J. Great Lakes Res. 29 (Supplement 1):386–402
Internat. Assoc. Great Lakes Res., 2003
Low-head Sea Lamprey Barrier Effects on Stream Habitat and
Fish Communities in the Great Lakes Basin
Hope R. Dodd1, 5,*, Daniel B. Hayes1, Jeffery R. Baylis2, Leon M. Carl3,6, Jon D. Goldstein2,
Robert L. McLaughlin4, David L. G. Noakes4, Louise M. Porto4,7, and Michael L. Jones1
1Michigan
State University
Department of Fisheries and Wildlife
East Lansing, Michigan 48824
2University
of Wisconsin
Department of Zoology
Madison, Wisconsin 53706
3Ontario
Ministry of Natural Resources
Trent University
1600 West Bank Dr.
Peterborough, Ontario K9J 8N8
4University
of Guelph
Axelrod Institute of Ichthyology and Department of Zoology
Guelph, Ontario N1G 2W1
ABSTRACT. Low-head barriers are used to block adult sea lamprey (Petromyzon marinus) from
upstream spawning habitat. However, these barriers may impact stream fish communities through
restriction of fish movement and habitat alteration. During the summer of 1996, the fish community and
habitat conditions in twenty-four stream pairs were sampled across the Great Lakes basin. Seven of these
stream pairs were re-sampled in 1997. Each pair consisted of a barrier stream with a low-head barrier
and a reference stream without a low-head barrier. On average, barrier streams were significantly
deeper (df = 179, P = 0.0018) and wider (df = 179, P = 0.0236) than reference streams, but temperature
and substrate were similar (df = 183, P = 0.9027; df = 179, P = 0.999). Barrier streams contained
approximately four more fish species on average than reference streams. However, streams with lowhead barriers showed a greater upstream decline in species richness compared to reference streams with
a net loss of 2.4 species. Barrier streams also showed a peak in richness directly downstream of the barriers, indicating that these barriers block fish movement upstream. Using Sørenson’s similarity index
(based on presence/absence), a comparison of fish community assemblages above and below low-head
barriers was not significantly different than upstream and downstream sites on reference streams (n =
96, P > 0.05), implying they have relatively little effect on overall fish assemblage composition. Differences in the frequency of occurrence and abundance between barrier and reference streams was apparent for some species, suggesting their sensitivity to barriers.
INDEX WORDS:
habitat.
Low-head barriers, low-head dams, Great Lakes, fish assemblage, physical
*Corresponding
author. E-mail: [email protected]
Address: Illinois Natural History Survey, Center for Aquatic
Ecology, Champaign, Illinois 61820
6Present Address: United States Geological Survey, Great Lakes Science
Center, 1451 Green Road, Ann Arbor, Michigan 48105
7Present Address: R.L. and L. Environmental Services Ltd., 201 Columbia Ave, Castlingar, British Columbia, V1N 1A2
5Present
386
Low-head Barrier Effects on Habitat and Fish
INTRODUCTION
The sea lamprey (Petromyzon marinus), a native
of the Atlantic Ocean, invaded the upper Great
Lakes following the construction of the Welland
Canal (Pearce et al. 1980). This parasitic species,
along with substantial fishing pressure, nearly eliminated native lake trout (Salvelinus namaycush) and
populations of other large commercial fishes in the
Great Lakes, resulting in the need to control sea
lamprey (Lawrie 1970, Pearce et al. 1980, Smith
and Tibbles 1980).
Since 1950, a variety of control methods have
been instituted to reduce sea lamprey abundance in
the Great Lakes. The primary control method used
in Great Lake tributaries is chemical treatment with
3-trifluoromethyl-4-nitrophenol (TFM). This lampricide targets ammocoetes buried in the stream bed
(Applegate et al. 1957, Applegate et al. 1961, Hunn
and Youngs 1980). Although TFM has little apparent effect on fish species other than lampreys (both
sea lamprey and native lampreys), public sentiment
and the high cost of chemical control has led the
Great Lakes Fishery Commission to search for alternative control methods to reduce the use of lampricides 50% by the end of the year 2000 (Great
Lakes Fishery Commission 1990).
An alternative to chemical treatment is the construction of low-head barriers. These barriers are
built to prevent adult sea lampreys from migrating
to suitable spawning habitat in Great Lakes tributaries. Early attempts at blocking spawning migrations included installation of mechanical weirs and
traps (Applegate and Smith 1951) and alternatingcurrent (AC) electrical barriers as well as low-head
barriers. Mechanical weirs and AC electrical barriers were deemed as ineffective, costly, and sources
of mortality to non-target species (Erkkila et al.
1956, McLain 1957) and were modified or discontinued by the 1970s (Dahl and McDonald 1980,
Hunn and Youngs 1980). By the mid-1970s, the
Great Lakes Fishery Commission approved construction of low-head sea lamprey barriers as part
of the Sea Lamprey Control Program (Hunn and
Youngs 1980). The low-head barriers in our study
ranged in head height from approximately 45 to 300
cm.
Although the use of barriers predates chemical
treatments in several Great Lake tributaries, there
has been little study on the effects low-head sea
lamprey barriers have on the entire fish community,
particularly at a basin-wide scale (Hunns and
Youngs 1980, Kelso and Noltie 1990). While low-
387
head sea lamprey barriers do not appear to cause direct mortality of non-target species, they can have
negative effects at several different scales, ranging
from species-level changes to changes at the
ecosystem or landscape scale (Pringle 1997). The
most obvious impact is the blocking of fish movement during periods of spawning or seasonal movement to locate habitat and food resources (Porto et
al. 1999). Low-head barriers may also indirectly affect fish communities by changing the geomorphology and water quality of the stream (Pringle 1997).
In this paper, evidence is provided for an impact
of low-head sea lamprey barriers on stream fish
communities throughout the Great Lakes basin. A
priori, streams containing low-head barriers were
expected to contain fewer species and have a
greater loss of species upstream of the barrier when
compared to upstream sections of nearby reference
streams (those without a barrier). Abundance of
some non-target species was also expected to decrease upstream of the barriers due to habitat alteration or blocking of movement upstream, thereby
altering the fish community structure and population abundance and size composition. The main
focus of this study was to examine fish assemblages
in streams with low-head barriers that were primarily built for sea lamprey control, however, the results of this study may apply to other types of small
dams or barrier structures.
STUDY SITES
Forty-seven tributaries were sampled across the
Great Lakes basin in the summer (June-August) of
1996, and 14 streams were re-sampled in the summer of 1997 (Table 1, Fig. 1). Streams were re-sampled in 1997 within 2 weeks of the 1996 sampling
dates in order to reduce annual variability in fish
assemblage data. Streams were paired, with each
pair containing a stream with a low-head barrier
(barrier stream) and a nearby reference stream
(without a barrier). Due to the lack of suitable reference streams, South Otter Creek in the Lake Erie
drainage was used twice in the pairings (Table 1).
Stream pairs were selected with the advice of sea
lamprey control agents and technical experts. Reference streams were selected based on proximity
and similarity to the barrier stream in terms of
stream size, geology, and geography (Table 1). The
majority of streams were sampled at six locations,
three sampling sites above and three below the barrier, or a corresponding location on the reference
stream. Location of barriers upstream of the mouth
388
Dodd et al.
