Grade: 10/10
Nick this is only the second perfect score on this assignment. You earned it b/c you put
in lots of detail, had a solid methods section, and used p-values for your results. Nice
job!
Nick Bankston
Black Earth Creek Outline
Introduction
 Many trout species have been introduced around the world and their introductions
are believed to have been responsible for changes in stream assemblages
(Zimmerman and Vondracek, 2006), so their interactions with other fish species
have been frequently studied.
 Black Earth Creek is inhabited by a variety of fish species, but the two most
abundant are the brown trout (Salmo trutta) and the mottled sculpin (Cottus
cognatus). Brown trout are sought after as game fish, while the mottled sculpin
are regularly not.
 Jenkins Jr. et al. (1999) found a steep growth-density relationship among brown
trout populations suggesting that density dependence in individual growth rates
may regulate populations. Brown trout need a certain amount of territory to feed
and successfully reproduce (Einum, 2005), which would lead to lower growth and
survival rates at high densities. Consequently, the largest brown trout (who
subsequently were able to grow the most) would inhabit the areas stream areas
with the lower trout densities.
 Studies have shown that brown trout preferentially eat the largest aquatic prey
items available (Ricón and Lobón-Cerviá, 1999). Mottled Sculpin are the most
abundant food source for the piscivorous brown trout in Black Earth Creek, so it
is likely the largest and most abundant mottled sculpin populations will have
parallel trout populations.
 The goal of this paper is to determine i) if brown trout in Black Earth Creek have
a negative feedback on their own growth and ii) what, if any, correlation is there
between the relative size and abundance of the brown trout and mottled sculpin
 The average size of the brown trout will be negatively affected by their own
density, but there will be a strong positive correlation between the average length
and density between the brown trout and mottle sculpin.
Methods Solid.
Field work (same process at Salmo Pond on 3/20/07 and Cross Plains on 3/21/07)
 Starting downstream, we anchored block nets on each end of the section where
electrofishing was going to happen and marked off every five meters along bank.
 Electrofishing team (one person using anode and towing boat, four to five people
using nets to catch fish and place in holding tub) worked their way up stream
catching fish and recorded the time took to do so.
 After electrofishing team moved to next section, habitat team (one recorder, two
to three measurers) recorded a wide variety of information about the physical
conditions of the stream section, including the depth, flow velocity, and dominant
substrate. The only habitat data pertinent to this study is the length of each stream
section (measured with a tape measurer) and the width of the stream section,
which was taken at each transect in the section. Only talk about what you need.
Readers won’t care about the stuff you measured but didn’t use.
 After moving fish from the holding tub to other containers, the workup team
records the species type, length, weight (for as many as possible) and the section
the fish was caught in for every fish caught, then releases them back into stream.
Analysis
 The data was complied and analyzed using Microsoft Excel.
 A Pivot chart was created to determine the count, average length, and average
weight for each species in each section and put into separate tables for the two
different sites.
 The average density of each species was calculated by dividing the number of fish
caught by the area of the stream section (which was calculated by multiplying the
total section length by the average width of the transects).
 A number of plots were created by comparing the average length of the brown
trout against the average density of the brown trout, the average density of the
mottle sculpin, and the average length of the mottled sculpin, as well as
comparing the average density of the two species against each other.
 Simple linear regression tests were performed on each of the relationships to
determine if any of them were statistically significant (p<0.05)
10
264
6
226.17
17
218.94
22
136.18
0
N/A
N/A
1
50
no data
Salmo Pond 7
Salmo Pond 6
Salmo Pond 5
6
144.17
Cross Plains 7
Cross Plains 6
Cross Plains 5
Cross Plains 4
Cross Plains 3
13
203.85
Salmo Pond 4
Variable
Count
Average Length (mm)
Salmo Pond 3
Species
Brown Trout
Salmo Pond 2
Variable
Count
3
29
25
16
46
29
Average Length (mm)
180
226.34
199.4
118.31 143.35 128.28
Average Weight (g)
62.33 156.52 157.04
19.56
47.37
no data
Mottled Sculpin
Count
41
47
111
112
130
84
Average Length (mm) 63.39 63.36
56.47
62.29
62.31
66.23
Average Weight (g)
4.9
6.74
no data no data no data no data
Table 1 - the count and average length/weight of the fish caught in the Cross Plains waters by section
Salmo Pond 1
Species
Brown Trout
Cross Plains 2
Cross Plains 1
Results Nix the grey backgrounds in the graphs
 In total, 239 brown trout were caught (148 in Cross Plains, 93 at Salmo Pond),
ranging in lengths from 85-500 millimeters and weights from 5-1286 grams. Far
more mottled sculpin were caught (526 in Cross Plains, 413 in Salmo Ponds) with
lengths ranging from 50-127mm and weight from 1-52g.
17
155
Mottled Sculpin
Average Weight (g)
Count
Average Length (mm)
187.5
19
67.16
124
18
66.83
126.38
23
78.7
137.82
29
76.28
no data
77
65.97
no data
120
71.14
Average Weight (g)
4.84
4.5
20.5
no data no data no data
Table 2 – the count and average length/weight of the fish caught in the Salmo Pond waters by section

average brown trout length (mm)

