Invasive Round Goby Neogobius Melanostomus Research Articles

Invasive Round goby Neogobius melanostomus distribution, relative abundance, and establishment in pools of the Illinois Waterway following 30 years of invasion

Round goby Neogobius melanostomus – a small, benthic fish native to Eurasia – was first introduced to North America in the 1980s through ballast water of cargo ships. In 1990, the Round goby was first discovered in the Laurentian Great Lakes Basin and rapidly spread through all Great Lakes from 1993 to 1998. The Round goby is an aggressive, prolific, and efficient egg predator that subsequently displaced native fishes from their preferred habitats and resources in the Great Lakes, where they are well established and abundant. From Lake Michigan, Round goby moved south into the Chicago Area Waterway System in 1993 and slowly progressed down the Illinois Waterway to the Mississippi River from 2004 to 2019, where less is known about their abundance, establishment, and impact. The goal of this study was to gain a comprehensive understanding of the first large river invasion by Round goby in the Mississippi River Basin by leveraging Round goby capture data from 2019 to 2022 on all pools of the Illinois Waterway. We describe their current distribution, relative abundance (i.e., catch-per-unit-effort), frequency of occurrence, and establishment (i.e., presence of young-of-year and adults) status throughout the Illinois Waterway. Results show that catch-per-unit-effort, frequency of occurrence, and the proportion of sites where multiple life stages are present are considerably higher in the upstream pools relative to more downstream pools of the Illinois Waterway. Our data support that the Round goby has established self-sustaining populations in the Chicago Area Waterway System, the upper Illinois River (i.e. Dresden Island Pool downstream through Starved Rock Pool), and a portion of the lower Illinois River (i.e. Peoria Pool downstream through Alton Pool) of the Illinois Waterway. In the lower Illinois River, Round gobies appear to only be established in Peoria Pool, with captures occurring infrequently in La Grange Pool, and no Round gobies being captured in Alton Pool.

Changes in the Baltic Sea coastal food web: A case study on the invasion of Round goby Neogobius melanostomus (Pallas, 1814)

We used dynamic food web modeling to assess the trophic effects of the increased abundance of the invasive Round goby Neogobius melanostomus (Pallas, 1814) on network flows and trophic levels in the open coastal zone of the south-eastern Baltic Sea. Available data on biomass and diet changes were incorporated in the Ecopath with Ecosim model, which estimated non-available data. Flow changes were related to Round goby predation on Blue mussels Mytilus edulis (Linnaeus, 1758), as well as to its contribution to the diet of piscivorous groups. The model presented changes in Long-tailed duck Clangula hyemalis (Linnaeus, 1758) biomass and consumption and an increase in its trophic level. However, the results showed no changes in the trophic level of other compartments nor average path length, the trophic level of fishery catch or the average trophic level of the community. This demonstrates the network's ability to maintain flows within given input and retain stability under conditions of changes induced by an invasive species. In regards to validating the model results in the representation of the study, trophic levels estimated by the dynamic model strongly correlated to ones calculated from stable nitrogen isotope (δ15N) ratios of consumers.

The Population Development of the Invasive Round Goby Neogobius melanostomus in Latvian Waters of the Baltic Sea

The invasive round goby (Neogobius melanostomus) was established in the coastal waters of the Baltic Sea in the early 1990s. The first observation of the species in Latvian waters was in 2004. In the intervening period, the population grew, the species became of significance for local fisheries, and it likely impacted the local ecosystem in the Baltic Sea. In this study, we characterize the spatial–temporal population development of round goby in Latvian coastal waters using data from three different scientific and fisheries-independent surveys. We also include data from commercial fisheries landings to describe the fisheries targeting the species. Our results suggest an exponential increase in population numbers of round goby in Latvian waters, peaking in 2018, followed by a sharp decline. This observation is also supported by data from commercial fisheries landings. We suggest that intensive commercial fishing had a considerable impact on the rapid decline of the species, but that the decline was potentially amplified through a wider scale decline, as observed in many areas of the Baltic Sea. The results of this study contribute to the knowledge base on the species and how fisheries can aid in limiting the development of invasive fish populations. Based on the results of the study, we also provide recommendations for better future monitoring of the species in the coastal waters of the Baltic Sea.

