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Using acoustic telemetry, we characterized movements and macrohabitat use of 46 Alligator Gars Atractosteus spatula in the lower 180 km of the Trinity River, Texas. Although several Alligator Gars used over 100 km of the river, 83% of the tagged fish had linear home ranges less than 60 km during the 22 months of study. As a result, home ranges of fish that were tagged in different parts of the study area rarely overlapped. Home range size varied by season, with the smallest home ranges occurring in winter. Greatest movements occurred during the spawn (May–June) and postspawn (July–October) seasons, and movements were correlated with increasing water temperatures based on detections of tagged fish at fixed receiver stations. Tagged Alligator Gars were most often associated with main‐channel habitats when river stage was at base level and during small flood pulses (<3‐m rise). When in the main channel, tagged Alligator Gars selected water that was deeper than the average within their home ranges. In contrast, during large flood pulses (≥3‐m rise), tagged fish were found in tributaries and inundated floodplains, regardless of season. Use of tailwater and estuarine macrohabitats was seasonal and limited to fish that had been tagged near those areas. Limited home ranges and observed spatial segregation of fish tagged near the upper and lower boundaries of the 180‐km study area suggest that the fish have access to critical habitats needed for reproduction, feeding, and migration within relatively small spatial scales. As such, Alligator Gars in the lower Trinity River do not appear to represent a single panmictic population, indicating that localized rather than regional management efforts would be appropriate.

We evaluated annulus formation and readers’ ability to recognize known annuli from otoliths, pectoral fin rays, and scales of alligator gar Atractosteus spatula using known‐age (0 and 1 years) and chemically marked fish. Chemical marks were generally associated with annuli, and confirmed annulus formation occurred around May. In all bony structures, annuli appeared as narrow translucent lines that immediately preceded wider opaque bands; however, annuli in pectoral fin rays and scales were more variable in appearance than otoliths. In otoliths, the number of observed annuli corresponded with the number of years fish were at large for 96% of the fish. In contrast, periodicity of annuli in pectoral fin rays and scales only corresponded with the number of years fish were at large in 19% and 12% of the fish, respectively. Precision of age estimates was initially poor for all structures; percent agreement between two independent readers was only 49% for otoliths, 43% for pectoral fin rays, and 37% for scales. Agreement increased to 83% for otoliths, 65% for pectoral fin rays, and 60% for scales following a second independent age assessment. Final average coefficients of variation between readers were 2, 5, and 11% for otoliths, pectoral fin rays, and scales, respectively. Increased precision was the result of experience and an improved ability to identify annuli because of chemical reference marks. Although correct identification of annuli required substantial training, our study validates annulus formation in otoliths of alligator gar. In contrast, annulus formation was not validated for pectoral fin rays or scales from alligator gar older than age 6, but age estimates from pectoral fin rays of young alligator gar may have some utility.

The use of transverse sections of sagittal otoliths has been validated for estimating the ages of largemouth bass Micropterus salmoides to age 5. However, previous research has indicated that the accuracy of this method is low for fish older than age 5. We used known-age fish of ages 0-16 to confirm that the use of otoliths is valid for estimating the ages of older largemouth bass. The estimated ages were correct for 97% of the fish. We concluded that past difficulties with using otoliths were more likely the result of preparation and reader error than of the structures depicting incorrect ages. The preparation method used in this study was simpler and faster than conventional methods of preparing thin sections and therefore should yield results that are more consistent.

We used proportional recapture data from mark–recapture experiments to directly estimate capture efficiency (percentage of fish captured per standard level of effort) and size selectivity (for 50‐mm size‐groups) of catfish sampling gears. Hoop‐net series were evaluated for collecting channel catfish Ictalurus punctatus, and low‐frequency, pulsed DC electrofishing was evaluated for collecting blue catfish I. furcatus. To examine spatial and temporal variability, capture efficiency and size selectivity were estimated in river and reservoir habitats during June, July, and September 2005. Selectivity of experimental gill nets was also assessed. Capture efficiency of hoop nets for channel catfish was consistent across months and between river and reservoir habitats (2.7–14.3% per 12 hoop‐net series). Capture efficiency of low‐frequency electrofishing was low (frequently, ≤1% per 120 min) and variable; recapture rates were greatest in river habitat during July and September. Hoop‐net series collected representative samples of channel catfish between 250 and 556 mm total length. Likewise, blue catfish between 250 and 855 mm were fully vulnerable to low‐frequency electrofishing. Although fish smaller than 250 mm were captured, they were frequently underrepresented in the catch of both gears. Size selectivity was not affected by habitat or month sampled for either gear type or either species. Capture efficiency of experimental gill nets was very low for both channel catfish and blue catfish (about 0.2% in 46 gill‐net nights), and gill nets were more size selective than other gears. Based on our findings, hoop‐net series and low‐frequency electrofishing provide accurate size structure data for adult channel catfish and blue catfish, respectively, from both river and reservoir habitat types. Hoop‐net series also provide consistent estimates of channel catfish relative abundance; however, relative abundance data for blue catfish collected with low‐frequency electrofishing should be used with caution due to observed variability in capture efficiency.

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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.