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J. Great Lakes Res. 29(1):34–40
Internat. Assoc. Great Lakes Res., 2003
The Round Goby (Neogobius melanostomus)
in Pennsylvania Tributary Streams of Lake Erie
Edward C. Phillips*, Meaghan E. Washek, Aaron W. Hertel, and Brian M. Niebel
Biology Department
Gannon University
109 University Square
Erie, Pennsylvania 16541
ABSTRACT. The round goby (Neogobius melanostomus) has successfully colonized the Great Lakes,
where it appears to be out-competing and possibly displacing native fish species. Movement of the round
goby into tributary streams of Lake Erie could further jeopardize native species. Sampling was done by
electrofishing in six Pennsylvania tributary streams of Lake Erie from June 2000 through October 2001.
Round gobies were collected from four of the six streams sampled: Elk Creek, Walnut Creek, Twentymile
Creek, and Sixteenmile Creek. The most extensive colonization has occurred in Elk Creek where round
gobies comprised 17.1% of the total number of fish where they were present, and occurred as far as 2.25
stream km upstream from the mouth of the creek. Round gobies fed almost exclusively on aquatic insects,
and the most important insects in the diet were chironomid larvae. Female round gobies matured at 1+
years old. Individual fecundity ranged from 86 to 591 eggs, and increased with fish length. The plasticity
of the diet, high fecundity, and aggressiveness of the round goby may make it a threat to native species in
Pennsylvania tributary streams.
INDEX WORDS:
Round goby, tributary streams, fecundity, age and growth, diet, Lake Erie.
INTRODUCTION
The round goby (Neogobius melanostomus) is a
recent, and very successful, invader of the Great
Lakes (Jude 2001). Since its introduction, the round
goby has been one of the most rapidly colonizing
invaders of a number of exotic species present in
the Great Lakes (Mills et al. 1994). They have
spread to all five of the Great Lakes from the St.
Clair River, and are very abundant near-shore residents in a number of locations. The round goby is a
benthic species that prefers a cobble substrate, and
uses the cover provided by the interstitial spaces in
rocky areas to avoid predation by piscivorous fish
(Jude 2001).
The round goby exhibits a number of characteristics that have allowed it to be successful in the
Great Lakes region. Those characteristics include
repeat spawning activity within a season, cavitynesting behavior, and an aggressive nature. Female
round gobies can spawn every 20 days and as many
as six times per year, and produce from 100 to
*Corresponding
5,000 eggs, depending on the size of the female
(Jude 1997, Corkum et al. 1998). Round goby reproductive behavior consists of territory establishment and defense by males, nest preparation,
courtship, spawning, and paternal care of eggs and
larvae (MacInnis and Corkum 2000). After spawning, males aggressively defend the eggs and
hatched larvae from potential predators (Wickett
and Corkum 1998).
Additionally, food competition may exist between round gobies and native benthic species
(French and Jude 2001). Round gobies possess
upper and lower molariform pharyngeal teeth, enabling them to crush and feed on bivalve mollusks,
which make up the major portion of their diet in
their native habitats (Skora and Rzeznik 2001, Simonovicå et al. 2001). The abundance of non-native
zebra (Dreissena polymorpha) and quagga (D. bugensis) mussels in the Great Lakes, a food resource
that native fish species are unable to effectively exploit, is a likely factor contributing to the population explosion of round gobies (Ghedotti et al.
1995, Ray and Corkum 1997, Weimer and Sowinski
1999). However, round gobies can be opportunistic
author. E-mail: [email protected]
34
The Round Goby in Tributary Streams
feeders and feed on a variety of invertebrates, fish
eggs, fish larvae, and adult fish (Carman 2002,
Weimer and Sowinski 1999, Miller 1986), which increases the potential for competition between round
gobies and native benthic fish species (French and
Jude 2001).
Round goby abundance is well documented in
the Great Lakes (Jude 2001). However, except for
the Detroit, St. Clair, and Flint rivers (Carman
2002, Jude 2001), little is known about the extent to
which round gobies have colonized Great Lakes
tributaries. The primary objective of this study was
to determine the extent to which round gobies have
colonized the Pennsylvania tributaries of Lake Erie.
Diets of round gobies were analyzed to determine if
there is a potential for food competition between
round gobies and native species. Additionally, age,
size distribution, and fecundity of round gobies inhabiting tributary streams were assessed to determine how these factors compared with similar
observations of round gobies in other bodies of
water.
