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Relative Abundance and Distribution of Ruffe (Gymnocephalus cernuus) in a Lake Superior Coastal Wetland Fish Assemblage
J. Great Lakes Res. 24(2):293-303 Internal. Assoc. Great Lakes Res., 1998
Relative Abundance and Distribution of Ruffe (Gymnocephalus cernuus) in a Lake Superior Coastal Wetland Fish Assemblage John C. Brazner1*, Danny K. Tanner!, Douglas A. Jensen 2 , and Armond Lemke3 I U.S.
Environmental Protection Agency Mid-Continent Ecology Division 6201 Congdon Blvd. Duluth, Minnesota 55804
2University ofMinnesota Sea Grant Program 2305 E. Fifth St. Duluth, Minnesota 55812 3National Senior Citizens Education and Research Center 8403 Colesville Rd. Silver Spring, Maryland 20910 ABSTRACT. Fish assemblages from Allouez Bay Wetland in the St. Louis River estuary were sampled with fyke-nets from May to October, 1995, to characterize typical use patterns in different seasons and microhabitats. The relative abundance and distribution of ruffe (Gymnocephalus cernuus) in these habitats was of interest because their recent invasion into the Great Lakes has the potential to disrupt native fish assemblages. A total of 15,867 fish comprised of 34 species were captured in 2,300 h of netting. The majority offish over the whole study were caught in the outer marsh (63%, 9,957 individuals), and seasonally during late June (7,384 individuals/4 net-nights) and early May (2,281 individuals). Yellow perch (Perea flavescens), brown bullhead (Ameiurus nebulosus), emerald shiner (Notropis atherinoides), and silver redhorse (Moxostoma anisurum) were the most abundant species, comprising 85 percent of the total catch. Ruffe was the seventh most abundant species captured (294 individuals), comprising only two percent of the total catch. They were the fifth most abundant species in the outer marsh, but only thirteenth most abundant in the inner marsh. Ninety-one percent of all rufte (268 individuals) were caught in the outer marsh. Of the 75 species by life-stage combinations derived by classifying all individuals captured into one of 3 life stage categories (YOY, yearling, and adult), yearling rufte were the twe(fth most abundant, adult rufte were sixteenth, and YOY rufte were twenty-seventh. While rufte have been the most abundant fish captured in bottom trawls in St. Louis River estuary during the 1990s, our results indicate the invasion of rufte in shallow, heavily vegetated areas like those in Allouez Bay has been much less successful. Our results also suggest further degradation of coastal wetlands and other vegetated habitats would eliminate significant refugia from rufte competition and could lead to increased dominance of rufte in shallow water habitats in the Great Lakes. INDEX WORDS: Rufte, coastal wetland, fish assemblage, microhabitats, fyke-nets, St. Louis/Allouez Bay, Lake Superior.
and Kindt 1992; Slade et al. 1994, 1995; Kindt et al. 1996; Edwards 1995; Selgeby and Edwards 1995; Czypinski et al. 1997). Ruffe tolerate a vari-
INTRODUCTION The ecology of ruffe, Gymnocephalus cernuus (for review see Ogle 1995), and their invasion and current distribution in North America have been relatively well-documented (Pratt et al. 1992; Slade
ety of environmental conditions from fresh to brackish, shallow to deep, cold to warm, and oligotrophic to eutrophic. Ruffe tolerate low dissolved oxygen concentrations and high levels of some contaminants although these relationships are not entirely clear (see Ogle 1995). One aspect of ruffe
*Corresponding author. E-mail: [email protected]
293
294
Brazner et al.
Study Site
N
t Bear Creek-
o !
10
kilo~eters
I
FIG. 1. Map of Allouez Bay Wetland showing approximate locations of the inner and outer marsh study sites (adapted from Sierszen et al.1996).
ecology that is not as well understood is habitat preference. Ruffe seem to prefer dark (Westin and Aneer 1987, Ogle et al. 1995), benthic environments (Bergman 1988, Kalas 1995), and areas of slow-moving water with soft bottoms and little macrophyte cover (Johnsen 1965). Although response to varying light conditions appears to be age, season, and ecosystem dependent (Kah\s 1995, Ogle et at. 1995), response to varying cover conditions has received little attention. Ruffe were seldom captured in the 0 to 4 m depth zone in Lake Mildevatn, Norway (Kalas 1995), but were captured in substantial numbers at 0 to 3 m depths in St. Louis River estuary, Lake Superior (Edwards 1995, Ogle et aI. 1995). This disparity between
catches may be related to differences in cover characteristics between these locations; the littoral zone in Lake Mildevatn has moderate to dense vegetative cover (Kalas 1995) while the shallow flats that were sampled in St. Louis River estuary have relatively sparse plant cover (Andy Edwards, U.S. Geological Survey, Great Lakes Science Center, Ashland, WI, pers. comm.). We conducted a study in 1995 to characterize typical use patterns of ruffe in relation to native members of the fish assemblage in Allouez Bay Wetland at the eastern end of St. Louis River estuary, Lake Superior (Fig 1.) in different seasons and microhabitats. We were also interested in determining the relationship of different fish species to
Ruffe in a Lake Superior Coastal Wetland varying macrophyte cover. By examining the relationship between ruffe and other fish species to macrophyte cover in Allouez Bay, we hoped to provide additional information not only about microhabitat preferences of fish that use Great Lakes coastal wetlands, but also the potential for competition between ruffe and other fishes present in St. Louis River estuary. We felt our results would be of particular interest since almost no information on basic fish community ecology in Lake Superior coastal wetlands has been published. Competition among ruffe, other exotics and native fishes in the Great Lakes has been a topic of much concern recently (Bergman and Greenberg 1994, Ogle et al. 1995, Savino and Kolar 1996, Sierszen et al. 1996, Bronte et al. 1998) as ruffe have become an abundant fish species in the St. Louis River estuary (Busiahn 1993, Edwards 1995), and have been captured in several south shore tributaries on the western end of Lake Superior (Czypinski et al. 1997). However, ruffe relative abundance estimates in the St. Louis estuary vary considerably among biologists who have worked on this problem (Lindgren et at. 1997; Dennis Pratt, Wisconsin Department of Natural Resources, Superior, WI, pers. comm.; Edwards 1995; Brazner, this manuscript). Given this disparity, another goal of our study was to provide additional information about the relative abundance of ruffe in the Allouez Bay portion of the St. Louis estuary. STUDY SITE AND METHODS The fish assemblages in two locations adjacent to the mouth of Bear Creek within Allouez Bay Wetland (Fig. 1) were sampled from May through October in 1995. Allouez Bay Wetland is at the eastern end of the St. Louis River estuary/Duluth-Superior harbor complex inside Wisconsin Point, a prominent barrier sand spit at the western end of Lake Superior. The heavily vegetated portion of the wetland covers 148 ha (Herdendorf et at. 1981) and is dominated by robust emergent vegetation such as burreed, Sparganium eurycarpum, and softstem bulrush, Scirpus validus. The adjacent open-water lagoon is approximately 100 ha, shallow « 2 m), and has patches of submerged and floating vegetation throughout (e.g., Potamogeton richardsonii, Ceratophyllum demersum, Utricularia vulgaris, Nuphar variegata). Clay-laden discharges from the Nemadji River and other smaller south shore tributaries limit benthic primary producers (Keough et at. 1996).
295
Two fyke-nets (13-mm and 4-mm bar mesh, 5-m length, 1.1-m x lA-m front opening) were set in an inner and an outer marsh site at 0.6 to 1.2 m depths (varied with date and seiche activity, average depth - 0.9 m) in a lead-to-lead orientation (15 m connecting lead, 3 m wings on each net) for four consecutive nights and tended daily from 8 to 11 May, 5 to 8 June, 26 to 29 June, 31 July to 3 August, 4 to 7 September, and 2 to 5 October. The inner marsh site was typified by dense emergent and submergent vegetation, and low wave energy. The outer marsh site had little or no emergent vegetation, moderate submergent macrophyte cover, and higher wave action because it was adjacent to the open water portion of Allouez Bay. Captured fish were identified to species, weighed (± 0.1 g), and measured (± 0.1 cm) in the field. Observed length-frequency distributions in relation to those reported by Becker (1983), and field observation of ontogeny were used to assign individuals to one of three life-stage categories; young-of-the-year (YOY), yearling (1 +), or adult. Areal coverage in macrophytes, macrophyte species, and the dominant macrophyte growth forms were estimated visually during a 15min wading survey each sampling period to quantify differences in habitat structure between inner and outer marsh locations. Temperature, pH, conductivity, and dissolved oxygen were measured between 1000 and 1200-h daily at mid-depth (- 0.5-m) in a central marsh location (Hydrolab 4041 multiprobe, Hydrolab Corp., Austin, TX) and a 500-mL water sample was taken for turbidity estimates (Hach 2100AN Laboratory Turbidimeter, Hach Co., Loveland, CO). Most fish catch results were summarized as catch-per-unit-effort (number of fish per 96 h fykenet set) by sampling period and/or location for the most common species and life-stage groups. Recognizing the temporal dependence of our samples, we felt it was important to include a more quantitative means of evaluating differences between marsh locations than would have been possible strictly through a graphical depiction of the data or by examining absolute or percentage abundance differences. Therefore, results of two-sample t-tests were used to approximate whether numbers of the ten most abundant species and species by life-stage combinations were substantially different between the inner and outer marsh sites across the entire sampling period. Similar tests were conducted for the five most abundant species in each sampling period. All data were log transformed prior to statisti-
Brazner et al.