FIG. 1. Location of streams sampled in the
Great Lakes Basin (Streams identified in Table 1).
varied among streams. Therefore, some streams
were sampled with fewer sites when the barrier was
too close to the mouth to allow placement of three
sampling sites downstream. Site location was determined primarily by access to streams with each site
separated by at least five to seven times the stream
width. The small impoundment just upstream of the
barrier was excluded because water depth was too
great to sample with our equipment, and the plunge
pool directly downstream of the barrier was excluded due to the potential of a localized effect of
the barrier to aggregate fish in this location.
METHODS
Each sampling site contained a downstream, upstream, and middle transect perpendicular to flow.
The downstream transect was marked where the
thalweg crossed the stream. The upper transect,
marking the end of the site, was placed five to
seven times the stream width from the downstream
transect, and a middle transect was placed at approximately half the length of the site. At each transect, stream width, maximum depth, and a pebble
count of 50 stream bed particles were measured to
determine in-stream habitat characteristics. Pebble
counts were taken by starting at one side of the
stream bank and walking along the transect. At
each step, the observer would reach down and de-
termine the size of a random stream bed particle
(Kondolf and Li 1992). In addition to physical habitat measurements, temperature and conductivity
were also measured at the downstream transect to
aid in setting the electroshocking unit.
A single upstream pass with a Smith-Root backpack electroshocker was used to assess fish species
composition, richness, and relative abundance (Simonson and Lyons 1995). Most fish were identified
in the field and total length was measured. Fish that
could not be identified in the field were fixed in
10% formalin and preserved in 70% isopropyl alcohol for further identification in the laboratory.
Voucher specimens that could not be identified due
to their small size or to damage during transport
and preservation were excluded from our analysis.
Because the primary interest was detecting differences between upstream and downstream fish assemblages in streams with low-head barriers, sites
were classified into above and below stream sections. An α value (Type I error) of 0.05 was used
for all statistical tests. To determine differences in
width, maximum depth, and particle type between
barrier and reference streams, a nested mixed model
analysis of variance (ANOVA, Littell et al. 1996)
design was used treating stream pairing, stream,
and position (Above or Below) within each stream
as random effects and stream type (Barrier or Reference) as the fixed effect. The relationship between stream habitat characteristics and species
richness (number of species caught) was examined
with a nested mixed model analysis of covariance
(ANCOVA) by comparing differences in richness
among stream types (Barrier vs. Reference) and
stream positions (Above vs. Below) using average
width, maximum depth, and substrate size as covariates.
The net decline in species richness (impact value)
due to the barrier was calculated using the formula:
I = (BA – BB) – (RA – RB)
(1)
where I is the net decline of species for a stream
pair and where other variables refer to species richness within a stream section for a stream pair (BA =
Barrier Above, BB = Barrier Below, RA = Reference Above, and RB = Reference Below). A twotailed t-test was used to compare our observed
species loss to our expected value of no net loss in
species richness. Influence of habitat on the number
of species lost above the barriers was examined
through regressions of average width and maximum
depth on loss of species for each stream pair. Simi-
389
Low-head Barrier Effects on Habitat and Fish
TABLE 1. Location and physical characteristics of study streams sampled in summer 1996 and re-sampled in summer 1997 (designated by *). Note: South Otter was used twice as a reference stream. Particle
sizes were classified as follows: 1 = clay, 2 = silt, 3 = sand, 4 = gravel, 5 = cobble, 6 = boulder, 7 = bedrock.
Stream
pair
no.
1*
1*
2*
2*
3*
3*
4
4
5
5
6
6
7
7
8
8
9
9
10*
10*
11*
11*
12
12
13
13
14
14
15
15
16*
16*
17
17
18
18
19*
19*
20
20
21
21
22
22
23
23
24
24
Stream name
East Branch AuGres
West Branch Rifle
Albany
Beavertail
Echo
Root
Koshkawong
Brown
Manitou
Blue Jay
Sturgeon
Mad
Betsie
Upper Platte
Kewaunee
Ahnapee
East Twin
Hibbards
West Branch,Whitefish
East Branch, Whitefish
Miners
Harlow
Big Carp
Little Carp
Stokely
Pancake
Days
Rapid
Misery
Firesteel
Middle
Poplar
Neebing
Whitefish
Clear
South Otter
Forestville
Fishers
Youngs
South Otter
Duffins
Lynde
Grafton
Salem
Little Salmon
Grindstone
Shelter Valley
Wilmot
Stream
type
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Barrier
Reference
Location
(State/
Province)
Michigan
Michigan
Michigan
Michigan
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Michigan
Michigan
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Michigan
Michigan
Michigan
Michigan
Ontario
Ontario
Ontario
Ontario
Michigan
Michigan
Michigan
Michigan
Wisconsin
Wisconsin
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
New York
New York
Ontario
Ontario
Lake
Huron
Huron
Huron
Huron
Huron
Huron
Huron
Huron
Huron
Huron
Huron
Huron
Michigan
Michigan
Michigan
Michigan
Michigan
Michigan
Michigan
Michigan
Superior
Superior
Superior
Superior
Superior
Superior
Michigan
Michigan
Superior
Superior
Superior
Superior
Superior
Superior
Erie
Erie
Erie
Erie
Erie
Erie
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Ontario
Mean
width
(m)
10.2
8.6
6.1
3.9
16.7
10.2
10.6
3.6
15.0
10.3
8.8
11.1
18.3
17.7
20.0
14.1
11.3
6.1
20.4
17.0
8.8
5.8
10.1
5.1
8.0
13.1
9.8
14.6
9.6
14.2
11.7
7.4
11.8
15.7
4.8
2.7
3.9
4.4
8.6
2.7
12.8
8.2
4.4
3.2
13.4
11.1
8.9
7.5
Mean
depth
(cm)
69.3
77.8
51.2
65.5
98.8
52.4
66.5
32.9
72.8
57.3
78.2
93.7
95.6
61.1
65.3
47.7
57.7
43.6
60.6
49.8
72.0
61.6
103.4
45.6
60.2
79.2
55.8
43.3
69.9
72.2
46.6
35.1
87.8
69.1
49.8
33.9
23.4
30.1
65.3
33.9
77.3
30.9
32.8
37.9
54.6
33.8
54.6
45.0
Mean
particle
size
3.4
3.5
3.6
2.9
3.6
4.5
5.1
4.0
5.0
4.9
2.8
2.5
3.3
3.6
4.8
3.8
4.0
3.3
5.3
4.8
3.8
3.4
3.1
3.2
3.9
4.4
4.6
5.6
3.4
3.5
5.0
5.2
3.2
4.4
2.4
2.9
2.9
4.1
3.4
2.9
3.7
4.1
4.3
3.0
5.6
5.1
3.8
4.1
Head
height
(cm)
67
77
54
43
83
60
70
107
180
97
80
45
52
55
77
152
65
47
35
70
75
45
300
55
390
Dodd et al.
lar to the calculation of an impact value for species
richness, an average decline in fish assemblage
mean size was estimated (i.e., mean length of all
fish at a site) above low-head barriers relative to
reference streams and a two-tailed t-test was used
to compare differences in mean length of the community due to the barrier.
