'King' salmon have less to eat

[Spiel]

'King' salmon have less to eat

 

March 04, 2008

Jeff Alexander / The Muskegon Chronicle

 

Chronicle file photo / Charter captains say the days of catching 30-pound salmon, whic were common in the 1970s and 1980s, are gone for now. These days, a 20-pound salmon chinook from Lake Michigan is considered a big fish.

 

 

The billion-dollar Lake Michigan salmon fishery remained strong last year despite a shrinking supply of fish food that has some scientists and anglers wondering if the good times will last.

Charter boat anglers in Michigan's half of the lake caught 84,600 chinook salmon in 2007, up from 81,700 the previous year, according to data compiled by the Michigan Department of Natural Resources. The state only tallies fish caught by anglers on charter boats, but the data are a reliable indicator of the fishery's health.

 

Lake Michigan anglers last year also caught 10,500 lake trout, 10,200 coho salmon, 7,700 rainbow trout and 600 brown trout. All of those numbers were up from 2006, according to DNR data.

 

The diagnosis: There still are lots of chinook salmon in the lake, but the so-called "kings" are becoming more Napoleonic in size.

 

"It would be nice to have more big fish, but people want action," said Denny Grinold, who owns a charter boat in Grand Haven. "The fishery may never return to the way it was in the 1970s, but it's still pretty good."

 

State data supported that claim.

 

The catch rate last year for chinook salmon on Lake Michigan -- the number of fish caught per hour of angler effort -- remained strong. Anglers on average caught one-third of a fish for every hour of effort. The catch rate for chinook has increased 68 percent over the past five years, according to state data.

 

The strong fishery has been good for Grand Haven, which logged more charter fishing trips last year, 1,939, than any other port on Lake Michigan. Anglers fishing out of Ludington caught the most chinook, 16,911, followed by Grand Haven, with 14,693, according to DNR data.

 

Muskegon did not rank among the top five ports for number of fishing trips or fish caught in 2007, primarily because of its relatively small fleet of charter boats.

 

Charter captains said it was common in 2007 for their customers to catch their limit of chinook, three per person, within two or three hours. But the days of catching 30-pound salmon, which were common in the 1970s and '80s, are gone for now. These days, a 20-pound chinook from Lake Michigan is considered a big fish.

 

Salmon and other species of fish are shrinking because the volume of prey fish in the lake -- the small fish eaten by larger fish -- has sunk to record lows in each of the past two years. Prey fish abundance in Lake Michigan last year was down 92 percent from the record volume of 400 kilotons recorded in 1989, said Chuck Madenjian, a research fishery biologist at the U.S. Geological Survey's Great Lakes Science Center.

 

The good news for salmon was that alewife abundance in Lake Michigan increased 18 percent last year. Still, the volume of alewife in the lake in 2007 was less than half that recorded a decade ago.

 

Scientists are at odds over what is causing a precipitous drop in the volume of prey fish.

 

Some researchers blame quagga mussels, a relative of the zebra mussel, which invaded Lake Michigan around 2001. Last year, there were an estimated 245 kilotons of quagga mussels, or 540 million pounds, in Lake Michigan, according to USGS data.

 

Quaggas account for 98 percent of the mussels in the lake and their numbers increased 13 percent in 2007.

 

As the quagga mussel population has exploded, prey fish abundance has plummeted. The volume of all prey fish in the lake -- alewife, bloaters and other small fish eaten by salmon, lake trout and whitefish -- dropped from 61 kilotons in 2006 to 30 kilotons in 2007, according to USGS data. That was the lowest figure recorded since the government began tracking prey fish densities in 1973.

 

"That's an enormous shift in the way Lake Michigan operates," said Al Steinman, director of Grand Valley State University's Annis Water Resources Institute.

 

Some researchers believe quaggas -- which filter a liter of water per day, per mussel -- are hogging the microscopic plants and animals that comprise the base of a food chain that ultimately supports salmon, whitefish and lake trout.

 

"The quagga mussels are all over the bottom of the lake," Madenjian said.

Still, Madenjian said increasing numbers of salmon and other predators in recent years might be responsible for the decline of prey fish.

 

The four states surrounding Lake Michigan cut salmon stocking in the lake by 25 percent in 2006. But 53 percent of the salmon now in the lake reproduced naturally in West Michigan rivers.

 

Pacific salmon were first stocked in Lake Michigan in 1966. For much of the past four decades, all the salmon were grown in hatcheries and stocked in rivers that flowed into Lake Michigan.

 

But the ocean fish have adapted well to their freshwater environment and are reproducing millions of offspring each year on their own, according to researchers.

 

Paul Jensen, a commercial fisherman in Muskegon, called the naturally reproduced salmon pouring into Lake Michigan from area rivers a "runaway train."

 

Biologists are trying to avoid a repeat of what happened in Lake Huron in 2003, where excessive numbers of salmon -- many of which reproduced naturally in rivers -- ate virtually all the alewife. With no food, the salmon fishery collapsed in 2004.

 

There are subtle signs that Lake Michigan's salmon population might be headed for trouble.

 

Researchers have found increasing concentrations of water, and less fat, in the muscle tissue of chinook taken from the lake. Less fat and more water means the fish aren't getting enough to eat, said Dave Clapp, manager of the DNR's fisheries research station in Charlevoix.

 

Clapp said chinook in Lake Michigan still were in good condition last year, despite their reduced size.

 

"Overall, the fish are in very good health," Clapp said. "We feel the condition of the chinook is relatively stable. ... We hope."

 

Grinold said he is "cautiously optimistic" about the future of the salmon fishery. "It's fragile," he said.