Fish do it: Fall-spawning trout study underway on the Madison

With the low morning sun just beginning to melt the frost off the grass and willows, Travis Lohrenz and Michelle McGree join throngs of anglers donning waders and heading to the Madison River. But instead of carrying rods, these two carry equipment designed to help gather information about the trout making their way upstream into Yellowstone National Park to spawn.

For the second time in as many years, the Montana Department of Fish, Wildlife and Parks is operating a fish weir on the Madison downstream of Yellowstone with cooperation from Gallatin National Forest and funding from PPL Montana.

As the brown and rainbow trout leave Hebgen Lake to make their annual spawning run to the gravelly spawning grounds in the park, the weir funnels the fish into traps that hold them until they can be removed.

Lohrenz and McGree then use nets to remove the fish from the traps, and record their length, weight and sex. Scale samples are also taken to help in determing the age of the fish. Once the data is collected, McGree inserts a uniquely numbered plastic tag behind the dorsal fin of the fish, and they are placed into another tank to be released.

"The primary objective of the weir is to learn about the characteristics of the fall rainbow trout spawning run" says Pat Clancey from the FWP field office in Ennis. Most rainbow trout tend to spawn in the spring, but the Hebgen Lake drainage has many rainbows that spawn in the fall. Lohrenz points out, "We pass a lot of ripe rainbows, which makes this system pretty unique."

It's possible that this behavior was intentionally bred in hatcheries in the sixties and seventies. Another possible cause is the influence of thermal features upstream in the park. The FWP hopes to be able to determine how much the fall-spawning rainbows contribute to the fishery in Hebgen Lake.

This year it appears the spawning run has begun quite a bit later than usual, probably due to the unseasonably warm weather. As of Monday, October 6, the weir had passed somewhere around 60-75 trout, the largest of which was a 23 inch rainbow. Last week the crew was manning fish-traps elsewhere, so the weir remained open, passing an unknown number of fish.

Some local anglers are concerned that the weir prevents fish from making their run upstream, impacting the fall fishing which so many anglers love dearly. Clancey points out that, "At most the weir delays fish for 24 hours, and the mortality rate is very low."

While it's not out of the question that the weir could turn a few fish back, hopefully the information gathered from the operation will help fisheries experts understand and protect the unique spawning runs in the Hebgen Lake system. Protecting these runs will help ensure that anglers have similar fishing opportunities for years to come.

Anglers who catch tagged fish in the Hebgen Basin are asked to note the color of the tag, the number printed on the tag, and the date caught and to call the FWP Field Office in Ennis at 406-682-7807.

Boaters on the river should be prepared to use caution and to portage their boats river-right on any floats through the area. Anglers are also asked not to target fish directly below the weir.

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