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At least 667 records · Page 37Linked to original sources
USGS2002

Sample size requirements for in situ vegetation and substrate classifications in shallow, natural Nebraska Lakes

We assessed the precision of visual estimates of vegetation and substrate along transects in 15 shallow, natural Nebraska lakes. Vegetation type (submergent or emergent), vegetation density (sparse, moderate, or dense), and substrate composition (percentage sand, muck, and clay; to the nearest 10%) were estimated at 25-70 sampling sites per lake by two independent observers. Observer agreement for vegetation type was 92%. Agreement ranged from 62.5% to 90.1% for substrate composition. Agreement was also high (72%) for vegetation density estimates. The relatively high agreement between estimates was likely attributable to the homogeneity of the lake habitats. Nearly 90% of the substrate sites were classified as 0% clay, and over 68% as either 0% or 100% sand. When habitats were homogeneous, less than 40 sampling sites per lake were required for 95% confidence that habitat composition was within 10% of the true mean, and over 100 sites were required when habitats were heterogeneous. Our results suggest that relatively high precision is attainable for vegetation and substrate mapping in shallow, natural lakes.

North American Journal of Fisheries Management↗
USGS2002

Uncertainty of exploitation estimates made from tag returns

Over 6,000 crappies Pomoxis spp. were tagged in five water bodies to estimate exploitation rates by anglers. Exploitation rates were computed as the percentage of tags returned after adjustment for three sources of uncertainty: postrelease mortality due to the tagging process, tag loss, and the reporting rate of tagged fish. Confidence intervals around exploitation rates were estimated by resampling from the probability distributions of tagging mortality, tag loss, and reporting rate. Estimates of exploitation rates ranged from 17% to 54% among the five study systems. Uncertainty around estimates of tagging mortality, tag loss, and reporting resulted in 90% confidence intervals around the median exploitation rate as narrow as 15 percentage points and as broad as 46 percentage points. The greatest source of estimation error was uncertainty about tag reporting. Because the large investments required by tagging and reward operations produce imprecise estimates of the exploitation rate, it may be worth considering other approaches to estimating it or simply circumventing the exploitation question altogether.

North American Journal of Fisheries Management↗
USGS2002

Recruitment variation of crappies in response to hydrology of Tennessee reservoirs

Black crappies Pomoxis nigromaculatus and white crappies P. annularis were sampled to index recruitment in seven Tennessee reservoirs (four main-stem and three tributary storage impoundments). Crappie recruitment in tributary storage impoundments appeared to be consistently higher in years of high discharge during the prespawn period (1 January-31 March). A similar relation was found in one main-stem impoundment; however, crappie recruitment in two main-stem impoundments was inversely related to discharge during the spawning period (1 April-30 May), and little recruitment variation was found in the fourth main-stem impoundment. In general, reservoir hydrology appeared to have a stronger effect on crappie recruitment in tributary storage impoundments than in main-stem impoundments, possibly because recruitment was more variable in tributary systems. Thus, it is likely that crappie populations will rarely have strong year-classes simultaneously over a wide geographic area or even within a single watershed.

North American Journal of Fisheries Management↗
USGS2002

Initial poststocking mortality, oxytetracycline marking, and year-class contribution of black-nosed crappies stocked into Tennessee reservoirs

Initial poststocking mortality, oxytetracycline mark persistence, and year-class contribution were evaluated for black-nosed crappies, a morphological variant of the black crappie Pomoxis nigromaculatus, stocked into Tennessee reservoirs during 1997-1999. Average initial poststocking mortality was low (x?? = 13%, N = 44). Lake temperature and the difference between lake and hauling tank water temperatures were significant in explaining variability in arcsine-transformed mortality estimates; however, the variability explained by these factors was low (R2 = 0.15). Oxytetracycline immersion was a highly effective marking tool; 97-100% of all crappies treated were marked, and 99% of the marks were visible 36-110 weeks after marking. All control otoliths were correctly scored as unmarked during the evaluation, and mortality rates did not differ between marked and unmarked crappies. Year-class contribution was variable across reservoirs and was highest in Normandy Reservoir (34-93% at ages 1-3). Contribution at ages 1 and 2 was 11-24% in Woods Reservoir. Stocking did not supplement the crappie population in Lake Graham. Black-nosed crappies made up a significant portion (>50%) of the crappies harvested by anglers in Center Hill Reservoir 3 years after stocking was initiated. Conversely, black-nosed crappies made up a relatively small percentage (???12%) of the crappies harvested in Cherokee Reservoir in the 4 years after initial stocking.

