Cottus Cognatus Research Articles

Total and methyl mercury accumulation in 1994–1995 Lake Michigan lake trout and forage fish

As part of the Lake Michigan Mass Balance Project, total and methyl mercury were determined for lake trout ( Salvelinus namaycush) and five forage fish species collected from Lake Michigan near Saugatuck, Michigan, and Port Washington, Sheboygan Reef, and Sturgeon Bay, Wisconsin, between 1994 and 1995. With a mean concentration of 179 ng/g wet wt., whole lake trout total mercury (Hg T) concentrations ranged between 27.6 and 348 ng/g wet wt. For combined sites, 1–4 yrs, 5–6 yrs, 7–11 yrs, and 12–15 yrs lake trout mean Hg T concentrations were 73.7, 130, 212, and 280 ng/g, respectively. Forage fish species alewife ( Alosa pseudoharengus), bloater ( Coregonus hoyi), slimy sculpin ( Cottus cognatus), deepwater sculpin ( Myoxocephalus thompsoni), and rainbow smelt ( Osmerus mordax) had mean Hg T concentrations of 63.8, 55.3, 36.7, 51.4, and 35.2 ng/g wet wt., respectively. With the exception of alewife, bloater, and slimy sculpin, all fish species contained approximately 100% methyl mercury (MeHg). Field bioaccumulation factors (BAF) were consistent with a Lake Michigan food chain that is more efficient at transferring MeHg to higher trophic levels than some inland lakes. This and other studies of lake trout from Lake Michigan document decreasing Hg T concentrations in lake trout from 1971 to 1985 and constant or increasing concentrations between 1985 and 2000. These observations were supported by a similar trend in Lake Michigan Hg sediment fluxes. To our knowledge, this is the most intense two year study of mercury in fish for any Great Lake or other large fresh water system and is one of the most complete studies of mercury cycling in the Lake Michigan food chain.

Spawning Season and Habitat Use of Slimy Sculpin (Cottus cognatus) in Southeastern Minnesota

ABSTRACT Slimy sculpin (Cottus cognatus) in Winona County, Minnesota spawned in late March and early April when water temperature reached 10°C. Relatively large rocks were preferentially used for spawning, and individual nests contained clutches from as many as nine females. Although artificial rock shelters were not used for spawning, large shelters were used for cover more often and small shelters less often than expected if shelter use was random with respect to shelter size. Use of shelters of different sizes did not differ significantly between large and small sculpins.

Polybrominated diphenyl ethers (PBDEs) in Lake Michigan forage fish

Polybrominated diphenyl ethers (PBDEs) were analyzed in 88 forage fish samples collected from Lake Michigan in 1995 and in 2002/2003. Lipid-normalized total PBDE concentrations ranged from 149 to 1094 ng/g. Total PBDEs in alewife and deepwater sculpin did not change significantly from 1995 to 2002/2003, while the levels in bloater chub and the slimy sculpin decreased. BDE-47 was the most abundant congener in the fish. All of the forage fish were depleted in BDE-99 relative to what would be expected based on the congener composition of the commercial formulation in use. The deepwater sculpins were particularly lacking in BDE-99. Changes in the food web brought about by the dramatic decline of Diporeia abundance (due to the invasion of zebra and quagga mussels) may have affected the levels of PBDEs in some of the forage fish.

Biogeography of Stream Fishes in Connecticut: Defining Faunal Regions and Assemblage Types

