Round Goby Abundance Research Articles

Temporal development of fish communities in brackish lagoons of the Baltic Sea considering the invasion of the non-indigenous round goby (Neogobius melanostomus)

Globally, successful invasions of non-indigenous species affect biodiversity and can push ecosystems beyond tipping points. This study aimed to identify factors that influence round goby (Neogobius melanostomus) abundances and distribution pathways along the eastern German coast of the Baltic Sea over a 12year period. The study further explored how the invasion of round goby affected the local fish and benthos assemblages in terms of species numbers and diversity. Round goby invaded various areas and estuaries and has established self-sustaining populations at low densities with further westward spread along the coast appearing to be ongoing. Salinity emerged as the most important predictor for overall round goby abundance, while the influence of macrozoobenthos abundance, vegetation cover, oxygen concentration, and water temperature were comparably low, indicating that round goby have a high tolerance in this regard. Negative impacts of round goby on benthic organisms and indigenous fish species, such as native gobiids, flounder (Platichthys flesus), ruffe (Gymnocephalus cernua), perch (Perca fluviatilis), pikeperch (Sander lucioperca), and cod (Gadus morhua), were not observed. This could be attributed to the comparably low densities of round goby at the sampling areas (0.0001 to 0.2 fish per m2) in combination with a potential surplus of benthic resources counteracting negative effects of predation and competition. The results suggest that its broad environmental adaptability could have enabled round goby to occupy a vacant ecological niche in coastal areas of the south-western Baltic Sea, which is generally considered to be species-poor due to strong environmental gradients. However, it cannot be excluded that certain effects of the round goby invasion may be too subtle to be detected. Thus, the results of our study underline the need for a specific long-term monitoring of the round goby invasion across taxa and habitats.

Round Goby Detection in Lakes Huron and Michigan—An Evaluation of eDNA and Fish Catches

Aquatic surveys for fish in large water bodies (e.g., Laurentian Great Lakes of North America) often require a flexible approach using multiple methods, surveying different depths, and sampling across seasons, especially when the target species is elusive in its natural habitat. The round goby (Neogobius melanostomus) is an invasive, bottom-dwelling fish inhabiting rocky areas of all five Great Lakes. While trawl surveys are typically used for abundance assessments, angling has been demonstrated as a means of supplementing surveys with additional data. Yet, round goby abundance and distribution is still not well described. Recently, with considerable success, scientists have explored sampling environmental DNA (eDNA) to complement traditional monitoring techniques for population abundance estimates, early detection of invasive species, and spawning or migration events. Therefore, we collected eDNA from water samples alongside bottom trawls and hook and line angling in Lakes Huron and Michigan to detect round goby. eDNA samples were analyzed by both droplet digital PCR (ddPCR) and quantitative PCR (qPCR) to maximize the likelihood of detection. Overall, round goby was captured in 23% of the trawls, but the eDNA based methods detected round goby in 74% and 66% of samples by ddPCR and qPCR, respectively, mostly in samples collected at <30 m depths, and mostly in the fall. More studies comparing eDNA based methods to traditional monitoring, especially trawls in large open waters, may contribute to a better understanding of using eDNA in population assessments.

Rapid response of the nearshore round goby population to temperature declines associated with upwelling events in Lake Ontario

Upwellings occur in all the Great Lakes in response to prolonged wind events. Several studies have modeled or measured changes in abiotic conditions associated with upwellings, but few direct observations of fish responses have been documented. Video-capture techniques were used in conjunction with moored temperature loggers to link the disappearance of benthic round gobies to temperature declines during upwelling events along the southern Lake Ontario nearshore in summer of 2019. Benthic water temperatures declined by as much as 18 °C within 18 h over as many as nine events. Round goby density estimates were as high as 50/m2 prior to upwellings, but declined to as low as 0/m2 during the events. Using just nine observation dates, ARMA trend analysis suggested a relationship between benthic temperature and round goby abundance (AIC = 78.7, t = 2.21, P = 0.063). Although the actual response of gobies to rapidly declining temperatures was unknown, this population was unobservable in our sample area during upwellings, yet returned to pre-upwelling densities within days. Understanding the magnitude and frequency of fish responses to these events can improve our understanding of the potential for this non-native benthic fish to affect the nearshore environment.

