As the population of invasive round gobies exploded in the mid to late 1990s in Lake Erie, resource managers feared trouble ahead for the smallmouth bass population.
“Agencies (all around the lake) went into protective mode for smallmouth bass,” said Kevin Kayle, a biologist with the Ohio Department of Natural Resources at the Fairport Harbor Fisheries Research Station.
They did so by implementing restrictive harvest regulations during spring. By reducing angler effort, they hoped, aggressive male bass wouldn’t be as likely to be pulled off nests, leaving eggs vulnerable to goby predation.
Fortunately, those fears have proven unfounded. Gobies have not damaged the smallmouth population, and likely they wouldn’t have even without protective spring regulations. Instead, bass have benefitted, as the small, exotic fish is now a dietary staple.
“Where we see the change is in growth of young smallmouth,” said Kayle. “They still top out at about 20 inches. But for the first three years, we’re seeing advanced growth.”
Why is this happening?
Gobies spawn late, while smallmouths spawn early. Thus, young-of-the-year bass can eat nutrient-rich fish --- larval and juvenile gobies --- during their first summer and fall.
But the goby invasion has damaged forage species that bass traditionally depended upon. “We’ve seen a decline in sculpins and darters because of gobies,” Kayle said.
For bass, meanwhile, spring storms seem to be the biggest limiting factor for abundance, the biologist added. Especially with a northeast or northwest wind, waves up to 15 feet go crashing into the near-shore areas, where bass spawn in waters of 20 feet or less.
“That storm surge jostles around the eggs and can force adults to abandon their nests,” Kayle explained.
Upwellings in the Central Basin during late summer and early fall also can harm bass, as well as most other species. Several days of wind out of the north or south pushes the surface water in one direction, while bottom water moves in the other. This churning action forces oxygen-depleted water to the top.
“When this anoxic water comes close to shore, we can see fish kills,” the biologist said. “Some years, it’s drum. But in the worst years, we see smallmouth too.”
Blooms of blue-green algae that die and then decay in deeper water feed the problem. “Bacteria down there decomposes the dead algae and uses up oxygen,” he said. “And no oxygen can come in (from above) because of the thermocline.”
Despite these naturally limiting factors, though, the smallmouth population of Lake Erie is doing well. “Long-term catch rates are relatively good, while total effort has gone down to what we saw in the 1990s,” Kayle said. “We’ve had more young fish in the last few years, after a dry spell in the mid to late 2000s.”
(This article appeared originally in B.A.S.S. Times.)