Custom-built Equipment Helps Hunt Down Invasive Lake Trout in Yellowstone Lake
New benthic sled scours lake bottom with jet water to find lake trout eggs
- By Lee Gregory Simard
Rubenstein Ecosystem Science Laboratory graduate student Lee Simard, working with Professer Ellen Marsden, returned to Yellowstone National Park this spring to continue his research investigating the feasibility of suppressing invasive lake trout populations during their early life stages in Yellowstone Lake. While management and research on Lake Champlain is focused on restoring lake trout populations, the National Park Service is leading a multi-agency effort to suppress lake trout in Yellowstone Lake where they threaten endangered native Yellowstone cutthroat trout. In addition to setting gillnets to remove lake trout, the NPS hopes to also target early life stages such as eggs and fry.
The focus of Simard’s research this spring was to locate potential areas in Yellowstone Lake where lake trout may spawn to direct future efforts that will kill eggs or fry on the spawning reefs. Spawning has been confirmed at five locations in the lake, but low egg and fry densities measured at each site suggest that other sites also exist. Surface and diver-deployed traps are frequently used to detect the presence of spawning, but are labor-intensive and inefficient at sampling large areas.
To efficiently sample larger areas of Yellowstone Lake substrate, R/V Melosira Captain Steve Cluett designed and built a benthic sled that can be used to collect lake trout fry and eggs. To dislodge eggs and fry, three water jets are directed into the substrate from a manifold at the front of the sled, powered by a pressure washer on board the tow boat. As the sled is slowly towed, the jets of pressurized water push material out of the interstices of rocky substrate into the water column. This material is then captured in a net attached to the sled; the net is checked and emptied on board the boat after each tow. Metal bars between the sled’s runners allow it to slide easily over large rocks and logs without hanging up.
The sled was used to sample 19 different sites this spring, chosen based on their substrate, information from gillnet catches during the spawning season, acoustic telemetry positional data, and bathymetric data. Lake trout fry were only detected at one site, but substrate data collected by cameras on the sled indicated several new sites that will be explored again to find eggs during the spawning season this fall.