Sculpin Densities Research Articles

Factors Influencing Brown Trout Reproductive Success in Ozark Tailwater Rivers

The reproductive success of brown trout Salmo trutta in White River, Arkansas, tailwater reaches is highly variable, resulting in the need for supplemental stocking. A better understanding of the physical and biotic factors affecting reproduction and survival would enhance the contribution of wild fish. We compared fecundity, reproductive chronology, physical habitat, water quality, trout density, food availability, diet, predation, and competitive interactions among four tailwater reaches to identify factors influencing brown trout reproductive success. The fecundity and condition factor of prespawning brown trout were significantly lower at Beaver Tailwater, a reach known for reproductive failure, than at other sites, among which no differences were found. Brown trout spawning was observed from 11 October to 23 November 1996, and juvenile emergence began on 28 February 1997. Significant among-site differences were detected for spawning and juvenile microhabitat variables, but the variables fell within or near suitable or optimal ranges reported in the literature for this species. Age-0 brown trout density differed significantly among sites, but growth and condition did not. Predation by Ozark sculpin Cottus hypselurus on trout eggs or age-0 trout of any species was not observed among the 418 stomachs examined. Ozark sculpin density and diet overlap with age-0 brown trout were highest and invertebrate food availability and water fertility were lowest at Beaver Tailwater relative to the other reaches. Our findings indicate that differences in trophic conditions occur among tailwater reaches, and a lower system productive capacity was identified at Beaver Tailwater. We suggest that management efforts include refining the multispecies trout stocking regime to improve production efficiency, enhancing flow regulation, and increasing habitat complexity to increase invertebrate and fish productivity. Such efforts may lead to improved natural reproduction and the increased abundance and quality of wild trout in this system and other regulated rivers.

Sculpins and Crayfish in Lake Trout Spawning Areas in Lake Ontario: Estimates of Abundance and Egg Predation on Lake Trout Eggs

Crayfish ( Orconectes spp.) and sculpins ( Cottus spp.) were collected at eight lake trout spawning reefs in Lake Ontario to assess abundance and potential to consume lake trout eggs. Abundance of crayfish ranged from a high of 9.5/m 2 in eastern Lake Ontario to 0/m 2 in western Lake Ontario where the absence or near absence at four reefs sampled was attributed to cold water upwelling. Sculpin abundance ranged from 4.2 to 50.1/m 2. Mean daily egg consumption (eggs/stomach) for sculpins 50 to 75 mm in length, ranged from 0 to 0.9 but differences among reefs were not significant. At one reef, significantly more eggs (2.5 eggs/stomach) were consumed by large sculpins (> 75 mm) than by small (44–49 mm) sculpins (0.2 eggs/stomach). Estimated egg consumption (eggs/stomach/m 2) for sculpins > 43 mm for the eight reefs for the period between estimated date of peak lake trout spawning and a standardized 30-d period post spawning, ranged from 0 to 496 eggs/m 2 consumed or from 0 to 54% of estimated egg abundance. No lake trout eggs were found in crayfish stomachs, because of their mode of feeding. Estimated egg consumption by crayfish was indirectly estimated from a relationship developed between carapace length and egg consumption using published literature and experimental work. Using this procedure, estimated egg consumption by crayfish for a standardized 30-d period after the date of peak spawning ranged from 0 to 65 eggs/m 2 consumed, or from 0 to 82% of potential egg abundance for the eight reefs. At low egg abundance (< 100/m 2), the density of crayfish and sculpin observed in Lake Ontario could result in sufficient egg consumption to cause almost 100% mortality of lake trout eggs. At higher egg abundance, however, mortality due to crayfish and sculpins appears to be relatively low. Deposition was sufficiently low at 5 of 8 sites to suggest the possible importance of sculpin and crayfish predation on lake trout recruitment failure in Lake Ontario.

