Invasion History,Proliferation, and Offshore Diet of the Round Goby Neogobius melanostomus in Western Lake Huron,USA

We used data from three trawl surveys during 1996–2003 to document range expansion, population trends, and use of offshore habitats by round gobies in the U.S. waters of Lake Huron. Round gobies (Neogobius melanostomus) were not detected in any survey until 1997, but by 2003 they had been recorded at 18 of the 28 sites sampled. The only areas not colonized were offshore habitats in northern Lake Huron. Round goby abundance increased during 1997–2001, thereafter overall abundance either increased (offshore) or became variable (near shore and Saginaw Bay). Mean lengths varied among surveys primarily due to high abundance of age-0 gobies in Saginaw Bay samples. Round gobies were found up to 34 km offshore at depths of 73 m. Round gobies consumed a wide range of invertebrate prey, but focused on dreissenids in shallow water (27–46 m), and native invertebrates at greater depths. The pattern of round goby dispersal was consistent with a pattern of simultaneous initial introductions at shipping ports followed by natural dispersal, and lake wide population size has probably not stabilized.     

Diet,trophic position of upper St. Lawrence River round goby giants reveals greater dependence on dreissenids with increasing body size

Round gobies (Neogobius melanostomus) from the upper St. Lawrence River (USLR) have an abundance of some of the largest individuals recorded from the Great Lakes (>230-mm total-length). We found a distinct separation in diet and isotopic signatures (δ¹⁵N and δ¹³C) between round goby classified as small (≤130-mm; n = 63) and large (>130-mm total-length; n = 75) from USLR coastal bays. At small sizes, round gobies had variable diets indicative of generalist and opportunistic feeding on native and non-indigenous benthic prey. Between 100 and 130-mm total-length, signatures of assimilated carbon (δ¹³C) indicated a directed shift towards a dreissenid-centric diet and once larger than 130-mm total-length, round gobies appeared to feed proportionally more on dreissenid mussels. We also found that large round gobies fed proportionally more on Hydrobiidae than small round gobies. A weak negative relationship between δ¹⁵N (indicative of trophic position) and round gobies total length resulted where smaller round gobies had slightly higher δ¹⁵N values than larger conspecifics. Round gobies larger than 180-mm total-length were common in nearshore habitats (≤2-m) during the spring, and dreissenid mussels and Hydrobiidae were the most frequently encountered prey. Our results demonstrate elevated reliance on dreissenids as round goby increased body size, but the diversity of prey suggest more complex trophodynamic pathways associated with coastal bay habitats.     

Environmental factors associated with the occurrence of the Ponto–Caspian gobies in a lowland river belonging to the central European invasion corridor

Ponto–Caspian goby fish belong to the most successful invaders in freshwater ecosystems of Europe and North America. So far, three alien goby species have been present in the Polish section of the Dnieper–Rhine River corridor: the monkey goby Neogobius fluviatilis, the racer goby Babka gymnotrachelus, and the western tubenose goby Proterorhinus semilunaris. Their assemblages in this region are unique because, in contrast to their native region or the Danube–Rhine corridor, they are unaffected by other gobiid species. We conducted electrofishing and habitat quality surveys to gather information on key environmental factors associated with the distribution of these fish in the lower river Vistula, which constitutes a vast middle part of the corridor used by the Ponto–Caspian species to migrate westward in Europe. We showed that the sandy bottom was beneficial for the monkey goby allowing the species to attain the highest abundance among the gobies in the river. Habitat complexity generated by artificial bank structures, as well as dense macrophyte coverage in the main channel, favoured mostly the expansion of the racer goby. Off‐channel areas with vegetation and a muddy bottom (old river beds and pools) were the most suitable habitats for the western tubenose goby. We did not find any negative spatial relationships among gobies of various species and sizes except the avoidance of the monkey goby by small western tubenose goby. Thus, our study demonstrates substantial habitat partitioning, suggesting a low level of interspecific competition among the three species in a lowland river.     

