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At least 685 records · Page 38Linked to original sources
USGS1999

Migration timing of Atlantic salmon smolts relative to environmental and physiological factors

We determined the migration timing of fry‐stocked smolts of Atlantic salmon Salmo salar relative to environmental and physiological factors, by using net weirs and counting fences in three tributaries of the West River, Vermont. Smolt migration began in late April and early May when water temperature was 5°C, peak movements occurred in early and mid‐May at temperatures exceeding 8°C, and migration was complete by early June. Within this seasonal window, significant differences in migration timing and gill Na + ,K + ‐ATPase activity occurred among tributaries. In both years of the study, smolts tended to migrate earlier and exhibit greater gill Na + ,K + ‐ATPase activity in the warmest tributary than in the coolest tributary. Smolt migration timing differed most among tributaries in mid‐May when (1) water temperatures were more than 8°C, (2) smolts peaked in gill Na + ,K + ‐ATPase activity, and (3) discharge peaked, stimulating smolt migration. Smolts captured after the migratory period had lower gill Na + ,K + ‐ATPase activity than migrating smolts. Relating smolt physiology to migration was crucial for explaining complex interactions among water temperature, discharge, and smolt behavior during both the onset and cessation of migratory activity. Because the period between onset of migration and loss of smolt physiological characteristics may be brief, delays in downstream passage that may occur at dams must be minimized to maximize the successful recruitment of smolts to the marine environment.

Transactions of the American Fisheries Society↗
USGS1999

Structure and stability of the midsummer fish communities in Chequamegon Bay, Lake Superior, 1973-1996

We analyzed the structure and stability of the summer fish communities of Chequamegon Bay, Lake Superior, during 1973–1996 from data collected with bottom trawls at 39 stations. Fifty‐three taxa were collected during the study, but we found that relative abundances for 20 taxa described most of the internal variability of the data for all taxa. Abundance data for the 20 species showed that two communities existed in the bay; one inhabited shallow water (≤3.0 m) whereas the other inhabited deeper water (>3.0 m). No temporal patterns of change were found in the structure of the shallow‐water community, whose variation was best described by abundances of 12 taxa. The deepwater community, whose variation was best described by eight taxa, underwent three periods ofstability; 1973–1978, 1979–1988, and 1989–1996. We conclude that the shallow‐water community was stable throughout the 24 years studied. Dynamics of the deepwater community were greatly affected by changes in stocking rates of lake trout Salvelinus namaycush and splake (hybrid of brook trout S. fontinalis × lake trout) and by rehabilitation of populations of lake herring Coregonus artedi and lake whitefish C. clupeaformis. Information on the existence, structure, stability, and habitats of fish communities in the bay will be useful for assessing changes in those communities that result from further changes in the bay or lake ecosystems.

Wisconsin↗
USGS1999

Testing and extension of a sea lamprey feeding model

A previous model of feeding by sea lamprey Petromyzon marinus predicted energy intake and growth by lampreys as a function of lamprey size, host size, and duration of feeding attachments, but it was applicable only to lampreys feeding at 10°C and it was tested against only a single small data set of limited scope. We extended the model to other temperatures and tested it against an extensive data set (more than 700 feeding bouts) accumulated during experiments with captive sea lampreys. Model predictions of instantaneous growth were highly correlated with observed growth, and a partitioning of mean squared error between model predictions and observed results showed that 88.5% of the variance was due to random variation rather than to systematic errors. However, deviations between observed and predicted values varied substantially, especially for short feeding bouts. Predicted and observed growth trajectories of individual lampreys during multiple feeding bouts during the summer tended to correspond closely, but predicted growth was generally much higher than observed growth late in the year. This suggests the possibility that large overwintering lampreys reduce their feeding rates while attached to hosts. Seasonal or size-related shifts in the fate of consumed energy may provide an alternative explanation. The lamprey feeding model offers great flexibility in assessing growth of captive lampreys within various experimental protocols (e.g., different host species or thermal regimes) because it controls for individual differences in feeding history.

