JACKSON - Ever wonder where fish go in the winter, when the river is frozen over? You’re not alone. The Wyoming Game and Fish Department recently completed a study on bluehead suckers in the Snake River near Jackson that looked at such seasonal movements and more.Bluehead suckers are a lesser-known native nongame fish primarily found in the Colorado River drainage. In fact, the population that occurs in the upper Snake River is one of only two isolated populations found outside of the Colorado River drainage, the other in the Bear River drainage.
In order to learn more about this isolated population, Jackson Fisheries Biologist Brian Hines, started surveying for bluehead suckers back in 2010, and implanting those he found with radio-transmitters. Hines found them throughout the Snake River between Jackson Lake and Palisades Reservoir, and in most of the major tributary streams, including the Gros Ventre and Buffalo Fork rivers and Fish, Flat, Pacific, Spread, and Two Ocean creeks.
A total of 60 fish were implanted with VHF (very high frequency) transmitters to follow their travels and track survival. The transmitters, about the size of a AAA-battery, were surgically implanted into the fish’s belly with a thread-like antenna left dangling out to allow transmission of the radio signal. Hines then spent countless days floating, flying and walking the Snake River, year-round, listening for his marked fish, each identified by its own unique radio frequency.
Interestingly, the distances bluehead suckers traveled proved to be quite variable, ranging from a low of 1.1 miles to a whopping 73 miles. “Fish typically moved longer distances downstream in late winter and upstream in autumn.
The areas of the Snake River that bluehead suckers occupied varied by season and year. During the harsh and long winter of 2010-2011, Hines found tagged fish primarily in two areas, Oxbow Bend in Grand Teton National Park and the Snake River Canyon. During the much milder winter of 2011-2012, fish were more widely distributed throughout the river.
Hines used their pectoral fin rays to estimate the fishes’ age and growth. Fish ranged from 4 to 24 years old. Hines found that when compared to other research on bluehead suckers, the Snake River population had higher growth rates and were also, generally, an older population than most. He credited this to a good food base.
As you might expect, suckers are bottom-feeders, feeding primarily on algae. But unlike other suckers who consume free-floating algae, blueheads have a rough, hardened bottom lip to scrape algae off of rocks and logs.
Black spot is a disease that can negatively affect some fish populations. Hines found a fairly high prevalence of black spot in the Snake River blueheads. The prevalence was highest in the sections furthest upstream, from Jackson Lake dam to Deadman’s Bar, where over 90 percent of the blueheads he captured had it. However, black spot disease did not seem to negatively affect on blueheads’ condition.
Despite marked declines across their native range, Hines found the Snake River bluehead sucker population to be stable. Where populations are declining, researchers blame habitat loss and hybridization with nonnative species, such as white sucker. Hines characterized the Snake River habitat as good, and fortunately, found little evidence of negative interactions with introduced species. Consequently, it appears there are no direct threats to this population at this time. However, Hines recommends that monitoring for the presence of nonnative species should remain a high priority, as it is one of the major threats for all fish species.
(Contact: Mark Gocke (307) 733-2321)