Stream fish survey data were analyzed to describe patterns of fish distributions in wadeable streams (primarily 1st–4th order) in Connecticut. Species occurrence within the United States Geological Survey 8-digit hydrologic unit code watersheds were used to aggregate similar watersheds into stream fish faunal regions. Within each identified region, multivariate analyses were used to identify major fish assemblage types and associate stream habitat with assemblage types. The analyses revealed an eastern and western faunal region defined primarily by distribution of a few native species. Native species associated with the western watersheds were: Semotilus atromaculatus (Creek Chub), Exoglossum maxillingua (Cutlips Minnow), and Cottus cognatus (Slimy Sculpin). Native fishes associated with the eastern watersheds were: Erimyzon oblongus (Creek Chubsucker), Esox niger (Chain Pickerel), and Esox americanus (Redfin Pickerel). Inclusion of non-indigenous species in the analyses resulted in a similar east–west grouping of watersheds. Five and four assemblage types were identified in the eastern and western faunal regions, respectively. Both regions harbored 3 fluvial assemblages defined longitudinally from headwater streams to larger wadeable streams and a macro-habitat generalist assemblage inhabiting streams with proportionately more pool habitat, but taxonomic membership and indicator species rankings among assemblages were not necessarily identical between the regions. A distinct assemblage dominated by Redfin Pickerel was recognized only in the eastern region. Streams in the western region were generally higher in elevation and colder in water temperature. The discovery and description of eastern and western fish faunal regions and their fish assemblage types will be useful in stratifying the biological monitoring of streams and other aquatic resource management actions in Connecticut.

Influence of lake characteristics on the biomagnification of persistent organic pollutants in lake trout food webs

The biomagnification of polychlorinated biphenyls (PCBs) and major organochlorine pesticides (OCPs) was studied using lake trout (Salvelinus namaycush) and other food web organisms collected from 17 lakes in Canada and the northeastern United States between 1998 and 2001. Whole lake trout (n = 357) concentrations of the sum (Sigma) of 57 PCB congeners ranged between 1.67 and 2,890 ng/g wet weight (median 61.5 ng/g wet wt). Slimy sculpin had the highest mean concentrations of SigmaPCB of all forage fish (32-73 ng/g wet wt). Positive relationships between log (lipid wt) concentrations of PCB congener 153, PCB congener 52, p,p'-dichlorodiphenyldichloroethylene, hexachlorobenzene, cis-chlordane, trans-nonachlor, or dieldrin and trophic level (determined using stable nitrogen isotope ratios) were found for most of the 17 food webs, indicating biomagnification of these PCBs and OCPs. The p,p'-dichlorodiphenyldichloroethylene had the highest trophic magnification factors (TMFs) of the 14 individual compounds studied, averaging 4.0 +/- 1.8 across the 17 lakes, followed by trans-nonachlor (3.6 +/- 1.5) and PCB congener 153 (3.4 +/- 1.2). Average TMFs for 14 individual PCBs or OCPs were significantly correlated with log octanol-water partition coefficient, implying that the rate of accumulation along the food web is dependent on hydrophobicity and recalcitrance. Significant correlations (p < 0.05) were found between TMFs of SigmaPCBs, hexachlorobenzene, alpha-hexachlorocyclohexane, and lindane and lake area, latitude, and longitude, but not for 11 other PCBs or OCPs. Overall, the results of the present study show that biomagnification of PCBs and most OCPs, as measured by TMFs, is only weakly influenced by such factors as latitude and longitude. Exceptions are hexachlorocyclohexane isomers and hexachlorobenzene, which had generally greater TMFs in northern lakes, possibly due to lower rates of elimination and biotransformation in the food web.

Cumulative Industrial Activity Alters Lotic Fish Assemblages in Two Boreal Forest Watersheds of Alberta, Canada

We evaluated the cumulative effects of land use disturbance resulting from forest harvesting, and exploration and extraction of oil and gas resources on the occurrence and structure of stream fish assemblages in the Kakwa and Simonette watersheds in Alberta, Canada. Logistic regression models showed that the occurrence of numerically dominant species in both watersheds was related to two metrics defining industrial activity (i.e., percent disturbance and road density), in addition to stream wetted width, elevation, reach slope, and percent fines. Occurrences of bull trout, slimy sculpin, and white sucker were negatively related to percent disturbance and that of Arctic grayling, and mountain whitefish were positively related to percent disturbance and road density. Assessments of individual sites showed that 76% of the 74 and 46 test sites in the Kakwa and Simonette watersheds were possibly impaired or impaired. Impaired sites in the Kakwa Watershed supported lower densities of bull trout, mountain whitefish, and rainbow trout, but higher densities of Arctic grayling compared to appropriate reference sites. Impaired sites in the Simonette Watershed supported lower densities of bull trout, but higher densities of lake chub compared to reference sites. Our data suggest that current levels of land use disturbance alters the occurrence and structure of stream fish assemblages.