Fish Assemblages and Environmental Variables Associated with Gobiids in Nearshore Areas of the Lower Great Lakes

We investigated which fish species and environmental variables were associated with the invasive round goby (Neogobius melanostomus) and tubenose goby (Proterorhinus marmoratus) in nearshore Canadian waters of the Huron-Erie corridor of the lower Great Lakes. We measured a suite of environmental variables and used triplicate beach seine samples to collect fishes in summer 2006. Thirty sites were sampled in the day and a subset (n = 14) at night. Of 1,955 individuals caught in daytime samples, round goby (21.0 %), spottail shiner (17.3%) and emerald shiner (14.2%) were most abundant. Of 1,521 individuals collected at night, the most abundant species were round goby (42.3%) and emerald shiner (24.1%). Tubenose gobies represented 1% and 1.7% of all individuals caught in the day and night, respectively. Rarefaction analysis showed that overall species richness was greater in the day than night. Significantly more emerald shiner (P = 0.017), rock bass (P = 0.046) and round goby (P = 0.035) were caught at night than in the day; more logperch were caught in the day than at night (P = 0.042). Round gobies were positively associated with water temperatures up to 24°, but there was no relationship between round goby abundance and warmer temperatures. There were too few tubenose goby captured to determine their statistical association with environmental factors; however, tubenose gobies were found only where round gobies were collected. Round goby and tubenose goby were associated with yellow perch and rock bass. The benthic round goby was the most abundant species, whereas other abundant species were pelagic, schooling fishes that occupied a habitat distinct from round goby.     

Morphology,Feeding, and Reproduction of the Round Goby,Neogobius melanostomus (Pallas), in the Danube River Basin,Yugoslavia

The round goby Neogobius melanostomus was the last Ponto-Caspian goby species to enter in the Danube River bordered by Serbia and Yugoslavia. There are five Ponto-Caspian goby species in the waters of Serbia including the sand goby Neogobius fluviatilis, the round goby Neogobius melanostomus, the racer goby Neogobius gymnotrachelus, the bighead goby Neogobius kessleri, and the tubenose goby Proterorhinus marmoratus. The sand, bighead, and tubenose gobies occur along the Yugoslav Danube and in the lower reach of the Danube's tributaries; the racer goby is found both upstream and downstream of the Djerdap II dam; and, the round goby has been collected only downstream of the Djerdap II dam. Investigations on the continuous morphological characters of the round goby revealed neither sexual dimorphism, nor significant differences in adult size-classes, although some suggestions of sexual dimorphism were found in cranial skeletal analyses. Analysis of external continuous characters revealed a west-east cline along the distribution range of the round goby in the Black Sea basin. Molluscivory for the round goby was corroborated along the Danube. Standard length of each age class for the round goby in the Danube was less than populations in the Caspian and Azov seas.     

Occurrence and Food Habits of the Round Goby in the Profundal Zone of Southwestern Lake Ontario

Little is known about the ecology of round goby (Neogobius melanostomus), an invasive benthic fish, in the profundal zone of the Great Lakes. In April 2002–2005 we caught increasing numbers of round gobies with a bottom trawl in the 45–150 m depth range of southwestern Lake Ontario. In 2005, we examined gut contents of 30 round gobies from each of three depths, 55, 95, and 130 m, and qualitatively compared gut contents with density of benthic invertebrates determined by Ponar grabs. Round goby guts contained mostly Dreissena spp. and opposum shrimp, Mysis relicta (Mysis); the frequency of occurrence of dreissenids in guts decreased with depth, whereas the frequency of occurrence of Mysis in guts increased with depth. Abundance of these invertebrates in the environment followed the same pattern, although dreissenids of optimum edible size (3–12 mm) were still abundant (1,373/m²) at 130 m, where round gobies primarily consumed Mysis, suggesting that round gobies may switch from dreissenids to more profitable prey when it is available. Other food items were ostracods and fish, with ostracods generally eaten by smaller round gobies and fish eaten by larger round gobies. Occurrence and increasing abundance of round gobies in the profundal zone and predation on Mysis by round goby could have far-reaching consequences for the Lake Ontario fish community.     

