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Norman D. Yan - One of the best experts on this subject based on the ideXlab platform.

  • modification of the diel vertical migration of bythotrephes longimanus by the cold water planktivore coregonus artedi
    Freshwater Biology, 2008
    Co-Authors: Joelle D Young, Norman D. Yan
    Abstract:

    Summary 1. The weak diel vertical migration observed in the large cladoceran Bythotrephes longimanus seems contradictory to the predator-avoidance hypothesis that predicts large zooplankton should have long migration amplitudes. However, cold-water Planktivores, especially Coregonus spp., are a main source of mortality for Bythotrephes and hence a deeper migration would result in a greater overlap with these hypolimnetic Planktivores. We hypothesized that Coregonus artedi (cisco) modifies the normal vertical migration pattern of Bythotrephes, such that the latter stays higher in the water column during the day and thus migrates less extremely at night. 2. The vertical distribution of Bythotrephes during the day was determined from single visits to six lakes in Ontario, Canada, all of which contain warm-water, epilimnetic Planktivores but differing in whether they contain cisco. One lake of each fish type was sampled day and night every 2–3 weeks over the ice-free season to examine daytime depths and migration amplitude. 3. The vertical migration of Bythotrephes differed in the presence and absence of cisco. In the lakes with cisco, there were significantly fewer Bythotrephes in the hypolimnion and they were higher in the water column during the day. Migration amplitude was smaller in the cisco than in the non-cisco lake. These observations were not attributable to differences in physical factors, and, although not conclusively attributable to cisco, are consistent with an effect of cisco. 4. We suggest that diurnal depth selection by Bythotrephes in lakes containing cisco is a trade-off between the risk of predation by warm- versus cold-water predators, balanced by the benefits of increased temperature and feeding rates near the surface. Even in lakes without cisco, however, the vertical migration of Bythotrephes was less than expected, suggesting that diurnal depth selection is a balance between the risk from warm-water Planktivores and access to sufficient light to feed effectively.

Richard C Lathrop - One of the best experts on this subject based on the ideXlab platform.

  • stocking piscivores to improve fishing and water clarity a synthesis of the lake mendota biomanipulation project
    Freshwater Biology, 2002
    Co-Authors: Brett M Johnson, M T Vogelsang, S R Carpenter, John J Magnuson, Thomas R. Hrabik, Richard C Lathrop, James F Kitchell, Timothy B. Johnson, Lars G Rudstam
    Abstract:

    SUMMARY 1. A total of 2.7 · 10 6 walleye fingerlings and 1.7 · 10 5 northern pike fingerlings were stocked during 1987–99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha )1 and stabilised at 4–6 kg ha )1 throughout the evaluation period. 2. Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3. Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300–600 kg ha )1 prior to the die-off and the fish stocking, to about 20–40 kg ha )1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4. During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5. In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6. The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the

  • Stocking piscivores to improve fishing and water clarity: a synthesis of the Lake Mendota biomanipulation project
    Freshwater Biology, 2002
    Co-Authors: Richard C Lathrop, Brett M Johnson, M T Vogelsang, John J Magnuson, Thomas R. Hrabik, James F Kitchell, Lars G Rudstam, Timothy B. Johnson, Stephen R. Carpenter, R. S. Stewart
    Abstract:

    1. A total of 2.7 × 10 6 walleye fingerlings and 1.7 × 10 5 northern pike fingerlings were stocked during 1987-99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha -1 and stabilised at 4-6 kg ha -1 throughout the evaluation period. 2. Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3. Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300-600 kg ha -1 prior to the die-off and the fish stocking, to about 20-40 kg ha -1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4. During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5. In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6. The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the diversity of fishing opportunities have improved for walleye, northern pike and, more recently, yellow perch.

Lars G Rudstam - One of the best experts on this subject based on the ideXlab platform.