Effects of un-ionized ammonia on histological, endocrine, and whole organism endpoints in slimy sculpin ( Cottus cognatus)

Ammonia is known to be an important toxicant in aquatic environments. Although ammonia toxicity has been well studied in many fish species, effects of chronic exposure on slimy sculpin ( Cottus cognatus), a critical biomonitoring species for northern aquatic habitats, are not well known. Further, with increasing mining development in Canada's north, this information is critical to better predict potential effects of mine effluent discharges on northern fish species. Slimy sculpin were exposed to six concentrations of un-ionized ammonia (NH 3) relevant to concentrations found in northern mining effluents: control (0 ppm), 0.278 ppm, 0.556 ppm, 0.834 ppm, 1.112 ppm, and 1.668 ppm. An LC 50 of 1.529 ppm was calculated from mortality data. Histopathological examination of gills indicated significant tissue damage, measured as lamellar fusion and epithelial lifting, at 0.834 ppm, 1.112 ppm, and 1.668 ppm. Using gill endpoints, NOEC and LOEC were calculated as 0.556 ppm and 0.834 ppm, respectively. An EC 50 of 0.775 ppm was determined for lamellar fusion and an EC 50 of 0.842 ppm for epithelial lifting. Hemorrhage of gills was present in mortalities, which occurred at 1.668 ppm of un-ionized ammonia. A significant decrease in liver somatic index (LSI) was seen in both male and female fish at 0.834 ppm and 1.112 ppm, respectively. Gonadosomatic index (GSI) in female fish significantly increased at 1.668 ppm un-ionized ammonia with an associated significant increase in total wholebody testosterone concentrations. GSI in male fish also significantly increased at 1.668 ppm but no differences were seen in testosterone concentrations. No significant differences were seen in gonad histopathological assessments or condition factor. Gill histopathology endpoints may be a more sensitive indicator for detecting effects in slimy sculpin exposed to ammonia than traditional chronic endpoints. Results from this study indicate that ammonia concentrations commonly reported in northern mine effluents hold potential to affect the health of slimy sculpin including acute, chronic, histological and endocrine endpoints.

Depth Distribution Dynamics of the Sculpin Community in Lake Michigan

AbstractUsing data from our annual lakewide bottom trawl survey of Lake Michigan, we calculated the mean depths of capture for deepwater sculpin Myoxocephalus thompsonii and slimy sculpin Cottus cognatus for each combination of transect (Frankfort, Ludington, Saugatuck, and Manistique in Michigan, Waukegan in Illinois, and Port Washington and Sturgeon Bay in Wisconsin) and year (1973‐2005). The mean depth of capture of both sculpin species significantly decreased during the recovery phase of the deepwater sculpin population at four of the transects but did not significantly change for either species at the other three transects during this time. During the postrecovery phase of the deepwater sculpin population, the mean depth of capture of deepwater sculpins significantly increased at six of the seven transects, whereas that for slimy sculpins significantly increased at only four of the seven transects. The mean depth of capture of deepwater sculpins was most strongly correlated with that of slimy sculpins at Frankfort (r = 0.73); the correlation was weakest at Manistique (r = 0.00). Long‐term mean depths of capture (averaged over all years) for deepwater sculpins ranged from 90 to 108 m among the seven transects, whereas the long‐term mean depths of capture for slimy sculpins ranged from 60 to 83 m. The long‐term mean depth difference between the two species was least at Frankfort (21 m) and greatest at Manistique (38 m); at all seven transects, the mean depth difference was significantly greater than zero. We concluded that these two sculpin populations in Lake Michigan maintained some degree of spatial separation during 1973‐2005.

Status and Distribution of Fish in an Acid-impacted Watershed of the Northeastern United States (Hubbard Brook, NH)

Stream acidifi cation across the northeastern US impacts fi sh abundance and fi sh communities. In this study, we document a fi sh community shift in the upper mainstem of Hubbard Brook (NH) from the presence of at least three species in the 1960s to the presence of only one species today. Cottus cognatus (Slimy Sculpin) and Rhinichthys atratulus (Blacknose Dace) are no longer present in this system, and we suggest that extirpation occurred during a period of chronic acidifi cation during the early 1970s. Today, Salvelinus fontinalis (Brook Trout) is the only fi sh species pres- ent in the upper reaches of the Hubbard Brook Valley. The current upstream extent of Brook Trout is limited primarily by physical obstructions such as waterfalls or cascades. Acidifi cation may lead to chemical barriers that limit upstream movement during high fl ow in a few streams. As recovery from acid deposition begins, and as regional climate changes, our observations demonstrate the value of periodic evalu- ations documenting shifts in the distribution and composition of fi sh communities in headwaters of the northeastern US.

