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At least 1,045 records · Page 58Linked to original sources
USGS2024

The use of conceptual ecological models to identify critical data and uncertainties to support numerical modeling: The northern Gulf of Mexico eastern oyster Crassostrea virginica example

Objective Increasing reliance on numerical simulation models to help inform management and restoration choices benefits from careful consideration of critical early steps in model development. Along the northern coast of the Gulf of Mexico, the eastern oyster Crassostrea virginica fulfills important ecological and economic roles. Using the eastern oyster as an example, we draw on several recent frameworks outlining best practices for model development and application for restoration, conservation, and management. Methods We identify priority model questions, outline a conceptual ecological model (CEM) to guide numerical model development, and use this framework to identify uncertainties and research needs. Result The CEM uses a nested design, identifying explicit vital rates, processes, attributes, and outcomes for the species (oysters), population, and metapopulation (i.e., network of populations) levels in response to drivers of species, population, and metapopulation changes and changing environmental factors. Most management actions related to oyster restoration and harvest affect population attributes directly, but many coastal management actions and changes (i.e., climate change and coastal and water resource engineering) impact environmental factors that alter vital rates and attributes of oysters, populations, and metapopulations. Conclusion Investment in studies targeting individual oyster‐ and population‐level multi‐stressor responses (filtration, respiration, growth, and reproduction) and improving hydrodynamic and environmental models targeting drivers that influence metapopulation vital rates and attributes (i.e., connectivity and substrate persistence) would contribute to reducing uncertainties. Development of numerical models covering the entire oyster life cycle and connectivity of populations using hydrodynamic models of current and predicted conditions to provide key abiotic and biotic factors influencing larval movement, recruitment, and on‐reef oyster vital rates would assist in balancing the goals of conservation, restoration, and fisheries management of this foundational estuarine species.

Marine and Coastal Fisheries: Dynamics, Management↗
USGS2018

Effects of summer air exposure on the survival of caught-and-released salmonids

Despite the success of catch‐and‐release regulations, exposing fish to air during release has emerged as a growing concern over the past two decades. We evaluated the effect of air exposure during midsummer on survival of Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri , Bull Trout Salvelinus confluentus , and Rainbow Trout O. mykiss exposed to catch‐and‐release angling. Fish were sampled by angling on Palisades Creek (August 2016), Sawmill Creek, and the Main Fork of the Little Lost River, Idaho (July−August 2017). After capture, fish were kept underwater while they were measured and individually tagged. Anglers, in groups of two to four, caught study fish and gave them an air exposure treatment of 0, 30, or 60 s. Single‐pass backpack electrofishing was then used to recapture tagged fish and estimate relative survival. In total, 328 Yellowstone Cutthroat Trout were sampled (0 s: n = 110; 30 s: n = 110; 60 s: n = 108), 278 Bull Trout (0 s: n = 92; 30 s: n = 94; 60 s: n = 92), and 322 Rainbow Trout (0 s: n = 103; 30 s: n = 106; 60 s: n = 113). The majority of fish were caught using artificial flies (≥92%) and were hooked in the corner of the mouth, lower jaw, or upper jaw (≥78%) in all three species. No difference in survival was observed among air exposure treatments for all three species. Results from the present study along with those from prior field studies of air exposure times during angling suggest that mortality from exposing fish to air for ≤60 s is not likely a population‐level concern in catch‐and‐release fisheries for these species.

Idaho↗
USGS2018

Effectiveness of ultrasonic imaging for evaluating presence and maturity of eggs in fishes in remote field locations

Ultrasonic imaging is an effective, nonlethal method used to determine sex and maturity in a variety of fishes. However, many previous studies of this technique have been performed in laboratory environments. Using Common Carp Cyprinus carpio , we developed a standardized method for ultrasonically scanning cyprinids, and we accurately sexed 78% ( N = 58) of those individuals. We then applied this method to endangered Humpback Chub Gila cypha and obtained 751 scans of Humpback Chub in remote field locations within the Grand Canyon, Arizona. Ultrasonic scanning took less than 1 min per fish to perform, and we identified females containing eggs based on two jpeg images and one 10-s video clip. Using ImageJ software to evaluate ultrasonic scans of ovulatory, captive Humpback Chub, we determined that female fish were potentially ovulatory when scanned eggs exhibited an ImageJ brightness value within the range of 32–44. Although we could successfully evaluate egg maturity, we were unable to estimate egg mass. Fisheries managers can use this noninvasive scanning method or a similar technique in remote field locations to collect ultrasonic scans from cyprinids to determine their reproductive status.