METHODS
Sampling by electrofishing was done in six tributary streams of Lake Erie. Twentymile Creek, Sixteenmile Creek, Twelvemile Creek, Walnut Creek,
Elk Creek, and Conneaut Creek were sampled from
June 2000 through October 2001. All streams were
sampled using a battery powered backpack electroshocker. Sampling was conducted from the
mouth of each stream (except Conneaut Creek,
where the mouth enters Lake Erie in Ohio) upstream until round gobies were no longer encountered, and that endpoint was recorded using GPS.
Sampling was then continued for at least 0.8 stream
km beyond the endpoint to be sure that the endpoint
was correctly identified. Additionally, streams were
sampled at sites farther upstream to determine if
there were any disjunct populations of round gobies, which could have been introduced by baitbucket transfer. The upstream sampling sites were
areas with relatively easy access where gobies
would most likely be introduced. Upstream sites
where round gobies were not collected were sampled for a distance of at least 0.8 stream km. Sampling time at each site in each stream was variable
because of variation in stream size. Streams were
sampled in an upstream direction by making a
crossing pattern in each stream to cover the water
as efficiently as possible. The electroshocker
recorded the time (in seconds) that electric current
35
was being generated during each sampling period.
After determining the upstream endpoint of round
goby colonization the distance in stream km was
measured using the odometer feature of a Garmin
GPS unit while walking the streambed. The latitude
and longitude of the upstream endpoint was
recorded so that future round goby movements
could be assessed.
Most collected fishes were preserved in a 10%
formalin solution. All gamefish, such as rainbow
trout (Oncorhynchus mykiss), brown trout (Salmo
trutta), and smallmouth bass (Micropterus
dolomieui) were released, but the number collected
was recorded. Preserved fish were returned to the
laboratory where they were identified to species
and counted. Round gobies were also weighed and
measured, and their stomach contents removed for
diet analysis. Scale samples were taken from each
round goby so that age determinations could be
made. Fish abundance was calculated for each
species in each stream as catch per unit effort
(CPUE). Catch per unit effort was calculated as the
number of fish captured per hr of electrofishing effort. The relative number of fish of each species in
each stream was also calculated.
Fish were measured (total length) to the nearest
mm, and weighed to the nearest 0.01g. The lengthweight relationship for round gobies was calculated
using the equation: ln W = a′ + b (ln L). Scales
were removed from the area near the tip of the pectoral fin of each round goby and mounted between
two microscope slides. Annuli were counted to determine age.
Diets were assessed by removing the stomachs of
preserved fish. Organisms contained in stomachs
were identified and counted. Food items of each
taxonomic group were then measured by alcohol
displacement in either a 5-mL graduated cylinder or
a 2-mL pipet to determine the volume of each type
of food item. Relative numbers (% N), relative volume (% V), and the relative frequency (% F) (number of fish containing that food item) of food items
in the stomach of each fish were calculated. From
these data, the index of relative importance (IRI)
(Pinkas et al. 1971) for each food item was calculated for each size group of fish using: IRI = (%N
+%V) % F. Values of IRI can range from 0 to
20,000, with higher values representing food items
of greater importance. Fish were divided into four
size classes (< 45 mm, 45 to 59 mm, 60 to 74 mm,
≥ 76 mm) to determine if diet changed with fish
size. Fish with empty stomachs were excluded from
the analysis.
36
Phillips et al.
TABLE 1. Catch per hr (CPUE) and relative abundance (% of total number collected) of fish electroshocked from Pennsylvania tributary streams of Lake Erie, 2000 and 2001. Common names assigned
according to Robins et al. (1991).
Common Name
Round Goby
Rainbow Darter
Fantail Darter
Johnny Darter
Logperch
Greenside Darter
Mottled Sculpin
Northern Hog Sucker
Rainbow Trout
Brown Trout
Bluegill
Pumpkinseed
Rock Bass
Largemouth Bass
Smallmouth Bass
Sea Lamprey
Stonecat
Yellow Bullhead
Brown Bullhead
Minnows
Total hr fished
Total fish collected
20mile
Elk Creek
Creek
CPUE %
CPUE
%
137.1 17.1 103.8 30.4
238.1 29.6 94.3 27.7
16.2
2.0 28.3
8.3
1.9
0.2
8.6
1.1
8.3
2.4
3.8
10.5
11.4
1.0
6.7
2.9
2.9
0.5
1.3
1.4
0.1
0.8
0.3
0.3
9.5
1.2
1.0
1.2
3.5
23.6
0.3
1.0
6.9
18.2
16mile
Creek
CPUE
%
13.7
1.5
5.4 610.3
0.8
3.3
5.7
0.3
1.0
1.7
11.5
3.4
4.1
1.2
1.6
2.5
0.8
0.5
0.7
0.3
68.6
36.6
0.1
352.4 43.7
6.1
1,227
Walnut
Creek
CPUE
%
42.6 12.7
47.5 14.2
8.2
2.4
77.8
22.9
5.6
771
Fecundity was determined by removing the
ovaries from gravid females, and then counting the
eggs. The relationship between fish length and
number of eggs was analyzed using simple linear
regression: ln number of eggs = a′ + b (ln L).
