Biologists fear danger for chinook fishery
Written by South Bend Tribune   
Monday, 26 September 2005 09:43

Biologists fear danger for chinook fisheryWhen fish agencies start discussing stocking cuts by as much as 50 percent, anglers usually get defiant.? But the pitch made to salmon fishermen at a conference in Wisconsin yesterday likely drew reluctant nods of approval.

Especially if those anglers were around in the late 1980s when the chinook salmon population (also known as kings) crashed following an outbreak of Bacterial Kidney Disease (BKD). Scientists from the four Lake Michigan states laid out four options for anglers to consider at yesterday's Salmon Stocking Conference. Three of those call for stocking cuts.

"We're concerned with the trends we're seeing in recent years and the similarity of those trends to what happened in the '80s," said Indiana Lake Michigan biologist Brian Breidert.

Those trends include tumbling alewife populations -- the forage fish that keep chinook healthy -- and a dwindling overall size in the salmon that are being caught. Furthermore, fish managers have documented a dramatic rise in natural reproduction of chinook salmon, which means there are actually more aggressive mouths out there than what the hatcheries are contributing.

"We have to do something, but we wanted to present the sportfishing community with our research and have them weigh in on the decision before we make a decision," Breidert explained.

The four options being considered are:

1) maintain the status quo of stocking 4.3 million chinook on a lake-wide basis.

2) Reduce the lake-wide stocking of kings by 25 percent.

3) Reduce the stockings by 50 percent.

4) Reduce stocking all species, except lake trout, by 25 percent.

"The sky isn't falling, but we want people to be aware of changes going on in the lake and to know that the ecosystem may not be able to support our current stocking rate," said Briedert.

But there is a sense of urgency. Anglers have until Oct. 1 to respond and a decision likely will be made by mid-December.

That would enable hatchery officials to enact the reduction before the 2006 stocking.

The facts are somewhat startling.

The Great Lakes Science Center has documented a 14 percent decline in the condition of alewives since the mid-1990s and has noted similar declines in the abundance of the forage for the last three years.

When BKD ravaged the chinook fishery in the 1980s, many experts theorized that lower prey abundance and high numbers of predators triggered the disease.

"Chinook are the biggest consumers of alewives in the lake," noted Breidert. "Other species (steelhead, browns and coho) eat alewives, too, but they also are more adaptive, feeding on other food sources that the kings don't eat as readily."

The rise in natural reproduction has been the surprising wild card in all this. A four-year study of fish caught from the lake has revealed as many as 50 percent of those fish weren't stocked by the states. Agencies know this because stocked fish are marked with a chemical imprint that shows up in laboratory tests. Analysis of several captured adults revealed no chemical markings, indicating they were born in the wild.

"We're not sure how many are reproducing, but we're comfortable with estimates that 50 percent of the fish out there are wild fish," said Breidert.

Oddly enough, only kings show significant numbers of wild fish, although other species haven't been studied as thoroughly.

Biologists believe most natural reproduction is occurring in Michigan tributaries where sufficient habitat and water quality is most prominent.

"I suspect some of that natural reproduction is happening right there in the St. Joseph River, and quite possibly in South Bend," Breidert added.

Another notable concern is that 2004 king harvest rates were highest they've been since 1986, which, coincidentally, occurred two years before the collapse.

"But anglers also are asking us why they're not seeing as many 25 pounders as they once did," said Breidert. "All of these factors are red flags to us and why we need to adjust stocking numbers to head off any potential problems."

 
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