Trap Creek Date Method Efficiency fyke Fish H. 12 May 1993 dye 14% fyke Fish H. 17 May 1993 dye 1... more Trap Creek Date Method Efficiency fyke Fish H. 12 May 1993 dye 14% fyke Fish H. 17 May 1993 dye 17% fyke Fish H. 27 May 1993 We 6%* fyke Fish H. 27 May 1993 Radish 5%* fyke Fish H. 9 June 1993 Radish 6% screw Alt L. 9 June 1993 Radish 30%* indicates ...
This Section II of the entire report describes the results of the limnological sampling conducted... more This Section II of the entire report describes the results of the limnological sampling conducted on Redfish, Altras, Pettit and Stanley Lakes from October 1994 through October 1995. Included are descriptions of winter limnological conditions and kokanee growth characteristics from 1993 to 1995, limnological conditions during the spring, summer and fall of 1995, comparison of characteristics among the four lakes; fertilization of Redfish Lake in 1995; effects of fertilization and effects of annual avriations in planktivorous fish abundance. Individual chapters and their subject areas are listed in following abstracts.
This report was funded by the Bonneville Power Administration (BRA), U.S. Department of Energy, a... more This report was funded by the Bonneville Power Administration (BRA), U.S. Department of Energy, as part of BPA's program to protect, mitigate, and enhance fish and wildlife affected by the development and operation of hydroelectric facilities on the Columbia River and its tributaries. The views in this report are the author's and do not necessarily represent the views of BPA.
Lake trout (Salvelinus namaychush) and arctic char (S. Alpinus) typically are not found coexistin... more Lake trout (Salvelinus namaychush) and arctic char (S. Alpinus) typically are not found coexisting in arctic Alaskan lakes. Lake trout and artic char are generally top predators in lakes where they do not coexist. During the summer of 2004, I examined the effects of lake trout on dietary and habitat selection of arctic char near the Toolik Lake Field Station in arctic Alaska. I examined lakes containing either lake trout or arctic char as the top predator, and lakes containing both lake trout and arctic char. Natural abundace of Delta 15N and Delta 13C of seston, zooplankton, macroinvertebrates, and fish were used to construct food webs to examine any dietary and habitat shifts of arctic char and lake trout when they coexist. Lakes differed in 13C signature of basal resources, but fish tracked benthic 13C in all cases. However, lake trout were more enriched in 15N than arctic char, suggesting greater piscivory. These results strongly suggest that interspecific interactions are not v...
We tested the hypotheses that benthic macroinvertebrates, especially chironomid larvae in the Tri... more We tested the hypotheses that benthic macroinvertebrates, especially chironomid larvae in the Tribe Chironomini, from small oligotrophic arctic lakes are only weakly linked to pelagic food sources, and that they are trophically linked to biogenic methane. All offshore benthic macroinvertebrates sampled from 20 lakes were depleted in 13 C compared with nearshore benthic macroinvertebrates. Nearshore macroinvertebrates had ␦ 13 C consistent with feeding on periphyton and/or terrestrial detritus. However, ␦ 13 C of offshore Chironomini, the dominant macroinvertebrate group, and oligochaetes, was more depleted than that of other offshore macroinvertebrates to a degree that could only be explained by a diet that included carbon derived from biogenic methane. Seston ␦ 13 C showed a small shift toward greater depletion in deeper lakes, but ␦ 13 C of Chironomini, oligochaetes, and predatory chironomids varied as a function of dissolved oxygen concentration (DO) at the sediment-water interface, which was generally lower in shallow lakes that were deep enough to stratify. In lakes with lower DO in bottom waters, the importance of methane-based carbon to Chironomini was greater. Experimental 15 N enrichment of phytoplankton in small-and mid-sized arctic lakes resulted in limited 15 N enrichment of most benthic macroinvertebrates, indicating that their productivity was not closely tied to pelagic production. It is likely that aerobic benthic metabolism of dissolved organic carbon (DOC) also is an important energy source for benthic macroinvertebrates in sediments because the link between benthic macroinvertebrate production and contemporary pelagic primary production was weak regardless of dependence on biogenic methane. Coupling of benthic and pelagic food webs historically has been neglected in limnological studies, which have fo