296
TABLE l. Mean physical-chemical conditions (range in parentheses) and location specific macrophyte cover in Allouez Bay Wetland during 1995 (n =5 for all means, macrophyte cover represents a single estimate each sampling period; na =not available). May
Early June
Temperature (OC)
9.1 (7.0-12.8)
17.7 (15.5-20.3)
pH
7.5 (7.3-7.8)
August
September
October
16.8 (16.3-17.5)
22.4 (22.1-23.1)
19.7 (15.9-21.7)
ILl (9.0-12.1)
6.9 (6.8-6.9)
6.8 (6.7-6.8)
6.5 (6.4-6.6)
6.9 (6.8-7.0)
6.9 (6.8-7.1)
na
7.1 (5.8-8.0)
6.3 (5.7-7.1)
5.7 (5.2-6.5)
8.2 (6.8-10.6)
8.0 (5.8-10.7)
Conductivity (us/sec)
150 (132-196)
155 (149-161)
157 (154-160)
153 (151-154)
146 (143-151)
180 (168-189)
Turbidity (ntu)
122 (54-251)
78 (30-243)
37 (34-46)
55 (45-81)
48 (34-71)
52 (44-63)
5 5
40 10
60 30
70 30
80 50
70 40
Dissolved Oxygen (mg/L)
Late June
% Macrophyte Cover
Inner Marsh Outer Marsh
cal analysis to maximize variance homogeneity and increase normality of the data distributions.
in the Great Lakes (Stephenson 1990, Brazner and Magnuson 1994).
RESULTS AND DISCUSSION
Fish Assemblages A total of 15,867 fish comprised of 34 species were captured in 2,300 h of netting (Table 2). This species richness is higher than most fish assemblages at individual coastal wetland sites elsewhere in the Great Lakes (Marean 1976, Chubb and Liston 1986, Stephenson 1988, Brazner 1997). Only at an undiked bottomland in Muddy Creek Bay on Lake Erie (an atypical Great Lakes coastal wetland) have more species (40) been captured (Johnson et al. 1996). The greatest number of species captured in any sampling period was 24 during May because of the large number of species spawning at that time (Table 3). The least number of species (16) were caught in early June before most YOY were a catchable size (Table 3). The largest catches were in early May (2,281 individuals) and late June (7,384 individuals), although greater than 1,750 fish were captured in each of the August, September, and October sampling periods (Table 3). The smallest catch was in early June (398 individuals). The large number of fish captured in early May was due primarily to an abundance of spawning emerald shiners, Notropis atherinoides, in the outer marsh. In late June, large numbers of young-of-the-year (YOY) yellow 'perch, and silver redhorse, Moxos-
Environmental Conditions Physical-chemical conditions (Table 1) were typical of coastal wetlands elsewhere in the Great Lakes (Chubb and Liston 1986, Stephenson 1990, Brazner and Beals 1997), and well within the tolerance limits of most northern fishes. Temperature and turbidity were the most variable; temperature peaked in August at 23.1 °C, and turbidity was highest in May and early June with maxima over 200ntu. High spring turbidities originated from clay sediments that erode from nearby tributaries (e.g., Nemadji River) during spring runoff, and from exposed shorelines that eroded during heavy spring storms (Banks and Brooks 1992, NRCS 1996). Although the number and composition of macrophyte species were similar at inner and outer marsh sites (l0 to 15 species), areal coverage was not. Macrophyte cover was dense by late June in the inner marsh (60%), peaked in September (80%), and remained high (70%) through October, while vegetation cover was only light to moderate (30 to 50%) during this same period in the outer marsh (Table 1). These macrophyte coverages were similar to those observed in turbid coastal wetlands elsewhere
297
Ruffe in a Lake Superior Coastal Wetland
TABLE 2. Total fish catch in ALlouez Bay Wetland in 1995 by species and location in decreasing order of overall abundance. Fish Species
Common Name
Outer Marsh
% Outer
Inner Marsh
% Inner
Perca flavescens Ameiurus nebulosus Notropis atherinoides Moxostoma anisurum Noturus gyrinus Notropis hudsonius Gymnocephalus cernuus Notemigonus chrysoleucus Catostomas commersoni Esox lucius Percopsis omiscomaycus Etheostoma nigrum Osmerus mordax Pomoxis nigromaculatus Morone americana Umbra limi M. macrolepidotum Percina caprodes Stizostedium vitreum Lepomis macrochirus Cyprinus carpio Ambloplites rupestris Culaea inconstans Pimephales promelas Couesius plumbeus L. gibbosus C. catostomus Pungitius pungitius Alosa pseudoharengus Lota Iota N. cornutus Salvelinus namaycush Cottus cognatus A. natalis
Yellow Perch 6,257 Brown Bullhead 160 Emerald Shiner 1,299 1,049 Silver Redhorse Tadpole Madtom 141 Spottail Shiner 364 Eurasian Ruffe 268 Golden Shiner 28 White Sucker 51 Northern Pike 47 Trout-perch 80 28 Johnny Darter Rainbow Smelt 45 Black Crappie 26 White Perch 38 Central Mudminnow 8 Shorthead Redhorse 15 Logperch 10 Walleye II Bluegill 4 Common Carp 1 Rock Bass 9 Brook Stickleback 3 Fathead Minnow 5 Lake Chub 4 Pumpkinseed 0 Longnose Sucker I Ninespine Stickleback 0 Alewife 0 Burbot 1 Common Shiner 0 Lake Trout 1 Slimy Sculpin 1 Yellow Bullhead 1
71% 7% 88% 80% 27% 71% 91% 15% 55% 52% 99% 47% 82% 48% 93% 20% 94% 67% 85% 33% 10% 90% 33% 71% 67% 0% 50% 0% 0% 100% 0% 100% 100% 100%
2,548 1,974 178 265 376 150 26 157 41 44
29% 93% 12% 20% 73% 29% 9% 85% 45% 48% 1% 53% 18% 52% 7% 80% 6% 33% 15% 67% 90% 10% 67% 29% 33% 100% 50% 100% 100% 0% 100% 0% 0% 0%
8,805 2,134 1,477 1,314 517 514 294 185 92 91 81 60 55 54 41 40 16 15 13 12 10 10 9 7 6 5 2 2 1
9,957 30
63%
5,910 30
37%
15,867 34
Total Number of Species
toma anisurum, were captured at both sites. Yellow perch, Perea Jlaveseens, YOY continued to comprise a majority (40 to 79%) of total catch in August and September, but by October brown bullhead, Ameiurus nebulosus, were most common (67% of total catch), primarily in the inner marsh (Fig. 2). Recruitment for both yellow perch and brown bullhead appeared to be high, despite recent concerns about declining populations of these species (Selgeby and Edwards 1995, Bronte et al. 1997).
I
32 10 28 3 32 1 5 2 8 9 I
6 2 2 5 I
2 I
0 I
0 0 0
TOTAL
I
1 I I
1
% of Total 55% 13% 9% 8% 3% 3% 2% 1% 1% 1% 1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% 100%
Yellow perch, brown bullhead, emerald shiner, and silver redhorse were the most abundant species, comprising 55, 13, 9, and 8 percent of the total catch respectively (Table 2). Although ruffe were the seventh most abundant species captured (294 individuals), they comprised only two percent of the total catch. Yellow perch were the most abundant species in every sampling period except May, early June, and October when they were either second or thir.d most abundant. Periods of high abundance for brown bullheads, silver redhorse, and
298 TABLE 3. Location Inner Marsh Outer Marsh Total
Brazner et al. Number offish species and number offish caught in Allouez Bay Wetland during 1995. May # spp. # fish
16 24 24
550 1,731 2,281
Early June # spp. # fish
14 13 16
142 256 398
Late June # spp. # fish
16 15 17
emerald shiners were more transient (Fig. 2). Ruffe were among the five most abundant species in May, August, and September, but never ranked higher than third. Species by life-stage rank abundances (Fig. 3) were very similar to overall species rank abundances in the top four positions (Fig. 2). Yellow perch YOY, brown bullhead YOY, silver redhorse YOY, and emerald shiner 1+ were the most abundant overall. This highlights the fact that our results reflect primarily the catch of young fishes, and that Allouez Bay, like other Great Lakes coastal wetlands, is an important nursery for many Great Lakes fish species (Stephenson 1990, Brazner 1997). Both adult and yearling (l +) yellow perch were among the ten most abundant species by lifestage (Fig. 3), supporting the contention that Great Lakes coastal wetlands are important to all life history stages of this commercial and sport fish species (Stephenson 1988, Johnson 1989, Brazner 1997). In contrast, yearling ruffe were only the twelfth most abundant species by life-stage group overall, adult ruffe were sixteenth, and YOY ruffe twenty-seventh. Yearlings and adult ruffe were most abundant during May when spawning was most intense, less abundant in early August and September, and least abundant in late June and early October. Ruffe YOY (20 to 30 mm in length) were first captured in late June from the inner marsh, but were most prevalent in August and September (40 to 60 mm) in the outer marsh (Fig. 4). These results lend little support to the finding that ruffe are the most abundant fish in the St. Louis River estuary (Edwards 1995, Busiahn 1996). It is important to recognize that our results may reflect conditions only in the Allouez Bay portion of the St. Louis River estuary due to our limited sampling range. It may be that bottom trawl samples that suggest ruffe are the most abundant fish in the estuary provide a more accurate overall estimate of population densities. Ruffe comprised 60% of the total catch in bottom trawls in the St. Louis River estuary in 1995 (Andy Edwards, USGS, Great Lakes Science Center, Ashland, WI, pers.
