The Effects of Lake Productivity and Campsite Usage on Crayfish Abundance Within the Boundary Waters Canoe Area Sarah Schieffer, Nicole Bauer, Brandon Urhammer, Sarah Bartholomew Faculty Mentor: Todd Wellnitz, Biology Department Percent of Rusty Crayfish Non sampled lakes 0% 1-40% 41-80% % Trip route r 2 = 0.23 P <0.001 Introduction Invasive rusty crayfish (Orconectus rusticus) have wide-ranging, negative effects on lake ecosystems (Strayer 2010) and threaten the Boundary Water Canoe Area Wilderness (BWCAW) of northern Minnesota. Building on a 2012 survey documenting the spread of rusty crayfish along a popular, 40-mile canoe route, this study had three objectives: 1.To map the extend of O. rusticus spread along the route’s 20 lakes. 2.To determine if a relationship exists between crayfish abundance and lake productivity – i.e., the rate of biomass production in a lake 3.To establish whether human presence at campsites affected shoreline crayfish distributions, in particular, rusty crayfish. Methods A B Active Sampling: Walking shorelines and collecting and counting crayfish at 10 minute intervals (A) near and away (> 30 m) from campsites. Passive Sampling: Lakes sampled using 12 baited traps (A) set near campsites overnight and capture crayfish (B) were processed the following morning. Results References Puth L, Allen T. (2005). Potential corridors for the rust crayfish, Orconectes rusticus, in northern Wisconsin (USA) lakes: lessons for exotic invasions. Landscape Ecology 20(5): Strayer D. (2010). Alien species in freshwaters: ecological effects, interactions with other stressors, and prospects for the future. Freshwater Biology 55(1): Discussion Of the seven lakes sampled, four had rusty crayfish (see map). Rusty crayfish dominated the assemblage (>75% of the catch) in 3 of the 4 lakes where they were found. As lakes became more productive, we found significantly more crayfish, although the relationship was poor (Fig. 1). There was a trend suggesting O. rusticus comprised a larger proportion of the crayfish assemblage as lake productivity increased (Fig. 2). Crayfish were significantly larger in more productive lakes (Fig. 3). Crayfish were more abundant near campsite then further away (Fig. 4). Figure 1. A Secchi disk (pictured) assesses lake productivity by measuring water clarity – the deeper the disk can be seen, the less productive the lake. Combining data our data with the 2012 study, we found a positive relationship between number of crayfish caught in traps and lake productivity. Figure 2. As lakes became more productive, a larger proportion of the crayfish assemblage was made up of O. rusticus. Figure 3. As lakes became more productive, the crayfish became larger. Figure 3. Crayfish were more abundant near campsites than they were at sites >30 m distant. Implications Lakes with higher productivity had more and larger crayfish, and a higher proportion of O. rusticus. Whether crayfish are causing or responding to lake productivity is unknown. Rusty crayfish can reduce aquatic plant density, which can lead to increased algal growth and enhanced lake productivity. Alternatively, crayfish may simply be responding to the food resources in more productive lakes. Enhanced crayfish numbers near campsites is probably due to enhanced food availability from camper’s cleaning their fish and dirty dishes. One study found that the presence of rusty crayfish in Northern Wisconsin lakes was positively related to an index of human use (Puth and Allen 2005). Future studies might examine whether lake campsite density correlated with lake crayfish abundance. Acknowledgements We would like to thank Todd Wellnitz for his guidance for this project, Anna Johnson and Dave Chaffin for their advice, and finally the Office of Research and Sponsored Programs.