We examined the effect of large (potentially piscivorous) lake trout (Salvelinus namaycush) on th... more We examined the effect of large (potentially piscivorous) lake trout (Salvelinus namaycush) on the dietary habits of small lake trout in an arctic lake. We hypothesized that large lake trout constrain the foraging of small lake trout, thus, in the absence of large lake trout, small lake trout will shift their diet from littoral to more abundant prey offshore. We tested this hypothesis using samples from a removal experiment where all lake trout large enough to be susceptible to gill nets were removed from a small arctic Alaskan lake during 1988-1989. We examined size at age and conducted stomach content and stable isotope analyses of lake trout collected during removal (1988), early recovery (1990), and late recovery (1999) portions of the study. Lake trout grew more quickly following removal. All lake trout fed on a variety of prey, but stomach analyses provided little information on segregation of diet between size classes. d 15 N and d 13 C analyses showed that small lake trout shifted their diet after large lake trout were removed, apparently toward more reliance on offshore zooplankton, which also implies a habitat shift to open water. Thus, we conclude that large lake trout are restricting the dietary habits of small lake trout, a restriction that was removed in an exploited population. Keywords d 15 N and d 13 C Á Foraging constraints Á Habitat Á Lake trout Á Stomach content analysis Á Trophic position Handling editor: M. Power
The prolific invasion of nonnative piscivores to Utah Lake is considered a major impediment to re... more The prolific invasion of nonnative piscivores to Utah Lake is considered a major impediment to recovery of the endangered June sucker. Our overall goal was to estimate predator consumption rates of the nonnative piscivorous fishes that currently dominate Utah Lake and to evaluate their potential impact on June suckers and other prey under current conditions and potential future management options. We synthesized all available information on lake temperature regime and the size, growth, and diet of walleye, catfish, white bass, and crappie as inputs into a bioenergetics analysis of predator consumption across one year, representing current conditions. We extrapolated our estimates of individual predator consumption to a population level using relative CPUE as a surrogate for abundance. Lastly, we compared isotopic-derived trophic position to diet composition, and re-ran a subset of model scenarios accordingly. Dominant predators (e.g., white bass, walleye, and catfish) consumed a high proportion of white bass, perch, carp, and crappie. However, unidentified fish in the diet make up a substantial portion of predator consumption; if even a small portion of the unidentified fish component is suckers, predatory impact on June suckers is likely significant. In addition, our predictions of predator consumption under a low carp abundance scenario (i.e., after removal) suggest that in years of poor recruitment of other predominant prey items (e.g., white bass and crappie), some predators may switch prey and consume a higher concentration of June suckers. Our comparison of isotopic-derived position to diet data indicated that: 1) Utah Lake is characterized by two primary pathways, a more pelagic food web and a more littoral food web, and 2) there appears to be fairly close correspondence between isotope-derived trophic position and diet composition for large top piscivores, and 3) more generalists (e.g., white bass) appear to be eating more fish (and potentially June suckers) than appears in the static diet samples. Lastly, we note that current modeling evaluations of the potential effects of different management scenarios are extremely limited by the lack of abundance information for almost all fishes of Utah Lake. Obtaining reliable estimates of relative abundance should be a top priority for future monitoring
Massive mortality ofplanktivorous fish had a dramatic impact on plankton community dynamics of La... more Massive mortality ofplanktivorous fish had a dramatic impact on plankton community dynamics of Lake Mendota, Wisconsin, USA. After fish mortality, the larger Daphniapulicaria replaced the smaller Daphnia galeata mendotae, resulting in greater grazing pressure on phytoplankton. This was accompanied by a much longer spring clear-water period and lower summer phytoplankton biomass compared to years before the fish mortality. Analysis of historical data (from the mid-1970's) showed that previous fluctuations in planktivorous abundance had similar effects on Daphnia abundance and species composition, and on spring phytoplankton biomass. However, the mid-1970's fish fluctuations had no detectable effect on summer phytoplankton. Concentrations of phosphorus were much higher in the 1970's (spring P 80-135/~g I-i) than in the 1980's (spring P 19-36/~g 1-1) and it is possible that high P concentrations may reduce trophic cascade effects on summer phytoplankton communities. This suggests that the success of biomanipulation programs may be dependent on lake nutrient status.
