“Whatchya doin’?” asked a fisherman who had wandered down to our camp on the Green River. We explained that we were sorting benthic invertebrates from Swallow Canyon. He peered at our tray of sorted stoneflies, mayflies, and amphipods and asked, “We don’t have any of those snails here, do we?”
The snails he was asking about are New Zealand mudsnails (NZMS), an invasive species that was introduced into the Snake River drainage 20 years ago that has since spread to many rivers across the Western U.S. This tiny snail was first noted in the Green River in 2001. Mark Vinson, a biologist at Utah State University, has documented their spread within the system and has found them in weed beds and under rocks within low velocity areas from Flaming Gorge Dam (RM 290) downstream to Limestone camp (RM 228). This species may be harmful to the Green River ecosystem because it has the potential to alter how nutrients flow through organisms.
The main vector of spread for NZMS are anglers that unknowingly transport this species within and between systems on gear and waders. Transport is facilitated by an operculum that seals the shell closed, preventing desiccation. As a result, these tiny snails can live out of the water for several weeks, especially when stored in damp waders.
Since the spread of the NZMS is tightly linked with human movement, it is important to inform the public about its presence. The Green River boasts a blue ribbon fishery, luring anglers from all over the world. As the fisherman’s lack of knowledge illustrated, many of these visitors are aware of the existence of the NZMS, but are not informed as to their actual status within systems. This suggests that public outreach beyond the existing effort (a few posted signs, news articles, etc.) is needed to control this invasive species. Further educating fishermen about NZMS would likely be an effective campaign, as this group of stakeholders is often responsive to issues concerning their hobby.
All anglers leaving the Green River, or any other system should thoroughly wash their gear and manually inspect it for NZMS, especially around laces and under the inner, removable soles of wading boots. Additionally, drying waders thoroughly in the hot sun is a good practice for reducing the spread.
Public education- Sign posted at Little Hole boat ramp. Photo by Julia Halverson