1,986 5,398 7,384
August # spp. # fish
14 20 22
691 1,227 1,918
September # spp. # fish
13 18 21
871 902 1,773
October # spp. # fish
19 16 20
1,670 443 2,113
comm., Table 4). However, long-term fish community indices compiled by Minnesota and Wisconsin Departments of Natural Resources for the St. Louis River estuary indicate that ruffe comprised a much smaller proportion of the entire fish community than estimated with bottom trawls (Table 4). Shoreline seining efforts from nine locations throughout the estuary in 1995 suggest that ruffe are only the fifth most abundant species, comprising less than 4% of the total catch (Table 4). Similarly, experimental gill-netting efforts from 21 locations throughout the estuary in 1995 indicated that ruffe were only the fourth most abundant fish (by number), comprising 14% of the total catch (Lindgren et al. 1997, Table 4). In addition, ruffe typically comprised between 1 and 5% of total fyke-net catches from Allouez Bay Wetland and Hog Island Wetland (an area approximately 4 km northwest of Allouez Bay) during 96 h sampling periods in August 1993 and 1994 (Brazner, unpublished data; Glen Black, USGS, Ann Arbor, MI, personal communication). It is well known that there is inherent bias with any particular gear type used to catch fish (Neilsen and Johnson 1983) and we feel it is important to recognize that estimates of ruffe relative abundance in the St. Louis River estuary/Allouez Bay fish community are strongly dependent on the method of capture and the specific habitat sampled. An effort to reconcile differences in catch estimates from the various habitats in the estuary would provide managers with valuable, less equivocal information. Standardization by the relative abundance of ruffe in different habitat types within the estuary and by season of catch might be useful. Over all of 1995 in our study, the majority of fish (63%) were caught in the outer marsh, but equal numbers of species (30) were captured at inner and outer marsh sites (Table 2). Seasonally, the number of species caught at our outer marsh site was higher than at the inner site in May, August, and September, but none of these differences were statistically significant (p > 0.05, Table 3). Proximity to the open portion of the adjacent bay and its large pool
299
Ruffe in a Lake Superior Coastal Wetland
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FIG. 2. Total catch (per 96 h fyke-netting) of the five most abundant fish species in Allouez Bay Wetland in 1995 by sampling period in the outer marsh (a), inner marsh (b), and overall (c). Asterisks denote significant differences between inner and outer marsh sites based on paired ttests, * = p ::; 0.05, ** = p ::; 0.01, *** = P ::; 0.001.
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EARLY JUNE LATE JUNE
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TOTAL
FIG. 4. Total catch of ruffe in Allouez Bay Wetland in 1995 by sampling period and marsh location. Asterisks denote significant differences between inner and outer marsh sites based on paired t-tests, * =p :::; 0.05, ** =p :::; 0.01, *** =p :::; 0.001.
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FIG. 3. Total catch of the ten most abundant species by life-stage (YOY = young-of-the-year, 1+ = yearling, AD = adult) in Allouez Bay Wetland in 1995, by outer and inner marsh locations (a), and overall (b). Asterisks denote significant differences between inner and outer marsh sites based on paired tests, * =p :::; 0.05, ** =p :::; 0.01, *** =p :::; 0.001.
of species probably contributed to this tendency. We also noted that the catch of some species was strongly biased toward a particular site. Based on statistical differences in their overall catch and the proportion of total catch at inner or outer marsh sites (~ 80%), brown bullhead, golden shiner, Notemigonus chrysoleucus, and central mudminnow, Umbra limi, could be characterized as inner marsh species, while ruffe, trout perch, Percopsis omiscomaycus, white perch, Morone americana, emerald shiner, and four others were primarily outer marsh species (Table 5). Ruffe were the fifth most abundant species in the light to moderately vegetated outer marsh, but only thirteenth most
abundant in the heavily vegetated inner marsh (Table 2). The fact that over 90% of all ruffe (268 individuals) were caught in the outer marsh may reflect a preference by ruffe for less vegetated areas (Johnsen 1965). Although this reported preference is based on few published data, a recent study in Norway also found that ruffe were far more abundant (> 90%) beyond the vegetated zone in Mildevatn (Kalas 1995). Avoidance of vegetated areas by ruffe probably results from several factors. Because of their sophisticated lateral line sensory system, ruffe are well adapted to foraging in deep, dark benthic habitats (Disler and Smirnov 1977, Bergman 1988, Janssen 1997) where macrophyte growth is inhibited by low light conditions. Ruffe are also relatively poor swimmers (Disler and Smirnov 1977), so dark benthic habitats may provide a better refuge from visual predators that tend to be associated with vegetated areas (e.g., northern pike, Esox lucius, and muskellunge, Esox masquinongy). This possibility is supported by observations in the St. Louis River estuary, where ruffe were prevalent in mostly unvegetated (Andy Edwards, USGS, Great Lakes Science Center, Ashland, WI, pers. comm.), shallow water habitats only at night (Ogle et al. 1995). However, it is also possible that the competitive advantage provided by the specialized sensory adaptations of ruffe would not be as effective in shallow, heavily vegetated areas where high back-
TABLE 4. Comparison of fish species relative abundance estimates in St. Louis Bay/Allouez Bay in 1995 based on catch-per-uniteffort data from four different research efforts (Brazner et al., data from this manuscript; Lindgren et al. 1997; Pratt et al., Wisconsin DNR, unpublished data; Edwards et al., U.S. Geological Survey/NBS, unpublished data). Sampling method, date, depth, and general location of each research effort is detailed in bottom half of the table. Bramer et at. u.s. EPA
% of Total Catch
1
Yellow Perch
55.5
2
Brown Bullhead
13.4
Rank Abundance
3
Emerald Shiner
9.3
~
% of Total Catch
Lindgren et al. MNDNR
% of Total Catch
Edwards et al. USGS/NBS
% of Total Catch
S~
Spottail Shiner
36.7
White Sucker
17
Euraian Ruffe
60.0
~
Yellow Perch
24.4
Lake Sturgeon
16
Trout-perch
12.1
Pratt et al. WDNR
Emerald Shiner
18.7
Walleye
15
Yellow Perch
6.8
4
Silver Redhorse
8.3
Black Crappie
8.4
Eurasian Ruffe
14
Spottail Shiner
6.8
5
Madtom
3.3
Eurasian Ruffe
3.8
Northern Pike
10
Emerald Shiner
4.9
6
Spottail Shiner
3.2
White Sucker
2.9
Channel Catfish
9
Black Crappie
2.6
7
Eurasian Ruffe
1.9
Golden Shiner
1.4
Shorthead Redhorse
7
Walleye
2.1
8
Golden Shiner
1.2
White Perch
0.6
Yellow Perch
5
White Sucker
1.2
9
White Sucker
0.6
Walleye
0.5
Silver Redhorse
2
White Perch
1.0
10
Northern Pike
0.6
Logperch
0.5
Black Crappie
1
Rainbow Smelt
0.6
....;:: t'"
~
;:0;-
~
V,
.§
......, .., g ~
Q
~
-$ '" !it
is'
;::
Method Mesh Size (mm) Depth (m) Date Sampled Location
Fyke-nets 4-13 <1.5 May-October Allouez Bay
Seine 5 <1.5 June-September St. Louis Bay/Allouez Bay
Gill-nets 19-51 1.5-8.2 July St. Louis Bay
Trawl 5(cod)-38(body) 2-9 April-September St. Louis Bay/Allouez Bay
~
302
Brazner et al.
TABLE 5. Species that were significantly more abundant (* $ 0.05, ** $ 0.01, *** $ 0.001) or had a majority of their total catch (c.80%) in the inner or outer marsh (limited to species with total catch >30). Inner Marsh Species
Outer Marsh Species
Brown Bullhead (93%)** Golden Shiner (85%)** Central Mudminnow (80)
Trout Perch (99%)*** White Perch (93%) Eurasian Ruffe (91 %)*** Emerald Shiner (87%) Rainbow Smelt (82%) Silver Redhorse (80%) Yellow Perch (71 %)* Spottail Shiner (71 %)*
ground stimulation is likely to be distracting (Disler and Smirnov 1977). With respect to the concern about ruffe competition with native fishes in the S1. Louis River estuary and elsewhere in the Great Lakes (e.g., Mayo and Selgeby 1996, Ogle et al. 1996), our data indicate that densely vegetated habitats like Allouez Bay Wetland may provide a refuge from intense competition with ruffe. It also suggests that further degradation of coastal wetland or heavily vegetated littoral habitats would lead to increased dominance of ruffe in shallow water habitats of the Great Lakes. In the S1. Louis River estuary, as in most other coastal estuaries in the Great Lakes, much of the historic wetland habitat has been lost to human developments (Krieger et al. 1992, MPCA/WDNR 1992). The high diversity of fishes supported by the remaining areas, along with the potential refuge they provide from invading species like ruffe, suggest that restoration and maintenance of coastal wetland habitats should be emphasized in remedial action plans and other rehabilitation efforts in the Great Lakes.