Two decades since first invasion: Revisiting round goby impacts on nearshore aquatic communities in the Upper St. Lawrence River

Time Since Invasion (TSI) at invaded sites is an important factor that can moderate invasive species abundances and their ecological impacts on resident communities, and yet it remains rarely addressed by invasion studies. We revisit the ecological impacts of round goby invasion in the Upper St. Lawrence River (Canada) on macroinvertebrate and fish communities, by taking into consideration the effects of TSI since initial invasion 20 years ago. Our objectives were to: 1) test the effect of TSI and invasion status on round goby abundance, and 2) investigate the effects of TSI, invasion status, and round goby abundance on macroinvertebrate and fish communities. Round goby abundance displayed a strong positive relationship with TSI. Environmental conditions, especially substrate and water conductivity were found to reduce round goby TSI and characterize uninvaded sites and >12 years TSI sites. However, we detected first potential signals of a reduction in round goby abundance at sites with TSI of 17–19 years compared with sites having 13–16 years TSI which had similar environmental conditions. Nonetheless, round gobies continued to have enduring impacts on total macroinvertebrate diversity, even at sites with TSI of 17–19 years, likely as a result of ongoing predation. This observation was supported by a negative association of round goby TSI on the abundance of dominant macroinvertebrate taxa at sampling sites in the Upper St Lawrence River, as well as dietary stomach content data. The fish community was less sensitive to round goby TSI than macroinvertebrate communities.

Exploring potential drivers of spatiotemporal variation in length-at-age and condition of two common nearshore fishes in southwestern Lake Michigan

Understanding factors like fish size and condition can be crucial to fisheries management. In the Great Lakes, long-term observations of these factors are used to describe the effects of ecosystem dynamics on fish ecology. Considering the diversity of available benthic habitat and dynamic environmental conditions in the nearshore zone of Lake Michigan, we sought to understand the variability in length-at-age and condition of yellow perch and round goby, two important members of the nearshore fish community. We measured these metrics from both species captured in gillnets across three locations in Illinois waters of southwest Lake Michigan from June through October 2008–2012 and related the spatiotemporal differences seen to observed variation in temperature, prey abundance, and competitor abundance. Yellow perch length-at-age varied annually for all three age-classes, with differences relating to thermal regime (age-0 and age-2) and alewife abundance (age-1). Yellow perch condition, measured as residual weight, varied spatially and annually, showing a negative relationship with round goby abundance. Round goby length-at-age was greater at the southern location, likely due to warmer temperatures, while condition was greater at the rockier location. In general, model selection analysis revealed several potential relationships between the relative abundances of competitor species and length and condition of yellow perch and round goby, while prey abundance may be related to round goby condition. These results demonstrate the importance of understanding the diversity in nearshore habitats and the influence of this diversity on factors affecting fish production, including size and condition, in southwest Lake Michigan.

Different refuge types dampen exotic invasion and enhance diversity at the whole ecosystem scale in a heterogeneous river system