North American Journal of Fisheries Management↗
USGS2002

Electrofishing for crappies: Electrical settings influence immobilization efficiency, injury, and mortality

Continuous direct current (DC) and pulsed DC (PDC) of varying frequency and pulse period are commonly used to immobilize and collect crappies Pomoxis spp. in freshwater. However, little information is available about the minimum electrical-setting thresholds required for immobilization or how the settings relate to incidence of injury. We investigated the effect of increasing power densities on the immobilization and injury of black crappies P. nigromaculatus (average total length = 154 mm) treated with DC and various PDC settings. Forced swimming toward the electrodes was observed in black crappies exposed to DC, but that was less apparent for PDC. The minimum peak power densities required to immobilize black crappies ranged from 0.10 to 6.5 mW/cm3 and depended on pulse frequency and period. The incidence of hemorrhaging ranged from 0% to 50% and that of spinal damage from 9% to 45%. However, the severity of injury also depended on pulse frequency and period. No fish suffered mortality at or below the immobilization thresholds, but mortality ranged from 0% to 15% at settings above the thresholds. Mortality was observed with PDC settings of 15 Hz only. Fish that were tetanized following electrical treatment were more prone to injury than those that exhibited narcosis.

North American Journal of Fisheries Management↗
USGS2003

Evidence of sexually dimorphic introgression in Pinaleno Mountain Apache trout

The high-elevation headwater streams of the Pinaleno Mountains support small populations of threatened Apache trout Oncorhynchus apache that were stocked following the chemical removal of nonnative salmonids in the 1960s. A fisheries survey to assess population composition, growth, and size structure confirmed angler reports of infrequent occurrences of Oncorhynchus spp. exhibiting the external morphological characteristics of both Apache trout and rainbow trout O. mykiss. Nonlethal tissue samples were collected from 50 individuals in the headwaters of each stream. Mitochondrial DNA (mtDNA) sequencing and amplification of nuclear microsatellite loci were used to determine the levels of genetic introgression by rainbow trout in Apache trout populations at these locations. Sexually dimorphic introgression from the spawning of male rainbow trout with female Apache trout was detected using mtDNA and microsatellites. Estimates of the degree of hybridization based on three microsatellite loci were 10-88%. The use of nonlethal DNA genetic analyses can supplement information obtained from standard survey methods and be useful in assessing the relative importance of small and sensitive populations with a history of nonnative introductions.

North American Journal of Fisheries Management↗
USGS2003

Comparison of electrofishing and rotenone for sampling largemouth bass in vegetated areas of two Florida lakes

We compared the sampling precision and efficiency of electrofishing and rotenone for assessing populations of largemouth bass Micropterus salmoides in vegetated portions of two Florida lakes. Sampling was conducted at Lochloosa and Orange lakes in north-central Florida from 1990 to 1999. Significant differences in length frequencies were determined between the two methods in 5 of 9 years for each lake. In years where differences existed, electrofishing collected larger fish than did rotenone. The maximum deviation between cumulative relative length frequencies for the two methods was not related to total vegetation, native emergent vegetation, or hydrilla Hydrilla verticallata coverage at either lake. Sampling precision was greater for electrofishing than for rotenone; electrofishing also required less sampling effort to detect changes in the abundance of juvenile and adult largemouth bass. Electrofishing was a more precise and cost-effective method than rotenone for estimating largemouth bass abundance.

North American Journal of Fisheries Management↗
USGS2003

Relation of age-0 largemouth bass abundance to hydrilla coverage and water level at Lochloosa and Orange Lakes, Florida

Changes in electrofishing catch per hour (CPH) of age-0 largemouth bass Micropterus salmoides were examined in relation to aquatic macrophytes and seasonal water elevation at Lochloosa and Orange lakes, Florida, during the 1990s. At Lochloosa Lake, stepwise multiple regression revealed a significant positive relationship between the mean CPH of age-0 largemouth bass and the percentage of areal coverage by hydrilla Hydrilla verticallata. At Orange Lake, mean CPH was directly associated with the percentage of areal coverage by hydrilla and inversely related to summer water levels. Thus, the influence of vegetation on age-0 largemouth bass abundance was similar at both lakes, but the effects of water levels were not. Further investigations into the effects of fluctuations in water levels on age-0 largemouth bass in natural lakes are needed.

