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Report to Perch Lake Association (Iron County, MI) Brett Peters, Graduate Student David Lodge, Director, Center for Aquatic Conservation This report includes results of biological surveys we conducted in Perch Lake in the summers of 2006 and 2007. The purpose of these surveys was to monitor the crayfish population, to assess the fish species present in the lake, and the amount of predation pressure fish may have on crayfish. Rusty crayfish are native to the Ohio River basin, but have been spread extensively throughout the Midwest by anglers who discard unused crayfish into lakes (Capelli and Magnuson 1983,). Once established in lakes, rusty crayfish displace native crayfish, reduce macroinvertebrates and aquatic vegetation (macrophytes), which ultimately can affect certain inland fisheries (Lodge et al. 1994, Olsen et al. 1991, Garvey et al. 2003, Dorn and Mittelbach 2004) Rusty Crayfish Population Monitoring In 2006 we sampled Perch Lake twice for crayfish using standard methods (modified minnow traps baited with 120±10 grams beef liver set over night) (Figure 1). In 2007 Perch Lake was sampled once for crayfish (Figure 2). We placed all traps at the same locations both years using GPS coordinates. No trend is apparent in trap catches in Perch Lake over time (Fig 3). Figure 4 shows the change in crayfish trap catches at individual sites, which Notre Dame has monitored from 2006 to 2007. The Perch Lake Association could compare this map to data they have for the crayfish removed from Association members to determine if crayfish trapping is having a noticeable effect on the crayfish population.

Figure 1. 2006 average crayfish trap catches.

Figure 2. 2007 crayfish trap catches.

45 Male (form 1) crayfish per trap 40 35 30 25 20 15 10 5 0 2002 2003 2004 2005 2006 2007 Year Perch Little Star Papoose

Figure 3. Trap catches for three lakes monitored by Notre Dame from 2002-2007. Error bars represent 95% confidence intervals.

Figure 4. Changes in crayfish trap catches from 2006 to 2007. Each number is the 2007 catch minus the 2006 catch for each site.

Fish Community We sampled the fish community of Perch Lake in the summer of 2006, and compare this with sampling we conducted in 2003. In both years fish were collected using DC electrofishing using the US Forest Service boat in 2003 and a University of Notre Dame boat in 2006. (Tables 1 and 2). In 2006, there was more effort (time shocking) than in 2003 so the number of fish collected in each year cannot be directly compared. Figures 5-7 show the size distributions of popular game species caught in 2003 and 2006. In addition to collecting length and weight data on fish captured, diet was also determined for many fishes using gastric lavage, a non-lethal method of collected stomach contents. No crayfish were found in the guts of fish lavaged in 2003 (Table 1). In 2006, 25% of rock bass lavaged had crayfish present in their guts and 10% of perch had crayfish

present in their guts (Table 2). The proportion of crayfish in fish diets mentioned above are similar to the levels of crayfish predation we see in most lakes with rusty crayfish. (Jody Murray unpublished data). In addition to sampling fish diets through gastric lavage, we also measured the predation pressure on crayfish in Perch Lake using tethered crayfish. In this study, 99 crayfish were tethered to a clay tile using superglue and monofilament fishing line. The 99 crayfish used in these trials are equally divided among 3 size classes: small (15-18mm Carapace Length (CL))), medium (23-25mm CL) and large (33-35mm CL) crayfish. The proportion of the crayfish removed overnight serves as an index of predation of crayfish. When compared to other lakes, Perch Lake had lower predation pressure on most crayfish size classes (Figure 8). Predation pressure is very low on medium crayfish compared to most other lakes (Figure 8). The low predation pressure on the medium sized crayfish is most likely attributable to a lack of large crayfish predators (Figures 5-7 and Tables 1-2). The other lakes in Figure 8 have smallmouth bass populations which are very effective at consuming larger crayfish. Small crayfish are being consumed at a rate that is similar to the other lakes surveyed (Figure 8). This is likely attributable to the rock bass and perch, which cannot consume large crayfish, and which are abundant in Perch Lake.