Effects of an introduced piscivorous fish on native benthic fishes in a coastal river

1. We used field surveys to compare the density and mesohabitat‐scale distribution of the native coastrange sculpin (Cottus aleuticus) and the prickly sculpin (C. asper) in coastal rivers in north‐western California, U.S.A., with and without an introduced piscivorous fish, the Sacramento pikeminnow, Ptychocheilus grandis. We also measured mortality of tethered prickly sculpin in a field experiment including river, habitat type (pools versus riffles) and cover as factors.2. Average sculpin density (C. aleuticus and C. asper combined) in two rivers without pikeminnow was 21 times higher than the average density in two rivers in a drainage with introduced pikeminnow. In riffles, differences in the density of sculpins among rivers could be linked to differences in cover. However, riffles in rivers without pikeminnow had an average sculpin density 77 times higher than rivers with pikeminnow, yet only nine times more cover. In pools, cover availability did not differ among rivers, but the density of sculpins in rivers without pikeminnow was 11 times higher than rivers with pikeminnow.3. In the field experiment, mortality of tethered sculpin varied substantially among treatments and ANOVA indicated a significant River × Habitat × Cover interaction (P &lt; 0.001). Overall, tethered prickly sculpin suffered 40% mortality over 24 h in rivers with pikeminnow and 2% mortality in rivers without pikeminnow, suggesting that predation is the mechanism by which the pikeminnow affects sculpins.4. The apparent reduction in sculpin abundance by introduced pikeminnow has probably significantly altered food webs and nutrient transport processes, and increased the probability of extinction of coastrange and prickly sculpins in the Eel River drainage.

Fish abundance and habitat relationships in forest and grassland streams, northern Hokkaido, Japan

The relationships between habitat variables and population densities of masu salmon (Oncorhynchus masou), rosyface dace (Leuciscus ezoe), Siberian stone loach (Noemacheilus barbatulus) and wrinklehead sculpin (Cottus nozawae) were examined by data collected at 55 reaches in forest and grassland streams in northern Hokkaido, Japan. Regression analysis suggested that salmon and dace densities were affected by water temperature (negative for salmon, positive for dace) and structural habitat factors (woody debris for salmon, pools for dace). Salmon density was higher in forest reaches than in grassland reaches, whereas dace density was higher in grassland reaches, suggesting that the removal of riparian forest had raised water temperature and allowed upstream invasions by dace. In contrast to salmon and dace, neither the density of loach nor sculpin differed between the forest and grassland reaches. For their densities, a negative effect of each on the other was most important, suggesting a strong effect of interspecific competition between loach and sculpin on their distributions. However, regression models also suggested that substrate heterogeneity mediated the outcome of their interspecific competition. On the basis of the results, a scenario is predicted for a fish‐assemblage change with a typical land‐development process in Hokkaido, and the importance of leaving or restoring riparian buffer for conservation and restoration of stream habitat is emphasized.

Influence of a Benthic Predatory Fish (Cottus cognatus) on Invertebrate Community Structure and Secondary Production in a Tributary of the Susquehanna River

Abstract Populations of sculpin (Cottus cognatus) were altered to create stream sites with increased and decreased fish density. Subsequently, the response of benthic insect species was observed. Sculpin predation appeared to have little or no effect on size distributions and secondary production of most benthic invertebrates. However, densities of some trophic groups increased by two- or three-fold following reductions of sculpin densities. Within sites of sculpin removal, densities of gatherer/scrapers were twice those of addition or reference sites. Densities of total insect populations in reduction or reference sites were two to three times greater than those in the addition sites. Several trophic groups, particularly scraper/gatherers, showed the highest densities in sites of unaltered sculpin densities. Filter-feeders presented a third response to the manpulated sculpin populations; their densities increased with increased sculpin density. This suggests a negative sculpin influence on competitors of...

