The Round Goby invasion and its influence on Angling tactics

The Round Goby is a small, aggressive fish that feeds on the bottom. It has the ability to proliferate in new surroundings due to its tolerance to a wide range of environmental conditions. It can spawn up to 4 times in one growing season. (www.invadingspecies.com)

The invasive Round Goby, native to the Black and Caspian seas in eastern Europe has successfully spread through all five Great Lakes and has moved its way to inland waters including Lake Simcoe. It is believed the fish was brought to North America in the ballast water of transoceanic ships from Europe.

Round Goby were first found in the Pefferlaw Brook in 2004 and there were concerns expressed for the potential impact to the Lake Simcoe biological resources. In 2005, efforts were made to eradicate the species from reaching Lake Simcoe. Unfortunately, the efforts were unsuccessful and since 2006, Round Goby have established a significant population in Lake Simcoe. The threat of these fish come from their aggressive ability to feed on fish eggs, insects and other small organisms found on lake and river bottoms. They directly compete for food with other native fish species like Mottled Sculpin. Their aggressive eating habits and ability to breed up to four times a season have helped them multiply and spread quickly.


The native Mottled Sculpin looks very similar to the Round Goby. The main difference is the sculpin does not have a black spot on its dorsal fin and has 2 pelvic fins and not one like the Goby. (www.invadingspecies.com)

Although Round Goby compete with native fish species, they've become a fundamental part of the Lake Simcoe food web. More specifically, Yellow Perch, Lake Trout and Whitefish are gorging themselves on the abundant populations in Lake Simcoe. Many anglers are reporting stuffed bellies of Gobies in most of their catches (and only Gobies) and have had to change tactics in order to catch and find fish. Anglers are also reporting larger than average sized Smallmouth, Lake Trout and Whitefish and attribute the increased sizes to the abundant and easily available Round Goby in the lake.

Historically, Lake Herring, Rainbow Smelt and Shiners made up the main forage for Lake Trout and Whitefish in Lake Simcoe (as well as Yellow Perch and Smallmouth Bass). Huge schools of these bait fish roamed the deep waters in Kempenfelt Bay and the main lake where they would be stalked and chased by larger predatory fish. Experienced ice anglers commonly used baits that included flashy spoons, Jigging Rapala's, shiners, minnow swim baits and other vertical jigging lures that best represented these silver, long and slender bait fishes. They would regularly be found fishing in water in depths from 80 to 120 feet deep.

Today, Lake Herring, Smelt and Shiners still make up a good portion of the diet of many of Lake Simcoe's Sport fish and traditional baits are still being used to catch fish. However, artificial baits resembling Round Goby are starting to outshine traditional methods. Some of the hottest selling baits on the market right now are the "Meeg's," the Badd Boyz, and small brown, soft plastic drop shot baits like the Set the Hook "Drifter". These baits are now appearing in every Simcoe anglers tackle box because they mimic Round Gobies to a tee.

Not only has the bait of choice changed, but the location of choice has changed as well. Ice anglers are now finding Lake Trout and Whitefish much shallower than traditionally found. They are reporting fish in unusually shallower water, often less than 30 feet. These fish are venturing into shallow waters in search of Round Goby. Round Goby prefer hard, rocky substrates and shallow shoals in Lake Simcoe are a perfect location for them. Although they prefer rocky, harder bottoms, they will use sand a silt bottoms as well.

Ice fishing baits that have performed well for Simcoe Gamefish due to their Goby like appearance.

A Lake Simcoe Whitefish that fell victim to a goby hair jig.

Although Round Goby provide an alternative food source for many fish in Lake Simcoe, it is difficult to say what long term effects may occur to the aquatic ecosystem. One positive note is that they feed on the invasive Quagga and Zebra Mussel. These freshwater mussels have completely changed the landscape of Lake Simcoe. They are filter feeders and consume large amounts of plankton and nutrients, robbing the lake of vital nutrients for other native fish species. By feeding on mussels, this may help unlock nutrients from the lake bottom and redistribute them throughout the aquatic food web.

Studies have shown that Round Goby out compete native species such as Mottle Sculpin. Both species are benthic and have similar requirements for nesting , feeding and shelter. Round Goby may have also caused the decline of logperch in the St Clair River and other Great Lakes fishes may also be affected by Round Goby including Darters and Madtoms.

Specific laboratory studies have shown that Round Goby feed on the eggs and fry of Lake Trout. A study in Lake Erie found when nesting Smallmouth Bass were removed by angling, round goby quickly entered the nest and consumed, on average 2000 eggs before the guarding male was returned. If the male was not removed from his nest, no eggs or larvae were consumed.

The round goby wreaks havoc outside of the water, too. Researchers believe the round goby is linked to outbreaks of Type E botulism. This bacteria can infect fish-eating birds, such as gulls, loons and cormorants. It can restrict their mobility, preventing them from flying or holding their head up. This can, unfortunately, cause the infected bird to drown. This toxin can be passed when an infected mussel is consumed by a round goby, and then the infected goby is eaten by a bird.

The establishment of Round Goby in Lake Simcoe will need to be continually monitored to understand the true impacts they may have on the Lake Simcoe fishery. Furthermore, how popular gamefish species will co exist with this non-native species. As an angler, we are enjoying larger creel sizes and are utilizing new and exciting methods to catch popular game fish due to the Round Goby. However, it is uncertain in the future how this species may impact the Lake Simcoe fishery.

Round Goby's feed on Zebra and Quagga mussels which may help to redistribute important nutrients from the bottom back into the aquatic foodweb.

Round Goby may be linked to Type E Botulism. The toxin can be passed to birds that eat Gobies which have eaten infected mussels. (Photo credit: https://toronto.citynews.ca)

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