North American Journal of Fisheries Management↗
USGS2018

Changes in growth of Rainbow Trout in a Catskill Mountain Reservoir following Alewife and White Perch Introductions

Rainbow Trout Oncorhynchus mykiss were introduced to the Esopus Creek watershed in the Catskill Mountains of New York in the early 1880s. This introduction created a renowned naturalized fishery that remains important to the local economy today. The objective of this study was to determine whether the growth and condition of Rainbow Trout in the Ashokan Reservoir changed following the establishment of (1) Alewives Alosa pseudoharengus in the 1970s and (2) White Perch Morone americana in the 2000s by analyzing historical scale samples from 502 Rainbow Trout. The resulting data were used to compare length at age, von Bertalanffy growth curves, age‐specific annual growth increments, and relative weight before and after each introduction. Results indicated that growth of Rainbow Trout of ages <5 years generally increased following each introduction, while insufficient data for ages 5 and 6 made trends for older fish unclear. Rainbow Trout of ages ≤2 are believed to primarily use riverine habitats in this watershed, and therefore fish of ages >2 may best reflect reservoir growth. The mean relative weight of Rainbow Trout also increased between each period. The largest increases in both growth and condition were observed during the period after the introduction of White Perch, which was unexpected considering this species may have some diet overlap with Rainbow Trout and should be a poor forage species. Changes in watershed management and density‐dependent growth effects may explain these unexpected results. Our results, which largely suggest increased growth and condition over time, eliminate growth effects as a possible explanation for declining Rainbow Trout populations and suggest recruitment issues in the watershed require further investigation. This study contributes to our understanding of the interactions between introduced species and underscores the value of maintaining long‐term monitoring programs for assessing biological trends.

New York↗
USGS2018

Population characteristics and management of lentic populations of nonnative Burbot in the Green River system, Wyoming

Fishes introduced outside of their native distributions have the potential to negatively affect their recipient ecosystems. Since their illegal introduction into the Green River, Wyoming, in the 1990s, Burbot Lota lota have been sampled in lotic and lentic environments throughout the Green River system where they pose a threat to native fishes and valuable sport fisheries. In response to this invasion, managers of the Green River have begun to explore the efficacy of a suppression effort targeting Burbot. This study sought to the describe population dynamics of Burbot in the lentic portions of the Green River system and compare with Burbot population dynamics in the Green River. We also sought to evaluate potential management scenarios for a suppression program. Burbot for this study were collected from Fontenelle and Flaming Gorge reservoirs in October and November 2016. Growth rates of Burbot in the lentic portion of the system were higher than for fish in the Green River. Total annual mortality rates of Burbot were approximately 10% lower in reservoirs (33%) than for fish in the Green River. Additionally, lentic Burbot matured earlier than lotic Burbot. An age-structured population model indicated that Burbot populations were growing rapidly (λ = 1.18) in the study reservoirs. Annual exploitation of juvenile Burbot would need to reach 7%. Exploitation of mature Burbot would need to increase to 33% or greater (A ≥ 57%) to effectively suppress Burbot in this system. Sensitivity analysis suggested that mortality of age-1 and age-2 Burbot had the greatest influence on population growth rate. However, due to difficulties in collecting juvenile Burbot in the system, focusing removal effort on mature Burbot may be the most realistic option for suppressing Burbot populations in the Green River system.