Transactions of the American Fisheries Society↗
USGS1999

Field test of two energetic models for yellow perch

Field data from a population of yellow perch Perca flavescens in Saginaw Bay, Lake Huron, were used to evaluate the ability of two energetic models to predict consumption by yellow perch. Field estimates of daily ration for age‐1–4 fish during May through October 1987 and 1988 were compared with independent predictions made by the Wisconsin energetic model and an energetic model developed by Karås and Thoresson. Predictions of daily ration using the Wisconsin model were lower than daily rations estimated from field data for all ages, primarily due to poor model–field agreement at temperatures above 22°C. This caused estimates of cumulative consumption from the Wisconsin model to be 25–50% lower than field estimates. Predictions of daily ration by the Karås–Thoresson model agreed with field estimates over a temperature range of 10–26°C for age‐1–3 yellow perch but not for older fish. Despite improvement, model predictions of cumulative consumption were 2–35% lower than field estimates. Although these tests of predicted and estimated rations may provide insight into which model produced more accurate results, it must be emphasized that field measures of daily ration are also estimates and may be in error, particularly at temperatures above 22°C where gastric evacuation rates were estimated. The Karås–Thoresson modification of the Wisconsin energetic model produced better fits to field ration data and is recommended for model applications.

Michigan↗
USGS1999

Vertical migration and nighttime distribution of adult bloaters in Lake Michigan

The vertical migration and nighttime vertical distribution of adult bloaters Coregonus hoyi were investigated during late summer in Lake Michigan using acoustics simultaneously with either midwater or bottom trawling. Bloaters remained on or near bottom during the day. At night, bloaters were distributed throughout 30–65 m of water, depending on bottom depth. Shallowest depths of migration were not related to water temperature or incident light. Maximum distances of migration increased with increasing bottom depth. Nighttime midwater densities ranged from 0.00 to 6.61 fish/1,000 m 3 and decreased with increasing bottom depth. Comparisons of length distributions showed that migrating and nonmigrating bloaters did not differ in size. However, at most sites, daytime bottom catches collected a greater proportion of larger individuals compared with nighttime midwater or bottom catches. Mean target strengths by 5‐m strata indicated that migrating bloaters did not stratify by size in the water column at night. Overall, patterns in frequency of empty stomachs and mean digestive state of prey indicated that a portion of the bloater population fed in the water column at night. Bloater diet composition indicated both midwater feeding and bottom feeding. In sum, although a portion of the bloater population fed in the water column at night, bloaters were not limited to feeding at this time. This research confirmed that bloaters are opportunistic feeders and did not fully support the previously proposed hypothesis that bloater vertical migration is driven by the vertically migrating macroinvertebrate the opossom shrimp Mysis relicta .

Illinois, Indiana, Michigan, Wisconsin↗
USGS1999

Dietary effects of metals-contaminated invertebrates from the Coeur d'Alene River, Idaho, on cutthroat trout

Benthic macroinvertebrates with elevated concentrations of metals were collected from the Coeur d'Alene (CDA) River, Idaho, pasteurized, and fed to cutthroat trout Oncorhynchus clarki in the laboratory from start of feeding until 90 d posthatch. Invertebrates were collected from two sites known to contain elevated concentrations of metals: near Pinehurst in the South Fork of the CDA River and at Cataldo, approximately 5 km below the confluence of the South Fork and the North Fork. Invertebrates collected from a relatively clean site in the North Fork were used as a reference diet. We performed measurements of fish health that indicate reduced fitness of fish fed the South Fork and Cataldo diets. Effects measured were reduced feeding activity, increased number of macrophage aggregates and hyperplasia of cells in the kidney, degeneration of mucosal epithelium in the pyloric caecae, and metallothionein induction. These effects would likely reduce growth and survival of fish in the wild. Vacuolization of glial cells were also observed in fish fed the Cataldo diet. Metals in the water often exacerbated the histological effects observed. Although the invertebrates collected near Cataldo had lower concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) than the invertebrates from the South Fork, fish fed the Cataldo diet had equally high or higher concentrations of all metals except as by day 44. The Cataldo diet also caused the most deleterious effects on survival and growth. These findings are especially important for early life stage fish, whose diet consists wholly of benthic macroinvertebrates. Therefore, fish feeding on invertebrates in the CDA River below the Bunker Hill smelting complex are at risk of reduced fitness.

