Henrys Fork Trout Population On The Rise

ISLAND PARK - As fishing season approaches, many anglers may be wondering how trout populations in the area look. In order to find out, biologists from the Idaho Department of Fish & Game (IDFG) recently completed annual population surveys on the Henrys Fork. The survey process involves using drift boats equipped with portable generators to run an electrical current into the water. Fish are temporarily stunned, which allows netters to collect them for marking and measuring. After one week, the biologists repeat the process, and record the ratio of marked to unmarked fish, which allows them to estimate the total population in that section of river. Nearly every year, surveys are conducted in the famous Box Canyon. This helps fishery and water managers learn how flows from Island Park Dam affect trout populations, thereby guiding future decisions. Unfortunately, low flows last spring precluded estimates for 2004. Other reaches of the river are surveyed on a multi-year basis. This year the stretch from Vernon Bridge to the Chester backwaters was surveyed. According to Regional Fishery Biologist Dan Garren, the surveys in Box Canyon showed the population is seeing some much needed reproduction. Though the overall numbers were only slightly better than in 2003, at about 1,700 fish per mile, the number of young fish coming into the population was very encouraging. "The number of two-year-olds was up about 80% over 2003," said Garren, "This is particularly important because these are the fish that were fry back in 2003, when the flows from Island Park Dam were shut off for dam repairs." Concerned stakeholders including representatives from IDFG, Fremont-Madison Irrigation District, Henrys Fork Foundation, and Bureau of Reclamation worked together to make the most of the situation with the available water after the dam was repaired. By increasing flows for the remainder of the winter, the group hoped to maximize survival of the juvenile trout. Fortunately, it looks like those efforts worked. Regional Fishery Manager Jim Fredericks is encouraged by the numbers, "In the winters of 2001-02 & 2002-03 we had two years with low flows resulting from the drought, and we did see juvenile production suffer." Since then, winter flows have improved. In fact, during the past two winter's flows have been over double what they were the previous two. "Practically speaking, this means that we've seen the worst in overall numbers, and now we're seeing the population rebuild," Fredericks said, "I think it's pretty clear that the efforts of those who've worked together to make the most of what water is available are paying off." Trout densities from Vernon to Chester were around 1,000 fish per mile. "The lower river doesn't have the same high densities that the Box Canyon does, but there are a lot of big fish in that reach!" said Garren.