The number of trout and salmon being stocked in Lake Michigan will exceed what can be supported by the available prey fish in the future.
Lake Michigan's salmon fishery thrives
What that means for future stocking of the "Kings."
Sometimes we hear stories of a program working so well that, in time, it needs to change. The story of Lake Michigan's Chinook salmon fishery is one of those tales. Chinook salmon, also known as "King" salmon, are not native to the Great Lakes. In fact, they were first introduced in 1887 but did not reproduce well and eventually disappeared. In the late 1960s, DNR fisheries biologists from New York, Wisconsin and Michigan gave Chinooks another look and began stocking them as a way to control alewives, an exotic species of fish, and create a new sport fishery.
Jump ahead more than four decades and we find an alewife population that has been drastically reduced. That is partially because of predation by the Kings, but is also the result of invasive species like zebra and quagga mussels that have changed the ecology of the lake. More mussels mean less food for alewives that leads to less food for a now thriving salmon fishery.
Natural reproduction survey
In 2006, Wisconsin joined Michigan, Indiana and Illinois, as well as tribal resource management agencies and the U.S. Fish and Wildlife Service (USFWS), in a cooperative effort to find out more about the Chinook salmon population in Lake Michigan. More specifically, scientists wanted to know the rate of natural reproduction, how the population is growing and what could be done to make hatcheries more efficient.
"There is so much we want to learn about the Kings," explained Brad Eggold, DNR Lake Michigan fisheries supervisor. "When we know more about their reproduction and movements within the lake, and the Great Lakes region as a whole, we can make a strong fishery even better."
This isn't the first time there has been an effort to take a closer look at the Chinook population. For years, state and federal agencies tried learning more about hatchery and naturally-produced Chinook salmon, but for various reasons the studies did not provide the information required to answer basic questions. In 2006, however, agencies came together and collaborated on a study looking at the contribution of hatchery-stocked Chinook to the entire population of Kings in Lake Michigan.
To do this, the Chinook from hatcheries in Wisconsin, Illinois, Michigan and Indiana needed to be marked. So, from 2006 through 2010, they were given food containing oxy-tetracycline (OTC), a chemical that forms a mark on the bony parts of the fish yet is safe for humans to eat. In 2007, fisheries biologists began collecting tails from Chinook salmon, looking for the mark on the tail bones. Finding a mark proved the fish was stocked from a hatchery and made it possible to estimate the percentage of wild versus stocked Chinook in Lake Michigan.
"The results of that five-year study found about 55 percent of 1-year-old Chinook in Lake Michigan didn't come from a hatchery," said Eggold.
The study was extended until 2013 to further investigate differences in life history characteristics between stocked and wild Chinooks. It's being done at a time when the older year classes of OTC-marked fish are making their way through the population.
The key to unlocking the mystery of Lake Michigan's chinook population may lie in a stainless steel tag. While it may be small, only about 1 mm long, it contains a wealth of information biologists hope will help them unravel questions about these large predators.
The process of tagging each and every Chinook is an immense undertaking. It is made possible with four massive tagging trailers owned and operated by the USFWS. For the past two years, USFWS staff has coded and wire tagged millions of fish with these computer-operated, automatic, state-of-the-art trailers. Each trailer is capable of tagging as many as 8,000 fish per hour. In addition to implanting the wire tag, the trailer also clips only the adipose fin, the small, fleshy fin just in front of the tail fin. It serves as an external indicator the fish is likely tagged.
Automated tagging has many advantages. First of all, more fish can be tagged in less time, as compared to manually inserting a tag. Secondly, there is a higher rate of success when it comes to the tag going in and staying in the snouts of juvenile fish. Finally, there is a cost savings. The USFWS estimates about an 11- percent reduction in total costs when using the automated system instead of tagging by hand.
In 2012, USFWS trailers tagged more than four million Chinook salmon stocked into lakes Michigan and Huron. In Wisconsin, trailers made stops at three DNR fish hatcheries: Wild Rose, Kettle Moraine Springs and Les Voigt. The trailers also travel among hatcheries in Illinois, Indiana and Michigan to tag Kings. Additionally, roughly five million lake trout are tagged at hatcheries run by the U.S. Fish and Wildlife Service.
Coded wire tags
When you hear "coded wire tags" you probably think of a piece of metal, stamped with a number, which is pinched onto the fin of a fish. The tags we are talking about today are much smaller. They are made of patented alloy steel that is injected into the snout of a fish. Despite their size, these tags provide the potential to collect a lot of information about the fish when it is captured.
Each tag is engraved with a number (the "code") that corresponds to a batch of fish. When the fish is caught, the tag is removed from the snout and examined. The number is recorded and, when combined with other tag returns, provides researchers with information about the age of the fish, where it was reared and where it was released.
The idea behind the tags is simple. Regardless of where the fish travels, if it is caught, state or federal biologists will be able to analyze the data from the tag and record it so all agencies can learn more about how Chinooks move, survive, grow and reproduce within the lake.
"The common objective for the state and tribal partners is to tag all Chinook stocked into the Great Lakes and use the information from tagged fish recovered from fisheries and agency assessments to improve fisheries management," explained Charles Bronte, fishery biologist and USFWS lead for mass marking implementation in the Great Lakes from the Green Bay National Fish and Wildlife Conservation Office.
A special tag detector can be used to determine if a tag is present in the snout of a Chinook. If it is tagged, biologists will record the date, length, weight and sex of the fish and find out where the fish was caught. The fish heads are then brought back to the lab where the tag is extracted. The number on the tag is recorded, along with data from the field, to determine the age of the fish, in which hatchery it was reared and perhaps learn if it was returning to spawn in the same waterway where it was originally released.
Most of the information gathered comes from tagged fish collected through the concentrated efforts of state and USFWS biologists working with fishermen at boat landings and fishing tournaments where heads can be collected. Wisconsin DNR and USFWS biologists recovered hundreds of coded wire tags from angler-caught Chinooks in Wisconsin during this past summer. Many of these tags have been processed and preliminary results indicate approximately 41 percent of these stocked Chinooks came from Wisconsin stocking sites, 43 percent originated from Michigan stocking sites and 16 percent came from Illinois and Indiana.
The next steps
Scientists are increasingly close to solidifying estimates of how many Kings are naturally reproducing in Lake Michigan. With every hatchery-raised Chinook now receiving a coded wire tag, and most fish living no more than five years, there will quickly come a point when any Chinook that doesn't have a tag will be known to have been born in the wild. The success of the tagging program doesn't lie solely in the number of fish tagged, but rather in the information gathered from them. The data collected during the next decade will prove invaluable in determining which changes need to be made in state stocking programs throughout the Great Lakes system. By learning more about Chinooks and how they live and reproduce, scientists can adjust the numbers and species that are stocked in hopes of maintaining a diverse and healthy fishery. As the program develops, scientists plan to tag and adipose clip all 20 to 25 million salmon and lake trout reared in state and federal hatcheries in the Great Lakes.
As more and more of Lake Michigan's fish are marked, it will become increasingly important for everyone, not just biologists and researchers, to bring forth their catch and have it recorded. It is only through the cooperative effort of state and federal agencies, and anglers themselves, that the ultimate goals of the tagging program will be reached.
Trish Ossmann is the regional public affairs manager for DNR's Northeast Region.