Effects of low-head barriers on assemblage composition was examined using Sφrensen’s similarity
index (Sφrensen 1948) which is based on
presence/absence data, and is computed using the
formula:
S = 2C / (A + B)
(2)
where S is similarity of fish assemblages between
two sites, A is the number of species in the first
site, B is the number of species in the second site,
and C is the number of species in common. Tukey’s
Studentized Range test was used to determine differences in mean similarity values. Species sensitivity to low-head barriers was determined by
comparing frequency of occurrence, mean catch,
and mean length for above and below sections of
barrier and reference streams.
RESULTS
Habitat Analysis
Both barrier and reference streams ranged widely
in size (Table 1). Streams with low-head barriers
had an average width of 11.0 m (n = 24, se = 0.9)
and an average maximum depth of 65.4 cm (n = 24,
se = 3.9), while the mean width and maximum
depth for reference streams was 9.4 m (n = 23, se =
1.0) and 52.2 cm (n = 23, se = 3.7), respectively.
The average difference in width of 1.9 m and maximum depth of 13.9 cm between barrier and reference streams was significantly different from zero
(ANOVA, df = 179, Pwidth=0.0236, Pdepth = 0.0018),
indicating barrier streams were wider and deeper on
average than reference streams (Table 1). Both barrier and reference streams consisted mainly of
gravel with no significant difference in predominant
substrate type between stream types (ANOVA, df =
179, P = 0.999). Mean water temperature for barrier
streams was 17.5 °C (n = 24, se = 0.5) and for reference streams was 18.1°C (n = 23, se = 0.5) with
no significant difference between stream types
(ANOVA, df = 183, P = 0.9027).
To study spatial patterns of habitat alteration by
low-head barriers, mean width, maximum depth,
particle size, and temperature was calculated for the
FIG. 2. Longitudinal trends in mean (± 1 standard error) stream width for barrier and reference
streams for all streams and years combined.
six sites across reference and barrier streams. Average width and maximum depth gradually increased
in a downstream direction for barrier and reference
streams, but barrier streams were generally wider
and deeper at all sites (Fig. 2, Fig. 3). At sites directly upstream of the barriers, mean maximum
depth was on average 15 cm greater than in the reference streams, suggesting that some effect of the
impoundment extended upstream to these sites. Unlike width and depth, mean particle size and temperature did not show a longitudinal trend, with
FIG. 3. Longitudinal trends in mean (± 1 standard error) maximum depth for barrier and reference streams for all streams and years combined.
391
Low-head Barrier Effects on Habitat and Fish
both habitat characteristics being similar among
barrier and reference sites.
Fish Community
Composition and Size Structure
Overall, barrier streams contained a greater number of fish species than reference streams. A total of
14 more species was caught in barrier streams compared to reference streams with six more species
occurring in above sections and 12 more species in
below sections of barrier streams (Table 2). When
comparing differences in average richness between
barrier and reference streams, above sections differed by 0.7 species on average. However, the
change in average richness between below sections
was much greater, differing by an average of 3.8
species. Within a stream type, 20 fewer species
were found upstream in barrier streams (4.7 fewer
species on average above the barrier) while only 14
fewer species were found upstream in reference
streams (1.6 fewer species on average in upstream
sections).
Although species richness varied across years in
individual streams, there was little difference in average species richness when comparing only those
seven stream pairs that were sampled in both 1996
and 1997 (Table 3). For these seven stream pairs,
species richness averaged 9.4 species in above barrier stream sections in 1996, and averaged 8.9 in
1997. Average richness was 15.1 in sections below
barriers in 1996 and 12.0 in 1997. Reference
streams likewise showed relatively small changes;
richness in above sections was 10.3 in 1996 and 9.1
in 1997, and richness in below sections went from
12.1 in 1996 to 9.9 in 1997. Although the composition of the fish community changed between years
in these streams, the overall patterns of richness
were remarkably stable, suggesting that these results are relatively robust to the year-to-year variability observed.
Species richness was examined at the site level to
detect spatial patterns in richness between barrier
and reference streams. In reference streams, average richness generally increased in a downstream
direction (Fig. 4). Within the barrier streams, average species richness was similar among sites above
the barrier. However, barrier streams showed a distinct peak of 10.8 species directly below the barrier
(the Below 1 site) that then declined toward the
mouth whereas reference streams showed a gradual
increase downstream. Comparing the longitudinal
patterns between barrier and reference streams, the
TABLE 2. Total and mean (in parenthesis, n =
sample size) number of species collected in sections above and below actual or hypothetical lowhead lamprey barriers for barrier and reference
streams in summer 1996 and 1997 combined.
Stream
section
Species richness
Barrier stream
Reference stream
Above dam
54
(11.3, n = 72)
48
(10.6, n = 69)
Below dam
74
(16.0, n = 65)
62
(12.2, n = 68)
Total
79
(18.6, n = 137)
65
(14.8, n = 137)
upstream sites were more similar in average richness than downstream sites.
Because stream width and depth differed between barrier and reference streams, an ANCOVA
was used to test if habitat alterations due to barriers
explained differences seen in species richness. Results of this analysis indicated that width and depth
are significant covariates (df = 173, Pwidth = 0.0046,
Pdepth = 0.0091), but that average species richness
was still significantly different between barrier and
reference streams (df = 173, Pbarrier = 0.0334), even
with the effects of these covariates removed. Using
a similar analysis comparing species richness in
above and below sections of barrier and reference
streams, significant differences in average richness
was found among the four stream positions (df =
43, Pstream position = 0.0334) with average richness in
the below barrier section being significantly higher
than the above barrier and the below reference sections (t-test, df = 43, P ba-bb = 0.0001, P bb-rb =
0.0057). In this analysis, stream width was the only
significant covariate (df = 43, Pwidth = 0.0219, Pdepth
= 0.2807).
