Status of Round Goby Invasion Fronts in New York and Quebec: Implications for Lake Champlain

This study documents the 2021–2025 monitoring of advancing round goby populations in New York and Quebec via the Hudson/Champlain Canal and Saint Lawrence/Richelieu River approaches to Lake Champlain, utilizing eDNA and traditional sampling to map their proximity to the lake, assess temperature-driven habitat use, and detect viral hemorrhagic septicemia virus to inform invasive species management strategies.

The Gist

Imagine Lake Champlain as a massive, pristine fortress protecting a unique ecosystem. For decades, this fortress has been under siege from an invasive "army" of small, tough fish called Round Gobies. These fish are like biological bulldozers: they eat the eggs of native fish, displace local species, and carry a dangerous virus (VHSV) that can wipe out entire populations.

This paper is the report card from a massive, international "watchtower" operation. Teams from the U.S. and Canada spent five years (2021–2025) tracking the front lines of this invasion as the gobies marched toward the fortress from two directions: the South (via the Champlain Canal) and the North (via the Richelieu River).

Here is the story of what they found, explained simply.

1. The Two Fronts of the Battle

Think of the invasion as a pincer movement, squeezing the fortress from both sides.

• The Southern Front (Champlain Canal): The gobies came up from the Great Lakes, through the Hudson River, and into a man-made canal system full of locks and dams. It's like a staircase of water. The fish were trying to climb the stairs to get to the lake.
• The Northern Front (Richelieu River): The gobies came down from the Saint Lawrence River, flowing north toward Lake Champlain. This is a natural river with a few big dams acting as speed bumps.

2. The Detective Tools: "Fishing" vs. "Sniffing"

The researchers used two different ways to find the fish, and the results were a bit like a detective story with conflicting clues.

• Physical Capture (The Net): This is like sending a fishing boat out to actually catch a fish. If you pull up a net and catch a goby, you know for sure it's there.
• eDNA (The Scent Trail): This is like a bloodhound. Fish leave tiny bits of DNA in the water (skin cells, poop, mucus). Scientists take a water sample, filter it, and look for the fish's "fingerprint." This method is super sensitive; it can smell a fish even if you can't see it.

The Conflict:

• In the South (Canal): The "nets" only caught fish near the bottom of the stairs (Lock C1). But the "bloodhounds" (eDNA) smelled the fish much higher up the stairs, near Lock C2.
• In the North (River): The "nets" only caught fish far away from the lake (82 km out). But the "bloodhounds" smelled them right at the border, just 4 km from the lake!

What does this mean? The fish might be closer to the fortress than the nets can see. The "scent" (DNA) travels faster and further than the fish themselves, or the nets are just missing the fish because they are hiding in deep water or moving at night. The scientists are saying, "We can't see them yet, but we can smell them, so we need to be very careful."

3. The Temperature Trap

The researchers discovered a weird quirk about the Round Goby's behavior in the canal.

• The Rule: When the water gets cold (below 10°C or 50°F), the gobies seem to vanish from the shallow, easy-to-catch areas. They likely dive deep into the warm, dark mud to hibernate, like bears in a cave.
• The Twist: In late 2025, the researchers caught a huge number of gobies even when the water was freezing (near 0°C). This suggests the fish might be getting tougher or changing their habits, which is bad news for the managers trying to stop them.

4. The Virus Question (VHSV)

There was a major fear that these gobies were carrying the Viral Hemorrhagic Septicemia (VHSV) virus—a deadly disease that causes fish to bleed internally.

• The Result: The scientists tested hundreds of gobies. In the North, zero had the virus. In the South, they found one positive fish and a couple of "maybe" results.
• The Verdict: It's too early to say for sure if the invasion front is carrying the virus. It's like checking a crowd for a cold; just because you haven't found a sick person yet doesn't mean the virus isn't in the crowd. They need to keep testing.

5. The "Traffic Cop" Strategy (Management)

Because the scientists found these clues early, they didn't just sit around waiting. They used the data to change how the canal works.

• The Locks as Gates: The Champlain Canal has locks that act like giant water elevators. The fish can swim through them.
• The New Plan:
  • Wait for the Cold: Since the fish hide in deep water when it's cold, the managers decided to keep the heavy gates on the locks closed longer in the winter. They only open them when the water is really cold (below 4.4°C), hoping the fish are too deep to swim through.
  • The "Flush" Button: When boats go through the locks, the water is flushed out. They increased this flushing to try and wash away any fish or eggs trying to sneak through.
  • Speed Limits: They limited how many boats could go through the locks per day to reduce the chance of fish hitching a ride on a boat propeller.

The Bottom Line

The Round Goby is a relentless invader, and it is getting very close to Lake Champlain. The "nets" say they are a few miles away, but the "scent" says they might be right at the door.

The good news is that the U.S. and Canada are working together like a well-oiled machine. By using high-tech DNA sniffing and smart water management, they are building a "digital and physical wall" to keep the fortress safe. They are watching the front lines closely, ready to slam the gates shut the moment the fish get any closer.

Technical Summary

1. Problem Statement

The invasive Round Goby (Neogobius melanostomus) has rapidly expanded eastward from the Great Lakes over the past two decades, threatening Lake Champlain, a critical ecosystem supporting endangered species (e.g., lake trout, copper redhorse) and a significant tourism economy.