Figures 1 and 2 below show no significant correlation between the average length
of the brown trout when compared to their own average density as well as that of
the mottled sculpin (p=0.364 and 0.862, respectively).
Take out the two outlier points (figure one has a point at 0,0. I know we said
zeros were important so good for you for paying attention, but for this particular
study it’s a “no-shit” statement that if you have no brown trout in a reach, their
average length is 0. In figure two, I would also remove the outlier point where
BT length = 0. Probably won’t effect the results very much).
300
250
200
R2 = 0.0692
150
100
50
0
0
0.05
0.1
0.15
0.2
0.25
average brown trout density (no./m²)
Figure 1 – average brown trout length vs. average brown trout density per section
0.3
no
data
127
71.1
no
data
average brown trout length (mm)
300
250
200
150
R2 = 0.0026
100
50
0
0
0.2
0.4
0.6
0.8
1
average mottled sculpin density (no./m²)
Figure 2 – average brown trout length vs. average mottled sculpin density per section

When the average length of the brown trout is compared to the average length of
the mottled sculpin, we do see a statistically significant relationship in Figure 3
(p=0.0473). Sorry Nick, but that 0 BT length is doing bad things to your data. I’d
take out the outlier and say that you’re only analyzing BT length when BT are
present. Or you can present both graphs (this one and one without an outlier)
average brown trout length (mm)
300
R2 = 0.2892
250
200
150
100
50
0
0
20
40
60
80
100
average mottled sculpin length (mm)
Figure 3 – average brown trout length vs. average mottled sculpin length per section

Figure 4 shows below that while there is a general trend in the comparison
between the average densities of the brown trout and the mottled sculpin it is not
statistically significant (p=0.0873). this is good, no outliers here.
average brown trout density
(no./m²)
0.3
0.25
0.2
R2 = 0.2241
0.15
0.1
0.05
0
0
0.2
0.4
0.6
0.8
1
average mottled sculpin density (no./m²)
Figure 4 - average brown trout density vs. average mottled sculpin density per section
Discussion
 While several studies have shown a density-dependent rate of growth and
mortality for brown trout (Jenkins Jr. et al. 1999, Einum, 2005), we did not find
this correlation in Black Earth Creek. There could be an abundant amount of
space for the trout so that these density-dependent factors did not seriously affect
the development of the brown trout in the stream.
 The strong correlation between the average length could be due to several factors:
o Mottled sculpin are the most abundant food source within Black Earth
Creek for piscivorous brown trout, and the larger mottled sculpin would
provide a higher amount of biomass allowing the trout to achieve greater
body lengths. This would also account for the similarities between the
densities, because the trout would want to inhabit the stream sections
where the sculpin were most abundant.
o Hesthagen et al. (2004) found a large overlap between the diets of brown
trout and the Siberian sculpin (Cottus poecilopus) in Norway, which could
indicate a similar relationship with the mottled sculpin. If the sections
inhabited by the larger trout and sculpin contained an extremely high
concentration of a shared prey item (ex. aquatic insects or benthic
crustaceans), they could achieve large body size while still sharing the
same stream reach. However, we cannot conclude any relationship
because we did not measure the invertebrate populations in Black Earth
Creek, but this could be the focus of a future study.
o Studies have also shown that adult trout are a source of predation to smalland medium-size sculpin (Zimmerman and Vondracek, 2006), so the large
mottled sculpin size could also consequently be a defensive response to
predation by the trout. A further study could be done to test if this is true
by determining the diets of the trout by flushing their stomachs and
comparing the relative amounts of prey items.


The correlation between the densities of the brown trout and mottled sculpin are
close to being statistically significant, and if we had sampled more stream sites we
might have seen a more pronounced relationship.
The lack of a correlation between the average length of the brown trout and the
average densities of either the trout themselves or the mottled sculpin suggest that
the relative densities of either fish has little to do with how large the trout are able
to grow.
Literature Cited
Einum, S. 2005. Salmonid population dynamics: stability under weak density
dependence?. Oikos 110: 630-633
Hesthagen, T., Saksgård, R., Hegge, O., Dervo, B.K., and Skurdal, J. 2004. Niche overlap
between young brown trout (Salmo trutta) and Siberian sculpin (Cottus poecilopus) in a
subalpine Norwegian river. Hydrobiologia 521: 117-125.
Jenkins Jr., T.M., Diehl, S., Kratz, K.W., and Cooper, S.D. 1999. Effects of population
density on individual growth of brown trout in streams. Ecology 80: 941-956.
Ricón, P.A., and Lobón-Cerviá, J. 1999. Prey-size selection by brown trout (Salmo trutta
L.) in a stream in northern Spain. Canadian Journal of Zoology 77: 755-765.
Zimmerman J.K.H., and Vondracek B. 2006. Interaction of slimy sculpin (Cottus
cognatus) with native and nonnative trout: consequences for growth. Canadian Journal
of Fisheries and Aquatic Sciences 63: 1526-1535.