Kelly Montenero
Zoology 511
Tuesday Lab
Black Earth Creek Research Paper
Due 4/17/07
Relationship of Species Distribution and Substrate Type in a Class 1 Wisconsin Stream
Abstract
Substrate of a stream bottom has been found to influence species distribution.
Black Earth creek, a class 1 stream in southwestern Wisconsin, was studied in order to
examine how the density of mottled sculpin is affected by the substrate of the stream
environment. Data on habitat was collected, as well as data on species present and species
distribution via electrofishing. It was found that the highest density of mottled sculpin
was significantly correlated with sand substrate, followed by cobble substrate. These
findings imply that species choose different environments and partition the habitat within
the stream ecosystem due to environmental variables that favor their specific biology and
life history.
Introduction
Substrate of a stream has been found to influence species distribution (Petty &
Grossman 1996). Black Earth Creek is a spring fed trout stream west of Madison, WI in
the terminal moraine area of the Wisconsin Glaciation. Black Earth Creek is consistently
rated as one of the Midwest’s top trout streams and its remarkable biodiversity is a major
factor in the high yield of trout per mile of stream (Black Earth Creek homepage). To
investigate factors contributing to this high biodiversity, we surveyed the stream’s habitat
variables. To determine species diversity present and species distribution within the
stream, we used electrofishing gear to capture and survey the fish population for size
demographics and species present.
The data collected was used to specifically examine the question of how densities
of mottled sculpin are affected by the stream environment, especially the substrate. It has
been found in previous research that sculpin prefer cobblestones to finer substrate, and
seek refuge as opposed to open pelagic in the absence of other species (Brown 1991). It
was also found that by analyzing energetic costs, that mottled sculpin prefer low velocity
microhabitats due to their morphological adaptations (Fadey & Grossman 1991). Finally,
mottled sculpin are significantly influenced the amount of coarse particulate organic
matter (CPOM), which in turn is influenced by the substrate environment of the stream.
Specifically, Petty and Grossman (1996) found that mottled sculpin occupied patches
with significantly higher CPOM amounts. These studies show that sculpin densities are
related to substrate, velocity and CPOM due to reproduction requirements, morphological
adaptations and prey densities. Due to these findings, we can expect that mottled sculpin
densities will be highest in areas of cobble substrate and also that species densities can be
predicted by environmental variables that define habitat partitioning in a stream’s
ecosystem.
Materials and Methods
The data was collected at Black Earth Creek near Cross Plains, Wisconsin on
March 20th and 21st. Two groups of researcher collected data in Cross Plains and Salmo
Pond, respectively. The stream was first partitioned into 5-meter transects from bank to
bank, with a net at the end of each transect to separate fish populations. Habitat data were
taken in each section. The natural buffer width was measured on each bank, and the land
cover on each side of the stream was recored. The depth was measured in 3 locations
laterally across the stream, and temperature and velocity were measured once in each
transect. The substrate was observed and recorded in each transect. The categories for
substrate were based on particle size, which were silt, sand, cobble and gravel, in
increasing size.
Data was collected via electrofishing to determine overall population density
estimates of fish species, as well as the population of each species in each run of the
stream. Individual species density and demographics were determined by using boat
mounted electrofishing equipment, which allowed data collectors to record the number,
length and weight of species found in Black Earth Creek. Electrofishing works by
creating an electric field in the water that momentarily stuns the fish by controlling
muscle reactions (Couchman 2007 website). Fish are attracted to the anode of the
electrofishing rod in the water, where they are removed from the water by net for survey.
Data collectors used waders, rubber gloves and nets of various sizes to capture the
stunned fish. Researchers electrofished for an average of 0.205 hours per transect, and for
a total of 2.667 hours in both Cross Plains and Salmo Pond.
Habitat data and fish population data were correlated to find an interaction
between specific substrate types in each transect and run and the types of species found
and the density of each species. Data analysis was completed using Microsoft Excel, with
ANOVA and T- tests implemented to compare group means and find trends in data.
Catch per hour effort of electrofishing (CPUE) for mottled sculpin was computed for
each run, and compared to the stream habitat bottom.
Results
To test whether there actually was a relationship between densities of mottled
sculpin and substrate type, a summary was first created compiling Catch per Unit Effort
in hours, (or CPUE) by species in each reach of the creek. These CPUE data were
compared to the dominant substrate type per reach. Since substrate type was reported for
each transect within a reach but CPUE was only reported for each reach, reaches were
classified as a specific substrate only if the specific substrates made up more than 50% of
the reported transects (See Figure 1). The mean CPUE per substrate type across all
reaches was also computed. It was found that sand had the highest mean CPUE, followed
by cobble as the next highest, then silt and finally gravel with the lowest CPUE of
mottled sculpin (See Table 1).
To test the statistical significance of the differences of means between the CPUE
of mottled sculpin in different substrate types, a single factor analysis of variance, or
ANOVA, was computed to compare group means. The ANOVA found a significant
difference between the catch per unit effort of mottled sculpin in transects with different
groups of substrate (p= 0.019). To pull apart this significance and determine trends within
the data, individual one-tailed T-tests were computed to find the greatest differences
between the mottled sculpin densities in different substrate areas. It was found that
cobble and gravel had a significant difference in mottled sculpin CPUE (p= 0.034, t=
2.22), with cobble having a significantly higher density of mottled sculpin. A significant
difference was also found between the mottled sculpin CPUE in transects of cobble and
sand (p=0.048, t= -1.96), with sand having a significantly higher density of mottled
sculpin. A nonsignificant but highly indicative trend was found between transects of
cobble and silt, with cobble having a higher density of mottled sculpin than silt (p=0.07,
t= 1.66) (See Table 2).
