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|July 01, 2015 Post 64|
One of the topics we'll cover in the Lake Ontario video is that of invasive species. From swans to water fleas- more than a hundred different non native plants and animals have had a profound impact on the lake's ecology since the late 19th century. In recent years the 'invaders' have included several fish, among them the ubiquitous little round goby which has proven pretty easy to take video of.
The round goby first showed up in Lake Ontario around 1998. It originally got to the Great Lakes from the Black Sea region via the ballast water tank of trans Atlantic cargo ships. One of the first areas it showed up in was the Bay of Quinte near Picton. It spread rapidly from there and before long had reached every area of the lake. It is often very abundant, a dozen or so per square meter near shore were evident this spring when I was taking pictures off the family land.
It's an easy fish to spot, as it likes to park itself atop a rock in the lake shallows and wait for something edible to come along. Gobies are not big- a full sized one runs about eight inches long and makes a nice meal for a water snake. Many of the fish you see in the shallows run four inches or less. With their froggy little upward looking eyes and puffy cheeks I think they're kind of cute. Most anglers despise them.
They compete with a number of inshore species in the lake and are voracious hunters frequently raiding unguarded sunfish and bass nests for their eggs. They also eat young fish, insect larvae and other invertebrates and the adult gobies eat zebra mussels. Unlike most native minnows and darters and sculpins they spawn several times during the summer and are aggressive defenders of their territory easily driving off native competition.
Their impact on the lake's food web has been mixed. They compete with and displace native bottom dwellers like the sculpins, and they greedily devour the eggs of popular game fish. But those same game fish greedily devour gobies, and a recent study published in late 2014* stated that smallmouth bass were growing faster to larger sizes on Lake's Erie and Ontario than in pre goby years. One study also found up to three quarters of the diet of small mouth bass in Lake Erie were gobies
Last year the gobies made it to Cayuga Lake. A lot of people aren't too thrilled about this as the little fish are considered bait stealing pests by shore fishermen. One bad thing about hardy invaders like this one is that they often displace several native species that simply disappear from the system. The lost biological diversity tends to simplify and destabilize the food web and make the remaining natives perhaps even more vulnerable to another invader and further disruption and simplification. The end result is a less resilient less diverse ecological community that is more likely to be severely disrupted by outside factors like disease or climate change. If the only thing around to eat is round gobies than you had better hope nothing happens to them. The lake's warm water fish community has already taken several hits, one of which is the loss of the American eel, once a huge presence in the lake's inshore areas.
This sort of simplification of the food web happened some years ago in the open lake after the arrival of the alewife that displaced the already stressed and overfished native ciscoes. Unfortunately, it seems one result was the failure of one the lake's native top predators the lake trout to adapt to a diet of alewives. It develops a vitamin deficiency that interferes with its ability to reproduce.
The goby is also viewed with some suspicion as possibly amplifying the impacts of botulism in the lake. Gobies can and do eat zebra mussels which can and do concentrate the botulism toxin. Botulism toxin is extremely deadly. A single gram if distributed evenly could kill a million or more humans. Since the early 1990's Botulism poisoning has killed tens of thousands of fish eating birds around the Great Lakes.
When a goby eats a zebra mussel that has concentrated the bacteria and is sickened by it, its behavior makes it vulnerable to capture by a loon or meganser of other fish eater. But the bird in turn is also poisoned. At least that's one theory about how the goby picks up the toxin.
We'll explore the botulism story in more detail in another post.The goby is only one player in the story. Three dollar a gallon milk also plays a role.