ACKNOWLEDGMENTS We thank John Lindgren from the Minnesota Department of Natural Resources, Dennis Pratt from the Wisconsin Department of Natural Resources, and Andy Edwards from the U.S. Geological Survey for providing comparative data and technical advice about ruffe populations in S1. Louis River estuary/Allouez Bay. We also thank Charles Bronte, Tom Coon, Gary Holcombe, J. Howard McCormick, Lars Rudstam, and Mike Sierszen for helpful reviews.
REFERENCES Banks, G., and Brooks, K 1992. Erosion-sedimentation and nonpoint source pollution in the Nemadji River watershed: status of our knowledge. Appendix L, The St. Louis River Remedial Action Plan, Stage One, Minnesota Pollution Control Agency, Duluth, MN, and Wisconsin Dept. of Natural Resources, Superior, WI. Becker, G.C 1983. Fishes of Wisconsin. Madison, WI: University of Wisconsin Press. Bergman, E. 1988. Foraging abilities and niche breadths of two percids, Perea fluviatilis and Gymnocephalus cernua, under different environmental conditions. J. Anim. Ecol. 57:443-453. _ _, and Greenberg, L.A. 1994. Competition between a planktivore, a benthivore, and a species with ontogenetic diet shifts. Ecology 75: 1233-1245. Brazner, J.C. 1997. Regional, habitat, and human development influences on coastal wetland and beach fish assemblages in Green Bay, Lake Michigan. J. Great Lakes Res. 23:36-51. - _ , and Beals, E.W. 1997. Patterns in fish assemblages from coastal wetland and beach habitats in Green Bay, Lake Michigan: a multivariate analysis of abiotic and biotic forcing factors. Can. J. Fish. Aquat. Sci., In Press. - _ , and Magnuson, J.J. 1994. Patterns of fish species richness and abundance in coastal marshes and other nearshore habitats in Green Bay, Lake Michigan. Verh. Internat. Verein. Limnol. 25:2098-2104. Bronte, CR., Evrard, L.M., Brown, W.P., Mayo, KR., and Edwards, AJ. 1998. Fish community changes in the S1. Louis River Estuary, Lake Superior, 1989-1996: is it ruffe or population dynamics? J. Great Lakes Res. 24(2):309-318. Busiahn, T.R. 1993. Can ruffe be contained before it becomes your problem? Fisheries 18(8):22-23. - - . 1996. Ruffe control program. Report to the Aquatic Nuisance Species Task Force, November, 1996. Chubb, S.L., and Liston, CR. 1986. Density and distribution of larval fishes in Pentwater Marsh, a coastal wetland on Lake Michigan. J. Great Lakes Res. 12:332-343. Czypinski, G.D., Hintz, AK, Johnson, G., and Keppner, S.M. 1997. Surveillence for ruffe in the Great Lakes, 1996. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. Disler, N.N., and Smirnov, S.A 1977. Sensory organs of the lateral-line canal system in two percids and their importance in behavior. J. Fish. Res. Board Can. 34:1492-1503. Edwards, AJ. 1995. Spatial changes in the distribution and abundance of ruffe (Gymnocephalus cernuus) and native fishes in the S1. Louis River estuary, 1989-1994. M.S. thesis, Univ. of Minnesota, Duluth, MN.
Ruffe in a Lake Superior Coastal Wetland Herdendorf, CE., Hartley, S.M., and Barnes M.D., eds. 1981. Fish and wildlife resources of the Great Lakes coastal wetlands within the United States. Volume 6. U.S. Fish Wildlife Servo FWS/OBS-81/02-v6. Janssen, J. 1997. A comparison of the sensitivity of the ruffe and yellow perch lateral lines to Daphnia and Hexagenia. In International Symposium on Biology and Management of Rufte-Symposium Abstracts, ed. D.A. Jensen, Minnesota Sea Grant Publication X48. Johnsen, P. 1965. Studies on the distribution and food of the ruffe (Acerina cernua) in Denmark, with notes on other aspects. Meddelelser fra Danmarks Fiskeri-og Havunderogelser 4: 137-156. Johnson, D.L. 1989. Lake Erie wetlands: fisheries considerations. In Lake Erie and its Estuarine Systems, ed. K.A. Krieger. Estuary-of-the-Month Seminar, U.S. Dept. of Commerce. Washington, D. C _ _, Lynch, W.E., Jr., and Morrison, T.W. 1996. Fish communities in a diked Lake Erie wetland and an adjacent undiked area. Wetlands 17: 43-54. KaHls, S. 1995. The ecology of ruffe, Gymnocephalus cernuus (Pisces:Percidae), introduced to Mi1devatn, western Norway. Environ. Bio!. Fish. 42:219-232. Keough, J.R., Sierszen, M.E., and CA. Hagley. 1996. Analysis of a Lake Superior coastal food web with stable isotope techniques. LimnoZ. Oceanogr. 41: 136-146. Kindt, K., Keppner, S.M., and Johnson, G. 1996. Surveillence for rufte in the Great Lakes, 1995. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. Krieger, K.A., K1arer, D.M., Heath, R.T., and Herdendorf, CE. 1992. A call for research on Great Lakes coastal wetlands. J. Great Lakes Res. 18:525-528. Lindgren, J.P., Ongstad, P.W., and Spurrier, J.R. 1997. The St Louis Bay fishery 1986-1994. Minnesota Dept. of Natural Resources, Division of Fish and Wildlife, Section of Fisheries, Study 4 Report, Job 442, St. Paul, MN. Marean, J.B. 1976. The influence of physical, chemical, and biological characteristics of wetlands on their use by northern pike. MS thesis, State University of New York, College of Environmental Science and Forestry, Syracuse, NY. Mayo, K.R., and Selgeby, J.H. 1996. Trophic relations of rufte and the status of on-going research in the St. Louis River estuary, Lake Superior, 1996. Report to the Great Lakes Fishery Commission, Lake Superior Committee meeting, March 19, 1996, Duluth, MN. National Biological Service, Ashland, WI. MPCA/WDNR. 1992. The St. Louis River system remedial action plan: stage one. Minnesota Pollution Control Agency, Duluth, MN, and Wisconsin Dept. of Natural Resources, Superior, WI. Neilsen, L.A., and Johnson, D.L. eds. 1983. Fisheries techniques. American Fisheries Society, Bethesda, MD.
303
NRCS. 1996. Sedimentation in the Nemadji River Basin. Draft Report, Natural Resources Conservation Service, Nemadji River Basin Project, Duluth, MN. Ogle, D.H. 1995. Ruffe (Gymnocephalus cernuus): a review of published literature. WDNR Admin. Report 38, Madison, WI. _ _, Selgeby, J.H., Newman, R.M., and Henry, M.G. 1995. Diet and feeding periodicity of ruffe in the St. Louis River estuary, Lake Superior. Trans. Am. Fish. Soc. 124:356-369. _ _, Selgeby, J.H., Savino, J.F., Newman, R.M., and Henry, M.G. 1996. Predation on ruffe by native fishes of the St. Louis River estuary, Lake Superior, 1989-1991. N. Am. J. Fish Manage. 16:115-123. Pratt, D.M., Blust, W.H., and Selgeby, J.H. 1992. Ruffe, Gymnocephalus cernuus: newly introduced in North America. Can. J. Fish. Aquat. Sci. 49:1616-1618. Savino, J.F., and Kolar, CS. 1996. Competition between nonindigenous ruffe and native yellow perch in laboratory studies. Trans. Am. Fish. Soc. 125:562-571. Selgeby, J.H., and A.J. Edwards. 1995. Trophic relations of rufte and the status of ongoing research in the St. Louis River estuary, Lake Superior, 1994. Report to Great Lakes Fishery Comminssion, Lake Superior Committee Meeting, Milwaukee, WI. Sierszen, M.E., Keough, J.R., and Hagley, CA. 1996. Trophic analysis of ruffe (Gymnocephalus cernuus) and white perch (Morone americana) in a Lake Superior coastal food web, using stable isotope techniques. J. Great Lakes Res. 22:436-443. Slade, J.W., and Kindt, K. 1992. Surveillencefor rufte in the Upper Great Lakes, 1992. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. _ _, Pare, S.M., and MacCallum, W.R. 1994. Surveillence for rufte in the Great Lakes, 1993. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. _ _, Keppner, S.M., and MacCallum, W.R. 1995. Surveillence for rufte in the Great Lakes, 1994. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. Stephenson, T.D. 1988. Significance of Toronto area coastal marshes for fish. In Wetlands: Inertia or Momentum, eds. M.J. Bardecki and N. Patterson. Federation of Ontario Naturalists. Don Mills, ON. ___. 1990. Fish reproductive utilization of coastal marshes of Lake Ontario near Toronto. J. Great Lakes Res. 16:71-81. Westin, L., and Aneer, G. 1987. Locomotor activity patterns of nineteen fish and five crustacean species from the Baltic Sea. Environ. Bio!. Fish. 20:49-65.
