LIFE

Wild-born salmon support lake’s fishery

Titus Seilheimer

For USA TODAY NETWORK-Wisconsin

As Jeff Goldblum said in “Jurassic Park,” the 1993 blockbuster film, “Life finds a way.”

That statement also applies to Lake Michigan’s Chinook salmon fishery.

First introduced in Lake Michigan in the mid-1960s, Chinook salmon are reproducing naturally, and wild, naturally produced fish constitute more than 70 percent of the Chinook salmon caught each summer by anglers.

Understanding the role of stocked and wild fish in Lake Michigan can help anglers make informed decisions about stocking needs now and in the future.

The U.S. Fish and Wildlife Service estimates 71 percent of the Chinook salmon caught from April to September in the years 2014 and 2015 were naturally reproduced fish. The remainder of the fish caught were stocked in Wisconsin (11 percent), Lake Huron (9 percent) and Michigan (7 percent), as well as a small number of fish stocked in Illinois and Indiana (less than 3 percent). This is the best data that have ever been available on the source of Lake Michigan’s Chinook salmon.

How can we tell the difference between stocked hatchery fish and naturally reproduced fish? Initially, otoliths (ear bones) were chemically marked in the hatchery, but now coded wire tags are being used in an effort led by the U.S. Fish and Wildlife Service. Tags are implanted in the snout of the small fish before they are stocked. Unique groups of code numbers can then be used to help track the origin of the stocked fish to state or even specific stocking locations. These wire-tagged fish also have their adipose fins (the small fins on the back of the fish, between the dorsal and tail fins) removed, which serves as a quick visual way to tell if a fish has a coded wire tag.

Additional efforts to count the number of wild Chinook salmon by anglers were also conducted by Michigan Sea Grant and Wisconsin Sea Grant. The Salmon Ambassador program asked volunteer anglers to record the presence of an adipose fin, size of fish and location of catch for all Chinook salmon. Anglers reported a high proportion (more than 65 percent) of wild fish caught since the program started in 2014, which is similar to the results from the U.S. Fish and Wildlife Service.

Because of the size and complexity of Lake Michigan, coordinated management by state and tribal agencies is important to maintaining sustainable fisheries. Recommendations to reduce the number of Chinook salmon stocked into Lake Michigan were presented and debated in 2016, and reduced stocking was recommended in response to low prey fish numbers in the lake. Natural resource managers can use stocking decisions to help balance the ratio of predators to prey to prevent a prey fish population crash.

Concern that Lake Michigan could have a population crash of alewives, one of the most abundant forage fish for predators, similar to the crash in Lake Huron in 2003, has been an important consideration in management recommendations.

Titus Seilheimer is a fisheries specialist with the Wisconsin Sea Grant, a state and federal partnership based at UW-Madison to conduct outreach, education and research on Great Lakes issues. The Wisconsin Sea Grant has four field offices, including at UW-Manitowoc.