Summary1. The distribution of species is affected by many factors operating at a variety of tempo... more Summary1. The distribution of species is affected by many factors operating at a variety of temporal and spatial scales in a heterogeneous landscape. In lakes, fish communities are dynamic, influenced by landscape‐level factors that control colonisation and extinction.2. We used classification and regression tree (CART) analyses to quantify the importance of landscape‐level factors in determining the distribution of fish species in 168 arctic Alaskan lakes. Factors including lake size, depth, outflow gradient, distance to other lakes, lake order, altitude, river drainage and age of glacial surface were analysed. These factors could affect either access of fish to a lake (colonisation variables), or their survival in a lake that already had been colonised (extinction variables).3. The presence of a species was predicted accurately in 78.4% ± 10.5% (mean ± SD) of cases, and absence in 75.0% ± 6.1% of cases. The relative importance of extinction versus colonisation variables varied wit...
After a period of relative stasis, the crustacean zooplankton of Lake Mendota underwent a pronoun... more After a period of relative stasis, the crustacean zooplankton of Lake Mendota underwent a pronounced change in species composition between 1987 and 1988 (Lathrop and Carpenter, Ch. 9). This change was concordant with a dramatic die-off of cisco (Vanni et al. 1990; Rudstam et al., Ch. 12), indicating that changes in predation rates on different zooplankton groups may have been responsible for the observed shifts in zooplankton species composition. To determine the degree to which varying predation pressure resulted in changes in zooplankton abundance patterns, we examined the feeding relationships of the dominant zooplanktivores in the pelagic region of the lake and estimated the ability of these predators to regulate the dominant herbivorous zooplankton species. We were interested in determining the relative importance of various predators and in quantifying both interannual and seasonal dynamics of zooplanktivores and their prey.
Analyzing the freeze-thaw dates of high latitude lakes is an important part of climate change stu... more Analyzing the freeze-thaw dates of high latitude lakes is an important part of climate change studies. Due to the various advantages provided by the use of SAR images, with respect to remote monitoring of small lakes, SAR image analysis is an obvious choice to estimate lake freeze-thaw dates. An important property of SAR images is its texture. The problem of
Trap Creek Date Method Efficiency fyke Fish H. 12 May 1993 dye 14% fyke Fish H. 17 May 1993 dye 1... more Trap Creek Date Method Efficiency fyke Fish H. 12 May 1993 dye 14% fyke Fish H. 17 May 1993 dye 17% fyke Fish H. 27 May 1993 We 6%* fyke Fish H. 27 May 1993 Radish 5%* fyke Fish H. 9 June 1993 Radish 6% screw Alt L. 9 June 1993 Radish 30%* indicates ...
This Section II of the entire report describes the results of the limnological sampling conducted... more This Section II of the entire report describes the results of the limnological sampling conducted on Redfish, Altras, Pettit and Stanley Lakes from October 1994 through October 1995. Included are descriptions of winter limnological conditions and kokanee growth characteristics from 1993 to 1995, limnological conditions during the spring, summer and fall of 1995, comparison of characteristics among the four lakes; fertilization of Redfish Lake in 1995; effects of fertilization and effects of annual avriations in planktivorous fish abundance. Individual chapters and their subject areas are listed in following abstracts.
This report was funded by the Bonneville Power Administration (BRA), U.S. Department of Energy, a... more This report was funded by the Bonneville Power Administration (BRA), U.S. Department of Energy, as part of BPA's program to protect, mitigate, and enhance fish and wildlife affected by the development and operation of hydroelectric facilities on the Columbia River and its tributaries. The views in this report are the author's and do not necessarily represent the views of BPA.
Lake trout (Salvelinus namaychush) and arctic char (S. Alpinus) typically are not found coexistin... more Lake trout (Salvelinus namaychush) and arctic char (S. Alpinus) typically are not found coexisting in arctic Alaskan lakes. Lake trout and artic char are generally top predators in lakes where they do not coexist. During the summer of 2004, I examined the effects of lake trout on dietary and habitat selection of arctic char near the Toolik Lake Field Station in arctic Alaska. I examined lakes containing either lake trout or arctic char as the top predator, and lakes containing both lake trout and arctic char. Natural abundace of Delta 15N and Delta 13C of seston, zooplankton, macroinvertebrates, and fish were used to construct food webs to examine any dietary and habitat shifts of arctic char and lake trout when they coexist. Lakes differed in 13C signature of basal resources, but fish tracked benthic 13C in all cases. However, lake trout were more enriched in 15N than arctic char, suggesting greater piscivory. These results strongly suggest that interspecific interactions are not v...