# of fish caught 1 4 1 1 2 3 6 16 7 32 # of fish lavaged 1 0 0 0 0 0 6 8 0 9 # of fish with crayfish in gut 0 0 0 0 0 0 0 0 0 0

Species Black Crappie Bullhead Golden Shiner Largemouth Bass Northern Pike Pumpkinseed Rock Bass Walleye White Sucker Yellow Perch

Table 1. Summary of 2003 electrofishing survey.

Species Black Crappie Bluegill Golden Shiner Minnow Northern Pike Pumpkinseed Rock Bass Walleye White Sucker Yellow Perch

# of fish caught 1 29 1 6 2 43 18 27 3 69

# of fish lavaged 0 3 0 0 0 13 8 10 0 10

# of fish with crayfish in gut 0 0 0 0 0 0 2 0 0 1

Table 2. Summary of 2006 electrofishing survey.

1 0.9 Proportion of total catch 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.03.9 4.05.9 6.07.9 8.09.9 10.0- 12.0- 14.0- 16.0- 18.0- 20.011.9 13.9 15.9 17.9 19.9 21.9 2003 2006

Total Length (inches)

Figure 5. Walleye size distributions in 2003 and 2006.

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.0-3.9 4.0-5.9 6.0-7.9 8.0-9.9 Total Length (inches)

Proportion on total catch

2003 2006

Figure 6. Rock Bass size distributions in 2003 and 2006.

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0-1.9 2.0-3.9 4.0-5.9 6.0-7.9 8.0-9.9 10.0-11.9 Total Length (inches)

Proportion of total catch

2003 2006

Figure 7. Yellow Perch size distributions in 2003 and 2006.

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Perch Ottawa Pomeroy Lake Star Little Star

Portion of size class missing

small medium large

Figure 8. Proportion of tethered crayfish removed in an overnight predation assay.

Summary and Recommendations Based on the long-term trapping (Figure 3) it appears that the Perch Lake crayfish population has remained low. The cause of the year-to-year variation in trap catches (Fig. 3) is not clear; it could be natural variation or it could include an effect of the trapping efforts by Perch Lake residents. It might be informative to compare the number of crayfish removed via trapping by the Association to the local declines found in 2007(Figure 4), although local trapping efforts might be swamped by immigration of crayfish from neighboring sites. It appears that the Forest Service has decided not to build a walleye spawning reef. With regards to preventing an increase in the rusty crayfish population, we believe this is a good decision...A walleye reef would add crayfish habitat and an increased

walleye population could suppress other fish populations such as yellow perch which are important crayfish consumers. The most important crayfish predator populations in Perch Lake are the rock bass and yellow perch populations. Rock bass are often treated as "rough fish" and killed by anglers. The removal or killing of rock bass should be discouraged if the goal is to prevent rusty crayfish from increasing. Signage at the boat launch may be useful is minimizing the unnecessary killing of rock bass. Most importantly, the crayfish population should continue to be monitored annually using standard methods. At the current level, the crayfish population is probably having little impact on the Perch Lake ecosystem.

Literature Cited Capelli, G.M., and J.J. Magnuson. 1983. Morphoedaphic and biogeographic analysis of crayfish distribution in northern Wisconsin. J. Crustac. Biol. 3: 548­564. Dorn, N.J., and G.G Mittelbach. 2004. Effects of a native crayfish (Orconectes virilis) on the reproductive success and nesting behavior of sunfish (Lepomis spp.). Can. J. Fish. aquat. Sci. 61: 2135­2143. Garvey, J.E., J.E. Rettig, R.A. Stein, D.M. Lodge and S.P. Klosiewski. 2003. Scaledependent association among fish predation, littoral habitat, and distributions of crayfish species. Ecology 18: 3339­3348. Lodge, D.M., M.W. Kershner, J.E. Aloi and A.P. Covich. 1994. Effects of an omnivorous crayfish (Orconectes rusticus) on a fresh-water littoral food-web. Ecology, 75: 1265­1281. Olsen, T.M., D.M. Lodge, G.M. Capelli and R.J. Houlihan. 1991. Mechanisms of impact of an introduced crayfish (Orconectes rusticus) on littoral congeners, snails, and macrophytes. Can. J. Fish. Aquat. Sci. 48: 1853­1861.


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