Submitted:30 April 1997 Accepted: 30 November 1997 Editorial handling: Charles R. Bronte
Relative Abundance and Distribution of Ruffe (Gymnocephalus cernuus) in a Lake Superior Coastal Wetland Fish Assemblage John C. Brazner1*, Danny K. Tanner!, Douglas A. Jensen 2 , and Armond Lemke3 I U.S.
Environmental Protection Agency Mid-Continent Ecology Division 6201 Congdon Blvd. Duluth, Minnesota 55804
2University ofMinnesota Sea Grant Program 2305 E. Fifth St. Duluth, Minnesota 55812 3National Senior Citizens Education and Research Center 8403 Colesville Rd. Silver Spring, Maryland 20910 ABSTRACT. Fish assemblages from Allouez Bay Wetland in the St. Louis River estuary were sampled with fyke-nets from May to October, 1995, to characterize typical use patterns in different seasons and microhabitats. The relative abundance and distribution of ruffe (Gymnocephalus cernuus) in these habitats was of interest because their recent invasion into the Great Lakes has the potential to disrupt native fish assemblages. A total of 15,867 fish comprised of 34 species were captured in 2,300 h of netting. The majority offish over the whole study were caught in the outer marsh (63%, 9,957 individuals), and seasonally during late June (7,384 individuals/4 net-nights) and early May (2,281 individuals). Yellow perch (Perea flavescens), brown bullhead (Ameiurus nebulosus), emerald shiner (Notropis atherinoides), and silver redhorse (Moxostoma anisurum) were the most abundant species, comprising 85 percent of the total catch. Ruffe was the seventh most abundant species captured (294 individuals), comprising only two percent of the total catch. They were the fifth most abundant species in the outer marsh, but only thirteenth most abundant in the inner marsh. Ninety-one percent of all rufte (268 individuals) were caught in the outer marsh. Of the 75 species by life-stage combinations derived by classifying all individuals captured into one of 3 life stage categories (YOY, yearling, and adult), yearling rufte were the twe(fth most abundant, adult rufte were sixteenth, and YOY rufte were twenty-seventh. While rufte have been the most abundant fish captured in bottom trawls in St. Louis River estuary during the 1990s, our results indicate the invasion of rufte in shallow, heavily vegetated areas like those in Allouez Bay has been much less successful. Our results also suggest further degradation of coastal wetlands and other vegetated habitats would eliminate significant refugia from rufte competition and could lead to increased dominance of rufte in shallow water habitats in the Great Lakes. INDEX WORDS: Rufte, coastal wetland, fish assemblage, microhabitats, fyke-nets, St. Louis/Allouez Bay, Lake Superior.
and Kindt 1992; Slade et al. 1994, 1995; Kindt et al. 1996; Edwards 1995; Selgeby and Edwards 1995; Czypinski et al. 1997). Ruffe tolerate a vari-
INTRODUCTION The ecology of ruffe, Gymnocephalus cernuus (for review see Ogle 1995), and their invasion and current distribution in North America have been relatively well-documented (Pratt et al. 1992; Slade
ety of environmental conditions from fresh to brackish, shallow to deep, cold to warm, and oligotrophic to eutrophic. Ruffe tolerate low dissolved oxygen concentrations and high levels of some contaminants although these relationships are not entirely clear (see Ogle 1995). One aspect of ruffe
*Corresponding author. E-mail: [email protected]
293
294
Brazner et al.
Study Site
N
t Bear Creek-
o !
10
kilo~eters
I
FIG. 1. Map of Allouez Bay Wetland showing approximate locations of the inner and outer marsh study sites (adapted from Sierszen et al.1996).
ecology that is not as well understood is habitat preference. Ruffe seem to prefer dark (Westin and Aneer 1987, Ogle et al. 1995), benthic environments (Bergman 1988, Kalas 1995), and areas of slow-moving water with soft bottoms and little macrophyte cover (Johnsen 1965). Although response to varying light conditions appears to be age, season, and ecosystem dependent (Kah\s 1995, Ogle et at. 1995), response to varying cover conditions has received little attention. Ruffe were seldom captured in the 0 to 4 m depth zone in Lake Mildevatn, Norway (Kalas 1995), but were captured in substantial numbers at 0 to 3 m depths in St. Louis River estuary, Lake Superior (Edwards 1995, Ogle et aI. 1995). This disparity between
catches may be related to differences in cover characteristics between these locations; the littoral zone in Lake Mildevatn has moderate to dense vegetative cover (Kalas 1995) while the shallow flats that were sampled in St. Louis River estuary have relatively sparse plant cover (Andy Edwards, U.S. Geological Survey, Great Lakes Science Center, Ashland, WI, pers. comm.). We conducted a study in 1995 to characterize typical use patterns of ruffe in relation to native members of the fish assemblage in Allouez Bay Wetland at the eastern end of St. Louis River estuary, Lake Superior (Fig 1.) in different seasons and microhabitats. We were also interested in determining the relationship of different fish species to
Ruffe in a Lake Superior Coastal Wetland varying macrophyte cover. By examining the relationship between ruffe and other fish species to macrophyte cover in Allouez Bay, we hoped to provide additional information not only about microhabitat preferences of fish that use Great Lakes coastal wetlands, but also the potential for competition between ruffe and other fishes present in St. Louis River estuary. We felt our results would be of particular interest since almost no information on basic fish community ecology in Lake Superior coastal wetlands has been published. Competition among ruffe, other exotics and native fishes in the Great Lakes has been a topic of much concern recently (Bergman and Greenberg 1994, Ogle et al. 1995, Savino and Kolar 1996, Sierszen et al. 1996, Bronte et al. 1998) as ruffe have become an abundant fish species in the St. Louis River estuary (Busiahn 1993, Edwards 1995), and have been captured in several south shore tributaries on the western end of Lake Superior (Czypinski et al. 1997). However, ruffe relative abundance estimates in the St. Louis estuary vary considerably among biologists who have worked on this problem (Lindgren et at. 1997; Dennis Pratt, Wisconsin Department of Natural Resources, Superior, WI, pers. comm.; Edwards 1995; Brazner, this manuscript). Given this disparity, another goal of our study was to provide additional information about the relative abundance of ruffe in the Allouez Bay portion of the St. Louis estuary. STUDY SITE AND METHODS The fish assemblages in two locations adjacent to the mouth of Bear Creek within Allouez Bay Wetland (Fig. 1) were sampled from May through October in 1995. Allouez Bay Wetland is at the eastern end of the St. Louis River estuary/Duluth-Superior harbor complex inside Wisconsin Point, a prominent barrier sand spit at the western end of Lake Superior. The heavily vegetated portion of the wetland covers 148 ha (Herdendorf et at. 1981) and is dominated by robust emergent vegetation such as burreed, Sparganium eurycarpum, and softstem bulrush, Scirpus validus. The adjacent open-water lagoon is approximately 100 ha, shallow « 2 m), and has patches of submerged and floating vegetation throughout (e.g., Potamogeton richardsonii, Ceratophyllum demersum, Utricularia vulgaris, Nuphar variegata). Clay-laden discharges from the Nemadji River and other smaller south shore tributaries limit benthic primary producers (Keough et at. 1996).
295
Two fyke-nets (13-mm and 4-mm bar mesh, 5-m length, 1.1-m x lA-m front opening) were set in an inner and an outer marsh site at 0.6 to 1.2 m depths (varied with date and seiche activity, average depth - 0.9 m) in a lead-to-lead orientation (15 m connecting lead, 3 m wings on each net) for four consecutive nights and tended daily from 8 to 11 May, 5 to 8 June, 26 to 29 June, 31 July to 3 August, 4 to 7 September, and 2 to 5 October. The inner marsh site was typified by dense emergent and submergent vegetation, and low wave energy. The outer marsh site had little or no emergent vegetation, moderate submergent macrophyte cover, and higher wave action because it was adjacent to the open water portion of Allouez Bay. Captured fish were identified to species, weighed (± 0.1 g), and measured (± 0.1 cm) in the field. Observed length-frequency distributions in relation to those reported by Becker (1983), and field observation of ontogeny were used to assign individuals to one of three life-stage categories; young-of-the-year (YOY), yearling (1 +), or adult. Areal coverage in macrophytes, macrophyte species, and the dominant macrophyte growth forms were estimated visually during a 15min wading survey each sampling period to quantify differences in habitat structure between inner and outer marsh locations. Temperature, pH, conductivity, and dissolved oxygen were measured between 1000 and 1200-h daily at mid-depth (- 0.5-m) in a central marsh location (Hydrolab 4041 multiprobe, Hydrolab Corp., Austin, TX) and a 500-mL water sample was taken for turbidity estimates (Hach 2100AN Laboratory Turbidimeter, Hach Co., Loveland, CO). Most fish catch results were summarized as catch-per-unit-effort (number of fish per 96 h fykenet set) by sampling period and/or location for the most common species and life-stage groups. Recognizing the temporal dependence of our samples, we felt it was important to include a more quantitative means of evaluating differences between marsh locations than would have been possible strictly through a graphical depiction of the data or by examining absolute or percentage abundance differences. Therefore, results of two-sample t-tests were used to approximate whether numbers of the ten most abundant species and species by life-stage combinations were substantially different between the inner and outer marsh sites across the entire sampling period. Similar tests were conducted for the five most abundant species in each sampling period. All data were log transformed prior to statisti-
Brazner et al.
