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USGS2008

Habitat use of juvenile pallid sturgeon and shovelnose sturgeon with implications for water-level management in a downstream reservoir

Natural recruitment of pallid sturgeon Scaphirhynchus albus has not been observed in the Missouri River above Fort Peck Reservoir, Montana, for at least 20 years. To augment the population, age-1 hatchery-reared juvenile pallid sturgeon were released in 1998. The objective of this study was to evaluate the habitat use of these fish and compare it with that of indigenous shovelnose sturgeon S. platorynchus. Twenty-nine juvenile pallid sturgeon and 21 indigenous shovelnose sturgeon were implanted with radio transmitters in 2003 and 2004. The two species showed no differences in habitat use in terms of mean depth, cross-sectional relative depth, longitudinal relative depth, column velocity, bottom velocity, and channel width. However, there were seasonal differences within both species for cross-sectional relative depth, column velocity, and channel width. Both shovelnose sturgeon and juvenile pallid sturgeon were primarily associated with silt and sand substrate. However, shovelnose sturgeon were associated with gravel and cobble substrate more than juvenile pallid sturgeon. Shovelnose sturgeon and juvenile pallid sturgeon both selected reaches without islands and avoided reaches with islands; the two species also selected main-channel habitat and avoided secondary channels. Mean home range was similar between juvenile pallid sturgeon (15 km; 90% confidence interval, ??5.0 km) and shovelnose sturgeon (16.5 km; ??4.7 km). Spatial distribution differed between the two species, with shovelnose sturgeon using upstream areas more often than juvenile pallid sturgeon. Twenty-eight percent of juvenile pallid sturgeon frequented 60 km of lotie habitat that would be inundated by Fort Peck Reservoir at maximum pool. Stocking juvenile pallid sturgeon can successfully augment the wild pallid sturgeon population in the Missouri River above Fort Peck Reservoir, which is crucial to the long-term recovery of the species. However, water-level management in downstream reservoirs such as Fort Peck can influence the amount of habitat available for pallid sturgeon. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2008

Field-based evaluations of horizontal flat-plate fish screens

Diversions from streams are often screened to prevent the loss of or injury to fish. Hydraulic criteria meant to protect fish that encounter screens have been developed, but primarily for screens that are vertical to the water flow rather than horizontal. For this reason, we measured selected hydraulic variables and released wild rainbow trout Oncorhynchus mykiss over two types of horizontal flat-plate fish screens in the field. Our goal was to assess the efficacy of these screens under a variety of conditions in the field and provide information that could be used to develop criteria for safe fish passage. We evaluated three different invertedweir screens over a range of stream (0.24-1.77 m3/s) and diversion flows (0.10-0.31 m3/s). Approach velocities (AVs) ranged from 3 to 8 cm/s and sweeping velocities (SVs) from 69 to 143 cm/s. We also evaluated a simple backwatered screen over stream flows of 0.23-0.79 m3/s and diversion flows of 0.08-0.32 m3/s. The mean SVs for this screen ranged from 15 to 66 cm/s and the mean AVs from 1 to 5 cm/s. The survival rates of fish held for 24 h after passage over these screens exceeded 98%. Overall, the number of fish-screen contacts was low and the injuries related to passage were infrequent and consisted primarily of minor fin injuries. Our results indicate that screens of this type have great potential as safe and effective fish screens for small diversions. Care must be taken, however, to avoid operating conditions that produce shallow or no water over the screen surface, situations of high AVs and low SVs at backwatered screens, and situations producing a localized high AV with spiraling flow. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2008

Fish passage in a western Iowa stream modified by grade control structures

Grade control structures (GCSs) are commonly used in streams of western Iowa to control bank erosion and channel headcutting but may be barriers to fish passage. From May 2002 to May 2006, we used mark-recapture methods to evaluate fish passage over a total of five GCSs, ranging in slope (run : rise) from 13:1 to 18:1 in Turkey Creek, Cass County, Iowa. Three structures, over which limited fish movement was documented from 2002 to 2004, were modified in the winter of 2004-2005 to facilitate fish passage. Before modification, the majority of recaptured fish were recaptured at the station where they were originally marked; only 1% displayed movement between sites and either upstream or downstream over a GCS. After modification fish passage improved, 14% of recaptured fish displayed movement either upstream or downstream over a GCS. Individuals of four target species - channel catfish Ictalurus punctatus, yellow bullhead Ameiurus natalis, black bullhead A. melas, and creek chub Semotilus atromaculatus - passed over at least one modified structure. The majority of documented movements over GCSs were in the upstream direction and occurred in late spring and early summer, when streamflow was relatively high. Although we documented low numbers of fish passing both upstream and downstream over GCSs, these structures are probably barriers to fish movement during periods of low flow and when there is a structural failure, such as in-channel movement of riprap. Grade control structures are pervasive in western Iowa streams; nearly every low-order stream contains at least one instream structure. To sustain fish populations, management efforts should focus on constructing or modifying GCSs to allow fish passage. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2008