  • stocking piscivores to improve fishing and water clarity a synthesis of the lake mendota biomanipulation project
    Freshwater Biology, 2002
    Co-Authors: Brett M Johnson, M T Vogelsang, S R Carpenter, John J Magnuson, Thomas R. Hrabik, Richard C Lathrop, James F Kitchell, Timothy B. Johnson, Lars G Rudstam
    Abstract:

    SUMMARY 1. A total of 2.7 · 10 6 walleye fingerlings and 1.7 · 10 5 northern pike fingerlings were stocked during 1987–99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha )1 and stabilised at 4–6 kg ha )1 throughout the evaluation period. 2. Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3. Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300–600 kg ha )1 prior to the die-off and the fish stocking, to about 20–40 kg ha )1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4. During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5. In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6. The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the

  • Stocking piscivores to improve fishing and water clarity: a synthesis of the Lake Mendota biomanipulation project
    Freshwater Biology, 2002
    Co-Authors: Richard C Lathrop, Brett M Johnson, M T Vogelsang, John J Magnuson, Thomas R. Hrabik, James F Kitchell, Lars G Rudstam, Timothy B. Johnson, Stephen R. Carpenter, R. S. Stewart
    Abstract:

    1. A total of 2.7 × 10 6 walleye fingerlings and 1.7 × 10 5 northern pike fingerlings were stocked during 1987-99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha -1 and stabilised at 4-6 kg ha -1 throughout the evaluation period. 2. Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3. Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300-600 kg ha -1 prior to the die-off and the fish stocking, to about 20-40 kg ha -1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4. During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5. In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6. The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the diversity of fishing opportunities have improved for walleye, northern pike and, more recently, yellow perch.

Thomas R. Hrabik - One of the best experts on this subject based on the ideXlab platform.

  • stocking piscivores to improve fishing and water clarity a synthesis of the lake mendota biomanipulation project
    Freshwater Biology, 2002
    Co-Authors: Brett M Johnson, M T Vogelsang, S R Carpenter, John J Magnuson, Thomas R. Hrabik, Richard C Lathrop, James F Kitchell, Timothy B. Johnson, Lars G Rudstam
    Abstract:

    SUMMARY 1. A total of 2.7 · 10 6 walleye fingerlings and 1.7 · 10 5 northern pike fingerlings were stocked during 1987–99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha )1 and stabilised at 4–6 kg ha )1 throughout the evaluation period. 2. Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3. Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300–600 kg ha )1 prior to the die-off and the fish stocking, to about 20–40 kg ha )1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4. During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5. In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6. The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the

  • Stocking piscivores to improve fishing and water clarity: a synthesis of the Lake Mendota biomanipulation project
    Freshwater Biology, 2002
    Co-Authors: Richard C Lathrop, Brett M Johnson, M T Vogelsang, John J Magnuson, Thomas R. Hrabik, James F Kitchell, Lars G Rudstam, Timothy B. Johnson, Stephen R. Carpenter, R. S. Stewart
    Abstract:

    1. A total of 2.7 × 10 6 walleye fingerlings and 1.7 × 10 5 northern pike fingerlings were stocked during 1987-99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha -1 and stabilised at 4-6 kg ha -1 throughout the evaluation period. 2. Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3. Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300-600 kg ha -1 prior to the die-off and the fish stocking, to about 20-40 kg ha -1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4. During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5. In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6. The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the diversity of fishing opportunities have improved for walleye, northern pike and, more recently, yellow perch.