North American Journal of Fisheries Management↗
USGS2003

Factors influencing poststocking dispersal of razorback sucker

Efforts to reintroduce razorback suckers Xyrauchen texanus to specific river reaches have been plagued by downstream drift and poor survival, which have been attributed to stress, disorientation, predation, and poor conditioning. Poststocking dispersal of eight test groups (15 fish each) of razorback suckers was examined for 28 d with telemetry equipment. Fish were released in three different locations in the Colorado River basin of Utah, Arizona, and Nevada: (1) a 65,000-ha reservoir, (2) a small (<1-ha) backwater, and (3) a large (30-ha) backwater on the mainstem river. At each location, subgroups were released immediately (reference) or held to acclimate them to the site (3–7 d) before release. Two of four subgroups for the large-backwater test were preconditioned to flow. Dispersal from the stocking sites was rapid and declined with time for all tests, as fish appeared to seek and find cover. Downstream drift was most pronounced (x = 69.5 km) from the small backwater and significantly (Kruskal–Wallis test, P < 0.01) greater than either the reservoir (x = 3.7 km) or large-backwater sites (x = 7.7 km). Site-acclimation tests were inconclusive, but downstream movement was significantly (Wilcoxon two-sample test, Z = −2.298, P < 0.01) less for fish preconditioned to flow (x = 1.9 km) compared with pond-reared fish (x = 7.7 km). We concluded that poststocking dispersal may decrease if razorback suckers are preconditioned to flow.

North American Journal of Fisheries Management↗
USGS2003

Influence of flow and temperature on survival of wild subyearling fall chinook salmon in the Snake River

Summer flow augmentation to increase the survival of wild subyearling fall chinook salmon Oncorhynchus tshawytscha is implemented annually to mitigate for the development of the hydropower system in the Snake River basin, but the efficacy of this practice has been disputed. We studied some of the factors affecting survival of wild subyearling fall chinook salmon from capture, tagging, and release in the free-flowing Snake River to the tailrace of the first dam encountered by smolts en route to the sea. We then assessed the effects of summer flow augmentation on survival to the tailrace of this dam. We tagged and released 5,030 wild juvenile fall chinook salmon in the free-flowing Snake River from 1998 to 2000. We separated these tagged fish into four sequential within-year release groups termed cohorts (N = 12). Survival probability estimates (mean ?? SE) to the tailrace of the dam for the 12 cohorts when summer flow augmentation was implemented ranged from 36% ?? 4% to 88% ?? 5%. We fit an ordinary least-squares multiple regression model from indices of flow and temperature that explained 92% (N = 12; P < 0.0001) of the observed variability in cohort survival. Survival generally increased with increasing flow and decreased with increasing temperature. We used the regression model to predict cohort survival for flow and temperature conditions observed when summer flow augmentation was implemented and for approximated flow and temperature conditions had the summer flow augmentation not been implemented. Survival of all cohorts was predicted to be higher when flow was augmented than when flow was not augmented because summer flow augmentation increased the flow levels and decreased the temperatures fish were exposed to as they moved seaward. We conclude that summer flow augmentation increases the survival of young fall chinook salmon.

North American Journal of Fisheries Management↗
USGS2003

Comparison of migration rate and survival between radio-tagged and PIT-tagged migrant yearling chinook salmon in the Snake and Columbia rivers

A study was conducted to compare the travel times, detection probabilities, and survival of migrant hatchery-reared yearling chinook salmon Oncorhynchus tshawytscha tagged with either gastrically or surgically implanted sham radio tags (with an imbedded passive integrated transponder [PIT] tag) with those of their cohorts tagged only with PIT tags in the Snake and Columbia rivers. Juvenile chinook salmon with gastrically implanted radio tags migrated significantly faster than either surgically radio-tagged or PIT-tagged fish, while migration rates were similar among surgically radio-tagged and PIT-tagged fish. The probabilities of PIT tag detection at downstream dams varied by less than 5% and were not significantly different among the three groups. Survival was similar among treatments for median travel times of less than approximately 6 d (migration distance of 106 km). However, for both gastrically and surgically radio-tagged fish, survival was significantly less than for PIT-tagged fish, for which median travel times exceeded approximately 10 d (migration distance of 225 km). The results of this study support the use of radio tags to estimate the survival of juvenile chinook salmon having a median fork length of approximately 150 mm (range, 127-285 mm) and a median travel time of migration of less than approximately 6 d.

