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
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
Percent of Rusty Crayfish
Non sampled lakes
0%
3. To establish whether human
presence at campsites affected
shoreline crayfish distributions, in
particular, rusty crayfish.
1-40%
41-80%
81-100%
Trip route
Results
r2 = 0.02
P < 0.015
100
60
40
0
2
B
Active Sampling:
Walking shorelines and
collecting and counting
crayfish at 10 minute
intervals (A) near and
away (> 30 m) from
campsites.
3
4
5
Secchi Depth (m)
6
120
100
80
60
40
20
0
• Rusty crayfish dominated the assemblage
(>75% of the catch) in 3 of the 4 lakes where
they were found.
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.
• 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).
Rustys
Natives
• Crayfish were significantly larger in more
productive lakes (Fig. 3).
1
Carapace Length (mm)
1
Crayfish Captured
A
• Of the seven lakes sampled, four had rusty
crayfish (see map).
80
20
Methods
Passive Sampling:
Lakes sampled using
12 baited traps (A) set
near campsites
overnight and capture
crayfish (B) were
processed the
following morning.
120
Discussion
2
3
4
5
Secchi Depth (m)
40
Lakes with higher productivity had more and
larger crayfish, and a higher proportion of O.
rusticus.
30
20
Figure 3. As lakes became more
productive, the crayfish became
larger.
10
0
1
Strayer D. (2010). Alien species in freshwaters: ecological effects, interactions with other
stressors, and prospects for the future. Freshwater Biology 55(1): 152-174.
2
• Crayfish were more abundant near campsite
then further away (Fig. 4).
Implications
r2 = 0.23
P <0.001
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): 567-577.
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.
Figure 2. As lakes became more productive, a
larger proportion of the crayfish assemblage
was made up of O. rusticus.
50
References
Acknowledgements
6
3
4
5
Sechhi Depth (m)
Crayfish Abundance
Crayfish Captured
140
150
100
50
6
Figure 3. Crayfish
were more
abundant near
campsites than they
were at sites >30 m
distant.
0
Away
Near
Distance Relative to Campsite
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.