RESULTS
Round gobies were collected from four of the six
streams sampled (Table 1). Catch per hr of round
gobies was greatest in Elk Creek where 137 round
gobies were collected per hr of electrofishing.
Where present, round gobies made up 17.1% of the
fish present in Elk Creek. Round gobies were collected as far as 2.25 stream km upstream from the
mouth of Elk Creek (N42°01.229′ and
W080°21.683′). Although no quantitative data were
collected about which areas of Elk Creek were most
heavily colonized, round gobies were collected
from all stream habitats. They appeared to be most
abundant in areas with moderate flow, which contained gravel and larger rocks. However, round gobies were also collected from shallow riffle areas
containing primarily gravel and from areas of
68.3
Conneaut
Creek
CPUE %
12mile
Creek
CPUE
%
90.6
100.0
9.2
10.1
163.0
88.9
25.7
14.1
3.1
206.3
0.3
20.8
57.8
9.0
69.1
10.9
1.2
1.2
0.2
0.2
7.7
118.8
12.0
6.3
0.6
4.1
188.4 56.25 146.3 18.4
5.3
2.2
842
606
465.6 47.0
2.1
517
12.4
2.0
240.7 37.9
2.6
513
bedrock, where they occupied horizontal ledges in
the bedrock.
The second greatest catch of round gobies occurred from Twentymile Creek, where 104 round
gobies were collected per hour of electrofishing. In
Twentymile Creek round gobies made up 30.4% of
fish collected, where round gobies occurred. Round
gobies occurred 0.64 stream km upstream from the
mouth of Twentymile Creek (N42°15.571′ and
W079°46.635′). Round gobies were collected primarily from stream areas with moderate flow and a
gravel/rock substrate.
The third greatest catch of round gobies occurred
from Walnut Creek where 43 round gobies were
collected per hour of electrofishing. Round gobies
made up 12.7% of fish collected where round gobies occurred. Round gobies were collected as far as
0.48 stream km upstream from the mouth of Walnut
Creek (N42°04.421′ and W080°14.075′). Round
gobies were collected primarily from areas with
moderate flow and a gravel/rock substrate.
Round gobies were also collected from Sixteenmile Creek at a rate of 14 round gobies per hour of
The Round Goby in Tributary Streams
37
TABLE 2. Diets of round gobies collected from four Pennsylvania Lake Erie tributaries during 2000 and
2001. Diet is shown for four size classes. % F = the percentage of fish containing that food item, % N = %
composition by number, %V = % composition by volume, IRI = index of relative importance = (% N + %
V) % F. Some columns of % N and % V do not add to 100% because of rounding error.
45–59 mm (N = 123)
%F %N %V IRI
60–74 mm (N = 76)
%F %N %V IRI
≥ 75 mm (N = 49)
%F %N %V IRI
64 13,912
92
84
56 12,880
78
83
53 10,608
78
63
40 8,034
8
21
899
32
15
5
7
2
1
19
9
4
832
165
25
38
14
16
5
1
2
17
4
11
836
70
208
65
22
55
14
2
11
15 1,885
4 132
31 2,310
2
3
9
3
99
54
7
17
1
4
5
3
42
119
14
22
1
4
7
3
112
154
55
4
4
440
22
3
3
132
20
22
1
2
2
1
60
66
30–44 mm (N = 72)
%F %N %V IRI
Food Item
Diptera
Chironomidae 94
Ephemeroptera
Caenidae
31
Baetidae
Heptageniidae
Trichoptera
Hydropsychidae 9
Hydroptilidae
6
Limnephilidae
Plecoptera
Perlidae
Other
12
84
3
3
33
16
2
electrofishing. Round gobies only made up 1.5% of
fish collected in Sixteenmile Creek. Round goby
catch was low because fish were collected only
from a pool a few meters above the mouth. Therefore no GPS coordinates were recorded for round
goby movement into Sixteenmile Creek.
Round gobies were not collected from
Twelvemile Creek or Conneaut Creek. Additionally,
no disjunct populations of round gobies were collected in upstream areas of any of the sampled
streams. In addition to the fish listed in Table 1, the
minnows (Cyprinidae) most commonly collected
during this study were: river chub (Nocomis micropogon), central stoneroller (Campostoma
anomalum), common shiner (Notropis cornutus),
sand shiner (Notropis stramineus), mimic shiner
(Notropis volucellus), longnose dace (Rhinichthys
cataractae), blacknose dace (Rhinichthys atratulus), and bluntnose minnow (Pimephales notatus).