Habitat and Site Affinity of the Round Goby

A study was conducted in 1996 to compare densities of the round goby (Neogobius melanostomus) in rock and sand habitats in day and night at three sites (Sarnia, St. Clair River; town of Belle River, Lake St. Clair; Peche Island, Detroit River). The sites represent an expansion in round goby distribution from Sarnia where gobies were first reported in 1990 downstream to Peche Island where gobies appeared in 1993. Site affinity at Peche Island was estimated using mark-recapture and observations of individual fish. Mean density of round gobies differed among sites (p < 0.001), light regime (p < 0.001), habitat (p < 0.001), and the interaction of light regime and site (p = 0.007). Mean densities of the round goby were 0.3 to 3 fish/m² (Peche Island), 0.5 to 3 fish/m² (town of Belle River), and 5 to 9 fish/m² (Sarnia). Overall, highest densities of the round goby occurred in the day and on rocks. Small (≤5 cm) round gobies were most common at Peche Island, the most recently colonized site, indicating that juveniles may disperse more rapidly than adults. Of 200 fish that were marked, 58% were recaptured, indicating high site fidelity among round gobies. The estimated mean (± SE) home range of the round goby determined using SCUBA (5 ± 1.2 m²) was likely underestimated because few fish were observed. Larger round gobies may induce smaller fish to leave preferred rock habitats and move to sand habitats from which they disperse.     

Activity,Aggression, and Habitat Use of Ruffe (Gymnocephalus cernuus) and Round Goby (Apollonia melanostoma) under Laboratory Conditions

Potential negative ecological interactions between ruffe Gymnocephalus cernuus and round goby Apollonia melanostoma (formerly Neogobius melanostomus) might affect the colonization dynamics of these invasive species where they are sympatric in the Great Lakes. In order to determine the potential for ecological interactions between these species, we examined the activity, aggression, and habitat use of round gobies and ruffe in single species and mixed species laboratory experiments. Trials included conditions in which food was concentrated (in light or darkness) or scattered. Results showed that ruffe were more active than gobies, particularly when food was scattered. Activity of both species was significantly lower during darkness. Round gobies were significantly more aggressive than ruffe, and total aggression was lower in mixed species trials. Habitat use by ruffe and round gobies overlapped considerably, but we observed significant differences between species in their use of specific habitats that depended on experimental conditions. Overall, ruffe used open habitats more often than did round gobies, primarily when food was scattered. Round gobies used rocks significantly more frequently than did ruffe, but their use of rock habitat decreased during dark conditions. Ruffe were found more often in plant habitats and less often near the wall of the pool in trials during daylight with concentrated food. Activity and habitat use of ruffe and round goby did not significantly differ between single and mixed species trials. Overall, we found little evidence for negative ecological interactions between ruffe and round goby in these laboratory experiments.     

Observations on Diet Composition of Neogobius melanostomus Pallas 1811 (Gobiidae,Pisces) in the Gulf of Gdansk (Baltic Sea)

This study documents the diet of Neogobius melanostomus (round goby) from three different habitats within the Gulf of Gdansk. Diet composition of the round goby in the Gulf of Gdansk appears similar to that in its natural environment within the Ponto-Caspian Basin. In its native habitat, the round goby feeds mainly on epibenthic organisms and opportunistically forages on seasonally abundant components of the benthic community. A natural mollusk-feeder, the round goby feeds mainly on the mussel Mytilus trossulus in the Gulf of Gdansk. This food preference most likely is due to the fact that M. trossulus is commonly distributed throughout most of the gulf and dominates the benthic biomass. The adult round goby prefers an environment full of hiding places that also can be used for nests. Thus, submerged stones or concrete structures covered with colonies of M. trossulus are its preferred habitat. Younger gobies are more abundant in the frontal areas of underwater concrete structures where the substrate is characterized by loose stones and the presence of Mya arenaria. These habitats have different faunal structures and, therefore, different trophic relations. The round goby, which is well suited for ecological expansion, has great potential to dominate the majority of the coastal zone of the Baltic Sea. Puck Lagoon, devoid of predatory fish and rich in mussel beds, is an ideal habitat for this gobiid species.     