Effects of Round Goby on the Benthic Invertebrate Community and on Diets and Growth of Yellow Perch and White Perch in Oneida Lake, New York

AbstractFood web changes from the introduction of nonnative species can be complex, with sometimes unexpected effects or little effect due to food web interactions. Invasive Round Goby Neogobius melanostomus became common in samples in Oneida Lake, New York, by 2014. Data from a long‐term monitoring program allowed us to document the Round Goby expansion through time. Using shoreline seine, fyke net, bottom trawl, and video surveys, we estimated that Round Goby density reached over 25,000 fish/ha 6 years after detection and subsequently varied between 4,110 and 26,565 fish/ha. Concurrent benthic invertebrate sampling and long‐term fish diet sampling allowed us to assess the impacts of Round Goby on densities of several benthic invertebrate taxa and on invertebrate consumption by fish. Significant decreases in density after Round Goby arrival were found for amphipods (Amphipoda), caddisflies (Trichoptera), snails (Gastropoda), and dreissenid mussels Dreissena spp. Invertebrate densities after Round Goby arrival ranged from 19% to 48% of densities in the pre‐Round Goby period. For amphipods, snails, and, in some cases, caddisflies and chironomids (Chironomidae), frequency of occurrence in the diets of Yellow Perch Perca flavescens and White Perch Morone americana was lower after Round Goby became established. The decreased consumption of these invertebrates did not lead to decreases in fish growth; growth increased for some age‐classes of Yellow Perch and all age‐classes of White Perch. Despite potential Round Goby predation, densities of burrowing mayflies Hexagenia spp. expanded during this time and likely helped to offset reductions in consumption of other invertebrates by Yellow Perch and White Perch, as did consumption of Round Goby. Long‐term monitoring shows that Round Goby decreased the density of several benthic invertebrate species and decreased the consumption of these invertebrates by fish, but the effect on growth of Yellow Perch and White Perch was offset by consumption of Round Goby and burrowing mayflies.

Identifying high-risk areas for introduction of new alien species: the case of the invasive round goby, a door-knocker for Norway

AbstractIdentifying new areas of colonisation by alien species is important for early detection and management. Door-knocker species pose problems for traditional predictive models because of lacking presence–absence data, but habitat suitability modelling might overcome this. We here identify the most likely areas for introduction and first establishment of the invasive round goby Neogobius melanostomus to Norway, where it has not yet been registered. We implemented knowledge on dispersal pathways and the species’ biology in a simplified suitability model based on spatial data representing the most relevant environmental variables: distance to international harbours in Norway, distance to the closest population in neighbouring country, salinity, wave exposure, depth and water temperature. The results suggest that there are many potential localities for introduction and first establishment and reveal several hotspots of such areas, especially in less-exposed coastal brackish areas of southern Norway. Especially the region around the Oslo Fjord stands out as being associated with higher risk. Our results could guide future monitoring programmes and increase the chance of early detection of this potential new invader. The study illustrates how spatial analyses can be used to identify the most likely areas for future invasion by an aquatic door-knocker species despite lacking presence–absence data.

FEEDING OF THE INVASIVE ROUND GOBY <i>Neogobius melanostomus</i> (Perciformes: Gobiidae) IN THE SOUTH-EASTERN BALTIC

The feeding of the Ponto-Caspian invasive round goby Neogobius melanostomus in the coastal zone of the Baltic Sea near the Curonian Spit, in the Vistula Lagoon and in the eastern part of the Gdansk Bay has been studied. The round goby in coastal waters prefers biotopes with various shelters - boulders, large pebbles, etc. In the diet of the round goby, there is a significant proportion of fouling organisms inhabiting these objects. If fouling organisms are absent for some reason, the goby switches to other types of prey: molluscs, free-living crustaceans, insect larvae and other groups of benthic and nektobenthic organisms. There is a connection between the food spectrum and the size of the round goby: large individuals consume larger prey. The round goby implements a food strategy, which consists in the fact that all organisms that are available territorially and in size are used for food. Such food plasticity is one of the reasons for the wide expansion of this species outside the native range.