To further examine the effect of low-head barriers on species richness, a decline in species above
the barriers (impact value) was calculated for each
stream pair. On average, barrier streams lost 4.1
species from below to above segments while reference streams lost only 1.5 species. The overall impact of the barriers on species richness was a net
loss of 2.5 species above the barrier relative to reference streams (Table 3). This loss of species was
significantly different from the expected value of
zero under the null hypothesis of no impact on
species richness (t-test, n = 24, P = 0.0126). Be-
Stream
Dates
pair
Sampled
1
12/6–21/6
2
24/6–26/6
3
18/7–21/7
4
27/7–31/7
23/7–25/7
5
17/7–18/7
6
7
5/8–13/8
9/7–16/7
8
9
10/7–16/7
10
30/7–6/8
11
6/7–9/7
12
22/7–28/7
13
24/7–1/8
2/8–4/8
14
26/7–28/7
15
16
5/8–7/8
20/7–24/7
17
4/7–8/7
18
2/7–3/7
19
20
5/7–9/7
21
25/6–28/6
17/6–20/6
22
23
7/30–8/1
24
6/20–6/26
Mean
Standard Error
Summer 1996
Barrier
Barrier
Reference Reference
Dates
above
below
above
below
Sampled
9
18
18
17
23/6–25/6
10
13
9
16
17/6–19/6
14
21
10
9
21/7–24/7
10
14
7
12
13
13
7
8
8
21
5
5
14
19
8
14
20
11
14
20
18
27
4
8
9
20
14
14
26/7
10
10
8
11
7/7–9/7
10
9
9
10
5
9
9
5
14
16
12
12
9
10
11
14
8
13
10
13
2/8
12
16
11
8
3
11
6
12
7/7–8/7
5
3
11
6
3
8
6
12
15
15
14
13
8
17
13
12
13
12
19
17
11
13
9
12
10.5
14.8
9.7
11.4
0.9
1.0
0.8
0.7
17
9
15
7
12.0
1.7
12
4
10
6
8.9
1.1
9.1
1.7
2
13
10
10
Summer 1997
Barrier
Barrier
Reference
above
below
above
10
18
15
11
9
5
9
9
9
Mean
Reference
impact value
below
(BA-BB)-(RA-RB)
12
–10.5
8
4.5
9
–4
1
1
–13
1
3
–5
16
–5
9
–1.5
2
–8
–2
2
9
–5.5
–7
–2
6
0
1
–1
–10
–1
1
9.9
–2.5
1.2
0.9
TABLE 3. Total number of species caught in sections above and below low-head lamprey barriers in barrier streams and equivalent
locations in reference streams, and mean number of species lost (impact value) for summer 1996 and 1997 combined. BA, BB, RA, RB
represent species richness in above (A) and below (B) sections of the Barrier (B) and Reference (R) streams. Dates sampled in 1996 and
1997 included in table.
392
Dodd et al.
Low-head Barrier Effects on Habitat and Fish
FIG. 4. Longitudinal trends in mean (± 1 standard error) number of species caught (species
richness) in barrier and reference streams for all
streams and years combined.
cause low-head barriers are constructed to prevent
passage of sea lamprey, their loss was expected
above the barrier in streams where they were observed below the barrier. When sea lamprey was
excluded from the assessment of a barrier impact on
decline in species richness, upstream sections of
barrier streams still lost 2.4 species on average, a
significant loss compared to the expectation under
the null hypothesis of no species loss above barriers
(t-test, n = 24, P = 0.0139). The effect of possible
habitat alteration by low-head barriers on the degree of impact was explored through regressions of
mean width and mean maximum depth on loss of
species above barriers. These regressions were not
significant (ANOVA, df = 22, Pwidth = 0.4194, Pdepth
= 0.7535) and showed substantial scattering of the
data, indicating that habitat differences between
stream types did not explain the net species decline
in individual streams.
Low-head barriers selected for this study ranged
in age from two to 26 years and in head height
(height from water level in the impoundment to
water level in the tailrace) from 45 to 300 cm, influencing the size of the impoundment as well as ease
of fish passage. The effects of barrier age, head
height, and time of last breach on the decline in
species upstream were analyzed and found to be
poor predictors of species loss above low-head barriers (ANOVA, df = 22, P age = 0.7952, P height =
0.7175, Pbreach = 0.2938). Not all low-head barriers
in this study were constructed specifically for sea
lamprey control and two of our low-head sea lam-
393
prey barriers (Big Carp River and Albany Creek)
were variable crest barriers that serve as barriers
only in the spring during sea lamprey migration.
When the larger non-sea lamprey barriers and the
variable crest barriers were excluded, age, height,
and time of last breach still had no significant effect
on loss of species.
Sφrensen’s similarity index based on species
presence/absence data was computed to compare
fish community composition between upstream and
downstream sections of barrier and reference
streams. The greatest similarity in species composition occurred between upstream and downstream
sections of reference streams with a mean index
value of 0.65 (Fig. 5). Above and below sections of
barrier streams were found to be the second highest
in mean species similarity (0.57). Comparing composition between barrier and reference streams, the
below stream sections were slightly more similar in
species composition (0.53) than the above sections
(0.49), although differences in species richness was
greatest between the below sections (Table 2). A
Tukey’s Studentized Range test performed on mean
similarity showed a significant difference only between the highest (within reference stream) and
lowest (between above sections) similarity values
(df = 92, P = 0.0316).
There was no detectable effect of barriers on
mean length of the fish community. Differences in
mean community size composition between barrier
and reference streams were determined by calculation of an impact value for each stream pair. The
difference in community size composition between
above and below barrier sections was 4.3 mm while
reference streams showed a difference of 3.4 mm
(Table 4). Overall, the fish community above the
barrier was 1.8 mm smaller relative to the reference
stream and was not significantly different from the
expectation of zero (t-test, N = 24, P = 0.7302), indicating barriers had little or no effect on the size of
the fish assemblage upstream.
For each species, frequency of occurrence and
relative abundance data were examined to give an
indication of the sensitivity of individual species to
low-head barriers (Appendix 1, Appendix 2). Impact values for relative abundance were calculated
to help indicate species that were positively (impact
score > 0) or negatively (impact score < 0) affected
by barriers, although frequency of occurrence may
have remained unaffected for that species. Three
species appeared to be negatively affected by lowhead barriers, meaning that a species was seen less
frequently or was less abundant upstream of the
394
Dodd et al.
FIG. 5. Distribution of Sφrensen’s Similarity Index comparing species composition between the four stream positions sampled (BA = Barrier Above, BB =
Barrier Below, RA = Reference Above, RB = Reference Below.).
low-head barriers compared to their frequency or
abundance in the remaining stream positions (Barrier Below, Reference Above, and Reference
Below). Sea lamprey, yellow perch (Perca
flavescens), and trout-perch (Percopsis omiscomaycus) were not caught above any barrier in the study
streams (Appendix 1), but were found frequently in
below barrier sites as well as in above and below
sites in the reference. Fish species seen more frequently or that were more abundant in above sections of barrier streams compared to the below
barrier and reference stream locations included
blacknose shiner (Notropis heterolepis) and brook
stickleback (Culaea inconstans) (Appendix 1, Appendix 2).
DISCUSSION
Based on the general habitat characteristics measured, streams with low-head barriers showed relatively little habitat alteration compared to reference
streams. Average width and maximum depth were
found to be significantly higher in barrier streams,
but mean substrate size and temperature were similar between the two stream types. Based on the
River Continuum Concept (Vannote et al. 1980),
width, depth, and temperature were anticipated to
increase and substrate size was expected to decrease in a downstream direction. Both barrier and
reference streams follow this general trend of in-
creased width and depth downstream, but sites directly above the impoundment (Above 1 site in barrier streams) are deeper on average compared to
those sites in reference streams (Fig. 2, Fig. 3). Although the area immediately upstream of the barriers was excluded from our sampling protocol, sites
closest to the barrier may have been within the impacted zone upstream of the small reservoir, explaining the greater average depth at these sites.
