bluuebunny/crossref_metadata_2025_split huggingface dataset:
Factors That May Be Influencing Nonnative Brook Trout Invasion and Their Displacement of Native Westslope Cutthroat Trout in Three Adjacent Southwestern Montana Streams
Authors: Shepard Bradley B. 
Published: August 2004

Abstract
I examined trends in community structure and abundance in populations of native westslope cutthroat trout (WCT) Oncorhynchus clarki lewisi and nonnative brook trout Salvelinus fontinalis and fish habitat characteristics in three adjacent southwestern Montana streams during 1988, 1993–1995, and 1997–1999. Delano and upper Jerry creeks had relatively undisturbed riparian forests, whereas Libby Creek's riparian forest was harvested along much (0.9 km) of the stream during 1971. Libby Creek had higher summer water temperatures (average daily temperatures were 1–2°C higher) than Delano Creek. Libby Creek also contained more woody debris, a higher percentage of fine sediments within the streambed, and a higher proportion of pool habitats than Delano and upper Jerry creeks. Brook trout dominated the trout community in Libby Creek (78– 91%), whereas WCT dominated in Delano and upper Jerry creeks (77–100%). Similarly, brook trout densities were significantly higher in Libby Creek, and WCT densities were significantly greater in Delano and upper Jerry creeks. These data suggest that brook trout invasion and the displacement of WCT in these streams may have been influenced by water temperature, debris and pool frequencies, erosion and deposition of fine sediments on the streambed, or some combination of these factors. Past research has linked changes in these physical parameters to riparian timber harvest activities. More research is needed to better quantify potential influences of abiotic factors on brook trout invasion and the subsequent displacement of WCT. Until such research is completed, resource managers who wish to protect and conserve stream populations of native WCT should consider the effects of land management and fish restoration activities on the aforementioned stream habitat conditions, especially in systems that contain or could potentially be invaded by nonnative brook trout.
Bias and Precision of Estimates from an Age-Structured Stock Assessment Program in Relation to Stock and Data Characteristics
Authors: Yin Yanshui , Sampson David B. 
Published: August 2004

Abstract
Assessments for many U.S. Pacific coast groundfish stocks have been developed using the statistical catch-at-age method known as Stock Synthesis. This study used Monte Carlo simulation and a fractional factorial experiment to evaluate the effects of input data errors and stock characteristics on bias and precision in estimates of ending exploitable biomass, rate of fishing mortality, depletion, and other output variables. Nine factors were examined: length of the data series, rate of natural mortality, shape of the fishery selectivity curve, trend in fishing mortality, recruitment pattern, and level of sampling error in the data for catch, fishing effort, a survey biomass index, and sample size for fishery and survey age compositions. Length of the data series, age composition sample size, survey biomass variability, and fishing effort variability were the most influential factors for most of the output variables. The estimates of depletion had the least bias and the estimates of starting biomass the smallest variability; the estimates of ending recruitment had the greatest bias and largest variability. For all the output variables examined the estimates appeared to be median-unbiased. For the conditions considered in the experiment, it appears that the accuracy of assessment estimates for ending exploitable biomass and projected catch would be more readily improved by increased age composition sampling than by comparable (but much more expensive) improvements in survey estimates of stock biomass.
The Efficiency of a Bycatch Reduction Device Used in Skimmer Trawls in the Florida Shrimp Fishery
Authors: Warner Daniel A. , McMillen-Jackson Anne L. , Bert Theresa M. , Crawford Charles R. 
Published: August 2004