Fish assemblages in a western Iowa stream modified by grade control structures

Over 400 riprap grade control structures (GCSs) have been built in streams of western Iowa to reduce erosion and protect bridges, roads, and farmland. In conjunction with a companion study evaluating fish passage over GCSs in Turkey Creek, we evaluated the differences in fish assemblage and habitat characteristics in reaches immediately downstream from GCSs (GCS sites) and reaches at least 1 km from any GCS (non-GCS sites). The GCS sites were characterized by greater proportions of pool habitat, maximum depths, fish biomass, and abundance of juvenile largemouth bass Micropterus salmoides than were non-GCS sites. Index of biotic integrity (IBI) scores were poor or fair (<43 on a 0-100 scale) and not significantly different between the GCS and non-GCS sites. Additionally, we investigated both the longitudinal changes in fish assemblages in this GCS-fragmented stream and the changes in fish assemblages after slope modifications of three GCSs to facilitate fish passage. Thirteen fish species were present throughout the study area, whereas another 15 species exhibited truncated distributions not extending to the most upstream sampling location. After modification of the GCSs, IBI scores increased at seven of nine sites (mean increase =4.6 points). Also, channel catfish Ictalurus punctatus were detected 7.3 km upstream at sites where, 2 years before GCS modification, they had been absent from collections. Given the number and distribution of GCSs in western Iowa streams, understanding the effects of these structures is vital to the conservation and management of fish assemblages in this and other regions where GCSs or similar structures are used. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2008

Effect of artificial sunlight on the retention of external calcein marks on lake trout

When choosing a fish marking technique to address fishery related questions, it is important to consider factors that affect mark retention. Calcein, a chemical marking agent, is under investigation for potential use on fish. Two laboratory trials were conducted with calcein-marked lake trout Salvelinus namaycush to determine the effect of artificial sunlight on calcein mark intensity. In trial 1, fish exposed to 18,000 lx for 7 d lost 90% or more of the calcein mark intensity (relative to the colorimetric key, mg/L) on the head, body, ventral region, and pectoral fins relative to mark intensity in fish that were maintained in darkness. In trial 2, light intensity was reduced 2.5-3.0-fold. After 7 d of light exposure, calcein mark intensity on the head was reduced by 40-45% relative to mark intensity in fish that were held in darkness; by day 14, calcein mark intensity on the head was reduced by 55-60% relative to that of dark-treated fish. No further decline was observed in light-exposed fish, and head mark intensity values did not differ among days 14, 21, and 28 for this treatment group. Of the four areas evaluated, the head and pectoral fin were more easily read using a colorimetric key than the lateral or ventral regions of the fish. The concentration of calcein spotted on filter paper to devise the colorimetric key ranged from 1 to 100 mg/L. A difference of approximately 7 mg/L in apparent calcein mark intensity means for the head region could be detected using the colorimetric key. These trials showed that calcein mark intensity on lake trout declined when fish were exposed to artificial sunlight, and the use of a colorimetric key improved the objectivity of calcein mark intensity assessment.

North American Journal of Fisheries Management↗

USGS2008

Length variation in age-0 westslope cutthroat trout at multiple spatial scales

Phenotypic diversity provides ecological and evolutionary functions, stabilizing populations in variable environments. Although benefits of larger body size in juvenile fishes are well documented, size variation may have value as well. We explored the distribution of length and length variation in age-0 westslope cutthroat trout Oncorhynchus clarkii lewisi at three spatial scales: area (102 km2), stream (101 km2), and site (100 km2). In addition, we examined relationships between length variables (mean length and interquartile range of length) and instream (temperature and conductivity) and landscape (aspect, elevation, headwater distance, and valley width) variables that were expected to be associated with fish size. Conductivity was included as a surrogate for productivity. Most variation in mean length and interquartile range of fish length was found among areas (62.2% and 62.6%, respectively). Mean length also varied among streams and sites (21.9% and 15.8%, respectively). Similarly, interquartile range of fish length varied among streams and sites (19.1% and 18.3%, respectively). Both length variables were associated with temperature and elevation. Mean fish length was also associated with conductivity, but the association between interquartile length range and conductivity was weak. We conclude that the conservation of variation in phenotypic attributes, such as length, in westslope cutthroat trout may require conservation of viable populations across broad areas and across environmental gradients that are associated with growth. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2008

