The Henry’s Fork below St. Anthony is a productive fishery with an increasing brown trout population. Recently IDF&G fisheries personnel have completed a survey of its salmonid population. The results of this survey are given below.
Trout Populations are Strong in the Henry’s Fork near St. Anthony
By John Heckel
Regional Fisheries Biologist
In early October 2020, we conducted our 6th population estimate on the St. Anthony reach of the Henry’s Fork of the Snake River. This estimate is conducted in the fall every three years and extends from the Railroad Bridge downstream to the Red Road Bridge. Based on our sampling data since 2010, we can see an increasing trend in Brown Trout abundance in this reach.
We can see in the figure above that the number of Brown Trout per mile has been increasing since we started surveying the reach in 2004 while Rainbow Trout abundance has remained low and relatively constant. Currently, Brown Trout make up 96% of the trout composition in this reach where we caught 1,468 trout in total. As can be seen in the images, there are some very large Brown Trout with fish up to 25” in this reach!
The trout population in this portion of the Henry’s Fork is managed as a wild trout fishery, so these large trout captured in this reach are in fact wild fish. Therefore, referring to the length distribution of fish captured here, this section of river grows some very large trout.
Although water temperature in this section of the Henry’s Fork can become warmer than 70°F during portions of the summer, trout can find thermal refugia from groundwater and spring inputs that help coldwater fish remain cool. In addition to Brown and Rainbow trout, we also estimated Mountain Whitefish abundance in the reach. There were 685 whitefish per mile. Based on our length frequency data from Mountain Whitefish we observed several age classes present, which is evident by the multiple peaks in different length groups.
Survey results indicate sport fish populations in the St. Anthony reach are healthy and in good numbers. Managing this section of the river as a wild trout fishery with a 2 trout limit appears to be conducive for growing large fish and allowing population numbers to increase.