Refuges that result from environmental heterogeneity within ecosystems have an important yet under-appreciated role in maintaining native community diversity in face of exotic invasion. The objective of our study was to determine if different refuge types constrain invasion impacts on native biodiversity at the whole ecosystem-scale of the Upper St. Lawrence River. We focused on the voracious round goby fish as a sentinel exotic species whose spatial distribution within this ecosystem is also representative of the species distributions of several other Ponto-Caspian invaders. We first explored if wetlands were acting as unknown refuges in reducing the local abundance of the round goby fish. We then tested the relative influence of a known broad-scale conductivity gradient compared with local wetlands on structuring the composition, diversity, and abundance of native macroinvertebrate and fish communities inside and outside each of these refuge types. We found that the two types of refuges, broad-scale conductivity gradient and local wetlands, limited round goby abundances at the whole ecosystem scale, and structured macroinvertebrate and fish community diversity. The broad-scale conductivity refuge was twice stronger than wetlands in limiting round goby abundance. Although wetlands were effective in constraining round goby abundance, the direct effect of wetlands rather than their indirect effects through limiting round goby abundance, were more powerful in explaining maintenance of macroinvertebrate and fish community diversity in invaded high conductivity waters. Our findings underscore the important role of environmental heterogeneity in producing different types of refuges that buffer invasion effects in freshwater ecosystems, and we advocate the preservation of wetlands as a part of this process.

Seasonal habitat use indicates that depth may mediate the potential for invasive round goby impacts in inland lakes

Abstract The round goby (Neogobius melanostomus) is among the fastest‐spreading introduced aquatic species in North America and is radiating inland from the Great Lakes into freshwater ecosystems across the landscape. Predicting and managing the impacts of round gobies requires information on the factors influencing their distribution in habitats along the invasion front, yet this information is not available for many recently invaded ecosystems. We evaluated the seasonal habitat use and biomass of round gobies in an inland temperate lake to define the spatiotemporal scope of biological interactions at the leading edge of the round goby invasion. Using novel statistical approaches, we combined hierarchical models that control for imperfect species detection with flexible smooth terms to describe non‐linear relationships between round goby abundance and environmental gradients. Subsequently, we generated accurate detection‐corrected estimates of the standing stock biomass of round gobies. Our results show seasonally differentiated habitat niches, where suitable round goby habitat in summer months is restricted to shallow depths (<18.4 m) with a mixture of vegetative and mussel cover. We found high round goby biomass of 122 kg/ha in occupied habitats during the summer, with a total lake‐wide biomass of 766,000 kg. In winter, round gobies migrate to deep offshore habitats and disperse, dramatically altering their scope for biological interactions with resident aquatic species across summer and winter seasons. The results of this study indicate that the scope of biological interactions in inland lakes may be seasonally variable, with potential for high round goby biomass in shallow lakes or at the periphery of deep lakes in the summer months. Such shallow‐water habitats may therefore present higher risk of ecological impacts from round gobies in invaded lentic ecosystems. As round gobies expand inland, consideration of seasonal habitat use will be an important factor in predicting the impacts of this pervasive invader.

Seasonal migration and fine‐scale movement of invasive round goby (Neogobius melanostomus) in a Great Lakes tributary

AbstractTo determine whether invasive round goby (Neogobius melanostomus) from Lake Ontario were establishing a year‐round population in a tributary stream or migrating to the lake, we assessed population and individual movement patterns using mark–recapture assessment generated from weekly backpack electrofishing from May until November 2016. Round goby abundance was low in spring, peaked in summer and decreased again in autumn, suggesting seasonal inward stream migration and outward migration back to the lake. Adult round goby movement patterns were positively associated with changes in water temperature, but this was not the case for juveniles. Juveniles displayed a preference for shallow, upstream habitats. Observations of reproductive individuals coupled with a peak in juvenile abundance following the peak in adult abundance indicate that the tributary was used for reproduction and recruitment. The individual movement was primarily upstream in spring, and there was little net movement in summer, likely during reproduction. Downstream movement occurred in autumn over a short time period, suggesting rapid outmigration to the lake. The combined observations of seasonal population structure and individual movement suggest that tributary streams connected to large, infested waterbodies can be used for round goby reproduction and recruitment, rather than year‐round residence. This study provides evidence of round goby seasonal migration and their individual movement patterns within tributary streams, which complements an earlier study in Lake Erie tributaries and may be a common occurrence in other Great Lakes tributaries.

