Round Goby Captured in a North American Estuary: Status and Implications in the Hudson River

Round Goby Neogobius melanostomus, a small benthic fish species native to Europe's Black and Caspian seas, was first documented in the Laurentian Great Lakes basin in 1990 (Jude et al. 1992). The species rapidly spread throughout the region, establishing populations in all five Great Lakes and eight U.S. states (USGS 2022a). In New York, populations from Lake Erie and Lake Ontario spread inland at least as early as 2001, with a confirmed capture in the Tonawanda Creek portion of Erie Canal (USGS 2022a). Over the next decade, Round Goby continued to spread east along the Erie Canal, establishing populations in the canal and connected lakes and waterbodies throughout central New York (Figure 1; Johnson et al. 2005a; Jackson et al. 2019; Andres et al. 2020).

In 2014, an angler captured a single Round Goby in the Erie Canal near Utica, New York, representing the first occurrence of Round Goby in the Mid-Atlantic drainage (USGS 2022a). In response to this interbasin expansion, the U.S. Geological Survey (USGS) and the Mohawk River Basin Program of the New York State Department of Environmental Conservation (NYSDEC) initiated a study to determine the distribution and rate of expansion of Round Goby in the Erie Canal and to identify the most effective methods to monitor the invasion front (George et al. 2021). Since 2016, the USGS annually monitors for Round Goby along the eastern portion of the Erie Canal to track the potential spread of Round Goby to the Hudson Valley and Lake Champlain basin. Environmental DNA and traditional fish sampling occurrs from the east end of Oneida Lake to the northern tidal portion of Hudson River approximately 0.5 km downstream of the Federal Dam at Troy, New York—a dam located on the Hudson River that separates the tidal portion of the Hudson River from the upper Hudson River and Lake Champlain basin. As of 2019, Round Goby collections occurred as far east as Utica (in the vicinity of 2014 angler collection). However, George et al. (2021) collected positive environmental DNA samples from numerous sites in the Erie Canal east of that location, including a weak detection in the Hudson River below the Federal Dam that was not reproduced in subsequent surveys. More recently, the USGS captured a single Round Goby with a backpack electrofisher in June 2020 at Frankfort, New York, and on 8 November 2020, an angler captured a Round Goby in Crescent, New York, approximately 150 km east of Utica and approximately 7 km from the confluence with the upper Hudson River (Figure 1).

Within the tidal portion of the Hudson River, the NYSDEC annually monitors diadromous fish populations since the early 1980s (Figure 2). Although monitoring efforts specifically target select species, the Department also collects information for nontarget species. On 13 July 2021, the NYSDEC collected three Round Goby (New York State Museum, catalog no. 88067) in the tidal portion of the Hudson River near Albany, New York, during NYSDEC routine fish monitoring (USGS 2022a). Over the subsequent summer and fall, personnel collected additional specimens between Albany and Poughkeepsie, New York, confirming the presence of a Round Goby population. These collections represent the first known specimens of Round Goby in the tidal Hudson River. The establishment of Round Goby in tidal Hudson River habitats is significant because Round Goby is found only in one other North American estuary—the St. Lawrence River—and very little information is known or documented about the status, distribution, or ecological niche of Round Goby in the lower tidal portion of the St. Lawrence River. Herein, we document the eastward and southern expansion of Round Goby to the Hudson River. We first provide details of the characteristics of the nascent population and then subsequently discuss the potential ecological implications of establishment of Round Goby in the Hudson River. We also outline priorities for research and monitoring that resource managers, policy makers, and other stakeholders may use when assessing the population in the future.

The tidal portion of the Hudson River extends 246 km north from the Battery, New York, to the Federal Dam at Troy, New York (Figure 1). The Federal Dam is the head of tide for the Hudson River and the associated Federal Lock and spillway does not prevent the upstream or downstream passage of most fishes. Above the Federal Dam, the upper Hudson River continues north for approximately 8 km where it reaches the confluence of the New York State Canal System, a network of canals, locks, and dams that connects many of the major waters in the state. This confluence is the eastern terminus of the Erie Canal where it branches west extending 584 km to Lake Erie and the southern terminus of the Champlain Canal where it continues north extending 97 km to Lake Champlain.

