Cool Critters: Lake Erie Water Snake
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Within and along the waters of Lake Erie (one of the five Great Lakes), there is a daily struggle for survival between natives and unwelcome invasive species. Most times, these unwanted invaders have negative consequences for the lake’s long-standing residents. However, there are rare occasions when the native actually benefits.
Kristin Stanford, herpetologist, researcher, and snake lover from Northern Illinois University, has been observing this struggle for over ten years as the Recovery Plan Coordinator for the Lake Erie water snake. She works out of Ohio State University’s Stone Laboratory on South Bass Island in western Lake Erie. An expert on these snakes, Kristin, aka “The Island Snake Lady,” works hard to educate students and the public about them, and encourages the islanders to co-exist peacefully with their slithery neighbors.
One of six species of snake found on South Bass Island, Lake Erie water snakes (or LEWS for short) are a species found only in the western basin of Lake Erie, in Ohio and southern Ontario, Canada. The reason the water snakes were listed as a state endangered, federally threatened species in 1999 was due to three primary threats to their population – low population size, habitat destruction, and human persecution.
South Bass Island is a very popular spot for vacationers, with homes built along the shore, boats in the harbor, and hundreds of visitors rattling around the island on golf carts every day. It’s not too far across the water from nearby Cedar Point Amusement Park. Kristin invited us out to the island, one of a series of three small islands – South, Middle and North Bass Islands – to search for snakes.
So, how does one count snakes? Kristin takes a group of five to ten hardy volunteers to fourteen different study sites on the island, to – as she says – “scour the shore line” for all of the adult snakes that they are able to catch.
Kristin’s prime hunting ground is the Scheeff East Point Nature Preserve on the northern point of the island. Our production crew arrived on a hot and humid June morning to find that mayflies had invaded the island, adding to the gross factor of our visit. These insects flew up out of the grass and covered our heads, clothes, and equipment. Luckily, they don’t bite as they don’t even have mouths! Their only career goal is to mate, lay eggs in the lake and die within three days. Once we got used to the mayflies, we turned our attention to snakes.
At some of their study sites, the researchers place heavy black mats on the ground. The snakes love to snuggle under the mats to keep warm. Kristin warned us that one mat in particular has been doing really well. “When I lift it up, there’s probably going to be about forty snakes underneath.”
YIKES! She wasn’t kidding. There were a bunch, and she gamely grabbed two handfuls of the writhing reptiles. Normally she has several people to help her. Today, she struggled by herself, and managed to get a few into a pillowcase she had brought along as a snake catching bag. And yes, they bite, but they’re not poisonous. She does get bitten in the course of gathering snakes, but they’re usually gone by the next day.
Kristin and her colleagues estimate the number of water snakes by utilizing “mark and recapture techniques.” They insert a small microchip called a pit tag under the skin of the adult snakes they capture, and use the ratio of marked animals to unmarked animals to generate population and density estimates for the Lake Erie water snake.
Kristin plucks a snake out of the grass near the lake shore, and points out the green mark on its back that means it’s been captured and given a pit tag recently. “So what we can do then is scan it and get the pit tag number and re-release it relatively quickly.”
“After we catch the animals, we take some appropriate and annual regular data on them including snout to vent length, mass, we score them for sex and color pattern, and then we also look for the presence of recently consumed prey items. And all that involves is looking for a little bulge inside the snake’s belly. When we see that, we slowly and gently regurgitate that and then we will bring those samples back to the laboratory for further analysis and we identify them to species and that’s how we’re able to determine that the water snakes are eating about 90% round gobies now.”
What are round gobies? No, they’re not fancy marbles. They are a small invasive fish species to Lake Erie, from the Black and Caspian Seas, arriving in the ballast of cargo ships about the mid-1990s. They are considered a very harmful species because they are voracious nest predators for many of Lake Erie’s bottom-dwelling fish and game fish. They gobble up all of the eggs and fry in a very short period of time. And there are BILLIONS of them in Lake Erie now.
So, normally there is not much good to say about an invasive species. But Kristin explained, “It was about the mid to late 1990s when we started seeing gobies pop up in Lake Erie water snake diet samples.” As they continued to study the snakes, they started seeing more and more gobies popping up in their diet samples, and now, Kristin tells us, round gobies are about 90% of the water snake’s diet.
And what effect is this new menu item having on the Lake Erie water snake? Kristin and her colleagues have been able to show that, since the water snakes have been eating round gobies, “they have increased their growth rate, they’ve increased their maximum body size, so they can grow bigger than they ever could before, they’ve increased their reproductive rate, as well as their survival rate, and population growth rate.” The result – a population explosion of water snakes on the Lake Erie Islands, and also the nearby mainland.
Due in part to the impact of the round gobies, the U.S. Fish & Wildlife Service announced on August 15 that the Lake Erie water snake has been removed from the federal list of threatened and endangered wildlife. And that is – at least from the point of view of the snakes AND the Island Snake Lady – “a really great ending to our story.”Related