Coded-Wire Tags Allow Fisheries Biologists to Track Stocked Trout and Salmon
July 8, 2010
Wanted: Fish heads from Chinook salmon and steelhead that are missing their adipose fins.
Reward: A free fishing lure for every head turned in found to contain a coded-wire tag.
Since 1986, personnel from the Department of Natural Resources and Environment's Fisheries Division have been implanting coded wire tags into the noses of some of the trout and salmon produced at the state's fish hatcheries. These tags are minuscule (1.1 mm in length, about the size of the 1 in the date on a penny), made of stainless steel wire, and have a bar code etched into them with a laser.
The code on each tag number corresponds to a unique batch of fish and can be traced back to where the fish were raised and when and where they were stocked.
Anglers who catch a trout or salmon fish missing the adipose fin - that's the fatty fin on the back between the tail and the dorsal fin; all members of the salmon family have them - are asked to save the head and drop it off at a Coded Wire Tag Drop Site. As list of these drop sites can be found by calling (517) 373-1280 or on the DNRE website.
"We actually need only part of the head, from behind the eyes to the back corner of the mouth - what we call the snout," said John Clevenger, the fisheries technician at the Charlevoix Fisheries Research Station who heads up the coded-wire tag program. "But many anglers find it is easier to turn in the whole head and that's fine."
Anglers who turn in fish heads will receive a letter from the DNRE explaining whether a coded wire tag was found and, if so, information about where and when the fish was released. (And, of course, the fishing lure.)
DNRE fisheries personnel have been tagging fish with coded wire tags since 1986. Every year since, anywhere between 300,000 to 1.4 million fish have been marked annually with a coded wire tag. The number tagged each year depends on a variety of criteria, including the project design and amount of funding available.
In 2010, the DNRE tagged 60,000 steelhead and 740,000 Chinook salmon. Wisconsin tagged close to 350,000 Chinook salmon, too.
In addition, the U.S. Fish and Wildlife Service has been tagging lake trout since the mid 1980s. DNRE staffers would like to look at tag returns from lake trout, too. Anglers who turn in those heads will get a letter with the information on their fish but they won't get the free fishing lure. (The Fish and Wildlife Service does not provide reward lures for the lake trout project.)
Tags are implanted when Chinook fingerlings are only about three inches long. Tag retention averages in the mid 90s percent range, Clevenger said.
Although the coded wire tagging was once only done by hand, it is now often achieved with an automated machine that simultaneously clips the adipose fin and inserts the tag. There are currently only a couple of the automated machines, mounted on trailers, in the Great Lakes region, owned by the U.S. Fish and Wildlife Service. (The state of New York has one of its own.) The trailers are available for use by the states.
Fisheries managers hope to, one day, be able to tag all trout and salmon that are released into the lakes, though that day is still in the future.
But the information from returned tags answers questions about what happens to fish that are stocked.
"We use that information to follow the stocking," Clevenger said. "We can make management judgments from that information."
"Some of the things that we have learned are that we tend to have better survival of Chinook salmon on some river systems if the fish are stocked closer to the mouth rather than upstream," Clevenger explained. "In some rivers we have better survival if the fingerlings are raised in net pens. We learned that the more northern stockings tend to show up in other lakes - the closer the plants are to the Straits, the more of tendency they have to show up in the other lake."
Biologists have used the data collected from coded-wire tags to determine that in recent years a significant portion of the salmon stocked in Lake Huron are ultimately caught in Lake Michigan or in Lake Michigan tributaries. This appears to be a function of the fish going to where the food is; ever since the alewife population crashed on Lake Huron, more of the fish stocked there are showing up in Lake Michigan.
But what applies to salmon doesn't always apply to steelhead, Clevenger said.
"With steelhead, we've found that some of the upstream stocking sites can be better than the downstream stocking sites," he explained.
The coded-wire tags will be found in fish that are only adipose-fin clipped. If fish have additional fin clips - a pectoral fin, for instance - it will not have a coded-wire tag.
Anglers who submit heads from fish that are missing their adipose fins are asked to supply the date and location of capture as well as the length and weight of the fish, if possible. Fisheries personnel also collect fish heads from the specimens they see while conducting creel surveys and at the weirs. But the cooperation of anglers is important to data collection.
"We're dependent on the anglers out there to help us with the tag returns," Clevenger said.