296
TABLE l. Mean physical-chemical conditions (range in parentheses) and location specific macrophyte cover in Allouez Bay Wetland during 1995 (n =5 for all means, macrophyte cover represents a single estimate each sampling period; na =not available). May
Early June
Temperature (OC)
9.1 (7.0-12.8)
17.7 (15.5-20.3)
pH
7.5 (7.3-7.8)
August
September
October
16.8 (16.3-17.5)
22.4 (22.1-23.1)
19.7 (15.9-21.7)
ILl (9.0-12.1)
6.9 (6.8-6.9)
6.8 (6.7-6.8)
6.5 (6.4-6.6)
6.9 (6.8-7.0)
6.9 (6.8-7.1)
na
7.1 (5.8-8.0)
6.3 (5.7-7.1)
5.7 (5.2-6.5)
8.2 (6.8-10.6)
8.0 (5.8-10.7)
Conductivity (us/sec)
150 (132-196)
155 (149-161)
157 (154-160)
153 (151-154)
146 (143-151)
180 (168-189)
Turbidity (ntu)
122 (54-251)
78 (30-243)
37 (34-46)
55 (45-81)
48 (34-71)
52 (44-63)
5 5
40 10
60 30
70 30
80 50
70 40
Dissolved Oxygen (mg/L)
Late June
% Macrophyte Cover
Inner Marsh Outer Marsh
cal analysis to maximize variance homogeneity and increase normality of the data distributions.
in the Great Lakes (Stephenson 1990, Brazner and Magnuson 1994).
RESULTS AND DISCUSSION
Fish Assemblages A total of 15,867 fish comprised of 34 species were captured in 2,300 h of netting (Table 2). This species richness is higher than most fish assemblages at individual coastal wetland sites elsewhere in the Great Lakes (Marean 1976, Chubb and Liston 1986, Stephenson 1988, Brazner 1997). Only at an undiked bottomland in Muddy Creek Bay on Lake Erie (an atypical Great Lakes coastal wetland) have more species (40) been captured (Johnson et al. 1996). The greatest number of species captured in any sampling period was 24 during May because of the large number of species spawning at that time (Table 3). The least number of species (16) were caught in early June before most YOY were a catchable size (Table 3). The largest catches were in early May (2,281 individuals) and late June (7,384 individuals), although greater than 1,750 fish were captured in each of the August, September, and October sampling periods (Table 3). The smallest catch was in early June (398 individuals). The large number of fish captured in early May was due primarily to an abundance of spawning emerald shiners, Notropis atherinoides, in the outer marsh. In late June, large numbers of young-of-the-year (YOY) yellow 'perch, and silver redhorse, Moxos-
Environmental Conditions Physical-chemical conditions (Table 1) were typical of coastal wetlands elsewhere in the Great Lakes (Chubb and Liston 1986, Stephenson 1990, Brazner and Beals 1997), and well within the tolerance limits of most northern fishes. Temperature and turbidity were the most variable; temperature peaked in August at 23.1 °C, and turbidity was highest in May and early June with maxima over 200ntu. High spring turbidities originated from clay sediments that erode from nearby tributaries (e.g., Nemadji River) during spring runoff, and from exposed shorelines that eroded during heavy spring storms (Banks and Brooks 1992, NRCS 1996). Although the number and composition of macrophyte species were similar at inner and outer marsh sites (l0 to 15 species), areal coverage was not. Macrophyte cover was dense by late June in the inner marsh (60%), peaked in September (80%), and remained high (70%) through October, while vegetation cover was only light to moderate (30 to 50%) during this same period in the outer marsh (Table 1). These macrophyte coverages were similar to those observed in turbid coastal wetlands elsewhere
297
Ruffe in a Lake Superior Coastal Wetland
TABLE 2. Total fish catch in ALlouez Bay Wetland in 1995 by species and location in decreasing order of overall abundance. Fish Species
Common Name
Outer Marsh
% Outer
Inner Marsh
% Inner
Perca flavescens Ameiurus nebulosus Notropis atherinoides Moxostoma anisurum Noturus gyrinus Notropis hudsonius Gymnocephalus cernuus Notemigonus chrysoleucus Catostomas commersoni Esox lucius Percopsis omiscomaycus Etheostoma nigrum Osmerus mordax Pomoxis nigromaculatus Morone americana Umbra limi M. macrolepidotum Percina caprodes Stizostedium vitreum Lepomis macrochirus Cyprinus carpio Ambloplites rupestris Culaea inconstans Pimephales promelas Couesius plumbeus L. gibbosus C. catostomus Pungitius pungitius Alosa pseudoharengus Lota Iota N. cornutus Salvelinus namaycush Cottus cognatus A. natalis
Yellow Perch 6,257 Brown Bullhead 160 Emerald Shiner 1,299 1,049 Silver Redhorse Tadpole Madtom 141 Spottail Shiner 364 Eurasian Ruffe 268 Golden Shiner 28 White Sucker 51 Northern Pike 47 Trout-perch 80 28 Johnny Darter Rainbow Smelt 45 Black Crappie 26 White Perch 38 Central Mudminnow 8 Shorthead Redhorse 15 Logperch 10 Walleye II Bluegill 4 Common Carp 1 Rock Bass 9 Brook Stickleback 3 Fathead Minnow 5 Lake Chub 4 Pumpkinseed 0 Longnose Sucker I Ninespine Stickleback 0 Alewife 0 Burbot 1 Common Shiner 0 Lake Trout 1 Slimy Sculpin 1 Yellow Bullhead 1
71% 7% 88% 80% 27% 71% 91% 15% 55% 52% 99% 47% 82% 48% 93% 20% 94% 67% 85% 33% 10% 90% 33% 71% 67% 0% 50% 0% 0% 100% 0% 100% 100% 100%
2,548 1,974 178 265 376 150 26 157 41 44
29% 93% 12% 20% 73% 29% 9% 85% 45% 48% 1% 53% 18% 52% 7% 80% 6% 33% 15% 67% 90% 10% 67% 29% 33% 100% 50% 100% 100% 0% 100% 0% 0% 0%
8,805 2,134 1,477 1,314 517 514 294 185 92 91 81 60 55 54 41 40 16 15 13 12 10 10 9 7 6 5 2 2 1
9,957 30
63%
5,910 30
37%
15,867 34
Total Number of Species
toma anisurum, were captured at both sites. Yellow perch, Perea Jlaveseens, YOY continued to comprise a majority (40 to 79%) of total catch in August and September, but by October brown bullhead, Ameiurus nebulosus, were most common (67% of total catch), primarily in the inner marsh (Fig. 2). Recruitment for both yellow perch and brown bullhead appeared to be high, despite recent concerns about declining populations of these species (Selgeby and Edwards 1995, Bronte et al. 1997).
I
32 10 28 3 32 1 5 2 8 9 I
6 2 2 5 I
2 I
0 I
0 0 0
TOTAL
I
1 I I
1
% of Total 55% 13% 9% 8% 3% 3% 2% 1% 1% 1% 1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% <1% 100%
Yellow perch, brown bullhead, emerald shiner, and silver redhorse were the most abundant species, comprising 55, 13, 9, and 8 percent of the total catch respectively (Table 2). Although ruffe were the seventh most abundant species captured (294 individuals), they comprised only two percent of the total catch. Yellow perch were the most abundant species in every sampling period except May, early June, and October when they were either second or thir.d most abundant. Periods of high abundance for brown bullheads, silver redhorse, and
298 TABLE 3. Location Inner Marsh Outer Marsh Total
Brazner et al. Number offish species and number offish caught in Allouez Bay Wetland during 1995. May # spp. # fish
16 24 24
550 1,731 2,281
Early June # spp. # fish
14 13 16
142 256 398
Late June # spp. # fish
16 15 17
emerald shiners were more transient (Fig. 2). Ruffe were among the five most abundant species in May, August, and September, but never ranked higher than third. Species by life-stage rank abundances (Fig. 3) were very similar to overall species rank abundances in the top four positions (Fig. 2). Yellow perch YOY, brown bullhead YOY, silver redhorse YOY, and emerald shiner 1+ were the most abundant overall. This highlights the fact that our results reflect primarily the catch of young fishes, and that Allouez Bay, like other Great Lakes coastal wetlands, is an important nursery for many Great Lakes fish species (Stephenson 1990, Brazner 1997). Both adult and yearling (l +) yellow perch were among the ten most abundant species by lifestage (Fig. 3), supporting the contention that Great Lakes coastal wetlands are important to all life history stages of this commercial and sport fish species (Stephenson 1988, Johnson 1989, Brazner 1997). In contrast, yearling ruffe were only the twelfth most abundant species by life-stage group overall, adult ruffe were sixteenth, and YOY ruffe twenty-seventh. Yearlings and adult ruffe were most abundant during May when spawning was most intense, less abundant in early August and September, and least abundant in late June and early October. Ruffe YOY (20 to 30 mm in length) were first captured in late June from the inner marsh, but were most prevalent in August and September (40 to 60 mm) in the outer marsh (Fig. 4). These results lend little support to the finding that ruffe are the most abundant fish in the St. Louis River estuary (Edwards 1995, Busiahn 1996). It is important to recognize that our results may reflect conditions only in the Allouez Bay portion of the St. Louis River estuary due to our limited sampling range. It may be that bottom trawl samples that suggest ruffe are the most abundant fish in the estuary provide a more accurate overall estimate of population densities. Ruffe comprised 60% of the total catch in bottom trawls in the St. Louis River estuary in 1995 (Andy Edwards, USGS, Great Lakes Science Center, Ashland, WI, pers.