Discussion
The data analyses found that mottled sculpin were most likely to be found in
transects of Black Earth Creek that had a substrate bottom of sand, followed by cobble.
This finding was contrary to some previous studies that found highest mottled sculpin
densities in areas with cobble substrate (Brown 1991). It should be noted, however, that
only one transect classified as more than 50% sand, and this transect had an unusually
high CPUE of mottled sculpin (See Figure 1). Silt and gravel had the lowest densities of
mottled sculpin as determined by CPUE. These results relate to the hypothesis in that
different species choose different environments within the stream ecosystem due to
environmental variables that favor their specific biology and life history, as well as
partition the habitat.
This pattern could be due to the fact that varying velocities will deposit varying
sizes of substrate, and the substrate type is a result of a certain flow velocity that mottled
sculpin prefer. Fast moving water will carry small substrate and particulates and deposit
large substrate, such as gravel and cobble. Slower moving water will deposit sand, and
slowest flow will allow silt to be deposited. Additionally, substrate type influences the
type of hydrological flow. Hydraulically smooth flows occur in sections of a riverbed
with fine sediments (e.g. sands, silts and clays. Hydraulically rough flows occur where
the substrate elements are larger (e.g. pebbles, cobbles and boulders) and are a function
of substrate roughness and depth of flow relative to the height of the roughness elements
(Davis & Barmuta 1989) Riffle flow is also highly oxygenated, which mottled sculpin
prefer. Finally, according to research completed by Petty and Grossman, 1996, sculpin
are found most often in runs with cobble as a substrate due to increased refuge area,
better reproduction conditions, and higher accumulation of CPOM.
The finding of highest sculpin densities in areas of sand and cobble substrate
could also be a function of habitat partitioning or predator avoidance, as well as mottled
sculpin preference for substrate, riffle, prey habitat and flow velocity. Perhaps sculpin
would indeed be the most successful in areas of cobble substrate with high amounts of
CPOM, but trout, the sculpins’ predator, inhabit these niches. Another influence on
substrate selection by mottled sculpin is spawning behavior. Males create protected nests
under ledges or small rocks in which the females deposit eggs (Schlosser 1982).
The findings of this study show specifically that mottled sculpin density and
substrate type are correlated. In Black Earth Creek, the catch per hour effort of mottled
sculpin was highest in areas of sand substrate, followed by cobble. These results were
moderately in accordance of the hypothesis that mottled sculpin would be found in
highest density in areas of cobble substrate. The larger implication is that different
species choose different environments within the stream ecosystem due to environmental
variables that favor their specific biology and life history, as well as partition the habitat.
References
Petty, J.D. and Grossman, G.D. 1996. Patch Selection by Mottled Sculpin in a Southern
Appalachian Stream. Freshwater Biology 35:261-275.
Facey, D.E. and Grossman G.D. 1991. The relationship between water velocity,
energetic costs, and microhabitat use in four North American stream fishes.
Hydrobiologia 239: 1-6.
Brown, L.R. 1991. Differences in Habitat Choice and Behavior among three species of
Sculpin in Artificial Stream Channels. Copeia 3:810-819.
Davis, J.A .and Barmuta, L.A. 1989. Ecologically Useful Classification of Mean and
Near-Bed Flows in Streams and Rivers. Freshwater Biology FWBLAB Vol. 21, No. 2, p
271-282
Schlosser, I.J. 1982. Fish Community Structure and Function along Two Habitat
Gradients in a Headwater Stream. Ecological Monographs Vol. 52, No. 4 p. 395-414
Black Earth Creek- Some Place Special (n.d.), Retrieved April 14th, 2007 from Cross
Plains Homepage: http://www.cross-plains.wi.us/black.html
Couchman, M. (2007) Electrofishing. Retrieved April 14th, 2007 from With a View to
Fisheries Website: http://www.fisheriesmanagement.co.uk/electrofishing.htm
Tables and Figures
Table 1. Mean CPUE of Mottled Sculpin by Substrate Type
Mean CPUE- silt
69.27
Mean CPUE- sand
370
Mean CPUE- cobble
149.72
Mean CPUE- gravel
57
Table 2. P-Values and T- Values of Significance of CPUE by Substrate Means
Substrate Type
Cobble
Gravel
Silt
P- Value
T- Value
Sand
0.04
-1.96
Gravel
0.03
2.22
Silt
0.07
1.66
Sand
0.09
-2.91
Cobble
0.03
-2.22
Silt
0.44
-0.15
Sand
0.08
-1.85
Cobble
0.07
-1.66
Gravel
0.44
0.15
Figure 1. Mean CPUE for Mottled Sculpin per Transect
Mean CPUE for Mottled Sculpin Per Transect in
Black Earth Creek, WI
400.0
Cross
Cross
Cross
Cross
Catch per Unit Effort
350.0
300.0
250.0
200.0
150.0
100.0
50.0
0.0
1
1
Reach
Reach
Plains
cobble
Cross1Plains
1
Plains
cobble
Cross2Plains
2
Plains
cobble
Cross3Plains
3
Plains
Cross4Plains 4
Cross5Plains
5
Cross Plains
cobble
Cross6Plains
Cross Plains
gravel6
Cross7Plains
7
Cross Plains
cobble
Salmo1 Pond
Salmo Pond
silt 1
Salmo2 Pond
Salmo Pond
silt 2
Salmo3 Pond
Salmo Pond
silt 3
Salmo4 Pond
Salmo Pond
gravel4
Salmo5 Pond 5
Salmo Pond
Salmo6 Pond
Salmo Pond
sand 6