Transactions of the American Fisheries Society↗
USGS1999

Effect of suspended sediment on vulnerability of young razorback suckers to predation

The decline of native fishes in North America is principally a result of altered habitats, and the impact of mainstream dams has accounted for many of the habitat changes. Diminished turbidity, and introduced nonnative predators were investigated as possible reasons for the decline of endangered razorback suckers Xyrauchen texanus in the Colorado River. In laboratory tests, young razorback suckers selected clear water over two water samples with higher concentrations of suspended sediment. In clear water, however, young razorback suckers were extremely susceptible to predation; native Colorado squawfish Ptychocheilus lucius consumed 90% of test razorback suckers, and nonnative green sunfish Lepomis cyanellus consumed 99.6%. As turbidity increased, razorback sucker predator avoidance improved and differences in predator success disappeared. Winter–spring spawning by razorback suckers in Lake Mohave, along with the extreme susceptibility of larvae to predation in clear water, may account for total recruitment failure in that lake. However, in upper basin rivers, suspended sediments remain high enough to limit predation by fishes tested, suggesting that other impacts, including contaminants and lack of floodplain habitat, may be thwarting recruitment in those rivers.

Transactions of the American Fisheries Society↗
USGS1999

Laboratory evaluation of a lake trout bioenergetics model

Lake trout Salvelinus namaycush , aged 3 and 6 years and with average weights of 700 and 2,000 g, were grown in laboratory tanks for up to 407 d under a thermal regime similar to that experienced by lake trout in nearshore Lake Michigan. Lake trout were fed alewife Alosa pseudoharengus and rainbow smelt Osmerus mordax , prey typical of lake trout in Lake Michigan. Of the 120 lake trout used in the experiment, 40 were fed a low ration (0.25% of their body weight per day), 40 were fed a medium ration (0.5% of their body weight per day), and 40 were fed a high ration (ad libitum). We measured consumption and growth, and we compared observed consumption with that predicted by the Wisconsin bioenergetics model. For lake trout fed the medium ration, model predictions for monthly consumption were unbiased. Moreover, predicted cumulative consumption by medium-ration lake trout for the entire experiment (320 d for smaller lake trout and 407 d for larger lake trout) agreed quite well with observed cumulative consumption; predictions were as close as within 0.1 to 5.2% of observed cumulative consumption. Even so, the model consistently overestimated consumption by low-ration fish and underestimated consumption by high-ration fish. The bias was significant in both cases, but was more severe for the low-ration trout. Because the low-ration and high-ration regimes were probably unrealistic for lake trout residing in Lake Michigan and because the model fit our laboratory data rather well for medium-ration trout, we conclude that applying the Wisconsin bioenergetics model to the Lake Michigan lake trout population in order to estimate the amount of prey fish consumed by lake trout each year is appropriate.

Transactions of the American Fisheries Society↗
USGS1999

Acute toxicity of an acid mine drainage mixing zone to juvenile bluegill and largemouth bass

The toxicity of an acid mixing zone produced at the confluence of a stream that was contaminated by acid mine drainage (AMD) and a pH-neutral stream was investigated in toxicity tests with juvenile bluegill Lepomis macrochirus and largemouth bass Micropterus salmoides. Fish mortalities in instream cages located in the mixing zone, below the mixing zone, and upstream in both tributaries were compared to determine relative toxicity at each site. In all tests and for both species, significantly higher mortality was observed in the mixing zone than at any other location, including the acid stream, which had lower pH (2.9-4.3). The mixing zone was defined chemically by rapid precipitation of dissolved aluminum and iron, which arrived from the low-pH stream, and by the presence of white precipitates, which were attached to the substratum and which extended below the confluence. Possible seasonal changes in mixing zone toxicity were investigated by conducting field tests with bluegill in June, July, and August 1996 and in January 1997 and by conducting field tests with largemouth bass in April and May 1997. Toxicity was not significantly different at the extremes of temperature, pH, and metal concentration that occurred in June and July, as compared with January. Toxicity was significantly lower in August; however, elevated stream discharge during the August test may have disturbed mixing zone characteristics. High toxicity in AMD mixing zones may lower the survival of fishes in streams, reduce available habitat, and impede movements of migratory fish.

Transactions of the American Fisheries Society↗
USGS1999

The growth-temperature relation of juvenile lake whitefish

The lake whitefish Coregonus clupeaformis supports major commercial fisheries in Lakes Superior, Huron, and Michigan, where it is managed on a sustained-yield basis; it also supports a recreational hook-and-line fishery in some Great Lakes embayments and nearshore areas. To better understand habitat use by juvenile lake whitefish in the Great Lakes, we acclimated groups of test fish in the laboratory to 5, 10, 15, 18, 21, and 24°C and fed them to excess twice daily for 55 d. The test fish increased in length and weight at all of the test temperatures and at the end of the study were heaviest and longest at 18.1°C. A curve fitted to the specific growth rate data indicated that the optimum temperature for growth was 18.5°C and, thus, that the fundamental thermal niche for juvenile lake whitefish is 15.5–19.5°C. Our results support the limited, published information on thermal ecology of wild, free-ranging juvenile lake whitefish in the Great Lakes.