Round Goby and Mottled Sculpin Predation on Lake Trout Eggs and Fry: Field Predictions from Laboratory Experiments

The accidental introduction of round gobies (Neogobius melanostomus) into the North American Great Lakes has raised concerns about their potential impacts on local fauna. Gobies have similar habitat and spawning requirements to mottled sculpins (Cottus bairdi) and slimy sculpins (C. cognatus), and may already be displacing sculpins where the ranges of the species overlap. Like sculpins, gobies are capable of penetrating interstitial spaces to acquire food, and therefore may become predators of interstitially incubating lake trout eggs. Laboratory experiments were conducted to compare egg consumption rates and critical size (the minimum size at which a fish was capable of ingesting an egg) between round gobies and mottled sculpins. Predation by both species on lake trout eggs and fry was also examined in two grades of substrate (cobble and gravel). Mottled sculpins consumed larger numbers of eggs than round gobies of similar size, and were capable of ingesting eggs at smaller sizes than gobies. Both gobies and sculpins had lower foraging success on smaller substrates (gravel) than on cobble. Gobies are currently present at higher densities than sculpins in areas where they are established in the Great Lakes. The similar predation of lake trout eggs by round gobies and mottled sculpin and high densities the goby has achieved at some Great Lakes sites leads to the prediction that the round goby may negatively affect lake trout reproduction and therefore rehabilitation.     

Size-selective predation by round gobies (Neogobius melanostomus) on dreissenid mussels in the field

Although numerous studies have shown that round gobies (Neogobius melanostomus) prey on dreissenid mussels (Dreissena polymorpha and Dreissena bugensis), there is an apparent shortage of detailed field studies on the subject. The 5-month field study described here quantifies predation by round gobies on dreissenids in Presque Isle Bay, Lake Erie. Dreissenids dominated the diet of round gobies, composing 92% of the prey items recovered. Over half of the 3870 valves (1935 mussels) recovered from 155 round gobies were crushed, while the remainder were swallowed whole. Crushed dreissenids were larger than those swallowed whole, and the tendency to crush dreissenids did not vary among three length classes of round goby. Round goby length was positively related to average size of dreissenids consumed, average size of whole and crushed dreissenids, largest whole dreissenid consumed, and largest crushed dreissenid consumed. Indices of selectivity revealed similarly shaped curves for three length classes of round gobies, a shift toward larger dreissenid size classes with an increase in round goby length, and peak preferences for 8-11 mm dreissenids. Factors such as gape limitation, availability and accessibility of differently sized dreissenids, forces generated while removing mussels from the substrate and crushing them, and caloric content of dreissenids all likely play roles in the observed size-selectivity and differential processing of dreissenids. Although factors influencing size-selectivity are not completely understood, the observed preference of round gobies for dreissenids near the size when they are first reproductive could impact the demography of dreissenid populations.     

Competitive Interactions between Round Gobies and Logperch

We examined territorial defense and behavioural interactions between two species of fish resident in Hamilton Harbour: non-indigenous round gobies (Neogobius melanostomus) and native logperch (Percina caprodes). Trials consisted of placing one fish, “the resident” (either a round goby or a logperch), in a tank with a shelter for 24 hours before adding another fish, “the intruder” (either a round goby or a logperch), and recording aggressive incidents. Overall, gobies exhibited more aggressive behavior than logperch, and in general resident status had no effect on amount of aggression displayed. Also, gobies spent more time in shelters than logperch, and overall resident status did not affect the amount of time spent under shelter. We also compared abundance data for gobies and logperch using electrofishing transects in Hamilton Harbour that were conducted in 1995 and 2001 and found a dramatic increase in round goby numbers and a non-significant decrease in logperch numbers. Our data suggest that gobies are superior space competitors and hence the range expansion coupled with an increasing population size of the round gobies in Hamilton Harbour is likely to have deleterious consequences for logperch populations.     

Comparison of Methods Needed to Estimate Population Size of Round Gobies (Neogobius melanostomus) in Western Lake Erie

The round goby (Neogobius melanostomus) is a small, demersal fish that was introduced into the Great Lakes basin in 1990. Since their arrival, the round goby has been implicated in many ecological changes—most notably changes in the flow of energy from the benthic to the pelagic food web through their consumption of dreissenid mussels. However, methods for evaluating the density and size of round gobies across different substrates are lacking, preventing the true quantification of the effects of round gobies on invaded ecosystems. In our study, we evaluated catch efficiency of numerous passive and active sampling methods for capturing round gobies. We then applied the best techniques to estimate the distribution, density, and biomass of round gobies in western Lake Erie. Visual census (underwater video transects) proved the best technique for assessing round goby size and density across a wide range of substrates. A combination of angling and bottom trawling proved most effective for obtaining biological samples. We estimated 9.9 billion round gobies in western Lake Erie in 2002. Continued efforts to describe abundance and demographics of round gobies in invaded ecosystems will enable scientists and managers to fully understand the impacts of this invading species.     

