
PMDs on the Henry’s Fork
PMDs were one of the hot topics on the Henry’s Fork in 2024, so here’s a few excerpts from the 10 Year Insect Report just published, specifically about this insect. Total numbers Abundance of PMDs on the Henry’s Fork ranged from 365 individuals/m2 at St. Anthony in 2017 to 30,511 at Flat Rock in 2016, with an average of 7,701 individuals/m2 over all sites and years. Another way of looking at PMD abundance is that it has ranged from 2% to 61% of the total invertebrate community, with an average of 21%. For reference, data from the Bighorn River show that PMDs are typically 4% or less of all individuals. Change over time PMD abundance has been systematically decreasing across the watershed for the past decade, driven primarily by a large decrease at Flat Rock and to a lesser degree by a modest decline at St. Anthony. Our data show no evidence of systematic trends in PMD abundance one way or the other at Last Chance, Osborne, or Marysville. We know that doesn’t necessarily reflect hatches experienced by anglers, but it is what the data is telling us. More on that below. Insects Overall By any measure, the aquatic invertebrate community

