A multitrophic approach to monitoring the effects of metal mining in otherwise pristine and ecologically sensitive rivers in Northern Canada

It is not known if current chemical and biological monitoring methods are appropriate for assessing the impacts of growing industrial development on ecologically sensitive northern waters. We used a multitrophic level approach to evaluate current monitoring methods and to determine whether metal-mining activities had affected 2 otherwise pristine rivers that flow into the South Nahanni River, Northwest Territories, a World Heritage Site. We compared upstream reference conditions in the rivers to sites downstream and further downstream of mines. The endpoints we evaluated included concentrations of metals in river water, sediments, and liver and flesh of slimy sculpin (Cottus cognatus); benthic algal and macroinvertebrate abundance, richness, diversity, and community composition; and various slimy sculpin measures, our sentinel forage fish species. Elevated concentrations of copper and iron in liver tissue of sculpin from the Flat River were associated with high concentrations of mine-derived iron in river water and copper in sediments that were above national guidelines. In addition, sites downstream of the mine on the Flat River had increased algal abundances and altered benthic macroinvertebrate communities, whereas the sites downstream of the mine on Prairie Creek had increased benthic macroinvertebrate taxa richness and improved sculpin condition. Biological differences in both rivers were consistent with mild enrichment of the rivers downstream of current and historical mining activity. We recommend that monitoring in these northern rivers focus on indicators in epilithon and benthic macroinvertebrate communities due to their responsiveness and as alternatives to lethal fish sampling in habitats with low fish abundance. We also recommend monitoring of metal burdens in periphyton and benthic invertebrates for assessment of exposure to mine effluent and causal association. Although the effects of mining activities on riverine biota currently are limited, our results show that there is potential for effects to occur with proposed growth in mining activities.

Nearshore Habitat and Fish Community Associations of Coaster Brook Trout in Isle Royale, Lake Superior

AbstractWe characterized the nearshore habitat and fish community composition of approximately 300 km of shoreline within and adjacent to the major embayments of Isle Royale, Lake Superior. Sampling yielded 17 species, of which 12 were widespread and represented a common element of the Lake Superior fish community, including cisco Coregonus artedi, lake whitefish C. clupeaformis, round whitefish Prosopium cylindraceum, lake trout Salvelinus namaycush, rainbow smelt Osmerus mordax, lake chub Couesius plumbeus, longnose sucker Catostomus catostomus, white sucker C. commersonii, trout‐perch Percopsis omiscomaycus, ninespine stickleback Pungitius pungitius, burbot Lota lota, and slimy sculpin Cottus cognatus. The presence of brook trout S. fontinalis in an embayment was associated with the common species of the Isle Royale nearshore fish community, particularly cisco, longnose sucker, and round whitefish. However, brook trout were present in only five embayments and were common only in Tobin Harbor. Most Isle Royale embayments had broadly overlapping ranges of nearshore habitats. Within embayments, fish were distributed along a habitat gradient from less‐protected rocky habitat near the mouth to highly protected habitat with mixed and finer substrates at the head. Embayments with brook trout had greater mean protection from the open lake, greater variation in depth, greater mean cover, and higher mean frequencies of large substrates (cobble, boulder, and bedrock). Within those embayments, brook trout were associated with habitat patches with higher mean frequencies of small substrates (particularly sand and coarse gravel). Within Tobin Harbor, brook trout were associated with midembayment habitat and species assemblages, especially those locations with a mixture of sand, gravel, and cobble substrates, an absence of bedrock, and the presence of round whitefish, white sucker, and trout‐perch. Comparison of embayments with the model, Tobin Harbor, showed that six embayments without brook trout had very similar arrays of habitat. However, four embayments with brook trout had relatively different arrays of habitat from Tobin Harbor. These results suggest that there is potential for further recovery of brook trout populations across Isle Royale nearshore habitats.