Barriers slow the flow of water entering an impoundment and often act as sediment traps (Ward
and Stanford 1983). From this, sites immediately
upstream of the barrier (Above 1 sites) would be
expected to have a greater portion of fine substrate
particles such as silt and sand and the site directly
downstream to have coarser substrate. This was not
evident in the data where substrate size was similar
at sites above and below the barrier. Surface release
dams, such as these low-head sea lamprey barriers,
might also be expected to increase temperature directly below the barrier relative to that site in the
reference stream (Fraley 1979) if these low-head
barriers notably alter stream flow. However, average temperature was not significantly greater in
streams with low-head barriers nor were sites directly below the barrier warmer on average than the
reference sites. This indicates that, unlike larger
surface release dams, these low-head barriers do not
retain water long enough to significantly change the
395
Low-head Barrier Effects on Habitat and Fish
TABLE 4. Mean total length (sample size in parentheses) of all fish collected above and below low-head
barriers in barrier and equivalent locations in reference streams and the difference in fish length for each
stream pair for summer 1996 and 1997 combined.
Mean total length (mm)
Stream pair
number
Barrier above
Barrier below
1
85.0 (304)
2
60.4 (265)
3
62.9 (301)
4
69.9 (72)
5
73.9 (107)
6
68.4 (80)
7
78.4 (192)
8
91.7 (376)
9
60.4 (168)
10
68.4 (375)
11
78.7 (164)
12
73.0 (268)
13
58.5 (248)
14
72.9 (190)
15
73.7 (58)
16
80.0 (215)
17
65.8 (141)
18
36.2 (27)
19
149.8 (98)
20
80.5 (60)
21
62.3 (132)
22
90.9 (163)
23
61.6 (202)
24
86.8 (205)
Mean
74.6 (24)
Standard Error
4.1
87.0 (368)
76.2 (335)
67.3 (188)
67.1 (121)
63.8 (244)
82.9 (99)
92.1 (213)
96.5 (347)
123.8 (311)
79.0 (315)
69.6 (254)
69.8 (23)
73.4 (210)
71.9 (176)
67.0 (77)
87.3 (364)
55.6 (326)
85.9 (26)
81.2 (99)
80.2 (47)
86.4 (177)
72.0 (524)
78.2 (105)
123.5 (94)
78.9 (24)
2.8
Reference above
substrate composition or to noticeably increase the
temperature of the stream. Beyond the small impoundment above the barrier and the plunge pool
just below, barriers did not appear to substantially
affect the physical habitat characteristics measured
in the study streams. Since habitat characteristics
were not measured in the impoundment and the
plunge pool, there may be localized effects on substrate and temperature in these areas which were
not detected due to the study protocol.
Species richness was higher in both upstream and
downstream sections of barrier streams relative to
reference streams. One plausible explanation could
be that barrier streams, being wider and deeper on
average, provided a greater amount of habitat, allowing more species to exist in these streams. However, deeper and wider sites within barrier streams
did not consistently have higher average species
richness and the sites directly below barriers which
contained the largest number of species were not
77.5 (476)
60.4 (108)
72.0 (388)
69.5 (97)
68.6 (130)
68.9 (10)
101.6 (497)
87.8 (276)
50.4 (124)
88.2 (160)
77.7 (125)
80.0 (79)
62.8 (172)
67.4 (210)
59.5 (185)
78.5 (243)
61.4 (129)
65.6 (39)
76.9 (125)
65.6 (39)
57.2 (380)
93.9 (96)
69.6 (205)
62.6 (138)
71.9 (24)
2.6
Reference below
81.4 (380)
64.9 (60)
66.8 (250)
67.5 (102)
54.7 (55)
82.4 (8)
122.1 (518)
132.3 (357)
83.9 (49)
75.3 (222)
100.2 (178)
57.6 (179)
55.8 (76)
69.7 (157)
51.4 (134)
81.3 (394)
58.1 (213)
78.8 (20)
91.2 (225)
78.8 (20)
56.4 (398)
80.5 (80)
73.8 (180)
62.3 (434)
75.3 (24)
4.2
Mean impact value
(BA-BB)-(RA-RB)
1.9
–11.3
–9.5
0.8
–3.7
–1.0
6.8
39.7
–29.9
–23.4
31.6
–19.2
–21.9
3.3
–1.4
–4.5
7.0
–36.4
82.9
13.5
–24.8
5.5
–12.4
–37.0
–1.8
5.3
the widest or deepest sites on average (Figs. 2, 3,
and 4). Width or depth did explain a portion of the
variation seen in species richness, but the longitudinal trends in habitat and mean richness within barrier streams are not as closely linked as they are in
reference streams, suggesting a mechanism of impact on the fish assemblage other than habitat differences between stream types.
A significant number of species, approximately
2.4 species (excluding sea lamprey), was lost above
low-head barriers, implying that these barriers are
affecting species richness in these streams. Although barrier streams were significantly wider and
deeper than reference streams, differences in habitat
did not account for the loss of species above lowhead barriers in this study. Due to the lack of influence of habitat characteristics on the decline in
species richness above barriers and the high peak in
richness found directly below the barrier, trends
seen in species richness within barrier streams can
396
Dodd et al.
best be explained by the blocking of fish movement
(Porto et al. 1999), resulting in an aggregation of
species directly downstream of the structure (Benstead et al. 1999).
With the potential for low-head sea lamprey barriers to impede movement of fish species that do
not normally exhibit strong jumping ability, the creation of a semi-isolated community above the barriers was anticipated. Fish could emigrate to
downstream areas, mimicking mortality to the upstream community, while fish below the barrier are
prevented from immigrating to areas above the barrier. Based on studies of larger dams without fish
passageways (Erman 1973, Bulow et al. 1988, Winston et al. 1991), a shift in the assemblage composition and size structure was expected. However, no
marked shift in fish assemblages in barrier streams
was found, as evidenced by the relatively high similarity indices. The similarity in fish assemblage
composition suggests that isolating mechanisms
had relatively small effects. Further, the fish assemblage composition was remarkably similar across
all stream sections, suggesting that the function of
the assemblage is not severely impacted by low
head barriers in this study.
In this study, effects of low-head barriers was examined by evaluating differences between upstream
and downstream reaches of streams with barriers
relative to reference or “control” streams. Although
the optimal study design to assess effects of lowhead barriers may be to sample both the barrier and
reference stream before and after installation of the
barrier, this design was not feasible given that public concern over possible effects of these barriers
was not raised until after construction. For this
study, reference streams were used as indicators of
the expected pattern in barrier streams if a barrier
had not been constructed on these streams. Using
reference streams to gauge shifts in barrier streams
was justified due to their close proximity and similarity in size, geography, and geology to barrier
streams. Further, both reference and barrier streams
in the study had been treated in the recent past with
lampricides. Thus, both stream types provide habitat and water quality conditions required for successful sea lamprey reproduction.