The Invasive Round Goby Neogobius melanostomus as a Potential Threat to Native Crayfish Populations.

Simple SummaryNeogobius melanostomus is a highly invasive fish that has colonized most major European rivers and is dispersing into their tributaries. Its foraging behaviour does not show particular prey preferences, which makes predicting its interactions with endangered members of the macrozoobenthic community in tributaries a challenge. We observed the interaction of N. melanostomus and crayfish juvenile or A. aquaticus in single- and multiple-prey systems to better predict its ecological impact. The results suggest an impact of N. melanostomus on crayfish similar to that on A. aquaticus, potentially making it a threat to crayfish population stability. Destabilization of a keystone species such as crayfish in river tributaries may lead to a trophic cascade in the ecosystem with irreversible consequences.Despite the spread of round goby Neogobius melanostomus into freshwater streams, there is a lack of information with respect to its effect on macroinvertebrate communities, especially crustaceans. We studied foraging efficiency of N. melanostomus on Procambarus virginalis and Asellus aquaticus, using a functional response (FR) approach. Stocking density of the prey species was manipulated to determine its effect on consumer utilization, with prey offered separately or combined at 1:1, 3:1, and 1:3 at each tested density. For both prey species, N. melanostomus exhibited type II FR, occasionally with a high proportion of non-consumptive mortality. Procambarus virginalis suffered a significantly higher attack rate compared to A. aquaticus. Neogobius melanostomus killed significantly more of the most prevalent prey, regardless of species. In trials with prey species of equal proportions, a difference in the number of each species killed was observed only at the highest density, at which P. virginalis was preferred. Neogobius melanostomus may be an important driver of population dynamics of prey species in the wild. The non-selective prey consumption makes N. melanostomus a potential threat to macrozoobenthic communities of river tributaries.

Personality‐dependent inter‐ and intraspecific foraging competition in the invasive round goby, Neogobius melanostomus

This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as "bold," fish that took more time to resume movement were categorized as "shy" and those that fell in between these two categories were determined to have "intermediate" boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Therefore, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus; nonetheless, results also show that competition is also governed by other mechanisms that require further study.

Differences in diet compositions and feeding strategies of invasive round goby Neogobius melanostomus and native black goby Gobius niger in the Western Baltic Sea

Differences in diet compositions and feeding strategies of invasive round goby Neogobius melanostomus and native black goby Gobius niger in the Western Baltic Sea

Alternative reproductive tactics are associated with sperm performance in invasive round goby from two different salinity environments.

During male–male competition, evolution can favor alternative reproductive tactics. This often results in a dominant morph that holds a resource, such as a nest for egg laying, which competes with a smaller sneaker morph that reproduces by stealing fertilizations. The salinity environment can influence male growth rates, for example, via osmoregulatory costs, which in turn may influence the use of sneaker tactics for small males competing for mating opportunities. Salinity can also affect sperm directly; however, little is known of how salinity influences sneaker tactics through sperm performance. We sampled males of the invasive round goby (Neogobius melanostomus) from two environments, a freshwater river and a brackish estuary. This fish has two male morphs: nest‐holding dark males and non‐nest‐holding light males. We examined the role of water salinity of 0, 8, and 16 on sperm performance and found that for estuarine males, a salinity of 0 reduced sperm velocity compared to a salinity of 8 and 16. Riverine males had low velocity in all salinities. Sperm viability also decreased by over 30% in 0 salinity, compared to 8 and 16, for fish from both environments. Gobies produce ejaculate contents in specialized glands that could in theory shield sperm in an adverse environment. However, gland contents did not improve sperm performance in our tests. Body mass and age estimates indicate that riverine males invested more in somatic growth compared to estuarine males. Estuarine light morph males had a high enough gonadosomatic index to indicate sneaker tactics. We propose that when sperm performance is low, such as for the riverine males, sneaker tactics are ineffective and will be selected against or phenotypically suppressed. Instead, we interpret the increased investment in somatic growth found in riverine males as a life‐history decision that is advantageous when defending a nest in the next reproductive season.