Population size and relative abundance of adult Alabama shad reaching jim woodruff lock and dam, Apalachicola River, Florida

We estimated the population size of migrating Alabama shad Alosa alabamae below Jim Woodruff Lock and Dam in the Apalachicola River (located in the central panhandle of northwestern Florida) using mark-recapture and relative abundance techniques. After adjustment for tag loss, emigration, and mortality, the population size was estimated as 25,935 (95% confidence interval, 17,715-39,535) in 2005, 2,767 (838-5,031) in 2006, and 8,511 (5,211-14,674) in 2007. The cumulative catch rate from boat electrofishing averaged 20.47 Alabama shad per hour in 2005, 6.10 per hour in 2006, and 13.17 per hour in 2007. The relationship between population size (N) and electrofishing catch per unit effort (CPUE) was modeled by the equation N = -9008.2 + (electrofishing CPUE X 1616.4). Additionally, in 2007 the hook-and-line catch rate averaged 1.94 Alabama shad per rod hour. A predictive model relating the population size and hook-and-line CPUE of spawning American shad A. sapidissima was applied to Alabama shad hook-and-line CPUE and produced satisfactory results. Recent spawning populations of Alabama shad in the Apalachicola River are low relative to American shad populations in other southeastern U.S. rivers. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2008

Adherence of Myxobolus cerebralis myxospores to waders: Implications for disease dissemination

The vectors involved in the spread of whirling disease, which is caused by Myxobolus cerebralis, are only partly understood. However, the parasite has rapidly become established in many regions, suggesting that it is easily disseminated. We gained insight into transport vectors by examining the surface porosity of common wading equipment materials and the adherence of M. cerebralis myxospores to them. Interstitial spaces within rubber, felt, lightweight nylon, and neoprene were measured on scanning electron microscope images. Myxospores were applied to each material, the material was rinsed, and the myxospores recovered to assess adherence. The mean interstitial space size of rubber was the smallest (2.0 ??m), whereas that of felt was the largest (31.3 ??m). The highest recovery rates were from rubber and the glass control. Percent myxospore recovery varied by material, the recovery from felt being lower than that from all other materials. The potential for felt to carry even small numbers of myxospores suggests that the introduction of M. cerebralis by felt-soled wading boots is possible. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2009

Effects of commercial harvest on shovelnose sturgeon populations in the Upper Mississippi River

Shovelnose sturgeon Scaphirhynchus platorynchus have become an increasingly important commercial species in the upper Mississippi River (UMR) because of the collapse of foreign sturgeon (family Acipenseridae) populations and bans on imported caviar. In response to concerns about the sustainability of the commercial shovelnose sturgeon fishery in the UMR, we undertook this study to describe the demographics of the shovelnose sturgeon population and evaluate the influence of commercial harvest on shovelnose sturgeon populations in the UMR. A total of 1,682 shovelnose sturgeon were collected from eight study pools in 2006 and 2007 (Pools 4, 7, 9, 11, 13, 14, 16, and 18). Shovelnose sturgeon from upstream pools generally had greater lengths, weights, and ages than those from downstream pools. Additionally, mortality estimates were lower in upstream pools (Pools 4, 7, 9, and 11) than in downstream pools (Pools 13, 14, 16, and 18). Linear regression suggested that the slower growth of shovelnose sturgeon is a consequence of commercial harvest in the UMR. Modeling of potential management scenarios suggested that a 685-mm minimum length limit is necessary to prevent growth and recruitment overfishing of shovelnose sturgeon in the UMR.