We tested the hypotheses that benthic macroinvertebrates, especially chironomid larvae in the Tri... more We tested the hypotheses that benthic macroinvertebrates, especially chironomid larvae in the Tribe Chironomini, from small oligotrophic arctic lakes are only weakly linked to pelagic food sources, and that they are trophically linked to biogenic methane. All offshore benthic macroinvertebrates sampled from 20 lakes were depleted in 13 C compared with nearshore benthic macroinvertebrates. Nearshore macroinvertebrates had ␦ 13 C consistent with feeding on periphyton and/or terrestrial detritus. However, ␦ 13 C of offshore Chironomini, the dominant macroinvertebrate group, and oligochaetes, was more depleted than that of other offshore macroinvertebrates to a degree that could only be explained by a diet that included carbon derived from biogenic methane. Seston ␦ 13 C showed a small shift toward greater depletion in deeper lakes, but ␦ 13 C of Chironomini, oligochaetes, and predatory chironomids varied as a function of dissolved oxygen concentration (DO) at the sediment-water interface, which was generally lower in shallow lakes that were deep enough to stratify. In lakes with lower DO in bottom waters, the importance of methane-based carbon to Chironomini was greater. Experimental 15 N enrichment of phytoplankton in small-and mid-sized arctic lakes resulted in limited 15 N enrichment of most benthic macroinvertebrates, indicating that their productivity was not closely tied to pelagic production. It is likely that aerobic benthic metabolism of dissolved organic carbon (DOC) also is an important energy source for benthic macroinvertebrates in sediments because the link between benthic macroinvertebrate production and contemporary pelagic primary production was weak regardless of dependence on biogenic methane. Coupling of benthic and pelagic food webs historically has been neglected in limnological studies, which have fo
We examined the effect of large (potentially piscivorous) lake trout (Salvelinus namaycush) on th... more We examined the effect of large (potentially piscivorous) lake trout (Salvelinus namaycush) on the dietary habits of small lake trout in an arctic lake. We hypothesized that large lake trout constrain the foraging of small lake trout, thus, in the absence of large lake trout, small lake trout will shift their diet from littoral to more abundant prey offshore. We tested this hypothesis using samples from a removal experiment where all lake trout large enough to be susceptible to gill nets were removed from a small arctic Alaskan lake during 1988-1989. We examined size at age and conducted stomach content and stable isotope analyses of lake trout collected during removal (1988), early recovery (1990), and late recovery (1999) portions of the study. Lake trout grew more quickly following removal. All lake trout fed on a variety of prey, but stomach analyses provided little information on segregation of diet between size classes. d 15 N and d 13 C analyses showed that small lake trout shifted their diet after large lake trout were removed, apparently toward more reliance on offshore zooplankton, which also implies a habitat shift to open water. Thus, we conclude that large lake trout are restricting the dietary habits of small lake trout, a restriction that was removed in an exploited population. Keywords d 15 N and d 13 C Á Foraging constraints Á Habitat Á Lake trout Á Stomach content analysis Á Trophic position Handling editor: M. Power
The prolific invasion of nonnative piscivores to Utah Lake is considered a major impediment to re... more The prolific invasion of nonnative piscivores to Utah Lake is considered a major impediment to recovery of the endangered June sucker. Our overall goal was to estimate predator consumption rates of the nonnative piscivorous fishes that currently dominate Utah Lake and to evaluate their potential impact on June suckers and other prey under current conditions and potential future management options. We synthesized all available information on lake temperature regime and the size, growth, and diet of walleye, catfish, white bass, and crappie as inputs into a bioenergetics analysis of predator consumption across one year, representing current conditions. We extrapolated our estimates of individual predator consumption to a population level using relative CPUE as a surrogate for abundance. Lastly, we compared isotopic-derived trophic position to diet composition, and re-ran a subset of model scenarios accordingly. Dominant predators (e.g., white bass, walleye, and catfish) consumed a high proportion of white bass, perch, carp, and crappie. However, unidentified fish in the diet make up a substantial portion of predator consumption; if even a small portion of the unidentified fish component is suckers, predatory impact on June suckers is likely significant. In addition, our