Increasing confidence for discerning species and population compositions from metabarcoding assays of environmental samples: case studies of fishes in the Laurentian Great Lakes and Wabash River

Community composition data are essential for conservation management, facilitating identification of rare native and invasive species, along with abundant ones. However, traditional capture-based morphological surveys require considerable taxonomic expertise, are time consuming and expensive, can kill rare taxa and damage habitats, and often are prone to false negatives. Alternatively, metabarcoding assays can be used to assess the genetic identity and compositions of entire communities from environmental samples, comprising a more sensitive, less damaging, and relatively time- and cost-efficient approach. However, there is a trade-off between the stringency of bioinformatic filtering needed to remove false positives and the potential for false negatives. The present investigation thus evaluated use of four mitochondrial (mt) DNA metabarcoding assays and a customized bioinformatic Bioinformatic pipeline to increase confidence in species identifications by removing false positives, while achieving high detection probability. Positive controls were used to calculate sequencing error, and results that fell below those cutoff values were removed, unless found with multiple assays. The performance of this approach was tested to discern and identify North American freshwater fishes using lab experiments (mock communities and aquarium experiments) and processing of a bulk ichthyoplankton sample. The method then was applied to field environmental (e) DNA water samples taken concomitant with electrofishing surveys and morphological identifications. This protocol detected 100% of species present in concomitant electrofishing surveys in the Wabash River and an additional 21 that were absent from traditional sampling. Using single 1 L water samples collected from just four locations, the metabarcoding assays discerned 73% of the total fish species that were discerned during four months of an extensive electrofishing river survey in the Maumee River, along with an additional nine species. In both rivers, total fish species diversity was best resolved when all four metabarcoding assays were used together, which identified 35 additional species missed by electrofishing. Ecological distinction and diversity levels among the fish communities also were better resolved with the metabarcoding assays than with morphological sampling and identifications, especially using all four assays together. At the population-level, metabarcoding analyses targeting the invasive round goby Neogobius melanostomus and the silver carp Hypophthalmichthys molitrix identified all population haplotype variants found using Sanger sequencing of morphologically sampled fish, along with additional intra-specific diversity, meriting further investigation. Overall findings demonstrated that the use of multiple metabarcoding assays and custom bioinformatics that filter potential error from true positive detections improves confidence in evaluating biodiversity.

Turning back the tide? Local‐scale impacts of climate change may have positive effects by restoring natural riverine habitat and reducing invasive fish density

Abstract Global biodiversity is increasingly threatened by habitat loss, climate change, and biological invasion. However, predictions of impacts on native fauna are hampered by an inadequate knowledge of how these factors interact and how climate change will affect the distribution, abundance, and behaviour of both native and invasive species, not least as most predictions are based on the long‐term effects of temperature alone. Here, we present a case study illustrating how local‐scale climate change impacts (increased temperature, reduced rainfall, shifts in peak rainfall) affected the hydrology of a channelised lowland European river (reduced flow, reduction in flood events, increased siltation, macrophyte growth), allowing native fish species to recolonise the bankside zone and reducing the density of invasive round goby Neogobius melanostomus by removing its preferred habitat. While most studies predict long‐term negative impacts on global fish populations, some suggest potential direct and indirect benefits at a local scale. We are of the opinion that, at a local scale, climate change impacts on fish will be more nuanced and complex than long‐term predictions suggest, resulting in both positive and negative effects, with consolation prizes in the face of larger losses. While impacts on fish will differ between regions and/or continents, depending on the specific impacts of climate change, identification of positive effects will be essential in clarifying long‐range forecasts and identifying management procedures for mitigating overall negative impacts.

Invasive round goby Neogobius melanostomus has sex-dependent locomotor activity and is under-represented in catches from passive fishing gear compared with seine catches.

The higher proportion of males of the invasive round goby Neogobius melanostomus in samples from two activity selective passive fishing gears compared with one activity non-selective fishing gear in three Dutch lakes is related to higher male locomotory activity and is a sex-dependent trait. This difference in activity reflects the different ecology of male and female N. melanostomus.