Wyoming↗
USGS2019

Size selectivity of sampling gears used to sample Kokanee

Kokanee Oncorhynchus nerka provide valued recreational fisheries and also serve as a prey resource for economically, socially, and ecologically important fishes. As such, management of kokanee is a major focus of natural resource agencies. Kokanee are typically monitored using midwater trawls, but the interpretation of data collected using midwater trawls is difficult due to the unknown size selectivity of the gear. We sought to assess the length selectivity of midwater trawls by comparing estimates obtained from midwater trawls with estimates obtained from gill nets adjusted for size selectivity. Experimental curtain gill nets and midwater trawls were used in conjunction to sample kokanee in seven lentic systems in Idaho. The size selectivity of gill nets was estimated by accounting for the probability of encounter and the probability of retention. Estimates of size selectivity were then used to adjust the length distribution of fish sampled in gill nets. The adjusted length distribution of fish sampled in gill nets was compared with estimates obtained from midwater trawls to identify potential size selectivity of midwater trawls. A pattern of size selectivity was apparent for both sampling techniques. The average length of kokanee sampled with midwater trawls was 111 mm; whereas, kokanee sampled with gill nets had a mean length of 235 mm. Our results suggest experimental gill nets are useful for common sampling of kokanee (e.g., trend monitoring) because the gear is less size selective than midwater trawls and is adjustable for size selectivity. However, midwater trawls are likely the best gear for addressing questions associated with early life history. Overall, our results provide a better understanding of gill-net and midwater trawl selectivity and ultimately improve the ability to sample and manage the species.

North American Journal of Fisheries Management↗
USGS2019

A statewide evaluation of Florida Bass genetic introgression in Tennessee

Largemouth Bass (Micropterus salmoides) are one of the most popular freshwater sport fish in the United States and managers in southeastern states have stocked the Florida Bass (M. s. floridanus) subspecies outside of its natural range to increase size structure of existing Largemouth Bass populations. In Tennessee, fisheries for Largemouth Bass are concentrated in reservoirs of the Cumberland and Tennessee River systems; however, Florida Bass stockings have to date been restricted to two reservoirs of the Tennessee River and have varied significantly in extent and duration. We quantified levels of genetic admixture between Florida Bass and Largemouth Bass using 38 species-diagnostic single nucleotide polymorphisms for 979 fish sampled from 14 reservoirs from the Cumberland and Tennessee River systems. We tested for differences in genetic admixture across river systems and evaluated the relative importance of fish stockings in explaining observed levels of genetic admixture. Levels of genetic admixture and associated variation was higher in reservoirs of the Tennessee River (range = 6.3 – 30.4 average percent Florida Bass alleles) relative to the Cumberland River (range = 5.7 – 13.4 %), but admixture was not solely related to stocking rates. The highest levels of Florida Bass introgression were detected in Chickamauga Reservoir, the most extensively stocked reservoir in the state. Linear models identified fish stocked as a significant overall predictor of admixture, but we also observed stocked and unstocked reservoirs with similar levels of admixture, suggesting factors other than stocking influence population genetics. Our statewide assessment of reservoir-level patterns of hybridization among black bass was performed prior to the recent expansion of Florida Bass stocking efforts in Tennessee, and thus, represents a baseline for evaluating future stocking.

Tennessee↗
USGS2019

Optimum electrofishing waveforms and parameters to induce a capture-prone response in juvenile Grass Carp

Grass Carp (Ctenopharyngodon idella) are a non-native species to North America that were first introduced for vegetation control in the 1960s. However, wild-reproducing Grass Carp can negatively impact aquatic habitats and aquatic communities by consuming substantial amounts of aquatic vegetation and increasing turbidity. Numerous fisheries techniques have been used in an attempt to control or eradicate Grass Carp, including electrofishing. However, electrofishing efficiency for Grass Carp has been variable, and optimum electrofishing waveforms and parameters for inducing a capture-prone response have not been determined. The objective of this study was to determine the optimum electrofishing waveforms and parameters to induce a capture-prone response at various water temperatures and conductivities in juvenile Grass Carp in a controlled, laboratory setting. Results indicated that rectangular pulse waveforms with 60 to 100 Hz frequencies were most effective for immobilization of juvenile Grass Carp. All duty cycles tested (20 – 48%) at these frequencies were effective; although at 60 Hz and 80 Hz frequencies, 24% and 30% duty cycles, respectively, may be more effective. Water temperature was positively related to voltage gradient immobilization thresholds whereas ambient water conductivity and fish size were inversely related to voltage gradient immobilization thresholds. This study provides important information to those seeking to control, eradicate, or detect Grass Carp using electrofishing and provides a framework for future studies focusing on adult Grass Carp.

