Gather ‘round anglers and residents of the Great Lakes watershed, as we dive into the fishy world of the invasive round goby. This small fish has caught the attention of fisheries managers and the public alike by outcompeting native species and rapidly reproducing throughout North American waters. These aggressive fish are making waves in the Great Lakes as they spread more rapidly than any other invasive fish has.
Due to their tendency to concentrate in nearshore and rocky habitats, round gobies are proving to be elusive targets for traditional fisheries survey equipment, leaving fisheries managers, researchers, and environmental stewards working to come up with innovative techniques for monitoring and managing their populations. But before we discuss these techniques, let’s get better acquainted with the round goby (Neogobius melanostomus).
Hailing from the distant waters of Eurasia, the round goby is native to the Black Sea and Caspian Sea. These intrepid travelers made an unexpected debut in the St. Clair River in the 1990s and within a mere decade, managed to conquer all five Great Lakes and stake their claim in inland waters across southern Ontario. It is believed that these sneaky stowaways hitched a ride in the ballast water of transglobal freighter ships.
Fully grown, these bottom-dwelling fish measure 6-16 cm in length, have a cylindrical body, and a rounded to blunt snout. Young gobies sport a slate grey colour while adult gobies flaunt a fashionable blotched black and olive colour, accessorized with a distinct black spot on their dorsal fin. They have a fused pelvic fin, a trait that helps distinguish them from native sculpin species that have two separate pelvic fins.
Round gobies prefer lake and river habitats less than 60 m deep featuring sand, rock, and/or gravel substrate. They are fueled by a diet of small aquatic organisms, including the eggs and young of native fish species, as well as the infamous zebra and quagga mussels (invasive species also from Eurasia). With an average lifespan of up to four years, and the ability to spawn every 20 days during their spawning season (April-September), it is no wonder these fish are so prolific throughout the Great Lakes.
But why do we consider these fish to be invaders and not just newcomers? It’s because of the significant negative impacts they have had on the aquatic ecosystem and the economy of the Great Lakes region.
- Consumption of native fish species. Round gobies feed voraciously on the eggs and fry of native fish species. With each gobble, they contribute to the decline of native fish populations, altering the delicate balance of the aquatic ecosystem.
- Competing for food resources. In addition to their predatory habits, round gobies compete for food with native bottom-dwelling species such as sculpin and logperch. This competition exacerbates the strain on native populations already struggling with stressors like warming waters and shoreline development.
- Transfer of toxins up the food chain. A major component of the round goby diet is zebra and quagga mussels, they can eat up to 78 mussels per day! These mussels can carry a toxin that causes Type E botulism. The toxin does not affect the mussels but is absorbed and passed up the food chain in a process called biomagnification. When larger fish and birds like gulls, loons, and cormorants feast on gobies that have consumed toxin-carrying mussels, the disease gets passed on to the predator, potentially resulting in death.
- Economic impacts. Recreational fishing in the Great Lakes is big business. Gobies competing for the same food resources and preying on the eggs and young of sportfish can have real-world impacts on the recreational fisheries that many local businesses rely on. For example, since 2004 the state of Ohio has closed the smallmouth bass fishery in Lake Erie during the months of May and June, months that previously accounted for 50% of the total smallmouth bass catch in Lake Erie. When male bass were removed from their nests by anglers, gobies were found to be consuming up to 4,000 bass eggs in just 15 minutes! By closing the fishery to anglers, male bass can defend their nests against hungry gobies, but not without an economic hit to local businesses.
Despite its status as an invasive species, the round goby has solidified its spot in the Great Lakes food web. Not only do gobies feed on invasive mussels, fish eggs, and fry, they are now a prey item for native predator species including walleye, yellow perch, smallmouth bass, lake trout, and lake whitefish.
Getting a Handle on Population Size & Distribution
To help quantify the round goby’s influence on the ecosystem and local economies, it is important to monitor and gather information on their range and population size. However, they are not easily captured using traditional survey designs. Their agility and small size allows them to avoid or easily escape traps, and they occupy water depths and habitats that pose challenges for research vessels and gear. As a result, innovative techniques are being tested to address some of these issues.
UGLMU Electrofishing Pilot
The Upper Great Lakes Management Unit of the Ontario Ministry of Natural Resources and Forestry ran a pilot project in 2021 to test out a new method of assessing round goby populations. This method involved pairing a deep water electrofishing unit with a high-resolution GoPro video camera to identify and count round gobies in the Owen Sound area of Georgian Bay.
The electrofisher lightly shocks the surrounding area which causes the gobies to move, making them easier to see in the video. Starting at a depth of 1 m, each sample is collected by shocking the area for 10 seconds. The paired devices are then moved perpendicular to a depth of 2 m and the process is repeated. The process continues, adding 1 m of depth, to a maximum depth of either 30 m or 50 m. Over 10 days and nights of sampling, more than 1,000 samples were collected across 34 transects (24 day, 10 night).
Approximately 1,500 round gobies were captured in this footage and were mainly concentrated at depths of 5-20 m. The researchers were able to gather information about the round goby’s geographical distribution, habitat, and feeding preferences. Furthermore, they were able to estimate a population of 118 million round gobies (144 tonnes biomass) in the Owen Sound area during day surveys and 144 million (237 tonnes biomass) during night surveys.
Overall, the researchers found this technique to be an effective method for nearshore round goby population assessment in Lake Huron. Future research using this method should further consider the advantages of night time sampling, determine the minimum sample size, focus on depths of up to 30 m during the summer, and examine how broad-scale monitoring can be utilized to answer questions about round gobies.
USGS GobyBot
In 2022, the United States Geological Survey (USGS) Great Lakes Science Center developed a new method for round goby assessment. An autonomous underwater vehicle (AUV) outfitted with cameras shoots high-resolution video and images to identify and collect information about fish found on the lake bottom. The AUV is affectionately known as the “GobyBot”.
In the summer of 2022, the GobyBot cruised 300 km through the waters of Lake Huron to collect 55,479 usable images for goby research. From this imagery, 42,496 individual round gobies were identified, providing profound insights on the species in the Great Lakes. This data includes information about round goby length, size, habitat, substrate preferences, and varying depth and regional population sizes. This information was used further to calculate biomass densities in relation to region, substrate type, and depth. The photos below demonstrate how gobies are identified and counted using the GobyBot imagery.
The USGS Great Lakes Science Center is planning to expand research coverage by replicating or sharing the GobyBot with scientists around the Great Lakes basin.
Not Going Anywhere Soon
Their journey across the world and throughout the Great Lakes watershed emphasizes the persistence of the round goby. The substantial environmental and economic impact the round goby continues to have on the Great Lakes highlights the importance of researching and monitoring populations of this abundant species. Innovative monitoring methods such as the MNRF’s Electrofishing Pilot Project and the USGS’ GobyBot are helping improve understanding of how these invaders are interacting with the Great Lakes ecosystem.
What YOU Can Do To Help
- Learn to identify the round goby, visit: Round goby | ontario.ca.
- Report sightings to EDDMapS Ontario.
- If you catch a round goby while fishing, do not return it to the water.
- Learn about and vote for policies that limit the spread of invasive species.