Oregon, Washington↗
USGS2003

Effects of flooding on abundance of native and nonnative fishes downstream from a small impoundment

Flooding can benefit native fishes in southwestern streams by disproportionately displacing nonnative fishes. We examined how the presence of an upstream impoundment affected this relationship in lower Sonoita Creek, Arizona. Nonnative species not found in the reservoir decreased in abundance in lower Sonoita Creek after flooding. The catch and relative abundance of some nonnative species found in both the reservoir and the creek increased in lower Sonoita Creek after flooding. Movement of nonnative fishes out of the reservoir via the spillway during periods of high water probably contributes to the persistence and abundance of these species downstream. Both preventing nonnative fishes from escaping reservoirs and the release of flushing flows would aid conservation of native southwestern fishes downstream.

North American Journal of Fisheries Management↗
USGS2003

A comparison of measures of riverbed form for evaluating distributions of benthic fishes

A method to quantitatively characterize the bed forms of a large river and a preliminary test of the relationship between bed-form characteristics and catch per unit area of benthic fishes is presented. We used analog paper recordings of bathymetric data from the Missouri River and fish data collected from 1996 to 1998 at both the segment (???101-102-km) and macrohabitat (???10-1-100-km) spatial scales. Bed-form traces were transformed to digital data with image analysis software. The slope, mean residual, and SD of the residuals of the regression of depth versus distance along the bottom, as well as mean depth, were estimated for each trace. These four metrics were compared with sinuosity, fractal dimension, critical scale, and maximum mean angle for the same traces. Mean depth and sinuosity differed among segments and macrohabitats. Fractal-based measures of the relative depth of bottom troughs (critical scale) and smoothness (maximum mean angle) differed among segments. Statistics-based measures of the relative depth of bottom troughs (mean residual) and smoothness (SD of the residuals) differed among macrohabitats. Sites with shovelnose sturgeon Scaphirhynchus platorynchus were shallower and smoother than sites without shovelnose sturgeon. When compared with sites without sicklefin chub Macrhybopsis meeki, sites with sicklefin chub were shallower, had shallower troughs, and sloped more out of the flow of the river. Sites with sturgeon chub M. gelida were shallower, had shallower troughs, and were smoother than sites without sturgeon chub. Sites with and without channel catfish Ictalurus punctatus did not differ for any bed-form variables measured. Nonzero shovelnose sturgeon density increased with depth, whereas nonzero sturgeon chub density decreased with depth. Indices of bed-form structure demonstrated potential for describing the distribution and abundance of Missouri River benthic fishes. The observed fish patterns, though limited, provide valuable direction for future research into the habitat preferences of these fishes.

North American Journal of Fisheries Management↗
USGS2003

Factors associated with stocked cutthroat trout populations in high-mountain lakes

High-mountain lakes provide important fisheries in the Rocky Mountains; therefore we sought to gain an understanding of the relationships among environmental factors, accessibility to anglers, stocking rates, and features of stocks of cutthroat trout Oncorhynchus clarki in high-mountain lakes of the Bighorn Mountains, Wyoming. We sampled fish with experimental gill nets, measured lake habitat features, and calculated factors affecting angler access among 19 lakes that lacked sufficient natural reproduction to support salmonid fisheries and that were stocked at 1-, 2-, or 4-year intervals with fingerling cutthroat trout. We found that angler accessibility was probably the primary factor affecting stock structure, whereas stocking rates affected the densities of cutthroat trout among lakes. The maximum number of years survived after stocking appeared to have the greatest affect on biomass and population structure. Our findings suggest that control of harvest and manipulation of stocking densities can affect the density, biomass, and structure of cutthroat trout stocks in high-elevation lakes.

