Here is a quick summary of the collaborative gill lice study that the Henry’s Fork Foundation and the Idaho Department of Fish and Game initiated in June, 2016. For background information on this study, check out these links:
Gill lice update #1 (7/27/2016)
Gill lice update #2 (9/21/2016)
- Total number of surveys: 78
- Breakdown of surveys by location:
- 41 from Harriman Ranch
- 26 from Henry’s Fork (Box Canyon, St. Anthony, etc.)
- 6 from South Fork Snake River
- 2 from Robinson Creek
- 2 from Henry’s Lake
- 1 from Fall River
- Total number of fish sampled: 242
- Results by species:
- 189 rainbow trout sampled, gill lice observed in 45.
- 39 rainbow trout with light infestation (< 50% of the gill edge covered)
- 6 rainbow trout with heavy infestation (> 50% of the gill edge covered)
- 37 brown trout sampled, no presence of gill lice found
- 16 cutthroat trout sampled, no presence of gill lice found
Figure 1. Number of Rainbow Trout sampled in the Upper Snake River region from July 1 through January 1, 2017, partitioned by Harriman Ranch reach (Harriman), all other reaches of the Henry’s Fork outside of Harriman Ranch (Henry’s Fork), and other rivers within the Upper Snake River region (Other).
Reports of gill lice continue to be primarily isolated to Rainbow Trout in the Harriman Ranch reach. One third of Rainbow Trout sampled in the Harriman Ranch reach had gill lice present and four cases were classified as having a “heavy” infestation. The percentage of Rainbow Trout reported with gill lice in other reaches of the Henry’s Fork and Upper Snake River region declined to 4% during October through December (down from roughly 20% during July through September). It is difficult to say whether this decline is product of a seasonal change but we hope to be able to identify temporal trends in gill lice prevelance, severity, and distribution as this study progresses. On that note, we continue to ask for your assistance in helping collect data by filling out surveys whenever you hit the water in 2017!
Thanks again to everyone who participated in the study so far. We greatly appreciate your time and effort!
If you have questions, comments, or concerns, feel free to contact me at Bryce@henrysfork.org or 208-652-3567