Upper Mississippi River↗

USGS2009

Defining and characterizing coolwater streams and their fish assemblages in Michigan and Wisconsin, USA

Coolwater streams, which are intermediate in character between coldwater “trout” streams and more diverse warmwater streams, occur widely in temperate regions but are poorly understood. We used modeled water temperature data and fish assemblage samples from 371 stream sites in Michigan and Wisconsin to define, describe, and map coolwater streams and their fish assemblages. We defined coolwater streams as ones having summer water temperatures suitable for both coldwater and warmwater species and used the observed distributions of the 99 fish species at our sites to identify coolwater thermal boundaries. Coolwater streams had June-through-August mean water temperatures of 17.0–20.5°C, July mean temperatures of 17.5–21.0°C, and maximum daily mean temperatures of 20.7–24.6°C. We delineated two subclasses of coolwater streams: “cold transition” (having July mean water temperatures of 17.5–19.5°C) and “warm transition” (having July mean temperatures of 19.5–21.0°C). Fish assemblages in coolwater streams were variable and lacked diagnostic species but were generally intermediate in species richness and overlapped in composition with coldwater and warmwater streams. In cold-transition streams, coldwater (e.g., salmonids and cottids) and transitional species (e.g., creek chub Semotilus atromaculatus , eastern blacknose dace Rhynichthys atratulus , white sucker Catostomus commersonii , and johnny darter Etheostoma nigrum ) were common and warmwater species (e.g., ictalurids and centrarchids) were uncommon; in warm-transition streams warmwater and transitional species were common and coldwater species were uncommon. Coolwater was the most widespread and abundant thermal class in Michigan and Wisconsin, comprising 65% of the combined total stream length in the two states (cold-transition streams being more common than warm-transition ones). Our approach can be used to identify and characterize coolwater streams elsewhere in the temperate region, benefiting many aspects of fisheries management and environmental protection.

Michigan, Wisconsin↗

USGS2010

Habitat selection and spawning success of walleye in a tributary to Owasco Lake, New York

Walleyes Sander vitreus are stocked into Owasco Lake, New York, to provide a sport fishery, but the population must be sustained by annual hatchery supplementation despite the presence of appropriate habitat. Therefore, we evaluated walleye spawning success in Dutch Hollow Brook, a tributary of Owasco Lake, to determine whether early survival limited recruitment. Spawning success during spring 2006 and 2007 was evaluated by estimating egg densities from samples collected in the lower 725 m of the stream. Environmental variables were also recorded to characterize the selected spawning habitat. Drift nets were set downstream of the spawning section to assess egg survival and larval drift. We estimated that 162,596 larvae hatched in 2006. For 2007, we estimated that 360,026 eggs were deposited, with a hatch of 127,500 larvae and hatching success of 35.4%. Egg density was significantly correlated to percent cover, substrate type, and depth : velocity ratio. Two sections had significantly higher egg deposition than other areas. Adult spawning walleyes selected shallow, slow habitats with some cover and gravel substrate in the accessible reaches of Dutch Hollow Brook. Our results show that walleyes found suitable spawning habitat in Dutch Hollow Brook and that egg and larval development does not appear to limit natural reproduction.

New York↗

USGS2010

Survival of shovelnose sturgeon after abdominally invasive endoscopic evaluation

The development of effective and minimally invasive techniques to determine gender and gonad developmental stage is particularly important in performing accurate fisheries assessments for use in conservation and restoration. The initial and latent survival of shovelnose sturgeon Scaphirhynchus platorynchus was assessed after exposure to a modified endoscopic technique designed to collect that biological information. Rather than inserting the endoscope through the urogenital canal or directly into the body cavity, we inserted a threaded trocar through a ventral incision and used a low-pressure air supply attached to the trocar to gently insufflate the body cavity. The initial survival of both experimental and control shovelnose sturgeon was 100%. Latent survival was 100% and 90% for the experimental and control fish, respectively. Our study suggests that incision endoscopy coupled with insufflation of the body cavity through the use of a trocar and an air supply is a safe and effective way to determine gender and examine the gonad developmental stage of shovelnose sturgeon. The short duration of the procedure and the high postprocedure survival suggest that this technique is suitable for shovelnose sturgeon and perhaps for the evaluation of other endangered fish species (e.g., pallid sturgeon S. alba ) as well.