1,986 5,398 7,384
August # spp. # fish
14 20 22
691 1,227 1,918
September # spp. # fish
13 18 21
871 902 1,773
October # spp. # fish
19 16 20
1,670 443 2,113
comm., Table 4). However, long-term fish community indices compiled by Minnesota and Wisconsin Departments of Natural Resources for the St. Louis River estuary indicate that ruffe comprised a much smaller proportion of the entire fish community than estimated with bottom trawls (Table 4). Shoreline seining efforts from nine locations throughout the estuary in 1995 suggest that ruffe are only the fifth most abundant species, comprising less than 4% of the total catch (Table 4). Similarly, experimental gill-netting efforts from 21 locations throughout the estuary in 1995 indicated that ruffe were only the fourth most abundant fish (by number), comprising 14% of the total catch (Lindgren et al. 1997, Table 4). In addition, ruffe typically comprised between 1 and 5% of total fyke-net catches from Allouez Bay Wetland and Hog Island Wetland (an area approximately 4 km northwest of Allouez Bay) during 96 h sampling periods in August 1993 and 1994 (Brazner, unpublished data; Glen Black, USGS, Ann Arbor, MI, personal communication). It is well known that there is inherent bias with any particular gear type used to catch fish (Neilsen and Johnson 1983) and we feel it is important to recognize that estimates of ruffe relative abundance in the St. Louis River estuary/Allouez Bay fish community are strongly dependent on the method of capture and the specific habitat sampled. An effort to reconcile differences in catch estimates from the various habitats in the estuary would provide managers with valuable, less equivocal information. Standardization by the relative abundance of ruffe in different habitat types within the estuary and by season of catch might be useful. Over all of 1995 in our study, the majority of fish (63%) were caught in the outer marsh, but equal numbers of species (30) were captured at inner and outer marsh sites (Table 2). Seasonally, the number of species caught at our outer marsh site was higher than at the inner site in May, August, and September, but none of these differences were statistically significant (p > 0.05, Table 3). Proximity to the open portion of the adjacent bay and its large pool
299
Ruffe in a Lake Superior Coastal Wetland
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FIG. 4. Total catch of ruffe in Allouez Bay Wetland in 1995 by sampling period and marsh location. Asterisks denote significant differences between inner and outer marsh sites based on paired t-tests, * =p :::; 0.05, ** =p :::; 0.01, *** =p :::; 0.001.
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of species probably contributed to this tendency. We also noted that the catch of some species was strongly biased toward a particular site. Based on statistical differences in their overall catch and the proportion of total catch at inner or outer marsh sites (~ 80%), brown bullhead, golden shiner, Notemigonus chrysoleucus, and central mudminnow, Umbra limi, could be characterized as inner marsh species, while ruffe, trout perch, Percopsis omiscomaycus, white perch, Morone americana, emerald shiner, and four others were primarily outer marsh species (Table 5). Ruffe were the fifth most abundant species in the light to moderately vegetated outer marsh, but only thirteenth most
abundant in the heavily vegetated inner marsh (Table 2). The fact that over 90% of all ruffe (268 individuals) were caught in the outer marsh may reflect a preference by ruffe for less vegetated areas (Johnsen 1965). Although this reported preference is based on few published data, a recent study in Norway also found that ruffe were far more abundant (> 90%) beyond the vegetated zone in Mildevatn (Kalas 1995). Avoidance of vegetated areas by ruffe probably results from several factors. Because of their sophisticated lateral line sensory system, ruffe are well adapted to foraging in deep, dark benthic habitats (Disler and Smirnov 1977, Bergman 1988, Janssen 1997) where macrophyte growth is inhibited by low light conditions. Ruffe are also relatively poor swimmers (Disler and Smirnov 1977), so dark benthic habitats may provide a better refuge from visual predators that tend to be associated with vegetated areas (e.g., northern pike, Esox lucius, and muskellunge, Esox masquinongy). This possibility is supported by observations in the St. Louis River estuary, where ruffe were prevalent in mostly unvegetated (Andy Edwards, USGS, Great Lakes Science Center, Ashland, WI, pers. comm.), shallow water habitats only at night (Ogle et al. 1995). However, it is also possible that the competitive advantage provided by the specialized sensory adaptations of ruffe would not be as effective in shallow, heavily vegetated areas where high back-
TABLE 4. Comparison of fish species relative abundance estimates in St. Louis Bay/Allouez Bay in 1995 based on catch-per-uniteffort data from four different research efforts (Brazner et al., data from this manuscript; Lindgren et al. 1997; Pratt et al., Wisconsin DNR, unpublished data; Edwards et al., U.S. Geological Survey/NBS, unpublished data). Sampling method, date, depth, and general location of each research effort is detailed in bottom half of the table. Bramer et at. u.s. EPA
% of Total Catch
1
Yellow Perch
55.5
2
Brown Bullhead
13.4
Rank Abundance
3
Emerald Shiner
9.3
~
% of Total Catch
Lindgren et al. MNDNR
% of Total Catch
Edwards et al. USGS/NBS
% of Total Catch
S~
Spottail Shiner
36.7
White Sucker
17
Euraian Ruffe
60.0
~
Yellow Perch
24.4
Lake Sturgeon
16
Trout-perch
12.1
Pratt et al. WDNR
Emerald Shiner
18.7
Walleye
15
Yellow Perch
6.8
4
Silver Redhorse
8.3
Black Crappie
8.4
Eurasian Ruffe
14
Spottail Shiner
6.8
5
Madtom
3.3
Eurasian Ruffe
3.8
Northern Pike
10
Emerald Shiner
4.9
6
Spottail Shiner
3.2
White Sucker
2.9
Channel Catfish
9
Black Crappie
2.6
7
Eurasian Ruffe
1.9
Golden Shiner
1.4
Shorthead Redhorse
7
Walleye
2.1
8
Golden Shiner
1.2
White Perch
0.6
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5
White Sucker
1.2
9
White Sucker
0.6
Walleye
0.5
Silver Redhorse
2
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1.0
10
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0.6
Logperch
0.5
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1
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Fyke-nets 4-13 <1.5 May-October Allouez Bay
Seine 5 <1.5 June-September St. Louis Bay/Allouez Bay
Gill-nets 19-51 1.5-8.2 July St. Louis Bay
Trawl 5(cod)-38(body) 2-9 April-September St. Louis Bay/Allouez Bay
~
302
Brazner et al.
TABLE 5. Species that were significantly more abundant (* $ 0.05, ** $ 0.01, *** $ 0.001) or had a majority of their total catch (c.80%) in the inner or outer marsh (limited to species with total catch >30). Inner Marsh Species
Outer Marsh Species
Brown Bullhead (93%)** Golden Shiner (85%)** Central Mudminnow (80)
Trout Perch (99%)*** White Perch (93%) Eurasian Ruffe (91 %)*** Emerald Shiner (87%) Rainbow Smelt (82%) Silver Redhorse (80%) Yellow Perch (71 %)* Spottail Shiner (71 %)*
ground stimulation is likely to be distracting (Disler and Smirnov 1977). With respect to the concern about ruffe competition with native fishes in the S1. Louis River estuary and elsewhere in the Great Lakes (e.g., Mayo and Selgeby 1996, Ogle et al. 1996), our data indicate that densely vegetated habitats like Allouez Bay Wetland may provide a refuge from intense competition with ruffe. It also suggests that further degradation of coastal wetland or heavily vegetated littoral habitats would lead to increased dominance of ruffe in shallow water habitats of the Great Lakes. In the S1. Louis River estuary, as in most other coastal estuaries in the Great Lakes, much of the historic wetland habitat has been lost to human developments (Krieger et al. 1992, MPCA/WDNR 1992). The high diversity of fishes supported by the remaining areas, along with the potential refuge they provide from invading species like ruffe, suggest that restoration and maintenance of coastal wetland habitats should be emphasized in remedial action plans and other rehabilitation efforts in the Great Lakes.
