08 September 2023

Collection of eDNA samples for Bull Trout detection

Written by: William Dokai

Environmental DNA (eDNA) is a relatively new scientific method that is often used for detecting aquatic organisms. Fish and other aquatic life introduce cellular material into the environment through sloughing of skin cells, mucous membranes, and the excretion of waste. The cellular material of all organisms contains DNA, and every species has DNA sequences that are unique to them. By filtering water from a river, lake, pond or the ocean across a very fine filter, this cellular material in water can be captured and a genetic analysis can then determine if an organism is present where that water was collected. This may seem like an overly complex way to determine where an aquatic species lives, but it is actually a quite efficient way to survey a large geographic area, with high sensitivity, and at a lower cost than traditional surveys.

The last two weeks were a whirlwind of eDNA water sample collection on the Helena- Lewis and Clark National Forest. My supervisor and I collected samples from 40 locations, many of which required long hikes to remote streams, and backpacking or camping. On the last two days of eDNA sampling, we hiked an estimated 22 miles with not only our backpacking gear, but with the added bulk and weight of eDNA sampling gear. Why would we go to all this effort? We were collecting eDNA samples for the detection of Bull Trout.

Bull Trout are a fish species that is federally listed as threatened with extinction, and they are a species of conservation concern on the Helena-Lewis and Clark National Forest. Bull Trout are native to the northwest United States, and Western Canada. Within Montana, they are native to the western portion of the state, predominantly west of the Continental Divide. They are a uniquely cold adapted species, which can only persist in cold water environments that rarely exceed 59 to 64 degrees F. Factors that have led to, and continue to contribute to the decline of Bull Trout are human caused, and numerous. Largely these include the loss, degradation, and fragmentation of habitat, the introduction of non-native fish species, and past and ongoing fishing practices. Climate change is also a major concern for the long-term survival of this species because of their requirement for very cold water.

The eDNA collection we recently conducted was within the Little Blackfoot River drainage, which was historically home to a robust Bull Trout population. However, in the last century water and land use practices have led to a severe decline of the Bull Trout here. Sadly, based on previous sampling data, it is unlikely that many of the samples we collected will lead to detection of Bull Trout. Although Bull Trout have the highest legal protection in the US- they are listed as threatened under the Endangered Species Act, they continue to decline. One of the hardest parts about this for me is that there is very little hope that any action within the boundaries of the National Forest will help the situation on the Little Blackfoot River. While the headwaters of the river are on National Forest land, the lower portions of the river are largely on private land, and these are the areas that continue to see land and water use that is incompatible with Bull Trout persistence.

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