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Update on Sparkling Lake predators, smelt, and crayfish densities

Update on Sparkling Lake predators, smelt, and crayfish densities. B.M. Roth, C.L. Hein, S.A. Lischka T.R. Hrabik, M.J. Vander Zanden, N. Mercado-Silva J.J. Magnuson, S.R. Carpenter, J.F. Kitchell. Eradication Gameplan: Smelt. Remove adults during spawning run with fyke nets

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Update on Sparkling Lake predators, smelt, and crayfish densities

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  1. Update on Sparkling Lake predators, smelt, and crayfish densities B.M. Roth, C.L. Hein, S.A. Lischka T.R. Hrabik, M.J. Vander Zanden, N. Mercado-Silva J.J. Magnuson, S.R. Carpenter, J.F. Kitchell

  2. Eradication Gameplan: Smelt • Remove adults during spawning run with fyke nets • Increase predation by stocking walleye (and muskies)

  3. Eradication Gameplan: Rusty crayfish • Intensively trap adults • Increase predation on juveniles John Magnuson

  4. Adult Smelt Removal : 375kg : 1800kg

  5. Smelt spawning temp Average Daily Temperature from Sparkling Lake 3/11 to 6/1(Courtesy of NTL-LTER) • Smelt spawn immediately after ice out (Water temp = 4.4 C) (Becker 1983)

  6. Smelt Us Counting Walleye Bioenergetics Smallmouth bass Bioenergetics Crayfish Katie Counting Smallmouth bass Bioenergetics Rock bass Bioenergetics Mortality Sources

  7. Smelt and Crayfish Mortality Crayfish Smelt

  8. Size Distributions of Rusty Crayfish in Sparkling Lake

  9. Smelt and Crayfish Mortality Crayfish Smelt

  10. Specific ecosystem responses to: • Fishery regulation changes • Exploitation • Increased predation

  11. Multiple Working Hypotheses • Fishery regulation changes (Predators) • Increase in number and size structure • Exploitation • Overall decrease in exotic populations/density (crayfish and smelt) • Decreased ambient carapace length (crayfish) • Increased production and/or survivorship of juveniles (crayfish) • Increased predation (smelt and crayfish) • Alternate prey become more prevalent in predator diets • Implications for predator growth?

  12. Predator Population Estimates • 2001: • All three species: Continuous Schnabel mark-recapture estimates during summer only • 2002: • Walleye: Spring mark, continuous mark-recap during summer • RB & SMB: summer mark-recap only • 2003 • Walleye & RB: Spring mark, continuous mark-recapture during summer • SMB: summer mark-recap only

  13. Predator Population Estimates

  14. Response of Exotics to Exploitation • Decreased population or density (smelt and crayfish) • Decreased ambient carapace length • Increased production and survivorship of juveniles • More macrophytes and snails

  15. Sampled 6 lakes in 2002 and 2003 • Early July • Late August • Variables measured: • Total crayfish density • YOY crayfish • Crayfish >10mm carapace length • Lengths • All crayfish >10mm carapace length

  16. 2002 2003 All collection done on cobble substrate ONLY (France 1985)

  17. (#/m2) Use Crayfish Density as a Proxy Aug 2003 Jul 2002 Aug 2002 Jul 2003 Density of crayfish >10mm actually went up on cobble substrate!!

  18. Smelt Population Estimates • 2001: 770,000 • 2002: 423,000 • 2003: ???,???

  19. Response of Exotics to Exploitation • Decreased population • Decreased ambient carapace length (crayfish) • Increased production and survivorship of juveniles (crayfish) • More macrophytes and snails

  20. Crayfish Size Distribution in Sparkling Lake No apparent change!!

  21. Increased Production of Juveniles (July Samples) Sparkling had the largest density decrease among lakes sampled

  22. Decreased Juvenile Mortality?? YOY mortality was higher in 2002 than in 2003

  23. Increased predation • Alternate prey become more prevalent in predator diets (smelt and crayfish) • Implications for predator growth?

  24. Smallmouth bass Rock bass

  25. Walleye

  26. Smallmouth bass Walleye

  27. Smallmouth bass Walleye

  28. Increased predation • Alternate prey become more prevalent in predator diets (smelt and crayfish) • Implications for predator growth? • Residuals of length-weight regression line grouped by year

  29. smallmouth bass rock bass walleye a b b a a ac b a b ac b c Two-way ANOVA, p < 0.001 Bonferroni post-hoc test for pairwise mean differences

  30. More to Come.. • How will crayfish densities, growth, and reproduction respond to continued exploitation? • Are smelt going to pull off a year class? • Will trends continue? • Predator growth • Diet shifts

  31. Acknowledgments • NSF-Biocomplexity, NTL-LTER • Steve Gilbert, WDNR • Greg Sass, Michele Woodford, Scott Van Egeren • Gretchen Anderson, Adam Ray, Ellen Feingold, Andrea Fowler, Patrick Hermann, Laura Kessler

  32. Mucky, weedy substrate Cobble substrate Rapid Establishment Slow Establishment Poor initial production Good initial production High YOY density Low YOY density Adult Densities Stay Low Adult Densities Rapidly Increase Macrophytes Remain Macrophytes Decline YOY predators remain high YOY predators decline Two Regimes Introduction ???

  33. Crayfish Consumption Smelt Consumption No Data

  34. Add Predators..

  35. Pre-removal Post-removal with Stocking

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