Seasonal feeding ecology of co-existing native and invasive benthic fish along a nearshore to offshore gradient in Lake Michigan

Relative abundance, diet composition and feeding strategy were determined for three benthic fish, the native deepwater sculpin Myoxocephalus thompsonii (Girard, 1851) and slimy sculpin Cottus cognatus (Richardson, 1836), and the invasive round goby Neogobius melanostomus (Pallas, 1814), along a nearshore to offshore gradient in southeastern Lake Michigan during March–December 2010, 2015, and 2016. Round goby were most abundant in the nearshore ( 75 m). Despite a large degree of spatial separation, some species did overlap, with slimy and deepwater sculpin occurring in sympatry throughout the year in the offshore and transitional zones, and round goby overlapping with both sculpin species seasonally in the transitional zone. Deepwater sculpin exhibited specialization on Mysis diluviana in all depth regions. Slimy sculpin in the offshore reduced diet overlap with deepwater sculpin by specializing on fish eggs during spring and fall, whereas in the transitional depth zone, there was considerable overlap between sculpin species due to the high importance of Mysis in diets. The invasive round goby had a mixed diet, with some diet overlap with native sculpin, especially slimy sculpin, in the transitional zone. In the nearshore zone, round goby displayed a generalized diet with many prey contributing to the diet, but the average contribution of any prey was generally low. Spatial separation and variable feeding strategies help reduce, but not eliminate shared resource use amongst these benthic fish in Lake Michigan.

Little association of biological trait values with environmental variables in invasive alien round goby (Neogobius melanostomus).

The relative importance of species‐specific biological trait characteristics and environmental factors in invasions of nonindigenous species remains controversial because both have mostly been studied independently. Thus, the main objective of this study was to examine the correlation of biological traits with environmental variation in the globally invasive round goby Neogobius melanostomus from the upper Danube River. Based on a sample of 653 specimens along a continuous 200 km river pathway, links between nine environmental factors (substrate‐type, six water measurements, and the communities of fishes and macroinvertebrates) and seven biological traits (nutritional and energetic status, trade‐offs of parasite resistance and resource allocation, and three growth proxies) were analyzed. Biological trait values of N. melanostomus hardly correlated with the environment, could not explain invasion progress and imply a general low overall importance for invasion success. Instead, alternative individual life‐history trajectories appear to determine invasion success. This is in line with up to 15% of all specimens having outlying biological trait values of potential adaptive value, suggesting a considerable importance of adaptive trait variation among single individuals for the whole invasion progress. This “individual trait utility hypothesis” gives an alternative explanation for success of invasive species by single individuals carrying particular traits, and it should be specifically targeted and analyzed at currently invaded sites.

Evidence for ontogenetically and morphologically distinct alternative reproductive tactics in the invasive Round Goby Neogobius melanostomus.

Alternative reproductive tactics are characterized by the occurrence of discrete alternative morphs that differ in behavioural, morphological and physiological traits within the same sex. Although much effort has been made to describe the behaviour, morphology and physiology of such alternative morphs, less effort has been invested investigating how much overlap there is in the characteristics of such morphs in natural populations. We studied random population samples of the invasive Round Goby Neogobius melanostomus from five different localities in the river Rhine system in the Netherlands. We found two morphologically and physiologically distinct male morphs which likely represent alternative reproductive tactics. Almost all mature males under 9.35 cm total length had a gonadosomatic index > 3%, suggestive of a sneaker tactic, while nearly all males above 9.35 cm has a gonadosomatic index of < 3%, suggestive of a parental tactic. Cheek size and eye diameter alone were sufficient to distinguish the two morphs. Gonads had a different relationship with size in the two morphs, indicating separate growth trajectories. The gonad mass of sneaker morphs would be ca. 7.5 times as high as the gonad mass of parental morphs of the same total length after extrapolation. Few (9%) intermediates were found, suggesting that the expression of alternative reproductive tactics is determined before the first breeding season. This contrasts with studies on other goby species, which show evidence of plastic tactics that can be affected by social circumstances. We conclude that it is possible to distinguish two alternative male morphs in the Dutch Round Goby population using morphological measurements alone. Although behavioural observations are needed to provide conclusive evidence, the difference in GSI between these morphs indicates that these morphs reflect alternative reproductive tactics.

