Modeled bull trout habitat in western Montana and northern Idaho. Color coding indicates the estimated likelihood of a stream providing spawning and rearing habitat for bull trout (Isaak et al. 2015)

Mounting evidence shows that the distribution of bull trout within individuals streams has been contracting in association with climate change; some historically occupied habitats may no longer support populations. Because of the difficulty and expense of sampling bull trout, current information about the species distribution is imprecise and many streams have been sampled infrequently or not at all. That uncertainty comes at a cost. Stakeholders may not be able to efficiently target their limited conservation resources, may forego or delay land management critical for other objectives, and may even avoid monitoring populations because of the added burden of obtaining sampling permits.

To reduce uncertainties (and regulatory gridlock) associated with bull trout, we recently developed and published the Climate Shield Habitat Occupancy Model, which uses NorWeST temperature information and other environmental covariates to accurately predict the probability of bull trout (and cutthroat trout) presence across the Columbia Basin (Fig. 1; Isaak et al. 2015). The fish and temperature data used to develop the NorWeST and Climate Shield databases and models were “crowd-sourced.” That approach was particularly powerful because it engaged hundreds of biologists working for dozens of agencies and leveraged their raw data to develop databases worth over $10,000,000. Building on those efforts, we propose to conduct a precise, up-to-date, range-wide bull trout status assessment through the use of crowd-sourcing, digital media, and new genomic techniques that are revolutionizing the cost-effectiveness of broad-scale species sampling.

Among the array of genomic techniques now available, environmental DNA (eDNA) has emerged as a powerful method for determining the occurrence of many species reliably and inexpensively.  The method involves collecting DNA shed by organisms (i.e., environmental DNA) by pumping water through a filter. We have also developed a field-proven eDNA sampling protocol that requires only 15 minutes of effort by a single person to collect a sample.

For bull trout, initial studies with eDNA have been directed at precisely delineating the their distribution within select watersheds, as well as confirming their absence from potential habitats and discovering previously unknown populations (Fig. 2). Samples collected to evaluate bull trout distributions can be used to evaluate many other species with no additional field costs and can serve as a multi-species baseline for future biodiversity assessments.

A comparison of eDNA detection of bull trout in the headwaters of Lolo Creek, Montana and previous electofishing. The arrow points to a small putative population that was previously undetected.