Abstract
Of principal concern to those who regulate shrimp harvesting gear are the quantity and composition of nontargeted species (bycatch) harvested by any allowable gear type. The use of skimmer trawls in the Florida shrimp fishery is a contested issue, in part because little bycatch characterization data exist for this gear. We characterized skimmer trawl bycatch and evaluated the efficiency of the Florida Fisheye (FFE) bycatch reduction device in a skimmer trawl typically used by commercial fishermen in Apalachicola Bay, Florida, an area with an active fishery for white shrimp Litopenaeus setiferus (also known as Penaeus setiferus). In general, the finfish bycatch in a 4.9-m-long × 3-m-wide skimmer trawl net equipped with an FFE was significantly lower than that in an identical net towed simultaneously but without the FFE; the two nets, however, did not differ in the quantity of shrimp retained. The magnitude of the reduction in bycatch in the FFE-equipped net varied between seasons (spring and fall) and among finfish species and, in the case of silver seatrout Cynoscion nothus and Atlantic croaker Micropogonias undulatus, between size- (i.e., age-) groups. Preliminary tests of FFEs in skimmer trawls in North Carolina also show a reduction in bycatch; we provide further details on how bycatch reduction devices work in skimmer trawls. Overall, our results indicate that skimmer trawls equipped with FFEs should compare favorably with other allowable shrimping gear.
Use of Ultrasound Imaging and Steroid Concentrations to Identify Maturational Status in Adult Steelhead
Authors: Evans Allen F. , Fitzpatrick Martin S. , Siddens Lisbeth K. 
Published: August 2004

Abstract
We sought to develop a rapid, noninvasive, and accurate method for distinguishing prespawn (mature or maturing) adult steelhead (anadromous rainbow trout Oncorhynchus mykiss) from postspawn adults (kelts). Ultrasound images of gonads were collected, and levels of plasma testosterone (T), 11-ketotestosterone (11-KT), and 17α-hydroxy-20β-dihydroxyprogesterone (DHP) were determined for adult steelhead before and after spawning. Results demonstrated that ultrasound images provided quantifiable selection criteria (number of eggs or gonad size) for the identification of prespawn versus postspawn adults. Mature females were easily identifiable by the presence of numerous, well-developed eggs. Conversely, only a few mature eggs remained in the body cavities of female kelts. Ultrasound investigation of the maximum testis area demonstrated that testes undergo substantial size changes following spawning. Mean maximum testis area was 2.86 cm2 in prespawn males and 0.62 cm2 male kelts. Distributions of testis measurements between the two maturational types did not overlap, and results of a discriminant function analysis suggested that a classification criterion (threshold) of 1.25 cm2 could accurately distinguish prespawn males from kelts. Median concentrations of T, 11-KT, and DHP were significantly higher in prespawn males (49.6, 78.4, and 13.0 ng/mL, respectively) than in kelts (&lt;1.2, 6.6, and 1.6 ng/mL), providing an independent verification of the ultrasound technique. Despite the high degree of corroboration between ultrasound measurements of gonad size and plasma steroid levels, application of ultrasound imaging may result in some classification error (a few percentage points) if substantial gonad mass is retained in the body cavity after spawning. Use of ultrasound to accurately identify postspawn steelhead is an important first step towards development of effective kelt management practices in the Columbia River basin.
Experimental Assessment of Age-0 Largemouth Bass and Juvenile Bluegill Competition in a Small Impoundment in Virginia
Authors: Brenden Travis O. , Murphy Brian R. 
Published: August 2004

Abstract
Previous research has found that early ontogenetic stages of largemouth bass Micropterus salmoides and bluegills Lepomis macrochirus may compete for food resources in small impoundments in northern-latitudes. We experimentally assessed whether competition also might occur in a southern-latitude system by stocking fish allopatrically and sympatrically in 1.0-m3 cages within a small impoundment in Virginia and monitoring fish growth and diets. Although growth was not significantly different between bluegills stocked with and without largemouth bass, largemouth bass grew significantly larger when stocked alone than when stocked with bluegills. Although bluegills maintained similar diets in terms of sizes, numbers, and types of items consumed, largemouth bass stocked alone consumed fewer but larger items than those stocked with bluegills. Further, largemouth bass consumed higher volumetric proportions of Diptera larvae and Odonata nymphs when stocked alone than when stocked with bluegills. Of these two items, only Diptera larvae constituted a large portion of bluegill diets. Competition between largemouth bass and bluegills apparently occurs in both southern- and northern-latitude small impoundments. Competition with bluegills may result in a competitive juvenile bottleneck for largemouth bass in regions where overwinter mortality is size related, which could affect management (i.e., stocking, establishing harvest regulations) of small-impoundment fisheries.
Evaluation of Shortnose Sturgeon Spawning in the Pinopolis Dam Tailrace, South Carolina
Authors: Duncan Michelle S. , Isely J. Jeffery , Cooke Douglas W. 
Published: August 2004

