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Fishery biologists and managers are increasingly consumed with the recovery and restoration of native trout and salmon throughout the western United States. These fish historically inhabited a variety of freshwater habitats, but have declined due to habitat degradation, fragmentation and introduction of nonnative species. Introduced fishes constitute a major threat to the persistence of native trout across the continent. For example, the introduction of lake trout (Salvelinus namaycush) into Yellowstone Lake, which has not evolved with a native predator, impacts the entire Greater Yellowstone Ecosystem. Yellowstone Lake once supported what was believed to be the largest genetically unaltered population of Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) in the world. Introduced lake trout were initially reported in Yellowstone Lake in 1994, and subsequently, Yellowstone cutthroat trout have become the major prey of lake trout. Recent evidence suggests that this aggressive predator has substantially altered the abundance and demography and Yellowstone cutthroat trout in the lake and currently threatens its long-term presence.

Yellowstone Lake trout

The National Park Service has been actively attempting to reduce the numbers of lake trout in Yellowstone Lake since 1996, primarily by passive capture using gill nets. Although gill nets may remove substantial numbers of lake trout, there are concerns that Yellowstone cutthroat trout may also be caught in the gillnetting operations. One effective alternative, electrofishing, has been used to capture lake trout as they migrate into shallow water to spawn, but safety concerns limit this approach. Research has also been initiated to develop techniques specifically for destroying lake trout embryos on spawning grounds, such as controlled electricity and suction technology. All of these efforts to increase direct removal and utilize innovative techniques for destroying lake trout embryos and larvae require knowledge regarding lake trout movement patterns and accurate information concerning the location of spawning areas.

Our collaborative research utilizes acoustic transmitters implanted in adult lake trout to document movement patterns in Yellowstone Lake. This will assist with active netting activity and identification of spawning area that can subsequently be targeted for embryo destruction. These data are critical for expanding management options for suppressive invasive lake trout. 

FAQ on Invasive Lake Trout in Yellowstone Lake


Yellowstone Lake at sunset.

Through the use of acoustic telemetry researchers have been able to track lake trout implanted with transmitters in Yellowstone Lake. These transmitters send out signals that are recorded and stored by acoustic receivers. Some of the current free swimming fish were tagged as far back as August of 2011. Other lake trout were implanted with tags that transmit depth and temperature data to receivers when fish come within range of monitoring sites. This information gives researchers further insight into the behavioral patterns and responses of this invasive species within the context of the spatial and temporal world.

Surgical Procedures: In order to implant lake trout with transmitters they must undergo a surgical procedure. Lake trout are anesthetized prior to the surgical procedure to reduce stress. During the surgical procedure, lake water is pumped across the gills of the lake trout to ensure it receives adequate oxygen. A small incision is made on the ventral side of the lake trout and a transmitter is implanted into the fish. The incision is then sutured closed with sterile monofilament synthetic sutures. The fish is then allowed to recover in a container of fresh lake water before being released into the Yellowstone Lake Ecosystem.

Receivers Deployment: Acoustic receivers are deployed using polypropelene rope, secured at one end to a 16 kg weight and at the other end to a surface buoy. The boat operator drives to the designated GPS coordinates and indicates to the other researchers when it is time to deploy the receiver. The weight is tossed over the bow and it is allowed to sink to the bottom of the lake. Once the weight is in place and secure, the other end of the rope is cut and secured to the surface buoy. 


Study Region

Yellowstone Lake is a complex ecosystem set in the Greater Yellowstone Ecosystem. The introduction of piscivorous lake trout has caused shifts in the dynamics of this ecosystem. Yellowstone cutthroat trout did not evolve in the presence of other piscivorous species and therefore may have difficulties adapting to the presence of the lake trout. Historically there were estimated to be 3.5 million cutthroat in the system during any given year. In the post lake trout introduction era the number of cutthroat present in the system has decreased to all-time lows while the average size of adult cutthroat has increased. For the purposes of our study we have examined the usage patterns of lake trout in this ecosystem by splitting the lake into four distinct regions ( based on geographic and bathymetric characteristics). 


Acoustic Biotelemetry Project Technology

Inserting a fish tag.
Tags: Lake trout used in this telemetry study are implanted with one of two types of tags. Non-coded tags are those that transmit only the tag number. Alternatively, coded tags are those that transmit both pressure and temperature data. These tags transmit data that allows researchers to retrace the fish movements across time.

Receivers: Acoustic receivers are used by researchers to record tag transmissions underwater. These devices are powered by a lithium tidarian battery that can last for more than a year. These receivers will remain in the water recording transmitters until they are removed and downloaded. Once the information from the receivers has been successfully downloaded, the receiver storage is cleared and it is redeployed at the same GPS coordinates from which it was retrieved.