CUTTHROAT TROUT TRACKING AND HABITAT EVALUATION UPDATE
01/20/04
Joe Dupont, Fisheries Biologist for Idaho Department of Fish and Game
We are into the 8th month of tracking our radio tagged cutthroat trout. This study has been a great success as we have learned many things that we believe can help improve this fishery. During the summer, we saw extremely warm water temperatures >78°F (>26°C), which led to some interesting findings. Most of the fish held tight to some type of cover and moved very little during this period. When viewing these fish underwater, it appeared to be a struggle for some of them as many were laying on the bottom gasping for oxygen. Fishing during this time of year would probably be terrible as most of the fish we saw were not feeding or leaving the cover. That’s probably why we saw so few fishermen out during this time of year. A few fish made movements into side channels during this warm period, and to our surprise when we measured the water temperature it was 5-9°F (3-5°C) cooler than the main river. We've long known that side channels are important for juvenile and over-wintering fish, but finding out they can also provide a cool temperature refuge during summer is very important. This will only increase our efforts to help protect the floodplain in the lower river where side channels typically would be found. When we snorkeled one of the cooler side channels during the heat of the summer we saw probably over 800 fish (cutthroat trout, rainbow trout and mountain whitefish) in an 80-yard length of stream.
Another important aspect we learned is that the majority (>75%) of the cutthroat we put radio transmitters in tended to remain in the same general area as they were tagged. For example fish that were tagged in the Little North Fork or Tepee Creek remained in those streams. In general, the fish tended to move downstream throughout the year but long migrations (> 10 miles), were uncommon. The importance of this finding is that our fishing regulations have set up catch-and-release areas in the upper half of the Coeur d’Alene River basin. There was some concern that many of the fish in the catch-and-release area would migrate downstream to where they could be harvested and essentially make this regulation ineffective. Based on our findings, the current regulations should accomplish what it set out to do, which is, provide a sizeable area where fish can grow old and large, as well as an area where limited harvest will be allowed for those who would like to keep a few fish for dinner.
Fishing regulations are only effective, if they are followed. This study has pointed out areas where poaching may be impacting the fishery. In a 20 mile section of the North Fork Coeur d'Alene River between the South Fork and the steel bridge, seven of our radio tagged fish spent over one month. Five or six of these fish were killed by fisherman, three of which were caught illegally. Based on this information, increased patrols by Fish and Game officers and increased education could help reduce this impact.
During the months of August and September, we were able to quantify habitat characteristics in most of the Coeur d'Alene River where our radio tagged fish occurred. These data will be very valuable in helping determine if certain types of habitat important to cutthroat trout are limited or not. This type of information will help direct future restoration projects in the basin. We have also pulled all of our thermographs (hourly temperature measuring device) that were put out for the study. These temperature data will tell us which stream reaches may provide cold-water refuges and which streams reaches may become too warm to support cutthroat trout during summer.
We currently are tracking 41 of the 66 cutthroat trout we originally tagged. Twenty-five of the fish have died from fisherman, predators, and unknown causes. The 41 fish we are still tracking should provide us valuable data on winter habitat use. In many systems it is believed that the quantity and quality of winter habitat often controls the number of cutthroat trout the system can support. Currently, the fish we are tracking are still scattered throughout the basin and appear to be selecting areas with very slow water velocities. This may be good news as it does not appear that fish have to migrate long distances to find suitable habitat to over-winter in. Continued investigations are needed to further evaluate the quality of the winter habitat the cutthroat trout are selecting.
Even though we are still tracking fish, we are also starting our initial data analysis. We will be looking at movement and try to determine if there are any environmental variables that help predict movement. We will also look at habitat and cover use and relate that back to habitat availability within the river system. Our plan is to have a draft presentation by early April, which we will present to all the clubs.
We should all thank Earl Frizzel, Jerry McBride, and Judy Kaufman for their efforts in coordinating the volunteers for all phases of the study. We had a great contribution from all the clubs. Volunteers contributed over 80 days of their time to the project to date. There is still time to volunteer your help and get one of those nifty T-shirts, as we will continue tracking the cutthroat trout until June.