Alewife hit record low in Lake Michigan

SHEBOYGAN - The biomass of prey fish in Lake Michigan – including alewife, the key forage for chinook salmon – continues to sag to or near record lows, prompting questions about trout and salmon stocking strategies by state agencies around the lake.

"The (Lake Michigan) picture looks very similar to what Lake Huron was like before it crashed," said Chuck Madenjian of the U.S. Geological Survey. "And nobody was prepared for how quickly it went over there."

Madenjian presented a report titled "Status and Trends of Prey Fish in Lake Michigan, 2017" Saturday at a meeting of the Wisconsin Federation of Great Lakes Sport Fishing Clubs.

It was the first public showing of the data obtained last year through bottom trawling and acoustic surveys.

Since 1973, scientists have used bottom trawls as the primary means to estimate the populations of adult forage fish in the lake. Acoustic surveys, conducted since 1992, are better at detecting young-of-the-year fish.

The sampling is performed annually at seven index sites, including Port Washington.

The 2017 bottom trawling data showed a total lake-wide prey fish biomass of 13.3 kilotonnes, fourth-lowest on record. The four lowest totals have come in the last four years.

Bloater chub had the highest biomass, 9.13 kilotonnes, followed by deepwater sculpin (2.75), rainbow smelt (0.62) and round goby (0.52).

Significant to sport anglers, alewife biomass was 0.09 kilotonnes, lowest ever recorded in the bottom trawl.

Madenjian said the lake's forage fish were undergoing a double whammy of top-down and bottom-up effects.

Not only are predator fish eating the smaller fish, but other organisms, principally quagga mussels, have limited the amount of food available for forage fish.

The age structure of the lake's alewife population is truncated, Madenjian said, with no fish older than 5 caught in the 2017 survey. Age 1 and 2 alewives dominated the catch.

The trend is not new. Since invasive dressenid mussels entered the lake in the 1990s, plankton levels have dropped, the water has cleared and the biomass of forage fish has declined.

State agencies have responded with trout and salmon stocking cuts, which so far appear to have helped balance the number of predator and prey fish in the lake.

In 2016, at the urging of the Lake Michigan Commitee of the Great Lakes Fishery Commission, Wisconsin, Michigan, Illinois and Indiana agreed to cut the number of fish, principally chinook, they planted in the lake.

Wisconsin differed from the other states by cutting brown trout by 50% but holding chinook level. The other states opted to cut chinook, which rely most heavily on alewife.

The coming years will tell if the strategy, lobbied for by the Wisconsin Lakeshore Business Association (largely composed of charter captains), was prudent.

It has already been heavily criticized by many Wisconsin sport anglers and some fisheries managers for cutting brown trout so heavily. The Wisconsin waters of Lake Michigan have earned a reputation as a world-class brown trout fishery. Further, brown trout eat a more varied diet than chinook and are more likely to survive a potential crash of alewife.

Data are expected to be available in the coming weeks on 2017 predatorprey ratio and the condition of salmon in the lake.

Fisheries managers are scheduled to review the data March 19-22 in Sault Ste. Marie, Ontario.

The Wisconsin DNR has not decided whether to adjust its stocking targets for future years, according to Brad Eggold, Great Lakes District Fisheries Supervisor.

Eggold said Wisconsin and the other state and tribal agencies on Lake Michigan will receive the latest information, including the weight of female age 3 fish returning to weirs, at the March meeting.

"Once all the information is collected, Wisconsin along with the other agencies will discuss whether changes to stocking levels will be recommended for 2019," Eggold said. "Right now, state agencies are completing stocking adjustments, recommended in 2016, in an effort to match the available prey with these important salmon and trout species.”

The first Wisconsin stocking in 2018 is planned in March, when yearling brown trout and coho salmon are planted.

Tagging change: To keep down costs, chinook salmon will no longer be implanted with a coded wire tag (CWT) before stocking, Eggold said. The fish will still receive an adipose fin clip.

Instead, CWTs will be implanted in all lake trout and rainbow trout stocked in the lake. This year will mark the first year rainbows will get the tags, part of an effort to better evaluate fish movements and returns on the species.