Environmental DNA (eDNA): A tool for quantifying the abundant but elusive round goby (Neogobius melanostomus).

Environmental DNA (eDNA) is revolutionizing biodiversity monitoring, occupancy estimates, and real-time detections of invasive species. In the Great Lakes, the round goby (Neogobius melanostomus), an invasive benthic fish from the Black Sea, has spread to encompass all five lakes and many tributaries, outcompeting or consuming native species; however, estimates of round goby abundance are confounded by behavior and habitat preference, which impact reliable methods for estimating their population. By integrating eDNA into round goby monitoring, improved estimates of biomass may be obtainable. We conducted mesocosm experiments to estimate rates of goby DNA shedding and decay. Further, we compared eDNA with several methods of traditional field sampling to compare its use as an alternative/complementary monitoring method. Environmental DNA decay was comparable to other fish species, and first-order decay was lower at 12°C (k = 0.043) than at 19°C (k = 0.058). Round goby eDNA was routinely detected in known invaded sites of Lake Michigan and its tributaries (range log10 4.8–6.2 CN/L), but not upstream of an artificial fish barrier. Traditional techniques (mark-recapture, seining, trapping) in Lakes Michigan and Huron resulted in fewer, more variable detections than eDNA, but trapping and eDNA were correlated (Pearson R = 0.87). Additional field testing will help correlate round goby abundance with eDNA, providing insight on its role as a prey fish and its impact on food webs.

Long-term monitoring of native bullhead and invasive gobiids in the Danubian rip-rap zone

As invaders of European and North American aquatic systems, Ponto–Caspian gobiids are believed to represent a significant negative threat to native fish assemblages and cottid species in particular. To date, relatively few studies have tried to document actual impacts, most being short-term and/or laboratory based. Here, we examine 8 years (2008–2015) of electrofishing data from a 1200-m stretch of rip-rap along the Austrian Danube, initiated following establishment of four non-native gobiids: tubenose goby Proterorhinus semilunaris, bighead goby Ponticola kessleri, racer goby Babka gymnotrachelus and round goby Neogobius melanostomus. While we registered 26 fish species in total, most native species were caught along the rip-rap only occasionally. Only native bullhead Cottus gobio and the four non-native gobiids were caught regularly. Although cottids are presently believed to be most vulnerable to gobiid invasion, we observed no negative trend in bullhead abundance over the 8-year dataset, the population remaining stable and at similar abundances to gobiids. While we observed no significant trend in round, racer or tubenose goby abundance, bighead goby showed a continuous decline. Our data contradict previous reports of drastic impacts on cottid abundance by gobiids (mainly round goby), suggesting potential region-specific effects following invasion.

Low-head dams facilitate Round Goby Neogobius melanostomus invasion

Round Goby Neogobius melanostomus invasion of the Grand River (Ontario, Canada) presents an opportunity to assess the role of abiotic gradients in mediating the establishment and impact of nonnative benthic fishes in rivers. In this system, sequential low-head dams delineate uninvaded and invaded river reaches and create upstream gradients of increasing water velocity. We hypothesized that flow refugia created by impounded reservoirs above low-head dams enhance local Round Goby abundance. Round Goby influence on the native fish community was determined by variance partitioning, and we used generalized additive models to identify small-bodied benthic fish species most likely to be impacted by Round Goby invasion. Round Goby abundance declined as the degree of reservoir effect decreased upstream. The distributions of four species (including the endangered Eastern Sand Darter Ammocrypta pellucida) in invaded reaches were best explained by inclusion of both reservoir-associated abiotic variables and Round Goby abundance as model terms. To determine establishment potential of the uninvaded reach immediately upstream, four environmental habitat characteristics were used in discriminant function analysis (DFA) to predict three potential outcomes of introduction: non-invaded and either lower or higher Round Goby abundance (low and high invasion status, respectively) than the median number of Round Goby at invaded sites. Our DFA function correctly classified non-invaded and high-abundance invasion status sites > 85% of the time, with lower (73%) success in classifying low-abundance invasion status sites, and the spatial pattern of our results suggest that likelihood of establishment is greatest in impounded habitat.

