Ludington, Mich. — Chinook salmon returns at two of the three major Lake Michigan weirs were at record low levels last year, a sign DNR officials believe is tied to low prey availability.
The total number of chinooks harvested at all weirs was 12,581 last year, which is below the average for the Little Manistee weir alone. DNR officials harvested a total of 20,332 chinooks in 2013 and 25,745 in 2012, according to data presented by DNR officials at a Michigan Sea Grant fisheries conference held earlier this month in Ludington.
Those fish also were much smaller than last year. The biggest chinook to reach a weir in 2014 was 22.5 pounds, compared with 31.2 pounds in 2013.
At the Little Manistee River weir, DNR officials collected a record low 2,781 chinooks. The average since 1990 is 12,918.
At the Boardman River weir in downtown Traverse City, it was a similar story. Officials collected 1,273 chinooks there, a record low, compared with an average of 4,924 since 1987.
Coho returns also were low in Traverse City, with a harvest of 568 compared with an average of 1,273.
The DNR weir on Medusa Creek in Charlevoix was the only major chinook weir for Lake Michigan that did not produce a record-low return, although it was below average. A total of 4,062 chinooks were collected, compared with an average of 6,520 since 1990.
“The low returns kind of confirm what we were hearing from anglers throughout the year – that they were not catching a lot of salmon,” said Todd Kalish, DNR Lake Michigan Basin coordinator.
“The fish that returned were mostly 3-year-olds … raised in 2011,” Kalish said. “And we know the 2011 alewife year-class was very poor.
“One of the major attributes of the Lake Michigan food web that contributes to the success of chinooks is alewives,” he said.
Kalish said chinook populations are important because “the chinook fishery in Lake Michigan roughly makes up 50 percent of the catch.”
Other research presented in Ludington shows the abundance and age range of alewives, the chinook’s primary food source, is continuing a downward trend, said Randy Claramunt, DNR fisheries research biologist stationed in Charlevoix.
DNR officials cut salmon stocking in 1999, 2006, and 2013 in an effort to balance prey and predator fish populations, and preliminary data suggest another cut may be necessary for 2015, Kalish said.
“We’re currently in the process of analyzing all the (lake-wide) data of 2014 (from Michigan and other states and provinces surrounding Lake Michigan),” he said. “It doesn’t sound like the 2014 alewife population was very strong.”
Claramunt said decreasing salmon numbers is not necessarily a bad thing.
“We cut stocking by 75 percent in 2013 because we thought the salmon abundance was too high,” he said. “So if the numbers continued to go up, we’d be alarmed.”
However, there’s a lot more to it than stocking cuts, Claramunt said.
The low weir returns “certainly suggest salmon abundance has come down. Now the question is, is it coming down because we cut stocking or is it coming down because survival is down?” he said.
“We have enough preliminary data to suggest that survival is down not only for our stocked fish, but for wild fish, and the reason that is happening is because of the low prey fish levels,” he added.
The situation convinced lake managers and researchers to change how they analyze the health of Lake Michigan’s salmon population. Previously, a coalition of fisheries managers from states and provinces surrounding the lake known as the Salmonoid Working Group used a “Red Flag Analysis” that relied on predetermined acceptable ranges for certain indicators, such as alewife populations, to guide stocking decisions. That type of trend analysis was replaced recently with a more precise population model that calculates the balance between chinook and alewife biomass in Lake Michigan, Claramunt said.
DNR officials applied the population model to data from previous years and found it supports the ecological principal that once predator biomass exceed 10 percent of prey biomass, bad things happen.
In Lake Huron, “When salmon biomass exceeded 10 percent of the alewife biomass … the salmon crashed,” Claramunt said.
Claramunt said previous data show Lake Michigan’s chinook population is at about 8 percent of the alewife population, but an updated ratio utilizing 2014 data will be available in March.
“The prediction for this year is the predator-prey balance will come down, but not as much as we anticipated when we cut stocking” in 2013, Claramunt said. “That’s because the prey population continues to decline.”