W. Lindsay Chadderton, The Nature Conservancy, South Bend, IN Randall M. Claramunt, Fisheries Division, Michigan Department of Natural Resources, MI

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1 Rusty Crayfish control on native fish spawning reefs in Northern Lake Michigan W. Lindsay Chadderton, The Nature Conservancy, South Bend, IN Randall M. Claramunt, Fisheries Division, Michigan Department of Natural Resources, MI Matthew E. Herbert, The Nature Conservancy, Lansing, MI Tracy L. Galarowicz, Biology, Central Michigan University, Mount Pleasant, MI Jackson Gross, Smith Root Inc.

2 Great Lake s Spawning Reefs

3 Study Site- Northern Lake Michigan reefs

4 Impediments to native fish recruitment on spawning reefs Low spawner abundance, low egg numbers on historically important spawning reefs

5 Impediments to native fish recruitment on spawning reefs Predation of eggs and fry Previously by Alewife Increasingly Round Goby and Rusty Crayfish Fitzsimons, J. D., et al.." Journal of Fish Biology 71.1 (2007): 1-16.

6 Our objectives Deplete crayfish prior to spawning through intensive trapping to reduce densities of crayfish during native reef fish egg deposition and egg development. Experimentally quantify the lethality, effective control range, and suppression duration of seismic guns on rusty crayfish (and especially goby).

7 Assumptions Trapping will be most effective when crayfish are most active (i.e. late July to September) Recolonization will be minimal during the cooler fall months as crayfish activity slows Seismic gun may allow rapid secondary treatment over a larger buffer area around the reefs immediately prior to spawning Trapping precedent from Hein et al. study

8 Seismic Gun Methods Lethality Tests July & Oct 2013 Small & Large gun 0-24 shots at 1,3,6, 12m from gun Behavioral Test Large gun, 20 minutes rapid fire over reef (~ 250 shots) Also simulated reef treatment Used baited underwater video to observe number of crayfish pre, during, post treatment

9 Results- Seismic Gun NO mortality in lethality experiments NO evidence of sub-lethal effects including ear bones NO evidence of behavioral effect

10 Methods Intensive Removal 2012 Baited Gee minnow traps (24-48 hr sets) 1 AUG to 9 SEP & 1 st week of OCT Tangle nets (OCT only)

11 Methods Intensive Removal cont Hand removal by SCUBA divers Tangle nets Limited minnow traps Delayed treatment (mid-sep to mid-nov (most sites); mid AUG to end OCT (Crib)

12 Approx removed Results- Removal

13 Results- Removal 2012 Trapping effort was comparable to previous successful eradication

14 Results- Removal 2013 Despite doubling numbers removed in 2013 Still NO evidence for significant reduction in crayfish densities

15 Results- Removal 2013 Evidence for reef recolonization NO indication of offshore migration late in season = Year round resident crayfish pop ns Transient home ranges Recolonization occurs quickly

16 Results- Removal 2012 Low CPUE in our study why?

17 Results- Removal 2012 Density 1.3 crayfish/m 2 (our study) vs. ~ 1 crayfish/m 2 (Sparkling Lake)

18 Results- Removal 2012 Low CPUE in our study why? Timing of life history (Hein et al. peak capture o C)

19 Results- Removal 2012 Low CPUE in our study why? Timing of life history increasing capture of females over time Consistent with reduce female activity in midsummer Possible evidence of delayed mating and/or molt

20 Management Recommendations Crayfish are abundant and resident on spawning reefs year-round. Crayfish control is warranted. Alternative capture methods are needed to replace standard minnow trap (hand removal/unescapable) Seasonality of removal matters (life history implications); narrow window for most effective removal Development of barriers to prevent recolonization are needed so removal efforts can be sustained Control efforts could be enhanced by integrating biological control approaches that increase native predator density

21 Results- Removal 2013 Increased total capture and capture efficiency

22 Alternative capture methods

23 Alternative capture methods and potential barrier

24 Barriers to recolonization

25 Alternate capture or barrier methods

26 Project supported by EPA under the terms of GLRI Grant #GL- 00E

27 Questions?

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