Relationships between habitat characteristics and round goby abundance in Lakes Michigan and Huron

Abstract Expanding round goby ( Neogobius melanostomus ) populations threaten many native species throughout the Great Lakes. The qualities that make a habitat suitable for round gobies are oftentimes considered as single factors (e.g., substrate type or dreissenid mussels). A more thorough understanding of the environmental characteristics related to round goby abundance can help identify habitats that are less susceptible to invasion. This study examined the habitat characteristics associated with round goby abundance in the Beaver Archipelago of Lake Michigan and the Les Cheneaux and Saginaw Bay regions of Lake Huron. Chemical and physical variables, zooplankton, macroinvertebrate, and fish assemblages were sampled from open water and wetland habitats. Gradients in habitat characteristics, determined using ordination analyses and diversity indices, were correlated with round goby catch per unit effort (CPUE) using fyke nets. Round goby CPUE in the Beaver Archipelago was positively related to increasing productivity and a more diverse fish community. Round goby CPUE at Les Cheneaux was related to wave disturbance and fish species associated with greater habitat complexity, though habitat type alone did not explain these relationships. In contrast, round goby CPUE in highly productive Saginaw Bay wetlands was very low where fish diversity was high and assemblages were dominated by littoral species tolerant of eutrophic conditions. Overall, CPUE was related to indices of biological productivity, with the direction of these relationships varying among regions. Areas with high productivity, including some wetlands, may be less hospitable for round gobies and could serve as refugia for native species.

Long-term impacts of invasive round goby Neogobius melanostomus on fish community diversity and diets in the St. Clair River, Michigan

Abstract This study examined long-term impacts of round gobies ( Neogobius melanostomus ) on native benthic fishes near Algonac State Park in the St. Clair River, Michigan. Fish community composition and diet overlap between round gobies and native species were surveyed in 1994 and compared with similar data from 2011. Fish were collected in trawls (3, 5, 7, 9, 11 m depths) and seines (1 m) in May, June, and September 1994, and May, July, and September 2011. Between 1994 and 2011, relative abundance of northern madtom ( Noturus stigmosus ) decreased significantly in the offshore zone, catch-per-unit effort (CPUE) for rainbow darter ( Etheostoma caeruleum ) and round goby significantly decreased in the nearshore zone while CPUE for channel darter ( Percina copelandi ), johnny darter ( Etheostoma nigrum ), mottled sculpin ( Cottus bardii ), and round goby significantly decreased in the offshore zone. In 1994 and 2011, adult round gobies consumed mainly zebra or quagga mussels ( Dreissena polymorpha ; D. bugensis ). Significant diet overlap between large round gobies and native rock bass ( Ambloplites rupestris ), logperch ( Percina caprodes ), and trout-perch ( Percopsis omiscomaycus ) occurred infrequently in 2011. Decreasing round goby abundance may be due to increased predation by native species. Negative impacts of the round goby invasion and establishment on fish species diversity within this part of the St. Clair River were confined to a few species and possibly due to competition for other resources, such as space.