predictions of predator consumption under a low carp abundance scenario (i.e., after removal) suggest that in years of poor recruitment of other predominant prey items (e.g., white bass and crappie), some predators may switch prey and consume a higher concentration of June suckers. Our comparison of isotopic-derived position to diet data indicated that: 1) Utah Lake is characterized by two primary pathways, a more pelagic food web and a more littoral food web, and 2) there appears to be fairly close correspondence between isotope-derived trophic position and diet composition for large top piscivores, and 3) more generalists (e.g., white bass) appear to be eating more fish (and potentially June suckers) than appears in the static diet samples. Lastly, we note that current modeling evaluations of the potential effects of different management scenarios are extremely limited by the lack of abundance information for almost all fishes of Utah Lake. Obtaining reliable estimates of relative abundance should be a top priority for future monitoring
Massive mortality ofplanktivorous fish had a dramatic impact on plankton community dynamics of La... more Massive mortality ofplanktivorous fish had a dramatic impact on plankton community dynamics of Lake Mendota, Wisconsin, USA. After fish mortality, the larger Daphniapulicaria replaced the smaller Daphnia galeata mendotae, resulting in greater grazing pressure on phytoplankton. This was accompanied by a much longer spring clear-water period and lower summer phytoplankton biomass compared to years before the fish mortality. Analysis of historical data (from the mid-1970's) showed that previous fluctuations in planktivorous abundance had similar effects on Daphnia abundance and species composition, and on spring phytoplankton biomass. However, the mid-1970's fish fluctuations had no detectable effect on summer phytoplankton. Concentrations of phosphorus were much higher in the 1970's (spring P 80-135/~g I-i) than in the 1980's (spring P 19-36/~g 1-1) and it is possible that high P concentrations may reduce trophic cascade effects on summer phytoplankton communities. This suggests that the success of biomanipulation programs may be dependent on lake nutrient status.
Summary1. The distribution of species is affected by many factors operating at a variety of tempo... more Summary1. The distribution of species is affected by many factors operating at a variety of temporal and spatial scales in a heterogeneous landscape. In lakes, fish communities are dynamic, influenced by landscape‐level factors that control colonisation and extinction.2. We used classification and regression tree (CART) analyses to quantify the importance of landscape‐level factors in determining the distribution of fish species in 168 arctic Alaskan lakes. Factors including lake size, depth, outflow gradient, distance to other lakes, lake order, altitude, river drainage and age of glacial surface were analysed. These factors could affect either access of fish to a lake (colonisation variables), or their survival in a lake that already had been colonised (extinction variables).3. The presence of a species was predicted accurately in 78.4% ± 10.5% (mean ± SD) of cases, and absence in 75.0% ± 6.1% of cases. The relative importance of extinction versus colonisation variables varied wit...
After a period of relative stasis, the crustacean zooplankton of Lake Mendota underwent a pronoun... more After a period of relative stasis, the crustacean zooplankton of Lake Mendota underwent a pronounced change in species composition between 1987 and 1988 (Lathrop and Carpenter, Ch. 9). This change was concordant with a dramatic die-off of cisco (Vanni et al. 1990; Rudstam et al., Ch. 12), indicating that changes in predation rates on different zooplankton groups may have been responsible for the observed shifts in zooplankton species composition. To determine the degree to which varying predation pressure resulted in changes in zooplankton abundance patterns, we examined the feeding relationships of the dominant zooplanktivores in the pelagic region of the lake and estimated the ability of these predators to regulate the dominant herbivorous zooplankton species. We were interested in determining the relative importance of various predators and in quantifying both interannual and seasonal dynamics of zooplanktivores and their prey.
Analyzing the freeze-thaw dates of high latitude lakes is an important part of climate change stu... more Analyzing the freeze-thaw dates of high latitude lakes is an important part of climate change studies. Due to the various advantages provided by the use of SAR images, with respect to remote monitoring of small lakes, SAR image analysis is an obvious choice to estimate lake freeze-thaw dates. An important property of SAR images is its texture. The problem of
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