The NYSDEC annually conducts two long-term beach seine surveys within the tidal portion of the Hudson River (river kilometer [rkm] 35–225) to monitor the relative abundance of young-of-year alosine species (i.e., American Shad Alosa sapidissima, Alewife Alosa pseudoharengus, Blueback Herring Alosa aestivalis) and Striped Bass Morone saxatilis. The alosine beach seine survey (1989–present) occurs at 28 fixed sites among four regions (Figure 2; Albany, Coxsackie, Poughkeepsie, and Newburgh). Daytime sampling occurs biweekly from the end of June through October by using a center-located 30.5-m bag seine (0.64-cm bar mesh) with 12.2 × 3.05 m wings. In each region, sampling occurs in a single day within a given week. The Striped Bass beach seine survey (1985–present) occurs at 13 fixed sites among two regions (Figure 2; Haverstraw and Tappan Zee). Daytime sampling occurs biweekly on the alternate week of the alosine beach seine survey from mid-July through early November by using an off-center 61-m (200-ft) seine (0.64-cm bar mesh) with one wing measured at 45.7 × 3.05 m, a second smaller wing at 9.1 × 3.05 m, and a bunt measuring 6.1 × 3.7 m. Sampling at Haverstraw and Tappan Zee occur in a single day within a given week. For both surveys, the net deployment is from a vessel with one end of the net held on shore; the remainder of the net is paid out in a semicircular path toward the shore and pulled in by hand. Personnel identified and enumerated all fishes to species and measured a subset for total length (TL). Only two other Gobiidae species inhabit the Hudson River (i.e., Naked Goby Gobiosoma bosc and Seaboard Goby Gobiosoma ginsburgi), both of which are predominantly scaleless and primarily distributed in the lower brackish section of the river. Therefore, it is easy to identify Round Goby from other Gobiidae species and other fish species based on distinguishing characteristics including the presence of scales, the presence of fused pelvic fins, and a black spot at the posterior base of the dorsal fin. Personnel measured all Round Goby collected in 2021 for TL and sexed a subset (n = 38) externally by visual examination of the urogenital papilla (Kornis et al. 2012) and internally by visual examination of gonadal tissue. Ichthyologists at the New York State Museum, Albany, also confirmed and archived several of the initial collections to species (catalog no. 88067 and 88068).

Alosine and Striped Bass beach seine survey sampling began on 28 June 2021 and 22 July 2021 and concluded on 22 October 2021 and 9 November 2021, respectively. In total, we collected 112 Round Goby at sites from the three northern regions (Albany, n = 92; Coxsackie, n = 3; Poughkeepsie, n = 17) ranging from rkm 116 to 225 (Table 1; Table S1, Supplemental Material). The downstream-most capture of Round Goby in the Poughkeepsie region occurred 22 August 2021, approximately 140 km downstream of the previous known capture at Crescent (Figure 3). We collected the majority of individuals in the Albany region where the relative abundance also increased throughout the sampling season (Figure 4; Table 1). In the Coxsackie and Poughkeepsie regions, the relative abundance of Round Goby was lower and generally remained constant over time. We did not collect Round Goby in the Newburgh, Haverstraw, or Tappan Zee regions. The size of individuals captured ranged from 20 to 87 mm TL, with a mean TL of 48 mm (Figure 5; Table 1; Table S2, Supplemental Material). We observed no difference in TL between Round Goby from Albany and Poughkeepsie (Mann–Whitney–Wilcoxon = 923, P = 0.24; the Coxsackie sample size [n = 3] was too small to include in comparison). Among the subset of sexed individuals, 20 were males and 18 were females, 5 of which were gravid.

The collection of Round Goby in the tidal portion of the Hudson River in 2021 documents the continued eastward expansion of Round Goby along the Erie Canal (George et al. 2021). This expansion raises concerns among resource managers, policy makers, and other stakeholders regarding potential ecological, recreational, and economic impacts to invaded ecosystems from this adaptable introduced species. The introduction of Round Goby in the tidal Hudson River will likely result in several novel ecological interactions among iconic migratory and marine species (e.g., Striped Bass, American Eel Anguilla rostrata, American Shad, Atlantic Sturgeon Acipenser oxyrhynchus, Shortnose Sturgeon Acipenser brevirostrum, Blueback Herring, Alewife, Blue Crab Callinectes sapidus) that are largely undocumented elsewhere in North America. However, current understanding of the scope for Round Goby impacts within the Hudson River and surrounding waterbodies remains uncertain due to a lack of knowledge about this species' ecological niche in newly introduced estuarine habitats and its ability to spread through connected waterways to upstream systems or seaward to marine locations.

