The relatively high accuracy and precision we observed prior to training indicated that side-scan sonar can be easily incorporated into large-scale fishery monitoring efforts for alligator gar.  However, our results also suggested that a rather minimal investment in training can further improve consistency and reduce uncertainty among novice users.