An aging study of freshwater drum or sheepshead – the names are interchangeable – in Manitoba waters of the Red River suggests they live a lot longer than sheepshead in warmer climates.
Researchers now are collecting freshwater drum on the U.S. side of the Red River to see if they live just as long as sheepshead in Manitoba, where even midsize fish were found to be 50 to 60 years old.
Quite likely, they do.
According to Mark Pegg, a fish ecologist and instructor at the University of Nebraska-Lincoln, the aging research started “five or six years ago now as a bit of a lark,” when one of his student technicians wanted to do a side project to supplement traditional survey work they were doing on the Manitoba side of the Red River.
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Pegg and UNL students began working in Manitoba about a decade ago as part of a multi-partner research project that started with tagging channel catfish on the Canadian side of the Red River.
The research in later years expanded to inserting radio transmitters into about 750 fish of several species throughout the Red River Basin and into Lake Winnipeg, Pegg said. Each transmitter emits a unique frequency that is picked up by a series of “listening stations,” anchored throughout the basin and Lake Winnipeg, every time a fish swims by.
Researchers then retrieve the listening stations once a year to download the data and change out the batteries. The study includes about 250 listening stations, including 23 on the U.S. side of the Red River from Wahpeton, N.D., to the Manitoba border.
Which brings us back to the sheepshead aging study.
As with all fish species, researchers age sheepshead by removing inner ear bones called otoliths from the fish’s head and cutting them into thin cross sections. They then count the growth rings, similar to the process for aging a tree.
In Manitoba, Pegg said, the technician collected about 100 midsize sheepshead in the 16- to 20-inch range.
“He started working them up, and it turned out they were way, way old,” Pegg said. “He had a couple that were in their low 60s for ages, so it kind of surprised me they were that old.”
By comparison, similar-sized sheepshead he aged in Nebraska were considerably younger.
“The same-size fish here is maybe 8 or 10 years old,” Pegg said.
Findings from Manitoba caught the attention of Nick Kludt, Red River fisheries specialist for the Department of Natural Resources in Detroit Lakes, Minn., who is working with Red River catfish guide Brad Durick to collect additional sheepshead for aging on the U.S. side of the river as part of a river-wide age and growth assessment.
Pegg eventually will age those fish, as well.
“It will be interesting to see if they actually have the same kind of age structure or if they’re older, younger or whatever,” Pegg said. “Hopefully, in the next six months to a year, we’ll have more details.”
The oldest sheepshead documented in research literature came from a cache of fish bones found at the site of an archaeological dig in northwest Iowa, Pegg said. That fish was 71 years old, but its size couldn’t be determined because only the skull, with otoliths intact, was found.
Based on the radio-transmitter research, sheepshead in Manitoba also get around, Pegg says. It’s not unusual to see sheepshead swim from the Lockport Dam downstream to Lake Winnipeg – some 30 river miles – and swim right back, Pegg said.
“They’re moving all over the place,” he said. “I mean, they’re probably one of the most mobile species that we’ve got tags in at the moment. It’s just crazy how much they move, and they were certainly a species that we didn’t expect would do that.”
The radio-transmitter study, which involves Manitoba Sustainable Development, the federal Department of Fisheries and Oceans, the North Dakota Game and Fish Department, the Minnesota DNR and UNL, among others, is scheduled to continue through at least the summer of 2023, Pegg said.
Up until COVID hit, and the U.S.-Canada border closed to nonessential travel, Pegg and various UNL students spent several weeks in Manitoba every summer.
“If the border opens, I’m going tomorrow,” Pegg said.
If sheepshead sampled on the U.S. side of the Red River ultimately turn out to be as old as similar-size fish in Manitoba, it will continue a trend of longevity that has been seen in other species in the basin. A bigmouth buffalo sampled from the Pelican River, a Red River Basin tributary of the Otter Tail River, in 2019, was 112 years old. Catfish older than age 20 also have been documented in the Red River.
Live long and grow slow, seems to be the trend.
“It’s seeming that way at this point,” Pegg said. “But we’ve only looked at a couple of species.”