ACKNOWLEDGMENTS We thank John Lindgren from the Minnesota Department of Natural Resources, Dennis Pratt from the Wisconsin Department of Natural Resources, and Andy Edwards from the U.S. Geological Survey for providing comparative data and technical advice about ruffe populations in S1. Louis River estuary/Allouez Bay. We also thank Charles Bronte, Tom Coon, Gary Holcombe, J. Howard McCormick, Lars Rudstam, and Mike Sierszen for helpful reviews.
REFERENCES Banks, G., and Brooks, K 1992. Erosion-sedimentation and nonpoint source pollution in the Nemadji River watershed: status of our knowledge. Appendix L, The St. Louis River Remedial Action Plan, Stage One, Minnesota Pollution Control Agency, Duluth, MN, and Wisconsin Dept. of Natural Resources, Superior, WI. Becker, G.C 1983. Fishes of Wisconsin. Madison, WI: University of Wisconsin Press. Bergman, E. 1988. Foraging abilities and niche breadths of two percids, Perea fluviatilis and Gymnocephalus cernua, under different environmental conditions. J. Anim. Ecol. 57:443-453. _ _, and Greenberg, L.A. 1994. Competition between a planktivore, a benthivore, and a species with ontogenetic diet shifts. Ecology 75: 1233-1245. Brazner, J.C. 1997. Regional, habitat, and human development influences on coastal wetland and beach fish assemblages in Green Bay, Lake Michigan. J. Great Lakes Res. 23:36-51. - _ , and Beals, E.W. 1997. Patterns in fish assemblages from coastal wetland and beach habitats in Green Bay, Lake Michigan: a multivariate analysis of abiotic and biotic forcing factors. Can. J. Fish. Aquat. Sci., In Press. - _ , and Magnuson, J.J. 1994. Patterns of fish species richness and abundance in coastal marshes and other nearshore habitats in Green Bay, Lake Michigan. Verh. Internat. Verein. Limnol. 25:2098-2104. Bronte, CR., Evrard, L.M., Brown, W.P., Mayo, KR., and Edwards, AJ. 1998. Fish community changes in the S1. Louis River Estuary, Lake Superior, 1989-1996: is it ruffe or population dynamics? J. Great Lakes Res. 24(2):309-318. Busiahn, T.R. 1993. Can ruffe be contained before it becomes your problem? Fisheries 18(8):22-23. - - . 1996. Ruffe control program. Report to the Aquatic Nuisance Species Task Force, November, 1996. Chubb, S.L., and Liston, CR. 1986. Density and distribution of larval fishes in Pentwater Marsh, a coastal wetland on Lake Michigan. J. Great Lakes Res. 12:332-343. Czypinski, G.D., Hintz, AK, Johnson, G., and Keppner, S.M. 1997. Surveillence for ruffe in the Great Lakes, 1996. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. Disler, N.N., and Smirnov, S.A 1977. Sensory organs of the lateral-line canal system in two percids and their importance in behavior. J. Fish. Res. Board Can. 34:1492-1503. Edwards, AJ. 1995. Spatial changes in the distribution and abundance of ruffe (Gymnocephalus cernuus) and native fishes in the S1. Louis River estuary, 1989-1994. M.S. thesis, Univ. of Minnesota, Duluth, MN.
Ruffe in a Lake Superior Coastal Wetland Herdendorf, CE., Hartley, S.M., and Barnes M.D., eds. 1981. Fish and wildlife resources of the Great Lakes coastal wetlands within the United States. Volume 6. U.S. Fish Wildlife Servo FWS/OBS-81/02-v6. Janssen, J. 1997. A comparison of the sensitivity of the ruffe and yellow perch lateral lines to Daphnia and Hexagenia. In International Symposium on Biology and Management of Rufte-Symposium Abstracts, ed. D.A. Jensen, Minnesota Sea Grant Publication X48. Johnsen, P. 1965. Studies on the distribution and food of the ruffe (Acerina cernua) in Denmark, with notes on other aspects. Meddelelser fra Danmarks Fiskeri-og Havunderogelser 4: 137-156. Johnson, D.L. 1989. Lake Erie wetlands: fisheries considerations. In Lake Erie and its Estuarine Systems, ed. K.A. Krieger. Estuary-of-the-Month Seminar, U.S. Dept. of Commerce. Washington, D. C _ _, Lynch, W.E., Jr., and Morrison, T.W. 1996. Fish communities in a diked Lake Erie wetland and an adjacent undiked area. Wetlands 17: 43-54. KaHls, S. 1995. The ecology of ruffe, Gymnocephalus cernuus (Pisces:Percidae), introduced to Mi1devatn, western Norway. Environ. Bio!. Fish. 42:219-232. Keough, J.R., Sierszen, M.E., and CA. Hagley. 1996. Analysis of a Lake Superior coastal food web with stable isotope techniques. LimnoZ. Oceanogr. 41: 136-146. Kindt, K., Keppner, S.M., and Johnson, G. 1996. Surveillence for rufte in the Great Lakes, 1995. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. Krieger, K.A., K1arer, D.M., Heath, R.T., and Herdendorf, CE. 1992. A call for research on Great Lakes coastal wetlands. J. Great Lakes Res. 18:525-528. Lindgren, J.P., Ongstad, P.W., and Spurrier, J.R. 1997. The St Louis Bay fishery 1986-1994. Minnesota Dept. of Natural Resources, Division of Fish and Wildlife, Section of Fisheries, Study 4 Report, Job 442, St. Paul, MN. Marean, J.B. 1976. The influence of physical, chemical, and biological characteristics of wetlands on their use by northern pike. MS thesis, State University of New York, College of Environmental Science and Forestry, Syracuse, NY. Mayo, K.R., and Selgeby, J.H. 1996. Trophic relations of rufte and the status of on-going research in the St. Louis River estuary, Lake Superior, 1996. Report to the Great Lakes Fishery Commission, Lake Superior Committee meeting, March 19, 1996, Duluth, MN. National Biological Service, Ashland, WI. MPCA/WDNR. 1992. The St. Louis River system remedial action plan: stage one. Minnesota Pollution Control Agency, Duluth, MN, and Wisconsin Dept. of Natural Resources, Superior, WI. Neilsen, L.A., and Johnson, D.L. eds. 1983. Fisheries techniques. American Fisheries Society, Bethesda, MD.
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NRCS. 1996. Sedimentation in the Nemadji River Basin. Draft Report, Natural Resources Conservation Service, Nemadji River Basin Project, Duluth, MN. Ogle, D.H. 1995. Ruffe (Gymnocephalus cernuus): a review of published literature. WDNR Admin. Report 38, Madison, WI. _ _, Selgeby, J.H., Newman, R.M., and Henry, M.G. 1995. Diet and feeding periodicity of ruffe in the St. Louis River estuary, Lake Superior. Trans. Am. Fish. Soc. 124:356-369. _ _, Selgeby, J.H., Savino, J.F., Newman, R.M., and Henry, M.G. 1996. Predation on ruffe by native fishes of the St. Louis River estuary, Lake Superior, 1989-1991. N. Am. J. Fish Manage. 16:115-123. Pratt, D.M., Blust, W.H., and Selgeby, J.H. 1992. Ruffe, Gymnocephalus cernuus: newly introduced in North America. Can. J. Fish. Aquat. Sci. 49:1616-1618. Savino, J.F., and Kolar, CS. 1996. Competition between nonindigenous ruffe and native yellow perch in laboratory studies. Trans. Am. Fish. Soc. 125:562-571. Selgeby, J.H., and A.J. Edwards. 1995. Trophic relations of rufte and the status of ongoing research in the St. Louis River estuary, Lake Superior, 1994. Report to Great Lakes Fishery Comminssion, Lake Superior Committee Meeting, Milwaukee, WI. Sierszen, M.E., Keough, J.R., and Hagley, CA. 1996. Trophic analysis of ruffe (Gymnocephalus cernuus) and white perch (Morone americana) in a Lake Superior coastal food web, using stable isotope techniques. J. Great Lakes Res. 22:436-443. Slade, J.W., and Kindt, K. 1992. Surveillencefor rufte in the Upper Great Lakes, 1992. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. _ _, Pare, S.M., and MacCallum, W.R. 1994. Surveillence for rufte in the Great Lakes, 1993. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. _ _, Keppner, S.M., and MacCallum, W.R. 1995. Surveillence for rufte in the Great Lakes, 1994. U.S. Fish and Wildlife Service, Fishery Resources Office Station Report, Ashland, WI. Stephenson, T.D. 1988. Significance of Toronto area coastal marshes for fish. In Wetlands: Inertia or Momentum, eds. M.J. Bardecki and N. Patterson. Federation of Ontario Naturalists. Don Mills, ON. ___. 1990. Fish reproductive utilization of coastal marshes of Lake Ontario near Toronto. J. Great Lakes Res. 16:71-81. Westin, L., and Aneer, G. 1987. Locomotor activity patterns of nineteen fish and five crustacean species from the Baltic Sea. Environ. Bio!. Fish. 20:49-65.
Submitted:30 April 1997 Accepted: 30 November 1997 Editorial handling: Charles R. Bronte