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Friday
Jun152012

Smallmouth Spawn Twice in Some Northern Waters

Peter Brown and his associates from the University of Wisconsin-Stevens Point were assessing young-of-the-year smallmouth survival on Nebish Lake early one fall, when they made a startling discovery.

“We were on the lake around Labor Day and I saw what looked like a fresh nest,” he recalled. “I put a handful of sand in the nest, and, the next day, it was gone.”

Within a few days, they saw eggs in the nest. They didn’t think that they would hatch.

But, instead, said Brown, “They hatched in record time.”

The discovery of that nest and 23 others in 2001 has turned upside down what resource managers thought they knew about smallmouth reproduction in northern waters. In at least some of those fisheries, perhaps the window for the spawn isn’t as narrow as previously believed. And maybe a year class in those lakes is based on two reproductive cycles, not one.

But much more remains to be learned, including whether a substantial number fry hatched that late in the year can survive the winter.

“This was a real eye opener,” said Brown, who now is doing his post-doctorate work at Montana State University. “It can help us learn a great deal about lakes in terms of habitat and climate and how fish use that habitat.”

Since that revelation of a second spawn during the late summer/early fall of 2001 on Nebish, evidence has filtered in of double spawns in other Wisconsin waters, as well as in other states.

“We heard anecdotal reports of male smallmouth bass being in an aggressive mode during the fall in the Lake of the Woods area,” Brown added.

This past fall, Brown went back to Nebish, hoping to again observe a second spawn. He didn’t find it there, but he did confirm that it was happening in two other nearby lakes, Pallette and Yawkey.

“Females were putting down eggs and fish were hatching,” he said.

Why is this happening? Brown theorizes that habitat might be a limiting factor for the number of nests built in spring.

“If you have a lot of bass and limited habitat, some of those fish might not be able to find a place in the spring,” the biologist said. “That’s what happens with bluegill and green sunfish.”

Climate, too, could play a role. “In most (northern) lakes, you have a long, cool spring and fish have a spawning window of 1 to 1 1/2 months,” he explained. “But a quick spring and fast warming could narrow that window.

“One of the things that we’re curious about is whether some of those bass that are ready to spawn in the spring have to wait until later.”

And when they do spawn in late summer/early fall, which sex provides the “cues” that prompt reproduction? In other words, are females stimulated by males, or vice versa?

“A bass can carry several clutches of eggs at any given time,” Brown said. “They’re all in different stages, and, in theory, a female can quickly develop a set of eggs.”

To learn more about what is going on, Brown collected gonads, ovaries, and testes from 150 bass in 2011. When funding is available for laboratory work, he hopes that the samples will tell him, among other things, whether females might be able to re-absorb the eggs that they didn’t lay in the spring and transfer that energy into a new clutch for the fall.

He also wants to determine whether bass born in the fall can survive a long northern winter. Marking the fry while they’re in the nest could help track them.

“When we went back to Nebish in the spring of 2002, we found only a few from the fall spawn,” he said. “That was a lot like looking for a needle in a haystack.”

(This article appeared originally in B.A.S.S. Times.)

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