Changes in age-0 yellow perch habitat and prey selection across a round goby invasion front

Abstract Round gobies (Neogobius melanostomus) are reported to have negative impacts on benthic invertebrate prey and are now highly abundant throughout most of the Laurentian Great Lakes. This study used the initial spread of round gobies north and south from the Milwaukee Harbor as a natural experiment to assess the competitive interactions between age-0 yellow perch and round gobies in western Lake Michigan. Habitat selection and diet of age-0 yellow perch in relation to round goby abundance were analyzed using fish captured in micro-mesh gillnets in 2006 and 2007 at six study locations from Sheboygan to Wind Point, Wisconsin. An age-0 yellow perch shift in habitat preference from rock to sand was associated with relatively high round goby abundance at rock sites. An increase in round goby catch per unit effort was also correlated with a decrease in benthic prey (chironomid larvae + amphipods) abundance at rock sites and occurrence of these prey items in age-0 yellow perch stomach contents. Our results suggest that age-0 yellow perch may have undergone local niche shifts as a consequence of competition with round gobies. Further study may help elucidate the causal mechanism behind our observations and determine what effect round gobies are having on the yellow perch population of western Lake Michigan, as a whole.

Persistence of an invasive fish (Neogobius melanostomus) in a contaminated ecosystem

Post-establishment dynamics of invasive species have been under-studied. However, understanding these dynamics is particularly important for the management of invasive species known to impact native communities. Following the invasion of a highly invasive species, the round goby (Neogobius melanostomus), we document long-term population changes after establishment and address how population dynamics of a successful invader change through persistence and integration. Round goby present a threat to the areas they invade by out-competing native species for resources. Furthermore, as a pollution tolerant species, round goby present a second threat by acting as a possible vector for contaminant transfer to higher trophic levels in invaded ecosystems with areas of contamination. We sampled round goby for 11 years (2002–2012) at four low contamination sites and two high contamination sites within Hamilton Harbour ON, Canada, an International Joint Commission Area of Concern. Across sampling years, we show that round goby abundance has declined at low contamination sites, while remaining stable at high contamination sites. Moreover, we show that average body size decreased and reproductive investment increased both across sampling years and between sites of low and high contamination. Our results document population demographic shifts in a persisting invasive species, and underscore the importance of management practices for this species in contaminated environments.

Invasion success and impact of an invasive fish, round goby, in Great Lakes tributaries

AbstractAimEnvironmental and biological characteristics interact in complex ways to determine ecosystem susceptibility to invasive species, and a greater understanding of their relative roles in invader spread and impact is needed. We evaluated relationships between environmental characteristics, biodiversity of indigenous species, and the abundance and ecological impact of an invasive fish, round goby (Neogobius melanostomus).LocationTributaries to Lake Michigan, WI, USA.MethodsWe assessed the distribution and abundance of round gobies and native fishes in tributaries via electrofishing. We compared fish community composition and diversity in streams with (n = 30) and without (n = 52) round gobies and examined how trends in round goby abundance from 2007 to 2010 correlated with changes in abundance of five native benthic fishes. We used redundancy analysis to determine how indigenous stream communities related to environmental characteristics and round goby abundance.ResultsRound goby abundance was best explained by environmental characteristics, with watershed area and temperature explaining 22.4% of the variation. Species richness and Shannon diversity only explained 6.9% of the variation in round goby abundance and only an additional 2.3% after considering environmental characteristics. Round goby abundance was not a significant predictor of fish community composition, which was best explained by seven environmental variables (30.3% of the variation). Invaded communities had significantly higher indigenous species richness than uninvaded communities (8.38 vs. 6.54). Round goby abundance was low compared with estimates from other studies, but showed an increasing trend in many tributaries (average 10.8‐fold increase from 2007 to 2010). Surprisingly, there were no temporal trends in native benthic fish abundance despite increases in round goby abundance.Main conclusionsEnvironmental characteristics favouring high fish diversity (e.g. resource availability and warm water temperature) were positively associated with round goby abundance. However, round goby density and impact are relatively low in most tributaries at present, emphasizing the importance of considering heterogeneity in an invader's abundance when assessing invasion success.