Another limitation of this study was that only
summer months were analyzed, and therefore, the
magnitude of low-head barrier impacts on fish assemblages during spring or fall were not assessed
(Porto et al. 1999). The more stable summer months
were selected to minimize the potential impacts of
spawning migrations and of fluctuations in water
level that often occur during spring and fall. In
spring, low-head barriers would be expected to
have less of an impact due to snow melt and spring
rains which increase water depths, potentially allowing fish to pass (especially for strong swimmers) over the small barriers in this study. In the
fall when water levels are usually at their lowest
point, the barriers would become more difficult to
traverse as fish would need to jump greater heights
over the barrier. Porto et al. (1999), however, found
that the impact on fish movement over low-head
barriers (as evidenced by mark-recapture data in a
subset of the 24 barrier streams examined in this
study) was greatest in spring and fall, and that some
species were able to traverse the barrier during
these seasons. Depending on the amount of precipitation during the winter and early spring, impacts
on migratory non-jumping species may vary from
year to year with an expectation of low-head barrier
effects being more pronounced in dry years.
The number of species lost above the barriers in
this study was not related to the head height or age
of the barrier, and fish composition and size structure were similar between upstream and downstream
sections within barrier streams. From this finding,
blockage of fish movement is probably not continuous year around, and some fish are able to traverse
low-head barriers, possibly during periods of flooding (Helfrich et al. 1999). Thus, low-head barriers
may not be a complete obstruction to movement for
certain species (Benstead et al. 1999, Porto et al.
1999), allowing for mixing of these populations. It is
important to note that most of the barriers in this
study were quite small and that this conclusion does
not extend to dams larger than examined in this
study. In studies of larger dams, upstream movement
of most fish species was blocked, resulting in a large
loss of species above these barriers and/or a large
shift in the fish composition and size structure above
barriers relative to downstream sites (Erman 1973,
Bulow et al. 1988, Winston et al. 1991).
In the analysis of individual species, certain
species appeared to be sensitive to low-head barriers. Sea lamprey, yellow perch, and trout-perch
were not captured from upstream reaches in any of
our barrier streams, suggesting these species are
negatively affected by low-head barriers. However,
sampling equipment used in this study was not
specifically designed for sea lamprey ammocoete
collection, and sample sizes for many individual
species were too small to allow us to determine the
impact of low-head barriers with adequate precision
to make generalizations. To adequately assess the
Low-head Barrier Effects on Habitat and Fish
degree of impact on specific populations, an extensive mark-recapture study of particular species
thought to be negatively affected by low-head barriers will be necessary.
CONCLUSIONS
There was relatively little effect of low-head barriers on the habitat measurements examined. A decline in number of species seen above barriers was
evident, but none of the habitat characteristics measured could explain the trend of high species richness below the barrier or the greater loss of species
upstream of the barrier, even though some habitat
variables were significant covariates. Therefore,
one of the principal mechanisms thought to be impacting species richness is the blockage of upstream
fish movement as opposed to habitat alteration. Although low-head barriers had some influence on
fish species composition, community size composition was not altered significantly.
In this study, indications of low-head barrier effects on non-target species were found. To reduce
effects of low-head sea lamprey barriers on nonjumping or non-target species, the Great Lakes
Fishery Commission has experimented with installing inflatable variable crest barriers. These barriers are in operation during the sea lamprey
spawning run in spring and then deflated during the
remainder of the year to allow fish passage. Inflatable variable crest barriers are expected to further
reduce the barrier effects observed in this study.
When the two variable crest barriers were excluded
in this study (Albany Creek and Big Carp River),
the results did not change substantially. However,
the effects of variable crest barriers warrants further
investigation. Although results of this study show
low-head barriers have an impact on the fish community, this impact must be weighed against the environmental, social, and monetary costs of using
chemicals in these streams to control sea lamprey.
This study will aid sea lamprey control agencies
and managers in making decisions on the tradeoffs
between chemical and mechanical controls and determine the best strategy for controlling sea lamprey in the Great Lakes while maintaining fish
diversity in it’s tributaries.
ACKNOWLEDGMENTS
Funding for this project was provided by the
Great Lakes Fishery Commission through the Sea
Lamprey Barrier Task force. We thank the Ontario
397
Ministry of Natural Resources, Fisheries and
Oceans Canada, and the U.S. Fish and Wildlife Service, for assistance in selecting study streams and
use of equipment. Thanks to the Michigan and Wisconsin Departments of Natural Resources and the
Ontario Ministry of Natural Resources for providing collection permits. E. Holm of the Royal Ontario Museum and T. Coon of Michigan State
University helped with fish identification. We also
thank the many student interns who were instrumental in collecting field data.
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Submitted: 21 December 2000
Accepted: 27 June 2002
Editorial handling: William D. Swink
APPENDIX 1. Number of streams in which each species was caught above and below a low-head barrier in barrier streams or an equivalent location in the reference streams. (BA refers to Barrier Above
stream sections, BB = Barrier Below, RA = Reference Above, RB = Reference Below). Scientific names
follow Robins et al. 1991.
Common name
American brook lamprey
American eel
Atlantic salmon
Black bullhead
Black crappie
Blackchin shiner
Blacknose dace
Blacknose shiner
Blackside darter
Bluegill
Bluntnose minnow
Bowfin
Brassy minnow
Brook stickleback
Brook trout
Scientific name
Lampetra appendix
Anguilla rostrata
Salmo salar
Ameiurus melas
Poxomis nigromaculatus
Notropis heterodon
Rhinichthys atratulus
Notropis heterolepis
Percina maculata
Lepomis macrochirus
Pimephales notatus
Amia calva
Hybognathus hankinsoni
Culaea inconstans
Salvelinus fontinalis
BA
6
0
0
2
1
1
20
5
3
1
4
0
4
13
8
Number of streams
BB
RA
6
1
1
0
0
0
3
1
1
0
0
1
21
14
2
2
2
5
1
3
9
4
1
0
4
1
7
9
7
8
RB
1
0
1
2
1
2
15
4
4
3
3
1
3
7
5
(Continued)
399
Low-head Barrier Effects on Habitat and Fish
APPENDIX 1.
Continued.