Transactions of the American Fisheries Society↗
USGS1999

Influence of externally attached trasmitters on the swimming performance of juvenile white sturgeon

We measured the critical swimming speed of juvenile white sturgeons Acipenser transmontanus equipped with externally attached dummy ultrasonic transmitters and of untagged control fish in the laboratory. White sturgeons ranging from 31.9 to 37.0 cm fork length were subjected to one of three treatments: Control (handled but not tagged), tag attached below the dorsal fin, and tag attached with the anterior insertion point between the fourth and fifth dorsal scutes. Although transmitters were of recommended weight, we found that the swimming performance of tagged white sturgeons was significantly less than that of untagged control fish. Swimming performance of tagged fish was not differentially affected by tag location. Our results suggest that data from ultrasonic telemetry studies of externally tagged juvenile white sturgeons should be interpreted with caution due to the reduced swimming performance caused by external transmitters.

Transactions of the American Fisheries Society↗
USGS1999

Growth, smoltification, and smolt-to-adult return of spring chinook salmon from hatcheries on the Deschutes river, Oregon

The relationship between smoltification and smolt-to-adult return (SAR) of spring chinook salmon Oncorhynchus tshawytscha from the Deschutes River, Oregon, was examined for four release groups in each of three successive years. Fish were reared, marked with coded wire tags, and released from Round Butte Hatchery, Pelton Ladder rearing facility, and Warm Springs National Fish Hatchery. Smolt releases occurred in nearly the same place at similar times, allowing a direct comparison of SAR to several characters representing smolt quality. Return rates varied significantly among facilities, varying over an order of magnitude each year. The highest average SAR was from Pelton Ladder, the lowest was from Warm Springs. Each of the characters used as metrics of smoltification - fish size, spring growth rate (February-April), condition factor, plasma hormone concentration (thyroxine, cortisol, and insulin-like growth factor-I [IGF-I]), stress challenge, gill Na+,K+-ATPase activity, and liver glycogen concentration - varied significantly among facilities and seasonally within hatchery groups. However, only spring growth rate, gill ATPase activity, and plasma IGF-I concentration showed significant relationships to SAR. These characters and SAR itself were consistently lower for fish released from Warm Springs Hatchery than for fish from Round Butte Hatchery and Pelton Ladder. This demonstrates that differences in the quality of fish released by facilities may have profound effects on subsequent survival and suggests that manipulations of spring growth rate may be used to influence the quality of smolts released from facilities.

Oregon↗
USGS2000

Composition of fish communities in relation to stream acidification and habitat in the Neversink River, New York

The effects of acidification in lotic systems are not well documented. Spatial and temporal variability of habitat and water quality complicate the evaluation of acidification effects in streams and rivers. The Neversink River in the Catskill Mountains of southeastern New York, the tributaries of which vary from well buffered to severely acidified, provided an opportunity to investigate the extent and magnitude of acidification effects on fish communities of headwater systems. Composition of fish communities, water quality, stream hydrology, stream habitat, and physiographic factors were characterized from 1991 to 1995 at 16 first- to fourth-order sites in the basin. Correlation and regression analyses were used to develop empirical models and to assess the relations among fish species richness, total fish density, and total fish biomass and environmental variables. Chronic and episodic acidification and elevated concentrations of inorganic monomeric aluminum were common, and fish populations were rare or absent from several sites in the upper reaches of the basin; as many as six fish species were collected from sites in the lower reaches of the basin. Species distributions and species richness were most highly related to stream pH, acid-neutralizing capacity (ANC), inorganic monomeric aluminum (Al im ), calcium (Ca) 2+ , and potassium (K) + concentrations, site elevation, watershed drainage area, and water temperature. Fish density was most highly related to stream pH, Al im , ANC, K + , Ca 2+ , and magnesium (Mg) 2+ concentrations. Fish biomass, unlike species richness and fish density, was most highly related to physical habitat characteristics, water temperature, and concentrations of Mg 2+ and silicon. Acidity characteristics were of secondary importance to fish biomass at all but the most severely acidified sites. Our results indicate that (1) the total biomass of fish communities was not seriously affected at moderately to strongly acidified sites; (2) species richness and total density of fish were adversely affected at strongly to severely acidified sites; and (3) possible changes in competitive interactions may mitigate negative effects of acidification on fish communities in parts of the Neversink River Basin.