Links between type E botulism outbreaks, lake levels, and surface water temperatures in Lake Michigan, 1963–2008

Relationships between large-scale environmental factors and the incidence of type E avian botulism outbreaks in Lake Michigan were examined from 1963 to 2008. Avian botulism outbreaks most frequently occurred in years with low mean annual water levels, and lake levels were significantly lower in outbreak years than in non-outbreak years. Mean surface water temperatures in northern Lake Michigan during the period when type E outbreaks tend to occur (July through September) were significantly higher in outbreak years than in non-outbreak years. Trends in fish populations did not strongly correlate with botulism outbreaks, although botulism outbreaks in the 1960s coincided with high alewife abundance, and recent botulism outbreaks coincided with rapidly increasing round goby abundance. Botulism outbreaks occurred cyclically, and the frequency of outbreaks did not increase over the period of record. Climate change scenarios for the Great Lakes predict lower water levels and warmer water temperatures. As a consequence, the frequency and magnitude of type E botulism outbreaks in the Great Lakes may increase.

Evidence for predatory control of the invasive round goby

We coupled bioenergetics modeling with bottom trawl survey results to evaluate the capacity of piscivorous fish in eastern Lake Erie to exert predatory control of the invading population of round goby Neogobius melanostomus. In the offshore (>20 m deep) waters of eastern Lake Erie, burbot Lota lota is a native top predator, feeding on a suite of prey fishes. The round goby invaded eastern Lake Erie during the late 1990s, and round goby population size increased dramatically during 1999–2004. According to annual bottom trawl survey results, round goby abundance in offshore waters peaked in 2004, but then declined during 2004–2008. Coincidentally, round goby became an important component of burbot diet beginning in 2003. Using bottom trawling and gill netting, we estimated adult burbot abundance and age structure in eastern Lake Erie during 2007. Diet composition and energy density of eastern Lake Erie burbot were also determined during 2007. This information, along with estimates of burbot growth, burbot mortality, burbot water temperature regime, and energy densities of prey fish from the literature, were incorporated into a bioenergetics model application to estimate annual consumption of round goby by the adult burbot population. Results indicated that the adult burbot population in eastern Lake Erie annually consumed 1,361 metric tons of round goby. Based on the results of bottom trawling, we estimated the biomass of yearling and older round goby in offshore waters eastern Lake Erie during 2007–2008 to be 2,232 metric tons. Thus, the adult burbot population was feeding on round goby at an annual rate equal to 61% of the estimated round goby standing stock. We concluded that the burbot population had high potential to exert predatory control on round goby in offshore waters of eastern Lake Erie.

Impacts of the Introduced Round Goby (Apollonia melanostoma) on Dreissenids (Dreissena polymorpha and Dreissena bugensis) and on Macroinvertebrate Community between 2003 and 2006 in the Littoral Zone of Green Bay, Lake Michigan

We show that the invasion of round gobies (Apollonia melanostoma) in Green Bay, Lake Michigan, has changed the benthic food web in fundamental ways related to their impact on invasive dreissenid mussels. Dreissenid mussels are of specific interest because they are one of the primary dietary items for round gobies. In this study, we collected rocks from each of 10 study sites along approximately 60 km of the eastern shoreline of Green Bay, Lake Michigan, to assess a temporal change in macroinvertebrate abundance related to the northward movement of the round goby invasion front from a point about midway along the shoreline in 2003 to the entire coast in 2006. The pattern of macroinvertebrate abundance in 2003 suggested that round gobies had already caused significant decreases in macroinvertebrate abundances south of the invasion front (interpretation of the data could have been compromised by confounding environmental gradients). In subsequent sampling in 2006 macroinvertebrates were picked off of sampled rocks in the field and underwater transects were videotaped to estimate round goby abundance at each site. Round gobies were collected for stomach analysis to assist in determining which invertebrates would likely be impacted by goby predation. Our results indicated that by 2006, round gobies had become abundant at those sites where they were absent in 2003 and zebra mussels (Dreissena polymorpha), quagga mussels (Dreissena bugensis), isopods, amphipods, trichopterans, and gastropods in the newly invaded sites had significantly decreased at the newly invaded sites.

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.