North American Journal of Fisheries Management↗
USGS2019

Variation in Bluegill catch rates and total length distributions among four sampling gears used in two Wisconsin lakes dominated by small Ffsh

Many Bluegill Lepomis macrochirus populations are dominated by fish ≤125 mm total length (TL) that may be underrepresented when using standard sampling gears. To identify efficient sampling methods for these populations, we compared catch per unit effort (CPUE) and TL frequency distributions of Bluegill captured in cloverleaf traps, boat electrofishing, mini-fyke nets, and beach seine hauls from two northern Wisconsin lakes supporting populations dominated by fish ≤125 mm TL. Mean Bluegill CPUE ranged from 41 (SE = 11) fish per cloverleaf trap lift to 16 (SE = 8) fish per beach seine haul. Cloverleaf traps generally captured smaller Bluegill relative to other gears and were the only gear to consistently capture Bluegill ≤80 mm TL. Conversely, boat electrofishing captured the widest TL range of Bluegill, and fish ≥80 mm TL composed a greater proportion of catch (37%) relative to other gears. With few exceptions, the effort required to detect 10% or 25% changes in Bluegill CPUE was >100 units of effort regardless of lake, sampling gear, or month. Furthermore, there was no consistency between lakes or months in terms of which sampling gear required the fewest number of samples to detect a 50% change in CPUE. Estimated units of effort needed to detect 10% or 25% changes in mean Bluegill TL were ≤16 for all sampling gears on the lake with consistently higher CPUE (i.e., more fish to measure per unit). In the lake with lower CPUE, cloverleaf traps consistently required less effort to detect changes in mean TL. We note that comparing sample size requirements among gears is not straightforward because gears are sampling differing segments of the Bluegill population. Our study emphasizes the importance of evaluating gear biases and sampling efficiency so that fisheries managers can develop suitable sampling protocols.

Wisconsin↗
USGS2019

Observations of American Shad Alosa sapidissima approaching and using a vertical slot fishway at the head-of-tide Brunswick Dam on the Androscoggin River, Maine

American Shad Alosa sapidissima have historically supported an important fishery along the Atlantic coastal waters of North America. However, the construction of dams reduced populations and restricted landings. Fishways are intended to mitigate obstacles to anadromous fish migrations, but a thorough evaluation of their efficiency is warranted. We analyzed data collected from video recordings, hydropower turbine operations, and telemetry conducted by the Maine Department of Marine Resources to evaluate American Shad behavior while approaching and using a vertical slot fishway at the head-of-tide Brunswick Dam on the Androscoggin River in Maine. American Shad passage at the dam has been poor, ranging from 0 to 1,100 fish per year, relative to passage at other facilities in the region. Additionally, our observations indicate that there are relatively high numbers of American Shad present downstream in the river (averaging 50,000) compared with the entrance of the fishway or its pools (<8,000). On average, the rates of observed American Shad on the side of the river near the fishway entrance were significantly higher (6.5–8.6 individuals/min) when the turbine closest to the entrance of the fishway was not operating compared with when it was operating (4.1 individuals/min). Most of the radio-tagged American Shad remained in the river below the dam or went undetected. Eleven of 57 tagged fish were detected at the fishway entrance and of those only five were detected in the lower fishway. Individuals that were detected were observed making multiple attempts at entering the fishway, but movements were restricted to the lower pools. Our results suggest that this fishway is not conducive to the passage of American Shad. Examining the relationship between hydropower operations and other environmental variables on the behavior and passage of migrating anadromous fish remain an area for further study.