New York↗
USGS2000

Effects of fall-to-winter changes in habitat and frazil ice on the movements and habitat use of juvenile rainbow trout in a Wyoming tailwater

Overwinter declines in the abundance of small rainbow trout Oncorhynchus mykiss have been observed in a section of the Big Horn River that lies downstream from Boysen Reservoir, where reservoir releases prevent surface ice formation. To provide insight into the possible causes of these declines in abundance, radiotelemetry was used to determine movement and microhabitat use of juvenile (20–25 cm total length) rainbow trout during the fall and winter of 1995–1996. Throughout the fall and winter, both stocked (hatchery) and naturally spawned (wild) fish were generally found in main-channel pools with cover that reduced current velocities to less than 2 cm/s near the bottom and with nearby (<2 m) water velocities that were greater than 15 cm/s. These locations provided refuges from the current, with adjacent flowing water that could deliver drifting aquatic invertebrates. The fish were generally associated with cover that was formed by aquatic vegetation early in the fall, but they shifted to cobble and boulder cover (in deeper water) as the aquatic vegetation decomposed and as winter progressed. Episodes of frazil ice in January and early February were associated with movements of wild fish in the upstream portion of the study area—from normal activity areas to refuges at the bottom of deep pools or under shelf ice in shallow water near shore. Frazil-ice episodes often initiated long-term movements among fish. Our results suggest that changing habitat features from fall to winter and frazil-ice episodes can cause juvenile rainbow trout to move and to modify their habitat use, depending on their location in a tailwater.

Wyoming↗
USGS2000

Interaction of infection with Renibacterium salmoninarum and physical stress in juvenile chinook salmon: Physiological responses, disease progression, and mortality

We experimentally infected juvenile spring chinook salmon Oncorhynchus tshawytscha with Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease (BKD), in order to compare the physiological responses of Rs-infected and Rs-noninfected fish to a series of multiple, acute stressors and to determine whether exposure to these stressors worsens the infection and leads to increased mortality. After subjecting groups of fish to a waterborne challenge of Rs, we sampled them biweekly to monitor infection levels, mortality, and some stress-related physiological changes. As infections worsened, fish developed decreased hematocrits and blood glucose levels and increased levels of cortisol and lactate, indicating that BKD is stressful, particularly during the later stages. Eight weeks after the challenge, when fish had moderate to high infection levels, we subjected them, along with unchallenged control fish, to three 60-s bouts of hypoxia, struggling, and mild agitation that were separated by 48-72 h. Our results indicate that the imposition of these stressors on Rs-infected fish did not lead to higher infection levels or increased mortality when compared with diseased fish that did not receive the stressors. Furthermore, the kinetics of plasma cortisol, glucose, and lactate over a 24-h period following each application of the stressor were similar between fish with moderate to high Rs infections and those that had low or no detectable infection. Some differences in the stress responses of these two groups did exist, however. Most notably, fish with moderate to high Rs infections had higher titers of cortisol and lactate prior to each application of the stressor and also were unable to consistently elicit a significant hyperglycemia in response to the stressors. Collectively, our results should be important in understanding the impact that BKD has on the survival of juvenile salmonids, but we caution that our results represent the combined effects of one type of stressor and one disease only and probably cannot be applied to other scenarios.