Differential habitat use by the round goby (Neogobius melanostomus) and Dreissena spp. in coastal habitats of eastern Lake Michigan

Abstract Shoreline modifications in Lake Michigan drowned river mouth (DRM) lakes can indirectly create habitats for the invasive round goby ( Neogobius melanostomus ) and dreissenid mussels ( Dreissena spp.), possibly resulting in their proliferation. To test this hypothesis, we sampled round gobies and dreissenids in Lake Michigan nearshore waters at pierheads and at adjacent DRM lake habitats containing natural and hardened shoreline features. Dreissenids were sampled by SCUBA diving and collecting specimens by hand, while round gobies were sampled using overnight replicate baited minnow traps. Round goby overall catch per unit effort (CPUE, number/trap night) was significantly higher at pierheads compared to the two DRM lake habitats; however, there was no significant difference in CPUE between the natural and the hardened DRM lake habitats. Similarly, dreissenid density was significantly higher at pierheads compared to natural DRM habitats; however, there was no significant difference between the hardened and the natural DRM lake habitats. We did not find any differences in the mean size or age of round goby among habitats. Stomach content analysis showed that soft-bodied prey comprised a larger portion of the round goby diet at pierheads, suggesting that round goby show preference for soft-bodied prey. Our results suggest that the current level of shoreline modification at DRM lake habitats may not be sufficient to evoke a biological response akin to what we found at pierheads; however, given continued shoreline hardening, DRM lake habitats will likely facilitate the proliferation of these invasive species.

Dissolved ions mediate body mass gain and predatory response of an invasive fish

Ecological impacts of invasive species are mediated by the environmental characteristics of the invaded habitats. The invasive round goby Neogobius melanostomus is a brackish-water adapted invader with high predatory and competitive impacts on native communities. We test the hypothesis that both body mass gain and predation rates of the round goby are reduced in low-dissolved ion waters in which they can establish, using calcium (Ca2+) as a focal ion of great importance to the physiology of aquatic animals. Round gobies were first acclimated for 36 days on a diet of shrimp pellets in either high (35 mg L−1) or low (12 mg L−1) Ca2+ concentration [Ca]. We then assessed the functional response (FR)—the relationship between predation rate and prey supply—of the round goby from high and low [Ca] on amphipod prey in either condition. Round gobies in high [Ca] consumed more pellets during the acclimation period and gained more mass compared to fish in low-[Ca] conditions. Functional response experiments revealed that round gobies at high-[Ca] levels for both acclimation and FR experiments had the highest predatory impact, whereas fish in low-[Ca] FR treatments had similarly low predation rates regardless of acclimation [Ca]. In a second experiment, non-acclimated round gobies had a higher FR on mayfly nymph prey at high [Ca] than fish at low-[Ca] levels. Our results indicate that the round goby has stronger ecological impacts in conditions that are more physiologically optimal for the species. Identifying key physico-chemical factors that mediate impacts of invaders would help prioritize habitats for management attention.

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.

Isotope evidence for preferential dispersal of fast-spreading invasive gobies along man-made river bank structures

Invasive round goby Neogobius melanostomus and bighead goby Ponticola kessleri have successfully colonized freshwater and coastal habitats worldwide. The objective was to use stable isotope analyses to study the foraging and movement of both species at small spatial scales in the Upper Danube River, considering 861 samples from two different years, seasons and sides of the river in an area where limited mixing at a confluence occurs. A difference in δ13C of 1 ‰ between gobies from both river sides was observed in both species and reflected the isotope spacing in their dominant benthic prey Dikerogammarus villosus. These results suggest an absence of goby movement across the Danube River which was unexpected, given the fast spread of gobies at invasion fronts. It can be concluded that their dispersal is highly preferential with longitudinal movement likely being facilitated by artificial rip-rap structures along river banks, which provide shelter and food.