We’re being invaded. Thankfully the culprits aren’t carrying guns or threatening our national security. The invasion is nonetheless serious, ongoing and at this point there is little we can do to prevent or eliminate future invasions. A surprising number of non-native species have been accidentally (or inadvertently) introduced into the Great Lakes. Most make the trip from a salt to fresh water environment inside the ballast water of commerce ships that travel from the Atlantic Ocean into the Great Lakes.
While ocean going ships that travel the Great Lakes now treat their ballast waters, the damage has already been done. The journey from salt to fresh water for these invaders is apparently a painless experience. Some species do so well in the Great Lakes that they quickly grow in numbers large enough to compete with native species.
This invasion is not exactly new or newsworthy. Nonnative species have been invading the Great Lakes for many decades. What is newsworthy is that some of these invasions, while far from planned, have actually benefited the sport fishing scene. Others are having such a profound impact that they are actually changing the food web on the Great Lakes which could lead to significant problems down the road.
Mixed bag catches of steelhead and walleye are becoming increasingly common thanks to an aggressive stocking effort that insures plenty of steelhead for open water trollers.
Frankly, the jury is still out on whether nonnative invaders are good or bad, but one thing is consistent. These unwanted introductions are forcing changes in the Great Lakes no one could have predicted just a few decades ago.
The changing face of the Great Lakes has researchers, fishery biologists and anglers alike concerned. Since no one has a crystal ball tuned to the future, there has been a lot of speculation as to what impact non-native invasions will have on the long term health of the sport fishing industry. Plenty of gloom and doom opinions have been bantered about, but the fact remains that everything associated with non-natives has not been bad.
“The Great Lakes has probably experienced more non-native species introductions than any other freshwater environment on Earth,” says Fred Snyder, Extension Specialist for Ohio Sea Grant a division of Ohio State University. “Just a few of the non-native species currently living in the Great Lakes include the rainbow smelt, gizzard shad, alewife, round goby, zebra and quagga mussel. As the populations of these nonnatives increases they begin to impact on both the native and nonnative species around them. Our job is to try and predict how these changes will impact on recreational fishing efforts.”
ZEBRA and QUAGGA MUSSEL
The tiny zebra mussels has without question had the most impact on the Great Lakes of all the current nonnative species. Small in size, but large in numbers, the zebra mussel is widespread throughout the entire Great Lakes system. These mollusks collect on just about anything hard in the water. Rocks, gravel, water intake pipes and even boat hulls become convenient homes for zebra mussels.
“A zebra mussel feeds by filtering microorganisms from the water,” says Snyder. “In doing so the zebra mussel has actually restructured the entire food web in the Great Lakes.”
Zebra mussels filter so much plankton from the water that certain species of baitfish are having a difficult time finding adequate amounts of food. Gizzard shad, which favor plankton rich waters, are a prime example of a species that is struggling to adjust to the environmental changes brought on by zebra mussels. As plankton levels drop, shad numbers have also decreased.
“Zebra mussels and the larger quagga mussels have reduced the amount of plankton in the water dramatically and this in turn means that the waters of the Great Lakes are also becoming clearer,” explains Snyder. “Prior to the arrival of the quagga mussel most of the plankton filtering problems were associated in shallow water. The quagga mussel thrives in deeper water and now waters both shallow and deep are being filtered by these non-native mussels.”
All this extra filtration of plankton has lead to increased water clarity. “Increased water clarity in turn allows better light penetration and triggers a number of other environmental changes,” says Snyder. “Clear water encourages weed growth to expand to deeper depths, creating improved fish habitat for species like smallmouth bass, northern pike and muskie.”
Not every species is benefiting from this change in the food web and increase in water clarity. The environmental conditions that are gripping the Great Lakes have not had a positive impact on walleye fishing. Walleye in Great Lakes waters fare best in plankton rich environments that support huge amounts of forage fish.
The clearing waters and changing forage bases of the Great Lakes has actually benefited some species like this smallmouth bass. Smallmouth have adapted to eating round gobies that have invaded all five of the Great Lakes. The brown tube bait that caught this fish does an excellent job of imitating a goby scurrying around near bottom.
Lake Erie is still without question the World’s richest walleye fishery, but the population of walleyes on Erie has steadily declined over the past two decades as a direct result of changes in the food web. This realization might be devastating for walleye anglers if it weren’t for a touch of irony.