Transactions of the American Fisheries Society↗
USGS2000

Progression and severity of gas bubble trauma in juvenile salmonids

We conducted laboratory experiments to assess the progression and to quantify the severity of signs of gas bubble trauma (GBT) in juvenile chinook salmon Oncorhynchus tshawytscha and steelhead Oncorhynchus mykiss exposed to different levels of total dissolved gas (TDG), and we attempted to relate these signs to the likelihood of mortality. When fish were exposed to 110% TDG for up to 22 d, no fish died, and there were few signs of GBT in the lateral line or gills. Bubbles in the fins, however, were relatively common, and they progressively worsened over the experimental period. When fish were exposed to 120% TDG for up to 140 h, chinook salmon had an LT20 (time necessary to kill 20% of the fish) ranging from 40 to 120 h, whereas steelhead had LT20s ranging from 20 to 35 h. In steelhead, bubbles in the lateral line, fins, and gills displayed poor trends of worsening over time, showed substantial interindividual variability, and were poorly related to mortality. In chinook salmon, only bubbles in the lateral line showed a distinct worsening over time, and the severity of bubbles in the lateral line was highly correlated with mortality. When fish were exposed to 130% TDG for up to 11 h, LT20s for chinook salmon ranged from 3 to 6 h, whereas those for steelhead ranged from 5 to 7 h. In chinook salmon, bubbles in the lateral line and fins, but not those in the gills, showed distinct trends of worsening over time. In steelhead, bubbles in the lateral line displayed the most significant trend of progressive severity. In both species at 130% TDG, the severity of all GBT signs was highly correlated with mortality. The progressive nature of GBT and the methods we developed to examine fish for GBT may be useful for monitoring programs that aim to assess the severity of dissolved gas supersaturation exposures experienced by fish in the wild. However, the efficacy of such programs seems substantially hindered by problems associated with (1) the variable persistence of GBT signs; (2) the inconsistent relation of GBT signs to mortality; (3) the insufficient knowledge of the relation between exposure history and GBT sign development for fish in the wild; and (4) an extreme amount of interindividual variation in terms of susceptibility to GBT.

Transactions of the American Fisheries Society↗
USGS2000

Growth and food consumption by tiger muskellunge: Effects of temperature and ration level on bioenergetic model predictions

We measured growth of age-0 tiger muskellunge as a function of ration size (25, 50, 75, and 100% C max ) and water temperature (7.5–25°C) and compared experimental results with those predicted from a bioenergetic model. Discrepancies between actual and predicted values varied appreciably with water temperature and growth rate. On average, model output overestimated winter consumption rates at 10 and 7.5°C by 113 to 328%, respectively, whereas model predictions in summer and autumn (20–25°C) were in better agreement with actual values (4 to 58%). We postulate that variation in model performance was related to seasonal changes in esocid metabolic rate, which were not accounted for in the bioenergetic model. Moreover, accuracy of model output varied with feeding and growth rate of tiger muskellunge. The model performed poorly for fish fed low rations compared with estimates based on fish fed ad libitum rations and was attributed, in part, to the influence of growth rate on the accuracy of bioenergetic predictions. Based on modeling simulations, we found that errors associated with bioenergetic parameters had more influence on model output when growth rate was low, which is consistent with our observations. In addition, reduced conversion efficiency at high ration levels may contribute to variable model performance, thereby implying that waste losses should be modeled as a function of ration size for esocids. Our findings support earlier field tests of the esocid bioenergetic model and indicate that food consumption is generally overestimated by the model, particularly in winter months and for fish exhibiting low feeding and growth rates.

Transactions of the American Fisheries Society↗
USGS2000

Natural and anthropogenic influences on the distribution of the threatened Neosho madtom in a midwestern warmwater stream

We attempted to discern the contributions of physical habitat, water chemistry, nutrients, and contaminants from historic lead–zinc mining activities on the riffle‐dwelling benthic fish community of the Spring River, a midwestern warmwater stream that originates in Missouri and flows into Kansas and Oklahoma. The Spring River has a fish community that includes the Neosho madtom Noturus placidus , a species federally listed as threatened. Although anthropogenic factors such as contaminants limited populations and densities of fishes, an integrated assessment of natural and anthropogenic factors was necessary to effectively estimate the influence of the latter. Fish populations in the Spring River, especially Neosho madtoms, seem to be limited by the presence of cadmium, lead, and zinc in water and in benthic invertebrate food sources and by physical habitat. The population density and community structure of fish in the Spring River also seem to be related to water chemistry and nutrients. Concurrently, diminished food availability may be limiting fish populations at some sites where Neosho madtoms are not found. Many of the natural factors that may be limiting Neosho madtom and other riffle‐dwelling fish populations in the Spring River probably are characteristic of the physiographic region drained by the upper reach and many of the tributaries of the Spring River. Our results indicate that competition between the Neosho madtom and other species within the riffle‐dwelling fish community is an unlikely cause of Neosho madtom population limitation in the Spring River.

Arkansas, Kansas, Missouri, Oklahoma↗