The consistent, widespread presence of Round Goby among the Albany, Coxsackie, and Poughkeepsie regions and the increasing trend in relative abundance in the Albany region indicate the likely establishment of a population in the Hudson River. The ability of Round Goby to spawn multiple times per year and its rapid population growth potential suggest Round Goby may continue to increase in abundance over time as observed in much of its introduced range. For example, Johnson et al. (2005a) estimated that the population of Round Goby in western Lake Erie reached 9.9 billion by 2002 after being first detected in the early 1990s. Similarly, Round Goby became the most abundant benthic fish in Oneida Lake within 2 y after its initial detection (Jackson et al. 2019). In river systems, there is also documentation of a quick increase in relative abundance of Round Goby. In previously unoccupied areas adjacent to a core, established population, relative abundance doubled and more than quadrupled within a single summer (Brownscombe and Fox 2012). By contrast, other research showed no establishment of large populations of Round Goby in a similar canal-facilitated (i.e., Chicago Area Waterway System) interbasin range expansion from Lake Michigan to the Illinois River, with the relative abundance of Round Goby remaining low over time (Irons et al. 2006; Merry et al. 2018). The expansion and population increase of Round Goby along the St. Lawrence River, the only other known North American estuary with an established population of Round Goby, may forecast anticipated trends in the Hudson River (Morissette et al. 2018). However, limited information is available on the distribution and abundance of Round Goby in the lower tidal portion of the St. Lawrence River (O. Morissette, Ministère des Forêts, de la Faune et des Parcs, personal communication). Because estuarine river environments in North America remain novel habitat for Round Goby, continuing to surveil and monitor the trajectory of the Hudson River population represents a potential priority for understanding how this species may fare in tidal rivers, estuaries, and nearshore coastal habitats.

The distance (∼140 km) between Crescent and the southernmost NYSDEC collections in Poughkeepsie may represent rapid movement and recent colonization of Round Goby in the Hudson River. Research documents a similar large-scale movement (193 km) in a single year along the invasion front of the Illinois River, and larval drift may be an important factor contributing to the apparent rapid spread of Round Goby (Irons et al. 2006; Merry et al. 2018). Batch spawning and a protracted spawning season can allow larval and juvenile Round Goby to drift for months, increasing the probability of early life stages encountering favorable conditions for recruitment (Janáč et al. 2013; Borcherding et al. 2016). USGS (2022b) measured several large discharge events at the Federal Dam from mid-July through October 2021, perhaps facilitating the spread of Round Goby from source populations in the Erie Canal. Length-at-age relationships developed for several Great Lake populations indicate the average length of age 0 ranges from 49 to 55 mm, age 1 ranges from 40 to 76 mm, and age 2 ranges from 61 to 104 mm (Kornis et al. 2012). Thus, the smaller individuals captured in this study may represent drift from the Erie Canal and indicate that Round Goby only recently colonized the Hudson River estuary in 2021.

Conversely, rapid and long-distance movement of Round Goby may be less likely, given their benthic nature and small home ranges (Kornis et al. 2012). Although dispersal rates are difficult to quantify, estimates suggest that North American populations of Round Goby disperse between less than 1 and 30 km within a year (Bergstrom et al. 2008; Brownscombe and Fox 2012; Merry et al. 2018), yet movement of telemetered individuals indicated maximum dispersal rates of approximately 20 m/d (Bergman et al. 2022). Based on the distance (∼140 km) between Crescent and Poughkeepsie, positive environmental DNA samples below the Federal Dam in summer 2017 (George et al. 2021), and the presence of gravid females and larger individuals (maximum 87 mm TL; presumably age 1 or age 2), Round Goby may have been present in the Hudson River earlier than indicated by the current collection records. This would be consistent with other studies where fish movement occurs in pulses and longer distance movements are often not detected (Gowan et al. 1994; Kornis et al. 2012). Thus, it is possible the smaller specimens collected in 2021 could represent offspring from a previously undetected reproductively mature population in the Hudson River. Furthermore, the similar size distribution observed between Albany and Poughkeepsie does not suggest recent colonization as observed in other systems where larger individuals are often the first to colonize a new location (Brandner et al. 2018). The NYSDEC extracted otoliths from a subset of individuals; therefore, potential future microchemistry analysis and corresponding age estimates may be able to differentiate whether the collected specimens in 2021 inhabited the Erie Canal before migrating to the Hudson River or originated in the Hudson River, similar to work conducted by Limburg et al. (2001) for Blueback Herring.