Maine↗
USGS2019

A brief introduction to integrated pest management for aquatic systems

Aquatic invasive plants and animals are increasingly becoming a problem, causing severe economic and ecological damage to critical freshwater systems. The best strategy for controlling an invasive pest employs an integrated pest management (IPM) approach using a combination of biological, physical, chemical, and social/cultural control methods. Here, we examine the history and development of IPM and provide a discussion of the components of an IPM program involving development, evaluation, and management. Control approaches will be reviewed and the application of this technique to aquatic systems will be discussed. A discussion of the Great Lakes Fishery Commission's (GLFC) Integrated Management of Sea Lamprey Petromyzon marinus Control Program will be provided to illustrate the application of IPM to an aquatic system.

North American Journal of Fisheries Management↗
USGS2019

Age and growth of Freshwater Drum and Gizzard Shad occupying two reservoir-river complexes with different groundwater contributions

Restoring groundwater flow is a management option that improves water temperature regimes and benefits fishes. Although this strategy applies more readily to river systems, the thermal character of reservoirs is heavily influenced by inflowing rivers. We examined differences in age, structure, and growth of both Freshwater Drum Aplodinotus grunniens and Gizzard Shad Dorosoma cepedianum that occupy catchments with varying groundwater contributions in the south‐central United States. Seepage run data indicated that the Kiamichi River was losing surface water to groundwater in summer 2016, whereas groundwater inflows were apparent in the Elk River basin. Summer 2016 data showed that the Elk River had cooler water temperatures than the Kiamichi River and Grand Lake O’ the Cherokees water temperatures were similar to those in the incoming Elk River. We found higher densities of older Freshwater Drum and Gizzard Shad (maximums of 32 and 8 years old, respectively) in samples from the Grand basin than among fish that were sampled from the Kiamichi River basin (21 and 6 years old, respectively). Freshwater Drum grew at similar rates in both basins even though they reached larger maximum lengths in the Grand basin (649 mm TL) than in the Kiamichi River basin (600 mm). The average asymptotic length was greater for the Kiamichi population ( L ∞ = 613 mm) than for the Grand population ( L ∞ = 557 mm). Gizzard Shad from the Grand basin were larger than those from the Kiamichi River basin, though the latter population grew faster initially (Brody growth coefficient: K = 0.787 versus K = 0.179, respectively), but they had smaller asymptotic length ( L ∞ = 206 mm versus L ∞ = 343 mm). The role that groundwater plays in temperature regulation in these basins partially explains the observed differences. Our results suggest that the metabolic theory of ecology can be applied to fisheries management at a finer spatial scale.

Oklahoma↗
USGS2019

Growth of hatchery‐reared chinook salmon in Lakes Michigan and Huron exhibits limited spatial variation but Is temporally linked to alewife abundance

Chinook Salmon Oncorhynchus tshawytscha were introduced into Lakes Michigan and Huron in the 1960s to diversify recreational fisheries and reduce overabundant, nonnative Alewife Alosa pseudoharengus. Alewife remain the primary prey of Chinook Salmon but have experienced substantial declines in abundance due to reduced food resources and salmonine predation pressure. The movements of Chinook Salmon have been linked to the density and spatial distribution of Alewife, but spatial patterns in Chinook Salmon growth have not been well documented and the temporal relationship between growth and Alewife density has not been evaluated during the current period of low Alewife abundance. We evaluated spatial and temporal variation in growth of Chinook Salmon in Lake Michigan and the U.S. waters of Lake Huron and explored linkages with Alewife density. Von Bertalanffy growth parameters were generally similar for recaptured coded‐wire‐tagged Chinook Salmon from different stocking locations and different recovery locations. Only a few small differences among stocking and recovery regions were evident, with regions divided into two subtly different groups with shared growth parameters. The small regional differences may be attributable to unique habitat and/or stocking characteristics of specific regions. In Lake Michigan average Chinook Salmon length at age also varied across years and was tightly coupled with annual lakewide densities of age‐1 and older Alewife, suggesting that Chinook Salmon growth from 2012 to 2016 was constrained by Alewife density. Our findings are consistent with evidence of lakewide movements associated with foraging and support continued management of Chinook Salmon in Lake Michigan as a single population. Furthermore, similar growth in Chinook Salmon from Lakes Michigan and Huron corroborates evidence that Chinook Salmon move from U.S. waters of Lake Huron to Lake Michigan to feed and reinforces the recent decision to include most fish stocked in northwestern Lake Huron in the Lake Michigan population when managing for predator–prey balance.