North American Journal of Fisheries Management↗

USGS2010

Development of standard weight equations for Caribbean and Gulf of Mexico amphidromous fishes

We collected and compiled length and weight information from four countries and one commonwealth to develop standard weight (W s ) equations for three amphidromous fish species native to the Caribbean and Gulf of Mexico regions: mountain mullet Agonostomus monticola (N = 9,768 individuals, 52 populations), river goby Awaous banana (N = 1,847 individuals, 62 populations), and bigmouth sleeper Gobiomorus dormitor (N = 2,983 individuals, 53 populations). Linear and quadratic W s equations for three quartiles (25%, median, 75%) are presented for these three species. The length-weight relationship from eight lentic bigmouth sleeper populations was significantly different from that of lotic populations, reflecting higher weights of juvenile fish (< 70 mm total length) in lentic environments. Thus, independent W(s) equations were developed for lotic populations of bigmouth sleepers. W(s) equations were not developed from lentic bigmouth sleeper populations alone due to the low number of applicable populations caused by life history constraints; the equation from combined lentic and lotic populations is suggested for application to lentic bigmouth sleeper populations. These morphometric relationships for amphidromous fishes may improve the ability to assess existing and potential sport fisheries and allow ecological assessment based on fish condition.

North American Journal of Fisheries Management↗

USGS2011

Growth and condition of alewives in Lake Michigan, 1984-2001

Diets of salmonines in Lake Michigan have been dominated by alewives Alosa pseudoharengus since the 1960s, and information on alewife population dynamics is critical to the management of salmonine fisheries. We monitored alewife size at age and condition ( K ) at several different locations in Lake Michigan during fall 1984–2001. Alewives were aged by enumerating annuli on otoliths. The results indicated that alewife length at age did not trend upward or downward between 1984 and the late 1990s but decreased from the late 1990s to 2001. Alewife weight at age was relatively constant between 1984 and the mid-1990s but decreased from the mid-1990s to 2001. Mean condition for a given alewife age was, on average, 13.7% higher during 1984–1994 than during 1995–2001. This decline in alewife condition was not a density-dependent response by the alewife population because alewife abundance trended neither upward nor downward during 1984–2001. The decline in alewife condition was possibly due to the lakewide decrease in the abundance of Diporeia spp. during the 1990s. Apparently, the availability of the large-bodied invertebrates Diporeia and Mysis spp. was an important regulator of adult alewife growth because alewives attained a substantially larger size in Lake Michigan, where these invertebrates were relatively important constituents of the adult alewife diet, than in Lake Ontario, where these invertebrates were not readily eaten by adult alewives. For age-2 or older females, mean length was 2–9 mm greater than for males. Alewife size at age and condition were slightly higher on the eastern side of Lake Michigan than on the western side.

Transactions of the American Fisheries Society↗

USGS2011

Effect of stock size, climate, predation, and trophic status on recruitment of alewives in Lake Ontario, 1978-2000

The population of alewives Alosa pseudoharengus in Lake Ontario is of great concern to fishery managers because alewives are the principal prey of introduced salmonines and because alewives negatively influence many endemic fishes. We used spring bottom trawl catches of alewives to investigate the roles of stock size, climate, predation, and lake trophic status on recruitment of alewives to age 2 in Lake Ontario during 1978–2000. Climate was indexed from the temperature of water entering a south-shore municipal treatment plant, lake trophic status was indexed by the mean concentration of total phosphorus (TP) in surface water in spring, and predation was indexed by the product of the number of salmonines stocked and relative, first-year survival of Chinook salmon Oncorhynchus tshawytscha . A Ricker-type parent–progeny model suggested that peak production of age-1 alewives could occur over a broad range of spawning stock sizes, and the fit of the model was improved most by the addition of terms for spring water temperature and winter duration. With the addition of the two climate terms, the Ricker model indicated that when water was relatively warm in spring and the winter was relatively short, peak potential production of young was nine times higher than when water temperature and winters were average, and 73 times higher than when water was cold in spring and winters were long. Relative survival from age 1 to recruitment at age 2 was best described by a multiple linear regression with terms for adult abundance, TP, and predation. Mean recruitment of age-2 fish in the 1978–1998 year-classes predicted by using the two models in sequence was only about 20% greater than the observed mean recruitment. Model estimates fit the measured data exceptionally well for all but the largest four year-classes, which suggests that the models will facilitate improvement in estimates of trophic transfer due to alewives.