Zebra mussels created an environment less suitable to walleyes. Ironically, zebra mussel numbers are now so high that the waste excreted when they feed on plankton is increasing the phosphorus levels in Lake Erie’s Western Basin. Increased levels of phosphorus in turn causes algae blooms to form, reducing water clarity in the process and making an environment more suitable for the types of forage fish walleye favor. Walleye anglers on Lake Erie appear to be enjoying a return to the blue/green waters and booming walleye populations of the 1970’s and 1980’s.
ROUND GOBY
The round goby is a bottom dwelling fish that seldom grows to more than a few inches long. An aggressive little critter, the goby has largely replaced an important native species known as the sculpin. “Anyone who has tried to fish live bait near bottom in the Great Lakes has undoubtedly come to know the annoying little goby,” says Snyder. “These aggressive fish nibble on live baits to the point that it’s difficult to catch walleye, bass or other species.”
The goby makes bottom fishing presentations frustrating, but in the same token they are also providing an important forage base for species including smallmouth bass and lake trout that feed mostly near bottom. “Research suggests that the goby may actually be making it possible for young-of-the-year smallmouth to increase winter survival rates,” says Snyder. “Because young-of-the-year smallmouth are big enough to feed on young-of-the-year gobies, smallmouth head into winter with the extra fat reserves required to insure survival.”
The drama between the goby and smallmouth bass runs even deeper. Evidence has shown that adult gobies eat bass eggs. The suggestion is that increasing goby populations could spell disaster for smallmouth bass in the Great Lakes. This is unlikely because both species seem to be doing a pretty good job of keeping each others numbers in check. One thing is for sure. Fishing tackle manufacturers have caught on to making lures that look like gobies!
In case you’re curious, gobies don’t eat walleye eggs because walleye spawn in shallow water early in the year when gobies are largely found in deep water. By the time that gobies start invading shallow water, walleye eggs have hatched and moved on.
Gobies are currently more of a nuisance than threat to sport fishermen, but trouble could be brewing in the future. Gobies eat a wide variety of foods including zebra mussels. While gobies can’t eat enough zebra mussel to keep them under control, they are eating enough of these mollusks to significantly increase chemical contaminants in their flesh. Because zebra mussels filter the water, they quickly bio-accumulate chemicals like mercury. This mercury is passed right up the food chain when gobies eat zebra mussels and perch or bass in turn eat the gobies.
Fortunately, more than 80% of the bass caught in the Great Lakes are not kept for food, but rather are released. Yellow perch however feed heavily on gobies and these fish are routinely kept for the table. Walleye also feed on gobies, but these bottom loving baitfish make up only a small percentage of the walleye’s more diverse dietary requirements.
Brown trout have historically been abundant along the east shore of Lake Michigan. These days the best brown trout fishing takes place in Lake Ontario from Niagara Falls east to the Salmon River. Other pockets of good brown trout fishing occur in the Milwaukee area where aggressive stocking efforts keep populations and fishing success high.
THE SPORT FISHING OUTLOOK
The sport fishing outlook on the Great Lakes remains bright despite the many non-native species that have invaded the lakes in recent years. Current forage types and water clarity conditions are favoring smallmouth bass, largemouth bass, yellow perch, muskies and northern pike. The overall populations of these fish are at current high levels.
Walleye numbers have declined over historic highs, but strong Lake Erie year classes in 2014, 2015 and 2016 are keeping walleye numbers high enough to produce world class sport fishing opportunities.
Steelhead numbers on Lake Erie have increased in recent years. The population levels of steelhead are controlled by stocking not natural reproduction and stocking efforts have increased in recent years.
The biggest declines in sport fishing fall on the backs of both coho and king salmon. Both of these species depend heavily on the alewife for forage and alewife populations are unstable due to a lack of plankton in the Great Lakes. Lake Michigan is currently suffering the most from the decline of the alewife and biologists have been forced to reduce stocking efforts on Lake Michigan to avoid crashing the forage base.
The best salmon fishing in the Great Lakes is currently taking place on Lake Ontario. Lake Ontario has the benefit of being the last lake in the five Great Lakes chain. Nutrients from all four of the other Great Lakes eventually enrich Lake Ontario, creating a more plankton rich and healthy environment for a wealth of forage species including smelt, alewife, gizzard shad and emerald shiners.
As salmon fishing continues to decline in other Great Lakes, Lake Ontario has enjoyed excellent fishing in recent years and that trend seems likely to continue.
About the only thing that’s consistent about the Great Lakes is that the sport fisheries these lakes support are inconsistent. Change is inevitable and as anglers we are tasked with modifying our fishing approach to remain successful in the face of these changes.
Despite these challenges we are still blessed with some of the most rich sport fishing resources on Earth, thanks to the five Great Lakes.