Regional fisheries biologist Ken Frazer is asking Bighorn River anglers to watch for symptoms of gas super saturation in trout that could start appearing with the higher flows. This issue, which is caused when atmospheric gases, and specifically nitrogen, are entrained in plunging water and absorbed by fish before the gases have a chance to dissipate. Symptoms in trout appear as small blisters initially appearing on gill plates and fins, but can appear just about anywhere on a fish’s body. When the nitrogen levels (PSAT) exceed normal levels and affect a trout’s gills and other vital organs, death can occur.
Bighorn trout have adapted somewhat to higher nitrogen levels (PSAT), but the higher flows tend to trap more nitrogen as water is released from the main dam, and again from the Afterbay spillway. Biologist monitoring PSAT levels have noted that bigger flows are producing higher PSAT levels in recent days.
The good news is the entrained nitrogen tends to be worse near the water’s surface, and the larger releases means deeper water which in turns means many of the fish can escape by moving to slightly deeper water. Also, in some cases, the Bureau of Reclamation can change release outlets to help lower PSAT levels.
Ken, who is has managed the Bighorn River fishery for over 30 years, is asking anglers to report gas bubbles seen on trout, or dead or dying trout to FWP HQ’s. That phone number is (406) 247-2940.