Lake Michigan, Lake Huron↗
USGS2019

Marking otoliths of Alligator Gar by immersion in oxytetracycline

Alligator Gar Atractosteus spatula are increasingly being stocked to restore populations, making the need to identify stocked individuals important for monitoring. Oxytetracycline (OTC) immersion allows for large numbers of fish to be marked simultaneously, thus eliminating the need to handle fish individually, but protocols for doing so have not been investigated fully for this species. In this study, we sought to identify dosages of OTC (concentration and duration of exposure) that would successfully mark juvenile Alligator Gar while minimizing mortality as a result of the marking procedures. Juvenile Alligator Gar (38 ± 4.4 mm [mean ± SE]) were collected from raceways at Tishomingo National Fish Hatchery 18–22 d after hatch and were marked during transport to the Oklahoma Fishery Research Laboratory. Ten individuals per treatment (360 total individuals) were randomly placed into one of three replicates containing one of four concentration × duration combinations of Pennox 343 OTC solution. Juvenile Alligator Gar were exposed to an OTC concentration of 0 (control), 500, 600, or 700 mg/L for a duration of 4, 5, or 6 h. Asteriscus, lapillus, and sagittal otoliths were examined for mark presence at 14 d postexposure by using fluorescent microscopy. The OTC concentration and duration both affected mean mark quality similarly among otolith types. Mortality increased with increasing OTC concentration, suggesting that a balance between concentration and duration is needed to achieve marking goals. Based on our findings, batch marking of Alligator Gar was successful at OTC concentrations from 500 to 700 mg/L for 4–6 h, although immersion at 500 mg/L for 6 h and 600 mg/L for 4–6 h produced the best balance between high mark quality and low associated mortality.

North American Journal of Fisheries Management↗
USGS2019

Movement dynamics of Smallmouth Bass in a large western river system

The Snake River, Idaho, between Swan Falls and Brownlee dams supports a popular fishery for Smallmouth Bass Micropterus dolomieu . Recently, anglers have expressed concern about harvest of Smallmouth Bass associated with seasonal congregations in and near the lower reaches of several major tributaries. Little is known about Smallmouth Bass movement in the system, and a better understanding of movement dynamics will help to guide future management. From March to August 2016, Smallmouth Bass (≥260 mm; n = 1,131) were tagged with T-bar anchor tags to evaluate large-scale movement patterns. Movement was estimated from 63 angler-reported tags for which area descriptions provided sufficient detail to assign a recapture location. Extent of fish movement varied among segments and tributaries from 0 to 128 river kilometers (rkm). From March to May 2017, Smallmouth Bass (≥305 mm; n = 149) in the Snake, Boise, Payette, and Weiser rivers and in Brownlee Reservoir were implanted with radio transmitters. Of the 149 Smallmouth Bass that were released with radio transmitters, 107 were relocated at least once. Additionally, 79.6% of fish with radio transmitters had a maximum extent of movement of 5 rkm or greater and 42.6% had a maximum extent of 30 rkm or greater; one radio-tagged fish moved 167 rkm upstream. Average daily movement of Smallmouth Bass varied among river segments and was greatest in the spring and summer. Fish from the Snake River, tributaries (e.g., Boise River), and Brownlee Reservoir moved all around the study area, indicating an absence of clear population boundaries. As such, Smallmouth Bass in the study area appear to function as one large population as opposed to multiple subpopulations, thereby indicating that management as one population is likely appropriate.