Round goby total length ranged from 22 to 112
mm, and weight ranged from 0.15 to 17.58 g. Based
on aging fish by counting scale annuli, four age
groups were collected: 0+, 1+, 2+, and 3+. Age
groups had considerable length overlap, but the
mean length (± SE) of each group was: 0+: 44.2
mm (± 1.7), 1+: 67.9 mm (± 1.9), 2+: 79.8 mm (±
3.2), and 3+: 93.5 mm (± 5.1). All four age 3+ fish
were females. Fish in the other size groups were
comprised of both males and females. The lengthweigh relationship (r 2 = 0.980, P < 0.0001) ob-
5
16
25
5
6
42
served is described by the equation: lnW = -11.632
+ 3.095 (lnL).
Round goby diets were analyzed based on four
size classes (N = 329 fish, 9 empty) and fish of all
size classes fed almost exclusively on benthic
macroinvertebrates, primarily aquatic insects (Table
2). In general, chironomid larvae and pupae (data
combined) were the most important food items for
all four size classes, but round gobies > 75 mm relied
less heavily on chironomids than round gobies in the
smaller size classes. Round gobies < 45 mm fed primarily on chironomids (IRI = 13,912), and had the
narrowest diet breadth of the size classes with only
seven different food items found. Round gobies in
the size class 45 to 59 mm also fed most heavily on
chironomids (IRI = 12,880), but had a wider diet
breadth feeding on 12 different food items. Round
gobies in the size class 60 to 74 mm again had similar diets, feeding mainly on chironomids (IRI =
10,608). Round gobies in this size class had the
greatest diet breadth feeding on 13 different food
items. Fish in the fourth size class, > 75 mm, also fed
mainly on chironomids (IRI = 8,034) but had a more
balanced diet, based on IRI, than fish from smaller
size classes. Fish in this size class also fed relatively
heavily on Heptageniidae and Caenidae. Other prey
items in the diets of round gobies not listed in Table
2 included Tipulidae, Elmidae, Ptilodactylidae,
Psephenidae, and Dytiscidae larvae, Formicidae
adults, water mites, and fish eggs. No adult or larval
fish were found in any stomachs.
38
Phillips et al.
Female round gobies became mature at 1+ years
old. The mean length of gravid females was 66 mm
(range 54 to 112 mm). Mean fecundity was 177
(range 86 to 591 eggs). The relationship (r2 = 0.87,
P < 0.0001) between length and fecundity is explained by the equation: ln number of eggs = -6.06
+ 2.79 (lnL) (where L = total length in mm).
DISCUSSION
While round gobies made up a substantial proportion of the fish collected (30.4% in Twentymile
Creek, 17.1% in Elk Creek, 12.7% in Walnut
Creek) in Pennsylvania tributary streams, Carman
(2002) found that they made up 79% of the fish collected from the Flint River, Michigan. The difference in round goby composition between the two
areas could be a result of greater overall fish diversity in the Pennsylvania tributaries, and/or less
human impact on the Pennsylvania tributaries.
Elk Creek is the largest of the tributary streams
studied and it contains few physical obstacles to
colonization. Therefore it is currently the stream
most likely to be colonized farther upstream by
round gobies. General habitat preference of round
gobies was relatively similar in each Pennsylvania
tributary stream, with round gobies preferring rocky
areas with moderate flow. However, unlike in Elk
Creek, round gobies were rarely collected from
areas of bedrock in Walnut Creek or Twentymile
Creek, possibly because the bedrock areas in those
streams were much shallower and contained fewer
ledges than bedrock areas in Elk Creek. These shallow bedrock areas may be acting as a physical barrier to the movement of round gobies farther
upstream in Twentymile and Walnut Creeks. Farther progression of gobies in Twentymile Creek appears to also be blocked by two small water falls.
Round goby abundance is relatively high directly
below the water falls and no round gobies were collected above the water falls.
Round gobies were not collected from
Twelvemile Creek or the Pennsylvania reaches of
Conneaut Creek. However, round gobies have been
collected from the lower reaches of Conneaut
Creek, Ohio (D. Jude, personal communication,
University of Michigan, Ann Arbor, MI). No disjunct populations of round gobies were found in
any upstream reaches of the tributary streams,
which indicates that thus far no round gobies have
been introduced by “bait-bucket transfer.” It is possible that further progression will occur into Pennsylvania tributary streams over time, and the
current locations will allow the monitoring of future
round goby movements.