Round Goby are known to compete with other small benthic fishes (e.g., sculpins and darters) for food and spawning habitat, and their diet can include eggs of native species (Lutz et al. 2020) and popular sportfish (e.g., Smallmouth Bass Micropterus dolomieu, Walleye Sander vitreus; Kornis et al. 2012) and Lake Sturgeon Acipenser fulvescens (Nichols et al. 2003). Early life stages of endangered Shortnose Sturgeon and Atlantic Sturgeon may be particularly vulnerable to predation because eggs and larvae are demersal and occur in rocky substrates (Hilton et al. 2016; Kynard et al. 2016), the preferred habitat of Round Goby (Kornis et al. 2012). Round Goby also consume dreissenid mussels, which are ubiquitous in the Hudson River, and their consumption could create new energy and nutrient pathways that have the potential to alter ecosystem dynamics (Johnson et al. 2005b). Round Goby may also become a dominate prey source for piscivorous species (Crane and Einhouse 2016; Luo et al. 2019), yet they could also cycle contaminants or botulism (Ruffing 2004; Hannett et al. 2011; Kornis et al. 2012) and may have the potential to introduce viral hemorrhagic septicemia (Farrell et al. 2017; Getchell et al. 2019). Thus, the uncertainty about the food web impacts of Round Goby within the Hudson River or other North American estuaries emphasizes a need to characterize trophic interactions associated with this introduced fish, such as through diet studies, isotope analyses, and foraging behavior analyses. Emerging molecular methods for analyzing diets are increasingly effective for soft-bodied or quickly digestible prey items (Carreon-Martinez et al. 2011; Ley et al. 2014) as demonstrated with Round Goby (Lutz et al. 2020) and for quantifying predation of early life stages of imperiled sturgeon species (Waraniak et al. 2019; Bunch et al. 2021).

The Round Goby captures in the Poughkeepsie region during 2021 indicate that the species is nearing or already reached brackish water in the Hudson River, opening another novel area for future research in this system and North America. In the lower St. Lawrence River, Round Goby is abundant near Québec City, Québec, Canada, but abundance decreases downstream toward the salt front and the species is nearly absent in mesohaline waters of the estuary. O. Morissette (personal communication) noted collection of a few specimens at salinities up to approximately 20 ppt, yet these captures appear to be a rare occurrence. Depending on freshwater flow and time of year, the Hudson River typically becomes brackish downstream of Poughkeepsie (Wells and Young 1992; Geyer and Chant 2006) and salinity typically averages less than 20 ppt throughout most of the lower river (rkm 35–109; Ralston et al. 2008). In their native range, Round Goby can tolerate oceanic salinity (NaCl) of less than 30 ppt (Kornis et al. 2012); thus, Round Goby could likely establish throughout most of the tidal Hudson River. Their ability to spread beyond the Hudson River to marine and coastal waters (e.g., New York Harbor and Long Island Sound) remains uncertain. Recent salinity trials using Round Goby obtained from a brackish population demonstrated individuals acclimated to moderate and high salinities (10 and 30 ppt) and exhibited limited stress response compared with higher stress response when exposed to a low salinity (0 ppt) environment (Puntila-Dodd et al. 2021). This suggests Round Goby exhibit phenotypic plasticity in salinity tolerance based on genetic origin and acclimatization to local conditions. Genetic analyses of Great Lakes populations indicate high genetic diversity and euryhaline-tolerant genotypes similar to Eurasian populations (Brown and Stepien 2009); therefore, Round Goby from the Hudson River may be tolerant to salinity. Moving forward, improved characterization of the adaptative capacity of Round Goby to acclimate to brackish and marine waters will be a priority for assessing the geographic scope for further range expansion to coastal systems along the northeast seaboard.