Effects of Experimental Fertilization on the Benthic Macroinvertebrate Community of an Arctic Lake

The benthic macroinvertebrate community of experimentally divided Lake N-2 (67°38′27″N, 149°37′30″W) was studied during six years of experimental fertilization. The dominant snail, Lymnaea elodes, increased on the fertilized side of the lake. Another snail, Valvata lewisi, previously shown to be competitively inferior to Lymnaea, did not increase in the fertilized sector until the fifth year of the study, but then increased dramatically. Chironomids were more abundant and had higher biomass on the reference side of the lake, an initial condition, and did not increase in the fertilized sector. Slimy sculpin, previously shown to control chironomids on bare sediments in nearby Toolik Lake, were the only fish predators on chironomids in Lake N-2; they did not grow faster in the fertilized sector. These results suggest that the dominant benthic invertebrates in N-2, chironomids and snails, were limited by different factors; chironomids were not food limited and appeared to be limited by predators, but snails, free from predation in N-2, appeared food limited. The planktonic model of cascading trophic interactions, if applied to benthic communities, would predict that, at low (zero) piscivore density, sculpin density and/or growth would increase as increased primary productivity was passed up the food web; they did not. The physical structure of the benthic zone is such that edible food can accumulate, whereas this cannot occur over extended time scales in planktonic systems. I suggest that this structural difference leads to functionally different constraints on planktonic and benthic communities.

Experimental Manipulation of Sculpin (Cottus cognatus) Populations in a Small Stream

Abstract We examined movement and age distribution of experimentally manipulated natural populations of slimy sculpin (Cottus cognatus) in streams having open and closed vegetation canopies. Densities were estimated in three treatments: reference populations (no transfers), reductions (fish removed from the sites), and additions (fish added to the sites). Biweekly replenishment of addition sites raised sculpin densities to over 10/m2 in the open canopy, at least 3 times that of reduction and reference populations. In closed canopy habitats, densities of addition populations (6/m2) were twice as great as reference populations (3/m2), although reduction populations (41m2) did not differ from either. Addition sites showed a net increase of numbers of sculpin over four summer months, in spite of a decline in older sculpin (age III-V years). Reduction sites showed no differences from reference sites regarding sculpin numbers, indicating that recruitment of fish to reduction sites did occur. However, more than ...

Effects of Winter Floods on Fishes in the Sierra Nevada

Winter floods in the Sierra Nevada mountains kill age 0 class brook trout (Salvelinus fontinalis) and Paiute sculpin (Cottus beldingi) because bed-material transport increases greatly when high flows are constrained by snow banks. In February 1982, dead Paiute sculpin were collected while sampling bedload during a rain-on-snow flood. Population estimates by electrofishing at nine permanent stations the following summer showed that density (3586∙ha−1) and biomass(12.9 kg∙ha−1) of Paiute sculpin were lower than the respective means (12 017∙ha−1 and 40.3 kg∙ha−1) obtained during previous studies from 1952 to 1961. These estimates were also below those obtained in 1956, after the largest winter flood from 1952 to 1961. Brook trout fry were also less abundant in 1982 than previously reported. Maximum flow depth, rather than discharge, were the likely cause offish mortality. Winter floods are severe because accumulated snowpack increases the effective height of the streambank and confines most or all of a rain-on-snow flood within the channel. Shear forces on the bed increase and as a result bed-material transport increases rapidly. These conditions directfy kill many benthic-living fishes such as the Paiute sculpin or buried eggs of fall-spawning fishes such as the brook trout by mechanical grinding or crushing. The impact of snow-constrained floods was not uniform along Sagehen Creek due to patchiness in types of riparian canopy. The relationship among canopy cover, snow accumulation, and winter floods points to one more critical role that buffer strips may play in ameliorating effects of timber harvesting.

The structure of sculpin populations along a stream size gradient

Data on spatial variation of sculpin density, growth and fecundity support the hypothesis that populations of stream fish are structured by changes in risk of predation and prey availability along a gradient in stream size. Cottus bairdi in warm streams and C. cognatus in cold streams exhibit similar patterns. Sculpins in large streams have faster individual growth rates and higher fecundities than those in small streams, but occur at lower density. The patterns appear to be persistent and suggest that predation reduces sculpin density in larger streams. Competitive release, variations in prey productivity, and local factors probably contribute to the variation in sculpin growth.