Transactions of the American Fisheries Society↗

USGS2011

Two alternative juvenile life history types for fall Chinook salmon in the Snake River basin

Fall Chinook salmon Oncorhynchus tshawytscha in the Snake River basin were listed under the Endangered Species Act in 1992. At the time of listing, it was assumed that fall Chinook salmon juveniles in the Snake River basin adhered strictly to an ocean-type life history characterized by saltwater entry at age 0 and first-year wintering in the ocean. Research showed, however, that some fall Chinook salmon juveniles in the Snake River basin spent their first winter in a reservoir and resumed seaward movement the following spring at age 1 (hereafter, reservoir-type juveniles). We collected wild and hatchery ocean-type fall Chinook salmon juveniles in 1997 and wild and hatchery reservoir-type juveniles in 1998 to assess the condition of the reservoir-type juveniles at the onset of seaward movement. The ocean-type juveniles averaged 112-139 mm fork length, and the reservoir-type juveniles averaged 222-224 mm fork length. The large size of the reservoir-type juveniles suggested a high potential for survival to salt water and subsequent return to freshwater. Scale pattern analyses of the fall Chinook salmon spawners we collected during 1998-2003 supported this point. Of the spawners sampled, an overall average of 41% of the wild fish and 51% of the hatchery fish had been reservoir-type juveniles. Males that had been reservoir-type juveniles often returned as small "minijacks" (wild, 16% of total; hatchery, 40% of total), but 84% of the wild males, 60% of the hatchery males, and 100% of the wild and hatchery females that had been reservoir-type juveniles returned at ages and fork lengths commonly observed in populations of Chinook salmon. We conclude that fall Chinook salmon in the Snake River basin exhibit two alternative juvenile life histories, namely ocean-type and reservoir-type. ?? Copyright by the American Fisheries Society 2005.

Idaho, Oregon, Washington↗

USGS2011

The fundamental thermal niche of adult landlocked striped bass

Researchers have described the temperatures selected by landlocked striped bass Morone saxatilis in different locales throughout the USA. However, seasonally low concentrations of dissolved oxygen (DO) in many systems prevented striped bass from using the cool waters (<22??C) they may have preferred. In Melton Hill Reservoir, a 92-km-long impoundment on the Clinch River in east Tennessee, 15 adult striped bass were tagged with temperature-sensing radio tags and tracked for an average of 418 d in 1999-2000. Cold, hypolimnetic discharges from an upstream dam and heated discharge from a steam-generating electric facility near the midpoint of this run-of-the-river reservoir provided a broad range of temperatures in most seasons, and hypoxic habitats were uncommon even during stratification. The mean temperature occupied by striped bass varied seasonally (repeated-measures analysis of variance, P < 0.0001) and was highest in summer (17.5??C), intermediate in spring and fall (15.4-16.9??C), and lowest in winter (13.0??C). The mean and modal temperatures occupied during the growing season (May-October 1999) were 17.5??C and 19.0??C, respectively; 30% of the observations were between 9??C and 15??C. These data indicate that the fundamental thermal niche of adult landlocked striped bass may be lower than literature estimates. These results also represent the first unbiased field estimates of the influence of season on the thermal ecology of adult striped bass. The thermal characteristics of habitats considered optimal in habitat suitability index models for adult landlocked striped bass (i.e., 18-24??C) should be revised to include cooler waters. ?? Copyright by the American Fisheries Society 2005.

Transactions of the American Fisheries Society↗

USGS2011

Effects of turbidity, light level, and cover on predation of white sturgeon larvae by prickly sculpins

White sturgeon Acipenser transmontanus occur in rivers of the western United States and southwestern Canada, but some populations are in decline because of recruitment failure. Many river systems in this area have been altered as a result of development that has caused major environmental changes. Our goal was to examine how three changes - lower turbidity levels, higher light levels, and altered substrates - might affect predation by prickly sculpin Cottus asper on white sturgeon larvae. We experimentally investigated predation at various turbidity levels and found that significantly more white sturgeon yolk sac larvae were eaten at lower turbidity levels. The effects of light level (1-4 and 7-15 1x), the presence or absence of rocks as cover, and prey size (14-17 mm and 20-24 mm total length) on the outcome of predator-prey interactions were also examined. Significantly fewer white sturgeon were eaten during trials that combined the lowest light level, cover, and the smallest larvae. Our results suggest that altered river conditions caused by impoundment and other factors have increased predation on white sturgeon larvae. ?? Copyright by the American Fisheries Society 2005.

Transactions of the American Fisheries Society↗