Within freshwater, Round Goby has the potential to spread among tributaries throughout the tidal Hudson River watershed (∼13,778 km²), which may further facilitate spawning and recruitment as observed in Great Lake tributaries (Blair et al. 2019, and references therein). Round Goby may also continue to use the New York State Canal System by traversing north through the Champlain Canal into Lake Champlain and parts of its 21,326-km² watershed spanning New York, Vermont, and Québec. Currently, there have been no captures of Round Goby in Lake Champlain or in the Champlain Canal. The potential and rate of upstream movement toward Lake Champlain remain uncertain. The USGS (2022a) documented the ability of Round Goby to traverse upstream through locks and around dams by its movement through the two downstream-most locks on the Fox River in Wisconsin and in the central portion of the Rideau Canal, Ontario, Canada (Bergman et al. 2022).

Understanding how populations and communities respond to the presence of nonnative species continues to challenge researchers and managers, despite the accelerating number of introductions (Ricciardi and MacIssac 2011; Strayer 2012). Long-term monitoring data that document the introduction, establishment, spread, and impact of nonnative species are rare (Strayer 2012), yet when available, these data provide critical information to better understand how ecosystems respond throughout the invasion process (e.g., Mihuc et al. 2012; Solomon et al. 2016; DeBoer et al. 2018). Long-term data sets from the Hudson River already demonstrate the benefits of systematic monitoring programs to understand the impacts of nonnative species such as dreissenid mussels (Strayer and Malcom 2007; Strayer et al. 2014). The continued collection of data by NYSDEC and other organizations will be useful to monitor the possible spread and potential impacts of Round Goby on fish populations in the Hudson River, yet their establishment provides another example of the spread of nonnative aquatic species between historically separated watersheds (Mills et al. 1996; Pimentel 2005). Numerous management options to prevent the spread of nonnative aquatic species (e.g., physical and nonphysical barriers, harvest, removals) have been identified and implemented in other basins connected through canal systems (Macnamara et al. 2016; Parker et al. 2016). Consideration of these options with other socioeconomic analyses when developing policy decisions can help prevent future introductions and improve ecosystem resiliency while also supporting economic and recreational opportunities in canal waterways. Continued financial commitments for ecosystem monitoring can further our understanding of ongoing invasion processes while also assessing the status and dynamics of managed systems under accelerating environmental and anthropogenic change (Gibson-Reinemer et al. 2017; Counihan et al. 2018).

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Table S1. Site-specific information and the number of Round Goby Neogobius melanostomus collected in 2021 at each site among regions in the tidal portion of the Hudson River, New York.

Available: https://doi.org/10.3996/JFWM-22-012.S1 (41 KB XLSX)

Table S2. Individual total length (mm) and sex of Round Goby Neogobius melanostomus collected in 2021 among regions in the tidal portion of the Hudson River, New York.

Available: https://doi.org/10.3996/JFWM-22-012.S2 (21 KB XLSX)

Reference S1. Jackson JR, VanDeValk AJ, Brooking TE, Holeck KT, Hotaling C, Rudstam LG. 2019. The fisheries and limnology of Oneida Lake 2018. Bridgeport: New York Federal Aid in Sport Fish Restoration, Job 2-2, Study 2, F-63-R.

Available: https://doi.org/10.3996/JFWM-22-012.S3 (2.589 MB PDF)

We thank Hayley Brown, William Eakin, Maura Grassi, Kelsey Gustafson, Emilie Hickox, Amanda Higgs, Sarah LaLumiere, Zoraida Maloney, Thomas Patwell, and Amanda Simmonds for their fieldwork and data collection. We also thank Associate Editor and editorial staff of the Journal, two anonymous reviewers, and David Kazyak for comments that improved an earlier version of this manuscript. This study was a partnership project between the NYSDEC and Cornell University, with funding from the Environmental Protection Fund through the Hudson River Estuary Program and the Ocean and Great Lakes Program. Any use of trade, product, website, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the New York state government.

Any use of trade, product, website, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.