Foskett Speckled Dace (Rhinichthys osculus ssp.) are a distinct evolutionary lineage of the widely distributed speckled dace, restricted to two spring sites — Foskett Spring and Dace Spring — in the Coleman Lake subbasin of southeastern Oregon. The species was listed as threatened under the federal Endangered Species Act in 1985 because of its limited range and the threat of habitat destruction from cattle grazing. Land acquisition and fencing by the Bureau of Land Management addressed those threats, and the species was removed from the Endangered Species List in 2019. The Native Fish Investigations Section monitors population abundance and habitat conditions at both springs in cooperation with the BLM and USFWS, under both a post-delisting monitoring plan and a long-term cooperative management plan. The species is considered conservation reliant: its habitat requires active management to maintain open water, because vegetation encroachment by tules and cattails can rapidly reduce the available habitat and carrying capacity for dace.
Foskett Spring is the species' native habitat — a natural spring that rises from a springhead pool, flows through a narrow brook into a series of shallow marshes, and disappears into the soil of the normally dry Coleman Lake bed. Long-term monitoring has shown a strong relationship between dace abundance and the amount of open-water habitat at Foskett Spring. When vegetation fills in the spring channels and marsh pools, dace numbers drop; when the BLM has cleared vegetation and excavated pools, numbers have rebounded. The most recent habitat enhancement, a mechanical excavation of eight pools in 2017, substantially increased open-water habitat and pool depth. NFI estimates population abundance using baited minnow traps deployed across the spring's three habitat types — the spring pool, the spring brook, and the tule marsh — over a two-day sampling period, with abundance estimated using a state-space model. In 2023, NFI estimated approximately 8,741 dace at Foskett Spring, similar to the 2019 and 2021 estimates and well above the post-delisting monitoring threshold of 500 adults that would trigger a management response. Young-of-year dace were observed in the tule marsh in both survey years, indicating continued recruitment.
Dace Spring, however, presents a more concerning picture. The refuge population was established by translocating fish from Foskett Spring — first in 1979–1980, and again in 2010–2014 after the original population collapsed. The spring consists of two excavated pools connected by a shallow channel. By 2023, the estimated population had declined to 189–388 dace, depending on the estimation method, down from nearly 2,000 in 2018. No small or young-of-year fish were captured in 2023, and all individuals were adult-sized, suggesting that recruitment has ceased and the population is aging. This pattern mirrors a previous collapse of the Dace Spring population in the late 1990s, which was also preceded by a lack of recruitment and loss of open-water habitat to vegetation. The spring channels have again become shallow and heavily choked with cattails. BLM excavated the north pool in 2021, but abundance continued to decline. NFI and its partners are evaluating whether clearing the spring and connecting channels and adding spawning gravel could restore conditions for successful reproduction.