Idaho↗
USGS2020

Effects of temperature on hatching rate and early development of alligator gar and spotted gar in a laboratory setting

Water temperature influences both morphological and physiological development in fishes. However, the effects of water temperature on the early development of Alligator Gar Atractosteus spatula and Spotted Gar Lepisosteus oculatus are not well understood. Both gar species were collected from natural environments and spawned in a hatchery setting. After spawning, fertilized embryos were collected and transferred to the Oklahoma Fishery Research Laboratory, where the embryos (50–72 embryos/treatment) were placed into one of five water temperature treatments (15.5, 20.0, 23.8, 27.5, and 32.2°C) and observed over time to estimate the time to hatch and the time to reach the free-swimming stage. Both species showed an inverse relationship between temperature and the timing of hatch and advancement to free-swimming fingerlings for all treatments. In addition, Alligator Gar embryos did not develop at the coldest water temperature tested, and Alligator Gar juveniles held at the warmest temperature tested were observed with developmental abnormalities, potentially affecting their survival. The same temperature extremes had no comparable negative effect on Spotted Gar. The results of this study are useful for understanding early life history dynamics of these two species in their natural environments and can also be used by hatchery managers who are seeking to optimize their production protocols.

North American Journal of Fisheries Management↗
USGS2020

Feeding ecology of age-0 gar at Lake Texoma inferred from analysis of stable isotopes

Conservation and restoration of gar (Lepisosteidae) populations in North America are increasingly of interest to fisheries managers. Alligator Gar Atractosteus spatula are being stocked as age-0 fish in efforts to re-establish extirpated populations. However, gars are known to be highly cannibalistic in hatcheries, suggesting that age-0 Alligator Gar introduced into natural habitats may face predation pressures from other gar species, limiting the likelihood of released fish recruiting to the population. Furthermore, introduced age-0 gar may not have the proper prey resources for rapid growth that would facilitate recruitment to adulthood. Texoma Reservoir, located on the Oklahoma–Texas border, hosts four native gar species, including the Alligator Gar, whose population is supported by supplemental stocking of age-0 fingerlings. We investigated feeding by age-0 gar to obtain a baseline level of trophic ecology for this group of fishes, including the potential for poststocking cannibalism. Food webs were reconstructed via analysis of carbon (δ 13 C) and nitrogen (δ 15 N) isotopes using Bayesian mixing model approaches. Isotopic values for age-0 fish of all four gar species were similar. Invertebrates represented a large fraction of the diet for all gars, followed by Common Carp Cyprinus carpio and Grass Carp Ctenopharyngodon idella . Competitive interactions among Bluegill Lepomis macrochirus , White Bass Morone chrysops , White Crappie Pomoxis annularis , and young gar may occur for invertebrates, shads Dorosoma spp., and Western Mosquitofish Gambusia affinis but are likely short-lived due to the rapid growth of age-0 gar after their transition to piscivory. Trophic position of age-0 Alligator Gar, Longnose Gar Lepisosteus osseus , and Spotted Gar Lepisosteus oculatus was positively related to TL, but this relationship was not observed for Shortnose Gar Lepisosteus platostomus . In Texoma Reservoir, the four native gar species, including stocked Alligator Gar, appear to have adequate food resources for recruitment, with little indication of within-family or interspecific predation. This suggests that stocked Alligator Gar quickly acclimated to their new environment.

North American Journal of Fisheries Management↗
USGS2020

Indexing age-0 Walleye abundance in northern Wisconsin lakes Before fall

Age-0 Walleye Sander vitreus recruitment is often indexed using fall electrofishing surveys. However, collecting fish before fall may provide timely information regarding stocking decisions and factors influencing recruitment. We evaluated sampling methods for age-0 Walleye in northern Wisconsin lakes that could be used to assess recruitment in spring and summer. Initial assessments on two lakes indicated surface tows of ichthyoplankton nets at night during May-early June and 0.64-cm micromesh gill nets set in July provided highest catches of age-0 Walleye among the methods we evaluated. Additional sampling on 13 lakes over two years indicated catch-per-effort (CPE) of age-0 Walleye using these two methods did not correlate with age-0 CPE in fall electrofishing. However, presence or absence of age-0 Walleye in micromesh gill nets was 92% accurate in predicting whether age-0 CPE in fall electrofishing was ≥ 15 fish/h, the threshold above which eventual recruitment to the fishery is expected to occur. Micromesh gill netting may provide a useful tool for allocating fingerling Walleye that are stocked in fall, a resource that is often limited due to space and forage constraints associated with propagation. Additionally, our sampling protocol may help to identify timing of potential recruitment bottlenecks occurring in some lakes.

Wisconsin↗