Response of Fish Populations to Natural Channel Design Restoration in Streams of the Catskill Mountains, New York

AbstractMany streams and rivers throughout North America have been extensively straightened, widened, and hardened since the middle 1800s, but related effects on aquatic ecosystems have seldom been monitored, described, or published. Beginning in the early 1990s, reach‐level restoration efforts began to base projects on natural channel design (NCD) techniques and Rosgen's (1994b, 1996) river classification system in an effort to duplicate or mimic stable reference reach geomorphology. Four reaches in three streams of the Catskill Mountains, New York, were restored from 2000 to 2002 using NCD techniques to decrease bed and bank erosion rates, decrease sediment loads, and improve water quality. The effects of restoration on the health of fish assemblages were assessed through a before–after, control–impact (BACI) study design to quantify the net changes in population and community indices at treatment reaches relative to index changes at unaltered reference reaches from 1999 to 2004. After restoration, community richness and biomass at treatment reaches increased by more than one‐third. Changes in fish communities were caused mainly by shifts in dominant species populations; fish community biomass and total fish abundance were generally dominated by daces or daces and sculpins before restoration and by one or more salmonid species after restoration. Density and biomass of eastern blacknose dace Rhinichthys atratulus, longnose dace R. cataractae, and slimy sculpin Cottus cognatus did not change appreciably, whereas net salmonid density and biomass increased substantially after restoration. These changes were driven primarily by large increases in populations of brown trout Salmo trutta. The findings demonstrate that the structure, function, and ultimately the health of resident fish populations and communities can be improved, at least over the short term, through NCD restoration in perturbed streams of the Catskill Mountains.

Bioaccumulation and Trophic Magnification of Short- and Medium-Chain Chlorinated Paraffins in Food Webs from Lake Ontario and Lake Michigan

Chlorinated paraffins (CPs) are complex mixtures of chlorinated alkanes used in a myriad of industrial applications as flame retardant plasticizers and additives. In this study, the distribution and bioaccumulation/biomagnification of short-chain CPs (C10-C13, SCCPs) and medium-chain CPs (C14-C17, MCCPs) were investigated in samples collected between 1999 and 2004 from Lake Ontario and northern Lake Michigan. Total (sigma) SCCPs and sigmaMCCPs concentrations in water from Lake Ontario were 1190 pg/L and 0.9 pg/L (data from 2004 only), respectively. CPs were also detected in invertebrates and fish from both lakes. SCCP predominated in organisms from Lake Michigan with the highest mean concentrations found in lake trout [Salvelinus namaycush, 123 +/- 35 ng/g wet weight (ww)]. In Lake Ontario, MCCPs predominated in most species with the highest levels detected in slimy sculpin (Cottus cognatus, 108 ng/g ww) and rainbow smelt (Osmerus mordax, 109 ng/g ww). Bioaccumulation and biomagnification of CPs was evaluated on an isomer basis (i.e., C10H17Cl5, C10H16Cl6, etc). Log bioaccumulation factors for lake trout (lipid based) ranged from 4.1 to 7.0 for SCCPs and 6.3 to 6.8 for MCCPs. SCCPs and MCCPs were found to biomagnify between prey and predators from both lakes with highest values observed for Diporeia-sculpin (Lake Ontario, C15Cl9 = 43; Lake Michigan, C10Cl5 = 26). Trophic magnification factors for the invertebrates-forage fish-lake trout food webs ranged from 0.41 to 2.4 for SCCPs and from 0.06 to 0.36 for MCCPs. Given the prominence of CPs, particularly in lake waters and in lower food web organisms, further investigation is needed to evaluate the magnitude of their distribution and accumulation/magnification in the Great Lakes environment.