Diet Choice by the Exotic Round Goby (Neogobius melanostomus) as Influenced by Prey Motility and Environmental Complexity

This laboratory study examined the influence of substratum complexity and water clarity/visibility on non-indigenous round goby (Neogobius melanostomus) diet choice between dreissenid mussels (Dreissena polymorpha and D. bugensis, 6 to 9 mm length) and the exotic amphipod Echinogammarus ischnus. When both prey items were offered simultaneously in bare 20-L aquaria holding clear ambient water, 6.5 to 8-cm round gobies chose primarily amphipods (> 85% of diet numerically) and consumed fewer dreissenids (< 2/h) than when mussels were offered alone (5.2/h). Round gobies could ingest substantially more biomass when feeding on a mixed diet (∼17 to 24 mg/h dry weight, not including dreissenid shells) or on amphipods alone (∼26 mg/h), than feeding on dreissenids alone (∼12 mg/h). Longer handling time of mussels may thus have influenced the round gobies’ preference for amphipods. Added substrata (stones or gravel) and/or diminished visibility (turbid water or darkness) shifted round goby diet markedly towards sessile dreissenids as motile amphipods found refuge. Two-way ANOVA indicated that both substratum and water clarity/visibility significantly influenced round goby diet, but did not interact. It is possible that the large contribution of dreissenids to round goby diet in the Great Lakes may not necessarily reflect a preference for them, but rather lower encounter rates with more profitable prey.     

Use of wetland versus open habitats by round gobies in lakes Michigan and Huron: Patterns of CPUE,length, and maturity

It has been suggested that some Great Lakes coastal wetlands may be resistant to invasion by several non-indigenous species including round goby, Neogobius melanostomus. However, there is inconclusive evidence regarding how susceptible exposed fringing coastal wetlands, in particular, are to round goby invasion. Therefore, we quantified round goby catch per unit effort (CPUE) using fyke nets in the Beaver Archipelago of Lake Michigan, and the Les Cheneaux islands and Saginaw Bay regions of Lake Huron. In addition, we examined the influence of body size and maturity on round goby habitat use. Catch per unit effort from fyke nets was highest in the Beaver Archipelago, where wetlands were dominated by small, immature round gobies and open water habitats were dominated by large adults. Fyke net catches within Les Cheneaux sites were similar between habitats and differences in size and maturity were not observed. Conversely, very few round goby were captured in wetlands of Saginaw Bay where CPUE was moderate in open water. This indicates that some exposed fringing wetlands in the Great Lakes, specifically those with high productivity, could have a higher degree of resistance to round goby invasion.     

Impact of Round Gobies (Neogobius melanostomus) on Dreissenids (Dreissena polymorpha and Dreissena bugensis) and the Associated Macroinvertebrate Community Across an Invasion Front

We studied the impact of round gobies (Neogobius melanostomus) on lithophilic invertebrates (having an association with a stony substrate) across an invasion front along the Door Peninsula, which flanks eastern Green Bay, Lake Michigan. We conducted both a cross-invasion front field survey and a rock-transfer experiment. For the field survey, we collected pairs of rocks from ten sites, including sites north of the invasion front and south of the invasion front. Zebra mussels (Dreissena polymorpha), quagga mussels (D. bugensis), and non-mussel invertebrates were removed from the rocks and enumerated. The rocks were measured and the algae removed and weighed. Round gobies were censused by videotaping along transects. There was a statistically significant negative relationship with round goby abundance for most invertebrates, including zebra mussels, quagga mussels, isopods, and snails, with the result for amphipods being suggestive. For the experiment, we transferred 20 rocks in bags from a round goby “absent” site with 10 going to a round goby abundant site and 10 being returned to the original site. The rocks incubated overnight, invertebrates were removed the next day, and the rocks were measured. There were significantly fewer zebra mussels, quagga mussels, isopods, amphipods, and snails from the rocks incubated at the round goby abundant site compared to those returned to the round gobyfree site. Thus, the results of the survey and rock-transfer experiment suggest that round gobies are influencing the benthic macroinvertebrate abundance through predation. The negative impact on mussels is probably due to direct predation while the negative impact on the other invertebrates may be a combination of direct predation and indirect effects due to the loss of the microhabitat or food that zebra mussels produce.     