North American Journal of Fisheries Management↗
USGS2003

Radio tag retention and tag-related mortality among adult sockeye salmon

Tag retention and tag-related mortality are concerns for any tagging study but are rarely estimated. We assessed retention and mortality rates for esophageal radio tag implants in adult sockeye salmon Oncorhynchus nerka . Migrating sockeye salmon captured at the outlet of Lake Clark, Alaska, were implanted with one of four different radio tags (14.5 × 43 mm (diameter × length), 14.5 × 49 mm, 16 × 46 mm, and 19 × 51 mm). Fish were observed for 15 to 35 d after tagging to determine retention and mortality rates. The overall tag retention rate was high (0.98; 95% confidence interval (CI), 0.92-1.00; minimum, 33 d), with one loss of a 19-mm × 51- mm tag. Mortality of tagged sockeye salmon (0.02; 95% CI, 0-0.08) was similar to that of untagged controls (0.03 (0-0.15)). Sockeye salmon with body lengths (mid-eye to tail fork) of 585-649 mm retained tags as large as 19 × 51 mm and those with body lengths of 499-628 mm retained tags as small as 14.5 × 43 mm for a minimum of 33 d with no increase in mortality. The tags used in this study represent a suite of radio tags that vary in size, operational life, and cost but that are effective in tracking adult anadromous salmon with little tag loss or increase in fish mortality.

Alaska↗
USGS2004

Acoustic-tracking and radio-tracking of horseshoe crabs to assess spawning behavior and subtidal habitat use in delaware bay

This study used telemetry to determine spawning behavior and subtidal habitat use of horseshoe crabs Limulus polyphemus. We attached combined acoustic and radio transmitters to 12 gravid female horseshoe crabs at Ted Harvey Beach and 12 at North Bowers Beach (both on the western shore of Delaware Bay) over a 5-d period before peak spawning on the new moon. Horseshoe crabs were acoustically tracked and radio-tracked daily for 8 d during both high tides and during the incoming dominant (higher) high tide. All horseshoe crabs were relocated at least once, and 83% of females spawned from two to six times (x?? = 3.35, SE = 0.18). Of these females, 85% spawned on two to five consecutive nights (x?? = 3.31, SE = 0.59). Most (95%) females spawned on the beaches where they were initially tagged. Typically, the shoreline used by an individual for spawning ranged from 70 to 1,160 m (x?? = 351 m, SE = 38 m). Between spawning events, horseshoe crabs remained 50-715 m offshore (x?? = 299 m, SE = 57 m) from their established spawning beaches. Following the new moon, all but one (96%) moved out of range of our survey area, which extended approximately 1 km from the shoreline. Multistate mark-recapture models were used to estimate recapture probabilities and daily probabilities of spawning and departure from the vicinity of the spawning beaches. The probability of recapture by acoustic telemetry was high and estimated to be 0.95 (95% confidence interval, 0.73-0.99). Horseshoe crabs equipped with acoustic and radio transmitters have high rates of recapture, can be tracked continually, and can be relocated in both foreshore and inshore habitats.

North American Journal of Fisheries Management↗
USGS2004

Imaging fall Chinook salmon redds in the Columbia River with a dual-frequency identification sonar

We tested the efficacy of a dual-frequency identification sonar (DIDSON) for imaging and enumeration of fall Chinook salmon Oncorhynchus tshawytscha redds in a spawning area below Bonneville Dam on the Columbia River. The DIDSON uses sound to form near-video-quality images and has the advantages of imaging in zero-visibility water and possessing a greater detection range and field of view than underwater video cameras. We suspected that the large size and distinct morphology of a fall Chinook salmon redd would facilitate acoustic imaging if the DIDSON was towed near the river bottom so as to cast an acoustic shadow from the tailspill over the redd pocket. We tested this idea by observing 22 different redds with an underwater video camera, spatially referencing their locations, and then navigating to them while imaging them with the DIDSON. All 22 redds were successfully imaged with the DIDSON. We subsequently conducted redd searches along transects to compare the number of redds imaged by the DIDSON with the number observed using an underwater video camera. We counted 117 redds with the DIDSON and 81 redds with the underwater video camera. Only one of the redds observed with the underwater video camera was not also documented by the DIDSON. In spite of the DIDSON's high cost, it may serve as a useful tool for enumerating fall Chinook salmon redds in conditions that are not conducive to underwater videography.

North American Journal of Fisheries Management↗