Predators reverse the direction of density dependence for juvenile salmon mortality

The effect of predators on prey populations depends on how predator-caused mortality changes with prey population density. Predators can enforce density-dependent prey mortality and contribute to population stability, but only if they have a positive numerical or behavioral response to increased prey density. Otherwise, predator saturation can result in inversely density-dependent mortality, destabilizing prey populations and increasing extinction risk. Juvenile salmon and trout provide some of the clearest empirical examples of density-dependent mortality in animal populations. However, although juvenile salmon are very vulnerable to predators, the demographic effects of predators on juvenile salmon are unknown. We tested the interactive effects of predators and population density on the mortality of juvenile Atlantic salmon (Salmo salar) using controlled releases of salmon in natural streams. We introduced newly hatched juvenile salmon at three population density treatments in six study streams, half of which contained slimy sculpin (Cottus cognatus), a common generalist predator (18 release sites in total, repeated over two summers). Sculpin reversed the direction of density dependence for juvenile salmon mortality. Salmon mortality was density dependent in streams with no sculpin, but inversely density dependent in streams where sculpin were abundant. Such predator-mediated inverse density dependence is especially problematic for prey populations suppressed by other factors, thereby presenting a fundamental challenge to persistence of rare populations and restoration of extirpated populations.

Adverse Effects of Alewives on Laurentian Great Lakes Fish Communities

AbstractThe alewife Alosa pseudoharengus, an invader to the Laurentian Great Lakes from the Atlantic Ocean, has been blamed for causing major disruptions of Great Lakes fish communities during the past 50 years. We reviewed the literature and examined long‐term data on fish abundances in the Great Lakes to develop a new synthesis on the negative effects of alewives on Great Lakes fish communities. The results indicated that certain fish populations are substantially more vulnerable to the effects of alewives than others. More specifically, the effects of alewives on other fish populations appeared to follow a continuum—from such fishes as slimy sculpin Cottus cognatus, lake whitefish Coregonus clupeaformis, and bloater Coregonus hoyi, which were relatively unsusceptible—to Atlantic salmon Salmo salar, lake trout Salvelinus namaycush, and emerald shiner Notropis atherinoides, which were highly susceptible. Intermediate species in this continuum included yellow perch Perca flavescens, deepwater sculpin Myoxocephalus thompsonii, and burbot Lota lota. The predominant mechanism by which alewives exerted their negative effect appeared to be predation on the larvae of other fishes. The key factor in the extirpation of Atlantic salmon from Lake Ontario, however, was probably early mortality syndrome induced by a diet rich in alewives. We conclude that the degree of restoration of the native Great Lakes fish community depends in part on the degree of control of the alewife population.

Fall diets of alewife, rainbow smelt, and slimy sculpin in the profundal zone of southern Lake Ontario during 1994–2005 with an emphasis on occurrence of Mysis relicta

In Lake Ontario, factors including the collapse of the burrowing amphipod, Diporeia spp., changes in the distribution and composition of the prey fish community, and occurrence of exotic cladocerans Bythotrephes longimanus and Cercopagis pengoi have led to changes in predation pressure on the remaining native profundal macroinvertebrate, Mysis relicta. We conducted a diet study on three important prey fishes, alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), and slimy sculpin (Cottus cognatus) in 2002–2005 at depths 75–130 m along the south shore of Lake Ontario to evaluate the current role of Mysis in the diets of these species relative to earlier studies and previously unpublished data from 1994–1995. Mysis have remained an important prey item for alewife, rainbow smelt, and slimy sculpin in the profundal zone of southern Lake Ontario through 2005, indicating that the population has been able to sustain itself following the collapse of Diporeia. Although the occurrence of Diporeia in prey fish diets was minimal in 2003–2005, Bythotrephes longimanus and Cercopagis pengoi played an important role in the diet of alewife and a minor role in the diet of rainbow smelt, and may actually serve to mitigate predation pressure on Mysis, particularly in years when they are very abundant. Conversely, without Diporeia, the benthic slimy sculpin was primarily reliant on Mysis as a prey item and would be most vulnerable to a decline in the Mysis population.

