Adopt-A-Fish update – May 25, 2006
 |
catfish are starting to move
By MATT JAEGER
Montana Fish, Wildlife and Parks
GLENDIVE – Using radio telemetry equipment to study the movement patterns of many of the species in the Missouri-Yellowstone Adopt-A-Fish program is pretty straight forward. Transmitters are surgically implanted and fish are tracked.
During the months of April and May, students get to track some of the implanted fish through Adopt-A-Fish. That generally works out pretty well by this time, the final installment of the program for students.
When flows and temperatures increase during April, most fish begin moving. However, channel catfish seem to be the exception, partly because of their behavior and partly because of their unique ability to give our radio transmitters the slip.
Previous Yellowstone River studies documented large movements by catfish. Fish tagged below Cartersville Diversion at Forsyth were recaptured by anglers 60 miles upstream near the mouth of the Big Horn River just few months later. Movements into tributaries, like the Powder and Tongue rivers have also been observed. However, most of the catfish in the Adopt-A-Fish program have been relatively sluggish so far this spring.
One possible explanation is that the transmitters we’re listening to have been ditched on the stream bottom by uncooperative catfish who got rid of them. Many species of fish are able to expel radio transmitters after they’ve been implanted but expulsion rates are usually fairly low.
Typically fewer than 10 percent of the transmitters we implant are expelled. In a recent laboratory study on juvenile pallid sturgeon, no transmitter expulsion occurred. However, when it comes to expelling transmitters, catfish are the kings.
When a foreign object, like a radio transmitter, is placed in the body cavity of a catfish, steps to rapidly remove it begin. The transmitter is first completely encapsulated or covered by tissue. The tissue capsule then adheres to and is passed into the intestine. Sometimes a whole new loop of intestine is actually formed with the transmitter inside. After the transmitter is in the intestine, it’s expelled just like other waste. This entire process can occur in less than two weeks!
To avoid this well-documented phenomenon of what they call “transintestinal expulsion,” we implanted transmitters as far forward in the body cavity as possible to keep them away from the intestine. We assumed that some expulsion would still occur but that we’d be able to detect shed transmitters because they wouldn’t move.
However, most of our catfish exhibited very little movement. During our last few tracking runs, the three catfish in the Adopt-A-Fish program moved less than half a mile combined. Few observed movements suggested that we may be tracking expelled transmitters instead of radio tagged fish and had us worried that our study may not accomplish its goals.
But careful examination of some of our relocation data, combined with observations in the field, have allowed us to breathe a little easier. Even though many catfish are at about the same river mile each week, they are actively swimming around the pools they live in.
As water levels rise, we’re starting to relocate catfish in side channels and backwaters that were previously dry. This type of localized home range is consistent with what was reported by studies in other river systems. Many catfish spent most of the year in less than a mile of river.
However, when the highest flows of the year occur, catfish tend to move long distances. Flows are beginning to peak and some of our radio-tagged fish are responding right on cue.
During our last tracking run, two fish moved over 60 miles to areas near the Tongue River, which appear to be important for spawning. The next few tracking runs will begin to provide an indication of catfish spawning movements and habitats, as well as how many fish still have intact transmitters.
Unfortunately, some of the most interesting things we’ll learn about catfish will happen during the summer months after the Adopt-A-Fish program is finished. But we’ll be sure to give a full report next winter when the program begins again.
Until then, enjoy the summer and, if you get a chance, spend a day on the Yellowstone or Missouri rivers in search of some of the native species we’ve gotten to know a little bit better this spring.
Adopt-A-Fish correspondents Dave Fuller, at Fort Peck, and Matt Jaeger, at Glendive, are fisheries biologists with Montana Fish, Wildlife and Parks. They posted weekly updates every Thursday throughout April and May in 2006 on this site and in the Outdoors section of The Billings Gazette.