Number of streams
Common name
Scientific name
BA
BB
RA
RB
Brown bullhead
Brown trout
Burbot
Central mudminnow
Channel catfish
Chestnut lamprey
Chinook salmon
Coho salmon
Common carp
Common shiner
Creek chub
Cutlips minnow
Emerald shiner
Fallfish
Fantail darter
Fathead minnow
Finescale dace
Flathead catfish
Golden redhorse
Golden shiner
Grass pickerel
Greater redhorse
Green sunfish
Hornyhead chub
Iowa darter
Johnny darter
Lake chub
Lake trout
Largemouth bass
Largescale stoneroller
Logperch
Longnose dace
Mimic shiner
Mottled sculpin
Ninespine stickleback
Northern brook lamprey
Northern hog sucker
Northern pike
Northern redbelly dace
Pearl dace
Pugnose minnow
Pumpkinseed
Rainbow darter
Rainbow trout
Red shiner
Redside dace
River chub
River darter
Rock bass
Rosyface shiner
Ruffe
Sand shiner
Sauger
Ameiurus nebulosus
Salmo trutta
Lota lota
Umbra limi
Ictalurus punctatus
Ichthyomyzon castaneus
Oncorhynchus tshawytscha
Oncorhynchus kisutch
Cyprinus carpio
Luxilus cornutus
Semotilus atromaculatus
Exoglossum maxillingua
Notropis atherinoides
Semotilus corporalis
Etheostoma flabellare
Pimephales promelas
Phoxinus neogaeus
Pylodictis olivaris
Moxostoma erythrurum
Notemigonus crysoleucus
Esox americanus vermiculatus
Moxostoma valenciennesi
Lepomis cyanellus
Nocomis biguttatus
Etheostoma exile
Etheostoma nigrum
Couesius plumbeus
Salvelinus namaycush
Micropterus salmoides
Campostoma oligolepis
Percina caprodes
Rhinichthys cataractae
Notropis volucellus
Cottus bairdi
Pungitius pungitius
Ichthyomyzon fossor
Hypentelium nigricans
Esox lucius
Phoxinus eos
Margariscus margarita
Opsopoeodus emiliae
Lepomis gibbosus
Etheostoma caeruleum
Oncorhynchus mykiss
Cyprinella lutrensis
Clinostomus elongatus
Nocomis micropogon
Percina shumardi
Ambloplites rupestris
Notropis rubellus
Gymnocephalus cernuus
Notropis stramineus
Stizostedion canadense
3
6
0
14
0
1
0
2
2
11
19
1
0
1
2
3
1
0
0
0
0
1
1
4
1
15
1
0
1
0
3
13
0
17
0
2
2
3
6
4
0
5
2
17
1
0
0
0
9
2
0
0
0
1
5
5
9
1
0
0
2
3
14
20
1
2
1
4
8
2
1
1
2
0
0
2
5
1
19
1
1
4
2
15
19
2
19
1
1
2
6
8
4
1
11
2
16
0
1
0
1
19
2
2
2
1
0
6
0
15
0
0
1
2
2
9
17
1
0
1
3
2
2
0
0
0
0
0
0
5
1
14
0
0
1
0
7
16
0
17
0
0
3
4
2
1
0
6
2
17
0
0
1
0
10
2
0
0
0
1
5
3
13
0
0
2
2
3
10
15
1
0
1
3
2
0
0
1
1
1
1
0
5
1
15
0
0
2
0
10
20
0
18
1
0
2
2
1
2
1
5
2
17
0
0
0
0
15
1
0
0
1
400
APPENDIX 1.
Dodd et al.
Continued.
Common name
Sea lamprey
Silver redhorse
Silver shiner
Slimy sculpin
Smallmouth bass
Southern redbelly dace
Spotfin shiner
Stonecat
Striped shiner
Threespine stickleback
Trout-perch
Walleye
White bass
White sucker
Yellow bullhead
Yellow perch
Scientific name
BA
Petromyzon marinus
Moxostoma anisurum
Notropis photogenis
Cottus cognatus
Micropterus dolomieu
Phoxinus erythrogaster
Cyprinella spiloptera
Noturus flavus
Luxilus chrysocephalus
Gasterosteus aculeatus
Percopsis omiscomaycus
Stizostedion vitreum
Morone chrysops
Catostomus commersoni
Ameiurus natalis
Perca flavescens
0
0
0
3
1
1
2
2
0
0
0
0
0
16
1
0
Number of streams
BB
RA
7
3
1
0
0
0
3
1
5
1
0
0
2
1
3
1
2
2
2
0
4
1
2
0
1
0
20
14
0
0
6
5
RB
6
1
1
1
4
0
1
2
0
2
1
0
1
17
0
3
APPENDIX 2. Mean catch (± one standard error) for each species caught above and below low-head
barriers in barrier streams or an equivalent location in the reference streams, summer 1996 and 1997
combined. Impact values were computed to scale the difference in mean catch in sections above barriers
(BA) and below barriers (BB) relative to the differences seen in reference streams (RA = reference above,
RB = reference below).
Species name
American brook lamprey
American eel
Atlantic salmon
Black bullhead
Black crappie
Blackchin shiner
Blacknose dace
Blacknose shiner
Blackside darter
Bluegill
Bluntnose minnow
Bowfin
Brassy minnow
Brook stickleback
Brook trout
Brown bullhead
Brown trout
Burbot
Central mudminnow
Channel catfish
Chestnut lamprey
Chinook salmon
Coho salmon
Common carp
Barrier above
(N = 72)
0.65 (0.23)
0.00 (0.00)
0.00 (0.00)
0.05 (0.04)
0.01 (0.01)
0.04 (0.04)
5.98 (1.03)
0.44 (0.30)
0.20 (0.10)
0.03 (0.02)
0.18 (0.09)
0.00 (0.00)
0.15 (0.10)
1.16 (0.36)
0.98 (0.31)
0.07 (0.04)
0.10 (0.04)
0.00 (0.00)
1.79 (0.51)
0.00 (0.00)
0.01 (0.01)
0.00 (0.00)
0.08 (0.05)
0.12 (0.08)
Mean catch
Barrier below Reference above
(N = 66)
(N = 69)
0.65 (0.32)
0.07 (0.04)
0.01 (0.01)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.03 (0.01)
0.02 (0.02)
0.01 (0.01)
0.00 (0.00)
0.00 (0.00)
0.04 (0.03)
4.95 (1.14)
5.95 (1.26)
0.08 (0.04)
0.03 (0.01)
0.43 (0.14)
0.03 (0.02)
0.04 (0.03)
0.03 (0.01)
0.06 (0.03)
0.50 (0.21)
0.02 (0.02)
0.00 (0.00)
0.09 (0.04)
0.03 (0.02)
0.45 (0.18)
0.48 (0.20)
0.90 (0.34)
0.12 (0.04)
0.01 (0.01)
0.00 (0.00)
0.08 (0.04)
1.86 (0.92)
0.82 (0.47)
0.00 (0.00)
0.62 (0.16)
2.49 (0.91)
0.01 (0.01)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.01 (0.01)
0.11 (0.09)
0.63 (0.36)
0.05 (0.03)
0.22 (0.10)
Reference below
(N = 68)
0.05 (0.03)
0.00 (0.00)
0.02 (0.02)
1.66 (1.32)
0.01 (0.01)
0.39 (0.36)
5.54 (0.96)
0.06 (0.03)
0.07 (0.04)
0.26 (0.14)
0.16 (0.09)
0.01 (0.01)
0.06 (0.04)
0.13 (0.06)
0.50 (0.22)
0.01 (0.01)
2.29 (1.07)
0.06 (0.04)
0.45 (0.14)
0.00 (0.00)
0.00 (0.00)
0.05 (0.04)
0.23 (0.20)
0.04 (0.02)
Impact value
(BA-BB)-(RA-RB)
–0.01
–0.01
0.02
1.66
0.01
0.40
0.61
0.40
–0.20
0.22
–0.22
–0.01
0.10
0.37
0.45
0.07
0.45
–0.76
–0.87
–0.01
0.01
0.04
–0.43
–0.11
(Continued)
Low-head Barrier Effects on Habitat and Fish
APPENDIX 2.
401
Continued.
