Can’t Live Without ‘Em: Bull Trout

October 20, 2011

A weekly homage to endangered species, large and small

You’ve probably heard of the proverbial “canary in the coal mine,” but have you heard of the “trout in the cold stream”? Neither have I, which is why I just made it up to highlight the fact that the threatened bull trout is an equally vital indicator of the health of mountain streams.

The presence of bull trout populations are an excellent indicator of stream health in the northwestern United States.

Bull trout are a member of the salmon family and depend on pristine waters, more so than almost any other fish. According to the U.S. Fish and Wildlife Service, bull trout habitat must meet strict requirements known as “the four C’s”: cold, clean, complex and connected.

Bull trout thrive in water that is below 60 degrees Fahrenheit. That explains why they’re only found in rivers, lakes and streams in parts of the northwestern United States and Canada where the water stays cold year-round. Bull trout embryos are even more finicky. Studies have shown that the survival rates of offspring are much higher when they’re born in water that tops out around 46 degrees Fahrenheit.

In addition, bull trout eggs are buried several inches beneath the stream bed, usually in gravel bottom streams that provide sufficient cover for the newborn fish once they hatch. Waters must be clear and relatively free of sediment, otherwise the embryos get trapped beneath sediment and fail to hatch. Juveniles do best in streams where there are logs, pools and shade beneath river banks that offer plenty of places to find food and shelter. And adults often travel more than 100 miles from lakes and large rivers to find smaller spawning streams that meet all these requirements.

For all these reasons, bull trout are extremely susceptible to disruptions to their natural environment, whether that’s extra sediment and runoff from nearby development, changes in stream temperature that result from global warming, or competition from non-native species. So when populations of bull trout start to disappear, as they have in recent decades, you know that something is wrong.

Bull trout once filled nearly 60 percent of the Columbia River basin and could be found in large numbers across much of Washington, Idaho, Montana, Oregon, northern California and even into Nevada. Now only small populations exist in those states, they have been completely wiped out in California, and only a tiny remnant survives on the border of northern Nevada. Today, they occupy only half of their historic range in the Columbia River basin and less than a quarter of their historic range along the Klamath River.

Conservation Pays

A massive bull trout is rescued from a net.

The species was listed as threatened in 1998 and has since started to recover, especially in parts of Oregon and Montana. Where select populations are sufficiently abundant and stable, some regulated fishing is even allowed, providing a boon for local economies. Migratory bull trout can grow to sizes larger than 20 pounds, making them a favorite for recreational fishermen like at Montana’s Hungry Horse Reservoir, Lake Koocanusa and the South Fork Flathead River (see Montana Fish, Wildlife & Parks bull trout fishing regulations). A recent economic study found that bull trout fishing in Montana alone results in additional income of $10 to 12 million, and double that once the money filters through the local economy.

Because of their threatened status, bull trout fishing comprises only a small portion of the regional fishing economy. But it could provide a much bigger boost if the fishery fully recovered.