  • predicting mercury levels in yellow perch use of water chemistry trophic ecology and spatial traits
    Canadian Journal of Fisheries and Aquatic Sciences, 2001
    Co-Authors: B K Greenfield, Thomas R. Hrabik, Chris J Harvey, Stephen R. Carpenter
    Abstract:

    Recent research suggests that wetland abundance surrounding lakes, fish trophic position, and fish community composition may influence the bioavailability of mercury (Hg) to fish. To compare the importance of these spatial and biological factors to chemical factors known to influence bioavailability, we determined the relationship between 24 lake traits and Hg concentrations in yellow perch (Perca flavescens; whole fish samples) for 43 northern Wisconsin lakes. Independent variables included biological traits such as fish trophic position and body condition, spatial traits such as lake hydrologic position and surrounding wetland abundance, and chemical traits such as pH and water color. The strongest predictor of fish Hg levels was pH (R2 = 0.42; p < 0.002). Of the biological traits measured, yellow perch body condition explained significant additional variation (final R2 = 0.54; p = 0.024). Trophic position explained limited variability and population abundance of Planktivores and piscivores were not cor...

Stephen R. Carpenter - One of the best experts on this subject based on the ideXlab platform.

  • Stocking piscivores to improve fishing and water clarity: a synthesis of the Lake Mendota biomanipulation project
    Freshwater Biology, 2002
    Co-Authors: Richard C Lathrop, Brett M Johnson, M T Vogelsang, John J Magnuson, Thomas R. Hrabik, James F Kitchell, Lars G Rudstam, Timothy B. Johnson, Stephen R. Carpenter, R. S. Stewart
    Abstract:

    1. A total of 2.7 × 10 6 walleye fingerlings and 1.7 × 10 5 northern pike fingerlings were stocked during 1987-99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha -1 and stabilised at 4-6 kg ha -1 throughout the evaluation period. 2. Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3. Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300-600 kg ha -1 prior to the die-off and the fish stocking, to about 20-40 kg ha -1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4. During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5. In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6. The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the diversity of fishing opportunities have improved for walleye, northern pike and, more recently, yellow perch.

  • predicting mercury levels in yellow perch use of water chemistry trophic ecology and spatial traits
    Canadian Journal of Fisheries and Aquatic Sciences, 2001
    Co-Authors: B K Greenfield, Thomas R. Hrabik, Chris J Harvey, Stephen R. Carpenter
    Abstract:

    Recent research suggests that wetland abundance surrounding lakes, fish trophic position, and fish community composition may influence the bioavailability of mercury (Hg) to fish. To compare the importance of these spatial and biological factors to chemical factors known to influence bioavailability, we determined the relationship between 24 lake traits and Hg concentrations in yellow perch (Perca flavescens; whole fish samples) for 43 northern Wisconsin lakes. Independent variables included biological traits such as fish trophic position and body condition, spatial traits such as lake hydrologic position and surrounding wetland abundance, and chemical traits such as pH and water color. The strongest predictor of fish Hg levels was pH (R2 = 0.42; p < 0.002). Of the biological traits measured, yellow perch body condition explained significant additional variation (final R2 = 0.54; p = 0.024). Trophic position explained limited variability and population abundance of Planktivores and piscivores were not cor...

  • Resilience and resistance of a lake phosphorus cycle before and after food web manipulation.
    The American naturalist, 1992
    Co-Authors: Stephen R. Carpenter, Clifford E. Kraft, Russell A. Wright, Patricia A. Soranno, James R. Hodgson
    Abstract:

    Parameters of a phosphorus cycling model were estimated for two configurations of a lake ecosystem. The piscivore-dominated configuration had one more trophic level than the planktivore-dominated configuration. We derived four main conclusions from analysis of the model. (1) Results support the argument of DeAngelis et al. that turnover rate of a limiting nutrient is directly related to ecosystem resilience. (2) Results support the hypothesis of Pimm and Lawton that longer food chains are less resilient. (3) Inputs of phosphorus to the pelagic system derived from inshore feeding by fishes were a large flux, which is comparable to inputs from physical-chemical fluxes. (4) Algal (seston) standing crops, unlike all other compartments, were less sensitive to phosphorus inputs in the piscivore-dominated system. Consistent with the trophic cascade hypothesis, the piscivore-dominated system had higher herbivore standing crops and lower algal standing crops than the planktivore-dominated system. Changes in trophi...