Benthic Invertebrate Community Responses to Round Goby (Neogobius melanostomus) and Zebra Mussel (Dreissena polymorpha) Invasion in Southern Lake Michigan

The round goby (Neogobius melanostomus Pallas), a fish native to eastern Europe, recently has become established in southwestern Lake Michigan. Because round gobies prey on zebra mussels (Dreissena polymorpha Pallas) and other benthic invertebrates, the effects of round gobies on invertebrates within zebra mussel colonies was investigated. Using a 2 × 3 factorial design, the effects of round gobies (present or absent) and zebra mussel densities (zero, low, and high) on non-mussel invertebrates was examined. Ten ceramic tiles of each mussel density were colonized in the laboratory and then anchored in Calumet Harbor, IL for 10 weeks. Round gobies had access to half the tiles while half were covered with coarse mesh screening that excluded round gobies, but allowed invertebrates to move into and out of the exclosures. Low and high zebra mussel density tiles supported significantly greater numbers of non-mussel invertebrates (p < 0.001) than zero density tiles, particularly amphipods (p < 0.001), hydroptilid caddisflies (p < 0.05), isopods (p < 0.05), and chironomids (p < 0.001). Chlorophyll a concentrations were highest (p < 0.001) at low zebra mussel densities. The presence of round gobies significantly reduced densities of total non-mussel invertebrates (p < 0.01) and leptocerid caddisflies (p < 0.05), resulting in a significant increase in chlorophyll a (p < 0.01) concentrations. A significant zebra mussel density x round goby interaction showed that total invertebrate biomass responded positively to the combined effect of high zebra mussel density and round goby absence. These results demonstrate that round gobies and zebra mussels are altering benthic invertebrate community structure and algal resources in nearshore rocky areas of southwestern Lake Michigan.     

Diel Vertical Migration of Round Goby Larvae in the Great Lakes

One hypothesis for the transcontinental and intra-Great Lakes basin transfer of round gobies (Neogobius melanostomus) has been that round gobies were pumped into the ballast water of ships. During June 2005 in Lake Erie, we obtained evidence of a vertical migration of round goby larvae, when we collected 167 round goby larvae in surface ichthyoplankton net tows at night and zero during day. These results complemented similar findings from the Muskegon River estuary of Lake Michigan during 2003 and 2004, documenting diel vertical migration for the first time in larval round gobies. We suggest vertical migration behavior may have allowed larval round gobies to be transported to and within the Great Lakes via ballast water and dispersed in the Great Lakes via advection of 6.5–8.5-mm long larvae at the surface. Based on our results, if ballast water was only taken on near the surface during daylight hours from May through September when larval round gobies were present, it would have mitigated the spread of round gobies throughout the Great Lakes.     

Recruitment Failure of Mottled Sculpin Cottus bairdi in Calumet Harbor,Southern Lake Michigan,Induced by the Newly Introduced Round Goby Neogobius melanostomus

This study documents a local extinction of mottled sculpins, apparently due to round gobies, and presents data pertinent to the mechanism of extinction. Mottled sculpins, Cottus bairdi, were assessed using SCUBA standardized diving transects during the invasion of the round goby, Neogobius melanostomus, into Calumet Harbor, southern Lake Michigan. Laboratory stream studies were conducted in which gravid male and female mottled sculpins were allowed to nest, then were exposed to one male round goby. Diet studies were conducted to assess the potential for competition for food at small sizes of both species. The SCUBA surveys showed that mottled sculpin populations rapidly declined, after the first round gobies were found in the area in 1994, despite the presence of a well established population prior to the round goby arrival. Mottled sculpins have been almost totally extirpated from the area in 1998 due to three proposed mechanisms: competition for food resources at small sizes, for space at intermediate sizes, and for spawning space at large sizes. The laboratory stream study confirmed that round gobies interfered with nest-guarding male mottled sculpins, seized their spawning shelters, changed to spawning coloration in preparation for spawning, and caused near loss of all the mottled sculpin eggs. It is concluded that recruitment failure and subsequent demise of mottled sculpins was most likely caused by spawning interference by round gobies.