Abstract
Fifty egg mats and up to five D-shaped plankton nets were deployed in the tailrace of Pinopolis Dam at river kilometer 77 on the Cooper River, South Carolina, to evaluate the spawning activity of shortnose sturgeon Acipenser brevirostrum. Spawning times were estimated by back-calculation based on developmental phase. Eggs were collected on 17 of 21 d sampled continuously from March 4 through March 25, 2002, when water temperatures were 10–16°C. A total of 31 shortnose sturgeon eggs were collected from egg mats. An additional 338 shortnose sturgeon eggs and 1 newly hatched yolk sac larva were collected from plankton nets. A minimum of 20 spawning events occurred in the tailrace during the 2002 spawning season. No relationship between mean daily discharge and spawning date was observed. Shortnose sturgeon spawned more often during the night than at any other time of day independent of generation.
Spatial Considerations in the Management of Atlantic Cod off Nova Scotia, Canada
Authors: Fu Caihong , Fanning L. Paul 
Published: August 2004

Abstract
A spatial, age-structured population dynamics model was developed for a stock of Atlantic cod Gadus morhua off eastern Nova Scotia to examine alternative management options. The model incorporates stock structure, seasonal migration, predation, Allee effects, and variation in natural mortality. The simulated dynamics of two substocks were compared under three management options: (1) historical catch levels; (2) combined management (substocks are managed as one unit) with a constant fishing mortality rate (F) of 0.4; and (3) separated management (substocks are managed individually) with the same F level. Three major conclusions emerged from the simulations. First, the population dynamics under historical catch levels tended to vary widely from complete extinction to a fourfold increase. Second, constant-F management produced stable population dynamics, reduced the probability of stock decline, and yielded a higher average catch. Third, the combined management option resulted in overfishing the more vulnerable substock; separated management helped to prevent the more vulnerable substock from collapse, but its performance was compromised when there was net immigration to the more vulnerable substock.
Status of Lake Trout Rehabilitation on Six Fathom Bank and Yankee Reef in Lake Huron
Authors: Madenjian Charles P. , Desorcie Timothy J. , McClain Jerry R. , Woldt Aaron P. , Holuszko Jeffrey D. , Bowen Charles A. 
Published: August 2004

Abstract
Six Fathom Bank, an offshore reef in the central region of Lake Huron's main basin, was stocked annually with hatchery-reared lake trout Salvelinus namaycush during 1985–1998, and nearby Yankee Reef was stocked with hatchery-reared lake trout in 1992, 1997, and annually during 1999–2001. We conducted gill-net surveys during spring and fall to evaluate performances of each of the various strains of lake trout, as well as the performance of the entire lake trout population (all strains pooled), on these two offshore reefs during 1992–2000. Criteria to evaluate performance included the proportion of “wild” fish within the population, spawner density, adult survival, growth, maturity, and wounding rate by sea lamprey Petromyzon marinus. Although naturally reproduced age-0 lake trout fry were caught on Six Fathom Bank and Yankee Reef, wild lake trout did not recruit to the adult population to any detectable degree. The density of spawning lake trout on Six Fathom Bank (&gt;100 fish/305 m of gill net) during 1995–1998 appeared to be sufficiently high to initiate a self-sustaining population. However, annual mortality estimates for all lake trout strains pooled from catch curve analyses ranged from 0.48 to 0.62, well exceeding the target level of 0.40 suggested for lake trout rehabilitation. Annual mortality rate for the Seneca Lake strain (0.34) was significantly lower than that for the Superior–Marquette (0.69) and Lewis Lake (0.69) strains. This disparity in survival among strains was probably attributable to the lower sea-lamprey-induced mortality experienced by the Seneca Lake strain. The relatively high mortality experienced by adult lake trout partly contributed to the lack of successful natural recruitment to the adult population on these offshore reefs, but other factors were probably also involved. We recommend that both stocking of the Seneca Lake strain and enhanced efforts to reduce sea lamprey abundance in Lake Huron be continued.
Impacts of Small Club Tournaments on Black Bass Populations in Connecticut and the Effects of Regulation Exemptions
Authors: Edwards Gordon P. , Neumann Robert M. , Jacobs Robert P. , O'Donnell Eileen B. 
Published: August 2004

