They are the king of the Great Lakes sport fish, luring thousands of anglers to Michigan waters every year for a chance to try to land them _ and helping fuel a multibillion-dollar fishing and boating tourism industry.
But the Chinook salmon's numbers are plummeting in Lake Michigan due to a combination of natural forces, unnatural invasive species, and the state Department of Natural Resources' own efforts to dial back the population and prevent a more permanent population crash as happened in Lake Huron about a decade ago.
The salmon population on Lake Michigan is down 75 percent from its 2012 peak, said Randy Claramunt, a DNR Great Lakes fishery biologist based in Charlevoix.
A leading cause is a reduction in alewives, a silvery fish up to 10 inches long that is the salmon's primary prey on the Great Lakes. The alewife population has been decimated by invasive zebra and quagga mussels that have changed the nutrient dynamics of the lakes.
And the salmon population matters for Michiganders, whether they fish or not: The DNR estimates fishermen spent $2.4 billion in fishing trip-related expenses and equipment in the state in 2011.
"We all have a stake _ it's not just the charter boat captains who do this for a living," said Denny Grinold, owner of Fish 'N' Grin Charter Service in Grand Haven. "Coastal communities, hotels, shopping will all be impacted."
The U.S. Geological Survey's Great Lakes Science Center in Ann Arbor conducts annual trawling and acoustic surveys on Lakes Michigan and Huron, looking at the populations of prey fish for the Chinook salmon and other sport fish.
"In recent years, basically what we're seeing is record- or near-record low biomass of alewife," said Science Center research fishery biologist David Warner. He attributes that to the record numbers of Chinook salmon on Lake Michigan in 2012, and their voracious appetite.
Since reintroducing Chinook salmon to the Great Lakes in 1966, the DNR has collected eggs and sperm from salmon migrating into rivers and streams to spawn every fall. The eggs are fertilized and raised in hatcheries, and juvenile fish _ called fingerlings _ are then stocked in the lakes in the spring to help boost naturally reproducing salmon populations.
The DNR has reduced stocking rates since 1999, from 7 million to 2.5 million Chinook salmon, as it saw the alewife populations sink.
The goal now is "to try to bring a better balance between salmon and the prey population in the lake," Claramunt said.
"We're back to 1970 stocking levels; we almost can't go any lower," he said.
In addition to stocking cuts, naturally spawning salmon from that peak year of 2012 also dropped dramatically, due in part to unusually warm conditions and shallow, inaccessible spawning streams that year, Claramunt said. The number of salmon surviving from the spawn that year dropped from 6 million to 1 million, he said.
Further complicating matters, the extremely cold winters of 2013 and 2014 increased the stress on alewife populations.
"We need the warm summers, good precipitation in the spring, and the nutrients coming out into the lakes and getting offshore _ like this year," Claramunt said.
Why don't the Chinook salmon feed on another small fish that are thriving in the zebra and quagga mussel-changed lake environment _ the invasive round goby? While lake trout and steelhead are doing just that, "Chinook are just hard-wired to feed on alewives," Claramunt said.
"They are meant to feed in open water on open schools of prey fish. They aren't bottom-feeders, and that's where the round goby go."
The DNR has worked closely with state commercial and sport fishing groups on what to do in Lake Michigan.
"They said, 'Prevent a crash that will keep the fishery down for a decade or more. Take action if you can,' " Claramunt said.
A reduced salmon population is a tough reality, but most fishermen understand, Grinold said.
"The bottom line is, we don't want what happened on Lake Huron to happen on Lake Michigan," he said. "To avoid that collapse, this is something we may have to live through for awhile."
In Lake Huron, it was the same story, but happened sooner. DNR officials had an indicator of problems in the lake by 2003, Claramunt said. By 2005, the salmon population there had collapsed, and hasn't recovered.
"The consumption that happened by predators exceeded the ability of alewife to reproduce at a rate that was sustainable. And you had a crash," Warner said. "Historically, there was a larger biomass of alewife in Lake Huron than there was in Lake Michigan."
Despite the cuts in DNR salmon stocking and natural spawning, Grinold said fishing charters don't seem to be down in his area.
"Only time may tell whether or not that impacts clients booking charters; whether they are satisfied with five, seven fish or less; or do they expect those double-digit figures they may have had a couple of years ago."
There are hopeful signs a salmon crash can be averted in Lake Michigan, Claramunt said. After 2013 and 2014 were "a bust," alewives appear to have rebounded this year.
Whether the salmon population decrease happened in time on Lake Michigan to prevent a replay of the Lake Huron crash is "the key question for me," Warner said.
"That's something we're consistently working on."