Mean catch
Species name
Common shiner
Creek chub
Cutlips minnow
Emerald shiner
Fallfish
Fantail darter
Fathead minnow
Finescale dace
Flathead catfish
Golden redhorse
Golden shiner
Grass pickerel
Greater redhorse
Green sunfish
Hornyhead chub
Iowa darter
Johnny darter
Lake chub
Lake trout
Largemouth bass
Largescale stoneroller
Logperch
Longnose dace
Mimic shiner
Mottled sculpin
Ninespine stickleback
Northern brook lamprey
Northern hog sucker
Northern pike
Northern redbelly dace
Pearl dace
Pugnose minnow
Pumpkinseed
Rainbow darter
Rainbow trout
Red shiner
Redside dace
River chub
River darter
Rock bass
Rosyface shiner
Ruffe
Sand shiner
Sauger
Sea lamprey
Silver redhorse
Silver shiner
Slimy sculpin
Smallmouth bass
Southern redbelly dace
Spotfin shiner
Barrier above
(N = 72)
1.89 (0.84)
2.61 (0.53)
0.21 (0.13)
0.00 (0.00)
0.02 (0.02)
0.91 (0.61)
0.03 (0.02)
0.06 (0.03)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.01 (0.01)
0.03 (0.02)
0.79 (0.38)
0.17 (0.10)
1.62 (0.37)
0.16 (0.11)
0.00 (0.00)
0.01 (0.01)
0.00 (0.00)
0.03 (0.02)
3.61 (0.84)
0.00 (0.00)
4.79 (0.68)
0.00 (0.00)
0.13 (0.08)
0.02 (0.01)
0.03 (0.02)
0.31 (0.12)
0.24 (0.17)
0.00 (0.00)
0.07 (0.04)
0.18 (0.11)
3.86 (0.91)
0.01 (0.01)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.72 (0.29)
0.05 (0.04)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.66 (0.23)
0.05 (0.03)
0.01 (0.01)
0.38 (0.23)
Barrier below Reference above
(N = 66)
(N = 69)
1.79 (0.46)
2.96 (0.58)
0.41 (0.24)
0.03 (0.02)
0.03 (0.02)
0.40 (0.18)
0.20 (0.06)
0.04 (0.02)
0.01 (0.01)
0.04 (0.04)
0.04 (0.03)
0.00 (0.00)
0.00 (0.00)
0.19 (0.12)
0.68 (0.24)
0.11 (0.10)
1.90 (0.37)
1.18 (0.84)
0.02 (0.01)
0.12 (0.05)
0.10 (0.05)
1.04 (0.33)
7.66 (1.55)
0.04 (0.03)
5.64 (1.04)
0.01 (0.01)
0.04 (0.02)
0.03 (0.01)
0.11 (0.04)
0.39 (0.16)
0.18 (0.11)
0.01 (0.01)
0.68 (0.24)
0.24 (0.19)
2.51 (0.56)
0.00 (0.00)
0.04 (0.03)
0.00 (0.00)
0.02 (0.02)
1.53 (0.36)
0.26 (0.18)
0.02 (0.01)
0.02 (0.01)
0.03 (0.02)
0.17 (0.06)
0.01 (0.01)
0.00 (0.00)
0.14 (0.06)
0.24 (0.10)
0.00 (0.00)
0.03 (0.02)
0.98 (0.37)
2.42 (0.54)
0.09 (0.06)
0.00 (0.00)
0.03 (0.03)
1.13 (0.62)
0.14 (0.09)
0.02 (0.01)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.34 (0.21)
0.01 (0.01)
1.50 (0.44)
0.00 (0.00)
0.00 (0.00)
0.03 (0.02)
0.00 (0.00)
0.31 (0.09)
5.53 (1.04)
0.00 (0.00)
4.18 (0.73)
0.00 (0.00)
0.00 (0.00)
0.61 (0.50)
0.18 (0.07)
0.26 (0.18)
0.03 (0.03)
0.00 (0.00)
0.06 (0.02)
1.34 (0.74)
4.52 (1.59)
0.00 (0.00)
0.00 (0.00)
0.02 (0.01)
0.00 (0.00)
0.52 (0.16)
0.18 (0.15)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.03 (0.02)
0.00 (0.00)
0.00 (0.00)
0.03 (0.03)
0.02 (0.01)
0.00 (0.00)
0.04 (0.03)
Reference below
(N = 68)
1.07 (0.29)
3.23 (0.65)
0.04 (0.03)
0.00 (0.00)
0.01 (0.01)
0.89 (0.49)
0.02 (0.01)
0.00 (0.00)
0.00 (0.00)
0.01 (0.01)
0.01 (0.01)
0.03 (0.02)
0.01 (0.01)
0.00 (0.00)
0.61 (0.27)
0.03 (0.02)
2.17 (0.53)
0.00 (0.00)
0.00 (0.00)
0.06 (0.05)
0.00 (0.00)
0.65 (0.18)
6.01 (1.31)
0.00 (0.00)
4.26 (0.93)
0.02 (0.02)
0.00 (0.00)
0.24 (0.16)
0.02 (0.01)
0.01 (0.01)
0.02 (0.01)
0.04 (0.03)
0.46 (0.33)
1.68 (0.81)
3.17 (1.26)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.80 (0.16)
0.54 (0.50)
0.00 (0.00)
0.00 (0.00)
0.01 (0.01)
0.06 (0.03)
0.01 (0.01)
0.04 (0.04)
0.01 (0.01)
0.07 (0.03)
0.00 (0.00)
0.01 (0.01)
Impact value
(BA-BB)-(RA-RB)
0.19
0.47
–0.25
–0.03
–0.04
0.27
–0.28
0.01
–0.01
–0.03
–0.03
0.03
0.02
–0.17
0.38
0.07
0.39
–1.03
–0.02
–0.08
–0.10
–0.67
–3.57
–0.04
–0.78
0.01
0.10
–0.38
–0.24
–0.33
0.05
0.04
–0.21
0.29
–0.00
0.01
–0.04
–0.02
–0.02
–0.53
0.14
–0.02
–0.02
–0.02
–0.14
0.00
0.04
0.50
–0.14
0.01
0.32
(Continued)
402
APPENDIX 2.
Dodd et al.
Continued.
Species name
Stonecat
Striped shiner
Threespine stickleback
Trout–perch
Walleye
White bass
White sucker
Yellow bullhead
Yellow perch
Barrier above
(N = 72)
0.09 (0.06)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
0.00 (0.00)
1.02 (0.28)
0.01 (0.01)
0.00 (0.00)
Mean catch
Barrier below Reference above
(N = 66)
(N = 69)
0.10 (0.05)
0.02 (0.01)
0.57 (0.56)
0.05 (0.02)
0.03 (0.02)
0.01 (0.01)
1.66 (0.29)
0.00 (0.00)
0.16 (0.06)
0.02 (0.01)
0.06 (0.04)
0.00 (0.00)
0.02 (0.01)
0.00 (0.00)
0.00 (0.00)
0.93 (0.20)
0.00 (0.00)
0.14 (0.05)
Reference below
(N = 68)
Impact value
(BA-BB)-(RA-RB)
0.02 (0.01)
0.00 (0.00)
0.02 (0.01)
0.10 (0.07)
0.00 (0.00)
0.01 (0.01)
1.33 (0.24)
0.00 (0.00)
0.31 (0.15)
–0.01
–0.08
–0.55
0.03
–0.03
0.00
–0.25
0.01
0.01