First Report of Schistocephalus sp. (Cestoda: Pseudophyllidea) in Slimy Sculpin, Cottus cognatus Richardson, 1836, from Lake Michigan, U.S.A

Plerocercoids of Schistocephalus sp. (Diphyllobothriidae) were found in the body cavities of 2 (0.9%) of 209 slimy sculpins, Cottus cognatus, collected in September 2003 from Lake Michigan, south of Manistique, Michigan, U.S.A. Mean intensity was 1. The mean lengths and weights of these 2 thawed, relaxed plerocercoids were 67 and 72 mm and 427 and 554 mg, respectively. The number of segments in each plerocercoid was 113, and both plerocercoids showed upturned edges of the first segment. The identification of these plerocercoids to species is discussed, and the occurrence of Schistocephalus sp. in fish from the Great Lakes is summarized. This is the first report of Schistocephalus in slimy sculpin from Lake Michigan and the second report of Schistocephalus infecting fish from this lake.

Interactions between Slimy Sculpin and Trout: Slimy Sculpin Growth and Diet in Relation to Native and Nonnative Trout

AbstractTo investigate whether introductions of nonnative trout affect growth and diet of nongame fish in small streams, we designed a field experiment to examine interactions between slimy sculpin Cottus cognatus and native brook trout Salvelinus fontinalis or nonnative brown trout Salmo trutta. We hypothesized that brown trout would compete with and reduce growth of slimy sculpin. We expected no change in slimy sculpin growth in treatments with brook trout because the two species co‐occur in their native range and thus may have evolved methods to partition resources and decrease competitive interactions. Enclosures (1 m2) were stocked with (1) juvenile brown trout and slimy sculpin, (2) juvenile brook trout and slimy sculpin, or (3) slimy sculpin alone (control). Fish were stocked at three densities to examine intraspecific versus interspecific competition. Replicates of each treatment were placed in riffles in Valley Creek, Minnesota, and six experimental trials were conducted over three summers (2002‐2004). Brown trout presence was associated with reduced growth of large slimy sculpin in enclosures, whereas brook trout presence produced no change in slimy sculpin growth; these effects did not depend on fish density. Brown trout or brook trout presence was not associated with shifts in the diets of slimy sculpin, indicating that reduced slimy sculpin growth in the presence of brown trout was not due to prey selection or prey availability changes. Our research suggests that effects on growth of slimy sculpin in Valley Creek differ between introduced brown trout and native brook trout; however, the mechanisms underlying changes in slimy sculpin growth are unclear. Although brook trout and brown trout appear to fill similar ecological roles in small, coldwater streams, brown trout may negatively impact growth of nongame fish.

Reproductive Ecology of Slimy Sculpin in Small New Brunswick Streams

AbstractThe male slimy sculpin Cottus cognatus guards a nest rock and provides parental care for the offspring of one or more females, which deposit all their eggs into the male's nest. The purpose of our research was to determine the timing of nest acquisition, spawning, and hatching and to describe biological (number of eggs) and physical characteristics of the nest. In total, we monitored 77 nests during the 2004 spawning period (April‐June). Females' egg masses contained an average of 106 eggs. Males guarded an average of 239 eggs; most guarded two or three females' egg masses. Most males (60%) began guarding nests in early May, about a week before egg deposition, and left the nest by the end of June. Males tended to use cobble in shallow water as nests. These findings suggest that slimy sculpin may be sensitive to changes in natural flow conditions during their reproductive period.

Do native species limit survival of reintroduced Atlantic salmon in historic rearing streams?

Reintroduction of extirpated populations creates a unique context that can exacerbate the effects of interactions among species. Thus, reintroduced populations may be particularly vulnerable to predators and competitors, including native species with which they historically coexisted. In this study, we evaluated the effect of native fishes on survival of reintroduced Atlantic salmon ( Salmo salar) in the Connecticut River basin, where the native salmon population is extinct. Juvenile salmon are stocked annually in many Connecticut River tributaries. We sampled salmon reintroduction sites across tributaries with different fish communities to determine whether native fish reduce the success of salmon reintroductions ( N = 19 site-years). Increased density of slimy sculpin ( Cottus cognatus), a native generalist predator, was associated with reduced recruitment of reintroduced salmon. Salmon first-summer survival declined with increased sculpin density across sites, and low first-summer survival led to reduced densities of overyearling salmon the subsequent year. Hierarchical partitioning analysis showed that the negative relationship between sculpin and salmon was independent of potentially confounding variation in other fish community or habitat characteristics. Negative effects of native, historically-sympatric species, particularly generalist predators, can impede restoration of extirpated populations.