Behind the Science

Goby Numbers Surge

Nature isn’t likely to make a dent on the round goby population in the Great Lakes. This invasive species continues to thrive in some of the world’s best smallmouth fisheries. Ontario scientists pegged the goby population in Lake Erie’s western basin at more than 8 billion fish. And this species has spread inland, colonizing new bodies of water.

Most Great Lakes anglers can hardly believe their good fortune these days, as they catch ever more and bigger bass. Clearly, adult bass are gorging on gobies and prospering. But do tables turn in spring when smallmouths are bedding? Are gobies gobbling up too many bass eggs?

A group of Ohio State University researchers led by Geoffrey Steinhart sought to answer that question by monitoring what happens when anglers catch nesting male smallmouths on Erie. While one team member hooked a bedding bass, another, wearing scuba gear, measured the rate at which gobies ate the unprotected eggs.

On average, three gobies started eating eggs as soon as the nest was unguarded. Factoring in elapsed time between catching the fish and releasing it to return to the nest, Steinhart estimated that 400 eggs are eaten every time an angler pulls a bass from its bed.

There are so many gobies in the Great Lakes that Steinhart estimates the males in Lake Erie spend 15 times more energy protecting their broods than bass in lakes where no gobies exist. And the fitness of fish in fall affects their winter survival.

Great Lakes weather systems bring another complicating factor. Spring storms with winds over 16 miles an hour are the norm on lakes like Erie. According to Steinhart, they can wash out 90 percent of the eggs in a smallmouth nest in two hours, making life even sweeter for the gobies. Could it be only a matter of time before the best smallmouth bass fishery on the planet is in trouble?

Bass Candy

Surprisingly, “no”, says Ridgway, who has studied smallmouth bass populations perhaps more than any other scientist. “Lake Erie has a bass profile unlike any other water. The fish are bigger than ever before. While there may be fewer small bass, survival and growth rates are phenomenal. Smallmouths eat gobies like candy, but they’re apparently nutritious.”

Ridgway says that the age composition of most bass populations resembles a pyramid, with most of the fish—the foundation of the pyramid—comprised of the youngest members. The pyramid then takes its familiar shape with ever fewer fish in older age groups. But Lake Erie’s population pyramid is inverted, with fewer small fish and ever growing numbers of older, gargantuan bass.

And consider inland waterways near the Great Lakes, like southern Ontario’s Lake Simcoe, where 5-fish catches of smallies weighing 25 pounds aren’t unusual. Now that gobies have  invaded the lake, might they wreck havoc with the bass population?

Ridgway says that might have been the case a decade ago. But now a powerful new buffer is at work, in the form of climate change and global warming. “Across all of North America, but especially in the northern portion of the smallmouth’s range,” he says, “lakes are warming earlier in spring and staying more stable. We’re seeing one-third more nests in our study lakes now than we saw as recently as the 1990s, and survival rates are higher.

“So, on one hand, weather and water conditions are more favorable for smallmouth bass, while on the other, gobies are a new and plentiful food source. Even if reductions are caused by goby nest invasion, we’re still seeing net gains for bass. That’s not the case for all species, but for smallmouths, it appears that gobies aren’t knocking them down as fast as climate change is pulling them up.”

An Ever Changing Game

Even more amazingly, Ridgway recently began noticing a new behavioral trend among the smallmouth bass spawning in his Algonquin Provincial Park study lakes. Nests there contain about half the number of eggs they did just a few years ago.

“A decade ago, it was common to observe a male smallmouth guarding 1,000 free-swimming fry,” he says. “Six hundred fry was a low count. Today, 600 fry is average. The eggs are as big as they’ve ever been and male size distribution is the same. Nest density and fry survival have increased.”

Ridgway says that only a few years ago, he would have observed 50 to 70 male smallmouths protecting nests along a major section of shoreline. Today, he finds 120 to 130 nesting males along the same stretch but nests have fewer eggs. “The net effect on reproduction is insignificant,” he says. “The game’s just being played differently. The population is growing by different means.”

Despite potential new dangers and ever-constant complications, the future for smallmouth bass in most regions continues to look rosy—make that golden bronze.

In-Fisherman Field Editor Gord Pyzer, Kenora, Ontario, has been writing about smallmouth bass in In-Fisherman for almost two decades.