Alewife numbers are encouraging

[Spiel]

Alewife numbers are encouraging

 

 

January 18, 2009

Kevin Naze / greenbaypressgazette.com

 

 

It's a well-known fact that Green Bay and Lake Michigan offer some of the most incredible multi-species freshwater fisheries found anywhere on the planet.

 

 

But when you move past the hundreds of miles of shoreline and go into the fish-filled waters, there are changes to the ecosystem that have many anglers concerned: populations of exotic invaders like quagga mussels and round gobies have exploded while many prey fish species — as well as the shrimp-like diporeia that provided a lot of food for young fish — have plummeted.

 

While plenty of guides and charter captains are wondering what the future holds for an industry that attracts thousands of clients from across the country each year, biologists and scientists familiar with the ever-changing lake urge caution before jumping to conclusions that the fishery will crash.

 

Even though quagga mussel mass is thought to far exceed the entire fish forage base, there are some encouraging signs.

 

Fisheries biologists around the lake saw a slight improvement in body sizes for chinook salmon last fall, which suggests the stocking cutbacks in recent years may have helped.

 

Additionally, while the fall lakewide bottom trawling transects by the U.S. Geological Survey's Great Lakes Science Center showed a decline in alewife — the baitfish of choice for most salmon and trout — the acoustic survey showed a better than 220 percent increase in alewife numbers.

 

Dave Warner, a research fishery biologist with the USGS Science Center in Ann Arbor, Mich., said the acoustic survey does a better job at finding fish still up in the water column, like young alewife, bloater (chubs) and smelt. The bottom trawl is best for larger and older alewife, bloater, gobies, sculpin, smelt and sticklebacks.

 

Warner has also been researching the abundance of mysis, another important invertebrate that lives mostly in deep water and has a high fat content that helps fish grow.

 

"Some of them can get to be an inch long, and you get a lot more bang for the buck if you're a fish," Warner said.

 

While mysis have declined in some areas, Warner said he's been doing mysis surveys since 2005 and has found no change in lakewide abundance.

 

"It's tough to say exactly how long it might take for something to make a drastic change in their abundance," Warner said.

 

Twenty years ago, just before exotic mussels were discovered here, the prey fish population in Lake Michigan was estimated at more than 880 million pounds. Last year's estimate was 46 million pounds.

 

By weight, round gobies accounted for more than 20 percent of all prey fish in the lake last year. Some species of fish — smallmouth bass, yellow perch, brown trout and whitefish, among others — are targeting and eating young gobies.

 

Whitefish have been found with mussels in their stomachs as well, but they aren't putting a dent in the population. Researchers estimate there are more than 300 trillion quagga mussels on the lake bottom. Mussels have been linked to increased algae blooms that have fouled beaches and to disease outbreaks that have killed thousands of fish-eating birds and countless fish species.

 

Randy Claramunt, a Michigan DNR fisheries biologist at Charlevoix, said early indications are that natural reproduction of chinook salmon on the Michigan side of the lake have decreased about 20 percent from earlier this decade. He believes it may be because female chinooks in recent years were smaller and more stressed.

 

Still, Claramunt said a lakewide study estimated that about 53 percent of the young chinooks in 2007 was naturally reproduced.

 

Data is not available yet for 2008.

 

"With the 25 percent lakewide salmon stocking cut and natural reproduction down, you're going to see a decent decline in (salmon) abundance, which is what managers wanted," Claramunt said. "We might expect that the fish will get bigger, but catch rates (in 2008) went down."

 

Warner said the 2005 alewife year class was fairly strong, and has some larger individuals that could have spawned last year. The 2007 year class was the one that led to the big increase in the acoustic biomass estimate. How they survive could have a big impact on the future of the fishery.

 

"We don't have as many of the old and big alewife as we used to," Warner said.