The plasticity of the round goby diet may be a
factor in its successful colonization of the Great
Lakes region. Round gobies generally prefer to feed
on mollusks (primarily zebra mussels) where they
are available (Ghedotti et al. 1995, Ray and
Corkum 1997, Weimer and Sowinski 1999, Simonovic et al. 2001, Skora and Rzeznik 2001).
However, in a study of the St. Clair River, Michigan, French and Jude (2001) found that round gobies fed mainly on zebra mussels in deep water, but
fed on other macroinvertebrates in shallower water.
In this study, along with other studies conducted in
waters that do not contain zebra mussels (Carman
2002), round gobies were found to readily change
their diets to include primarily non-mollusk benthic
invertebrates. In the Flint River, Michigan, Carman
(2002) found that round gobies fed primarily on
chironomid larvae, which is very similar to the
findings in this study in Pennsylvania tributary
streams. Round goby diets from Pennsylvania tributary streams of Lake Erie, however, were very different from the diets of round gobies collected from
Lake Erie. Weimer and Sowinski (1999) found that
round gobies in Lake Erie fed predominantly on
zebra mussels and zooplankton, with larger fish relying more heavily on zebra mussels and smaller
fish relying more heavily on zooplankton. In the
tributary streams sampled in this study all size
classes of round gobies fed most heavily on chironomids and almost exclusively on non-mollusk
benthic macroinvertebrates; whereas, in Lake Erie
only approximately 30% of round gobies fed on
chironomids (Weimer and Sowinski 1999).
Round goby fecundity was previously studied in
the Detroit River by MacInnis and Corkum (2000),
and results from that study were very similar to our
findings in Pennsylvania tributary streams. In both
areas, females were mature at 1 year old, which differs from European populations of round gobies
which mature at 2 to 3 years old (Miller 1984,
Miller 1986). The length of gravid females from the
Detroit River ranged from 42 to 92 mm (standard
length) (mean = 60 mm) which is similar to the
findings in this study of a range of 54 to 112 mm
(total length) (mean = 66 mm). Individual fecundity
in the Detroit River ranged from 84 to 606 eggs,
and in Pennsylvania tributary streams it ranged
from 86 to 591 eggs.
Although this study did not focus directly on
round goby spawning in tributary streams there is
evidence that spawning is occurring there. A num-
The Round Goby in Tributary Streams
ber of males that showed spawning/nest guarding
colors were collected from Elk Creek, Twentymile
Creek, and Walnut Creek. This, coupled with the
collection of a relatively large number of gravid females in the streams, indicates that round gobies are
probably spawning there. This could lead to a much
more dramatic colonization of tributary streams in
the future, because much of the colonization success of round gobies has been attributed to their
ability to spawn multiple times per year. MacInnis
and Corkum (2000) estimated that females spawn
three times per year in the Detroit River, and that
absolute individual fecundity ranges from 252 to
1,818 eggs per round goby female. Similar annual
fecundity, coupled with fertilization and hatching
rates as high as 95% (Charlebois et al. 1997) could
produce dramatic increases in round goby density
in Pennsylvania tributary streams.
The aggressiveness of the round goby may allow
it to displace less aggressive native species, such as
the mottled sculpin (Cottus bairdi), that have similar habitat requirements (Hoekstra and Janssen
1985, Jude et al. 1995, Dubs and Corkum 1996,
Janssen and Jude 2001). Dubs and Corkum (1996)
found that round gobies aggressively drove mottled
sculpins from their shelters. Round gobies also interfere with nest-guarding male mottled sculpins
which exposes the nest to egg predation, which was
the case in Calumet Harbor, where mottled sculpin
recruitment failure contributed to dominance by
round gobies (Janssen and Jude 2001). In Lake Erie
tributary streams it was found that mottled sculpins
were absent from, or had very low densities in,
streams invaded by round gobies (Elk Creek, Walnut Creek, Twentymile Creek). However, in
Twelvemile Creek, which contained no round gobies and had good mottled sculpin habitat, relatively
high numbers of mottled sculpins were collected.
These data suggest that round gobies may be displacing mottled sculpins in tributary streams. However, there are no background data describing
sculpin densities and distributions prior to the round
goby invasion. Further monitoring of streams such
as Twelvemile Creek may provide insight into interactions between round gobies and mottled
sculpins in Great Lake tributary streams.
ACKNOWLEDGMENTS
We thank the Pennsylvania Sea Grant and Gannon University for grants, which supported this research.
39
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Submitted: 9 February 2002
Accepted: 18 September 2002
Editorial handling: John Janssen