Abstract
Annual tournament-associated mortality of largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu (≥30 cm) was quantified at Mansfield Hollow Reservoir and Gardner Lake, Connecticut, during 2001 and 2002 to determine the effects of tournaments on black bass populations. Nontournament and tournament anglers followed a 30-cm minimum length limit during both years. Tournament anglers—but not nontournament anglers—were exempt from new, more restrictive regulations (a 30–41-cm protected slot length limit at Mansfield Hollow Reservoir; a 41-cm minimum length limit at Gardner Lake) imposed in 2002. Annual tournament-associated mortality of largemouth bass was 2.4–8.4% of total annual mortality, 1.0–3.2% of the population size, and 2.0–20.8% of annual fishing mortality. For smallmouth bass, tournament-associated mortality was approximately 7% of total annual mortality, 4% of the population size, and 29–52% of annual fishing mortality. Based on the levels of total annual mortality, annual fishing mortality, and annual tournament-associated mortality, impacts of tournament angling appeared low in these two lakes. Tournament-associated impacts would have been lower if anglers were prohibited from exemptions. If exemptions were prohibited year-round or only during the summer, 80–94% of the tournament catch would have been immediately released. Relative to fishing effort, tournament anglers in Connecticut contributed a greater proportion of annual fishing mortality than nontournament anglers. In lakes where tournament-associated mortality is high, prohibiting exemptions (especially during summer) may help to reduce tournament-associated mortality. In lakes with low tournament impacts, allowing exemptions (except during summer) may protect tournament angling opportunities for most of the fishing season, while at the same time decreasing tournament-associated mortality during the warmest months.
The Importance of Beaver Ponds to Coho Salmon Production in the Stillaguamish River Basin, Washington, USA
Authors: Pollock Michael M. , Pess George R. , Beechie Timothy J. , Montgomery David R. 
Published: August 2004

Abstract
The use of beaver Castor canadensis ponds by juvenile coho salmon Oncorhynchus kisutch and other fishes has been well established. However, the population-level effects on coho salmon resulting from the widespread removal of millions of beaver and their dams from Pacific Coast watersheds have not been examined. We assessed the current and historic distributions of beaver ponds and other coho salmon rearing habitat in the Stillaguamish River, a 1,771-km2 drainage basin in Washington and found that the greatest reduction in coho salmon smolt production capacity originated from the extensive loss of beaver ponds. We estimated the current summer smolt production potential (SPP) to be 965,000 smolts, compared with a historic summer SPP of 2.5 million smolts. Overall, current summer habitat capacity was reduced by 61% compared with historic levels, most of the reduction resulting from the loss of beaver ponds. Current summer SPP from beaver ponds and sloughs was reduced by 89% and 68%, respectively, compared with historic SPP. A more dramatic reduction in winter habitat capacity was found; the current winter SPP was estimated at 971,000 smolts, compared with a historic winter SPP of 7.1 million smolts. In terms of winter habitat capacity, we estimated a 94% reduction in beaver pond SPP, a 68% loss in SPP of sloughs, a 9% loss in SPP of tributary habitat, and an overall SPP reduction of 86%. Most of the overall reduction resulted from the loss of beaver ponds. Our analysis suggests that summer habitat historically limited smolt production capacity, whereas both summer and winter habitats currently exert equal limits on production. Watershed-scale restoration activities designed to increase coho salmon production should emphasize the creation of ponds and other slow-water environments; increasing beaver populations may be a simple and effective means of creating slow-water habitat.
Fish Total Length Measurement Error from Recreational Anglers: Causes and Contribution to Noncompliance for the Mille Lacs Walleye Fishery
Authors: Page Kevin S. , Grant Gerold C. , Radomski Paul , Jones Thomas S. , Bruesewitz Richard E. 
Published: August 2004