• Threats: Round goby displace native benthic fish, prey on gamefish eggs, and act as a primary reservoir for Viral Hemorrhagic Septicemia Virus (VHSV), which causes fish kills.
• Invasion Routes: The species is approaching Lake Champlain via two primary corridors:
  1. Southern Approach: Upstream through the Hudson River and the Champlain Canal (NY, USA).
  2. Northern Approach: Downstream through the Richelieu River (Quebec, Canada), which flows out of Lake Champlain.
• Management Gap: There was a lack of fine-scale spatial and temporal data regarding the exact location of the invasion front, the presence of VHSV in these populations, and the effectiveness of physical barriers (dams/locks) in halting upstream movement.

2. Methodology

The study (2021–2025) was a multi-agency international collaboration involving USGS, NYSDEC, Parks Canada, MELCCFP, and others. It utilized a dual-method approach: Environmental DNA (eDNA) and Physical Capture.

Study Areas & Sampling Regimes

• Champlain Canal (Southern Approach):
  • Scope: 60 km section between Waterford and Fort Edward, NY, containing seven locks/dams (C1–C7).
  • eDNA: Collected by USGS (7 fixed sites, 4x/year) and NYSDEC (3–9 sites/month). Analyzed via qPCR using the ReesCOI marker.
  • Physical Capture: Backpack electrofishing (near-shore, wadeable) and benthic trawling (channel/shoulders) conducted twice annually.
  • VHSV Testing: Collected annually (May/June) from the Mohawk/Hudson confluence; tested via qRT-PCR on brain and composite organ tissues.
• Richelieu River (Northern Approach):
  • Scope: 124 km river from the Saint Lawrence River to Lake Champlain, featuring the Saint-Ours and Chambly dams.
  • eDNA: Collected by MELCCFP (upstream of Saint-Ours) and Parks Canada (Chambly Canal). Analyzed via a new, specific qPCR assay.
  • Physical Capture: Beach seining (standardized 120 m² area) targeting young-of-the-year copper redhorse and targeted surveys upstream of Saint-Ours Dam.
  • VHSV Testing: Collected May 2024 at the Saint Lawrence confluence; tested via qRT-PCR on composite tissues.

Data Analysis

• eDNA: Positive if ≥1 qPCR replicate amplified (Cq ≤ 40 for Champlain; ≤ 50 for Richelieu).
• VHSV: Classified as Positive, Inconclusive, or Non-detection based on amplification curves and reproducibility.
• Environmental Variables: Water temperature was correlated with electrofishing catch rates.

3. Key Results

Distribution and Invasion Front

• Champlain Canal:
  • Physical Capture: Goby captured as far north as the downstream side of the C1 Dam (97 km from Lake Champlain). No physical captures occurred upstream of C1.
  • eDNA: Positive detections occurred as far north as the upstream side of the C2 Dam (90 km from Lake Champlain).
  • Discrepancy: eDNA detected the species 7 km further upstream than physical captures, suggesting the invasion front is closer to the lake than capture data alone indicates.
• Richelieu River:
  • Physical Capture: First upstream capture occurred in Saint-Marc-sur-Richelieu (82 km from Lake Champlain) in 2025.
  • eDNA: Positive detections occurred near the Canadian-US border (4 km from Lake Champlain) in 2021 and 2025.
  • Discrepancy: eDNA detected the species ~78 km further upstream than physical captures. No goby were found in Lake Champlain proper during the study period.

VHSV Status

• Champlain Canal: Of 250 specimens tested, 1 brain sample was positive, 2 were inconclusive, and the rest were non-detections.
• Richelieu River: All 170 specimens tested were non-detections.
• Conclusion: Current data are insufficient to confirm if the invasion fronts are actively carrying VHSV, though the presence of the virus cannot be ruled out due to low prevalence during dormant periods.

Ecological Drivers

• Temperature Influence: In the Champlain Canal, catch rates in near-shore habitats dropped significantly when water temperatures fell below 10°C.
  • Exception: In late 2025, large catches occurred at temperatures as low as 0.1°C, suggesting the species may be adapting or that other factors (e.g., flow, habitat structure) influence winter behavior.
• Barriers: The C1 Dam (Champlain Canal) and Saint-Ours Dam (Richelieu) have effectively slowed physical expansion, though eDNA suggests some upstream movement or DNA transport may be occurring.

4. Key Contributions

• Methodological Integration: Demonstrated the critical value of combining eDNA (high sensitivity, early detection) with physical capture (confirmation of population establishment) to map invasion fronts accurately.
• Barrier Efficacy: Provided empirical data on how navigation infrastructure (locks/dams) impacts upstream expansion rates. The C1 Dam's winter gate removal was identified as a potential (but currently unconfirmed) pathway for upstream movement.
• Management Feedback Loop: The study directly informed a Trigger Action Response Plan (TARP) for the Champlain Canal.
  • Operational Change: Tainter gates at C1 are now kept in place longer (until water < 4.4°C for 24 hours) to prevent winter upstream passage.
  • Traffic Control: Following eDNA positives upstream of C2, lock traffic was restricted (max 3/day), and double-flushing protocols were expanded to Locks C3 and C4.

5. Significance

• Early Warning System: The study validates eDNA as a superior tool for detecting the leading edge of an invasion before a population is dense enough to be captured physically.
• Ecosystem Protection: By identifying the proximity of the invasion front to Lake Champlain, managers can implement adaptive measures to protect high-value species like lake trout and copper redhorse from predation and disease.
• Scalability: The findings regarding temperature-driven habitat shifts and the efficacy of dam operations as a management tool offer a template for managing round goby and other invasive species in dammed river systems across North America and Europe.
• Policy Impact: The research directly led to immediate, actionable changes in infrastructure operations and regulatory enforcement, demonstrating the feasibility of rapid response to invasive species threats.