Abstract
To estimate angler noncompliance with size limits due to measurement error by anglers, we used estimates of measurement error derived from (1) lengths of walleye Sander vitreus tagged and measured by biologists subsequently caught and voluntarily measured by anglers and (2) from dead walleyes of known length that anglers voluntarily measured during interviews at lake access sites. We also investigated the potential for postmortem changes in fish length. Monte Carlo simulations suggested that angler measurement error accounted for 41–100% of observed angler noncompliance with a 14-in to 16-in harvest slot limit for Mille Lacs lake, Minnesota. Simulations underestimated harvest (retention) rates for walleyes of lengths approaching the harvest slot boundaries compared with actual measures by anglers of the tagged fish they caught; this suggests greater attentiveness of anglers at measuring fish near the slot limits or angler intent to retain protected fish. When reporting total lengths of the tagged walleyes they caught, more anglers rounded measurements to 1-in or 1/2-in increments, whereas more anglers rounded to 1/4-in or 1/8-in increments when reporting lengths of tagged walleyes they retained or when measuring dead fish during interviews. Length measurement errors may be compounded by postmortem physical changes in harvested fish. Although postmortem changes will not influence angler retention of fish, temporal changes in the physical condition of fish may influence whether a creel clerk or conservation officer observes a fish as noncompliant. Understanding the level and characteristics of measurement error is important for understanding the factors influencing angler noncompliance with size limits.
Effects of Holding Environment and Exercise Conditioning on Swimming Performance of Southwestern Native Fishes
Authors: Ward David L. , Hilwig Kara D. 
Published: August 2004

Abstract
Rare native fish are often reared in ponds or tanks at hatcheries for later stocking into streams with depleted populations. Fish reared in standing water may experience increased stress, downstream displacement, or high predation mortality when released into lotic environments. We compared the swimming performance of captive fish held in standing water, captive fish exercised in flowing water, and wild fish captured from a stream to evaluate the effects of exercise conditioning and holding environment on swimming performance. The swimming performance of flannelmouth sucker Catostomus latipinnis, bonytail Gila elegans, razorback sucker Xyrauchen texanus, and spikedace Meda fulgida held in standing water increased by 10, 15, 26, and 40%, respectively, after exercise conditioning in flowing water (10–100 cm/s) for as little as 10 d. Exercising fish reared in standing water may improve swimming performance and increase survival.
Age Structure and Mortality of Walleyes in Kansas Reservoirs: Use of Mortality Caps to Establish Realistic Management Objectives
Authors: Quist Michael C. , Stephen James L. , Guy Christopher S. , Schultz Randall D. 
Published: August 2004

Abstract
Age structure, total annual mortality, and mortality caps (maximum mortality thresholds established by managers) were investigated for walleye Sander vitreus (formerly Stizostedion vitreum) populations sampled from eight Kansas reservoirs during 1991–1999. We assessed age structure by examining the relative frequency of different ages in the population; total annual mortality of age-2 and older walleyes was estimated by use of a weighted catch curve. To evaluate the utility of mortality caps, we modeled threshold values of mortality by varying growth rates and management objectives. Estimated mortality thresholds were then compared with observed growth and mortality rates. The maximum age of walleyes varied from 5 to 11 years across reservoirs. Age structure was dominated (≥72%) by walleyes age 3 and younger in all reservoirs, corresponding to ages that were not yet vulnerable to harvest. Total annual mortality rates varied from 40.7% to 59.5% across reservoirs and averaged 51.1% overall (SE = 2.3). Analysis of mortality caps indicated that a management objective of 500 mm for the mean length of walleyes harvested by anglers was realistic for all reservoirs with a 457-mm minimum length limit but not for those with a 381-mm minimum length limit. For a 500-mm mean length objective to be realized for reservoirs with a 381-mm length limit, managers must either reduce mortality rates (e.g., through restrictive harvest regulations) or increase growth of walleyes. When the assumed objective was to maintain the mean length of harvested walleyes at current levels, the observed annual mortality rates were below the mortality cap for all reservoirs except one. Mortality caps also provided insight on management objectives expressed in terms of proportional stock density (PSD). Results indicated that a PSD objective of 20–40 was realistic for most reservoirs. This study provides important walleye mortality information that can be used for monitoring or for inclusion into population models; these results can also be combined with those of other studies to investigate large-scale differences in walleye mortality. Our analysis illustrates the utility of mortality caps for monitoring walleye populations and for establishing realistic management goals.