A second chance for the Foskett Spring speckled dace: habitat restoration and reintroduction as recovery tools.[ILLUSTRATION OMITTED]
The Foskett Spring speckled dace (Rhinichthys osculus ssp.) is a small fish known from a single population inhabiting Foskett Spring in south-central Oregon. In 1985, it was listed under the Endangered Species Act as threatened, due to habitat loss and its restricted distribution.
Populations of the Foskett Spring speckled dace were probably distributed throughout prehistoric Coleman Lake in the Warner Basin. The Warner Basin includes portions of southeast Oregon, northern Nevada, and northern California. The dace became isolated in Foskett Spring as the lake began to dry nearly 10,000 years ago. The salt content of the lake water increased and the amount of freshwater habitat available to the dace was reduced to just a few spring systems.
Foskett Spring is a natural system that rises from a springhead pool, flows through a narrow brook into a series of shallow marshes, and then disappears into the soil of the normally dry Coleman Lake.
In 1979, 100 dace from Foskett Spring were introduced into Dace Spring by the U.S. Bureau of Land Management (BLM)--located just half a mile south of Foskett Spring--in an attempt to establish a second population. This attempt failed, however, due to a lack of suitable spawning habitat.
In 1987, BLM acquired, through exchange, a 160-acre (65-hectare) parcel of land containing both Foskett and Dace springs. Both sites were fenced to exclude livestock, thereby minimizing habitat disturbance.
The Oregon Department of Fish and Wildlife's (ODFW) Native Fish Investigations Project then began monitoring the Foskett Spring population on a biannual basis. Its biologists found the population to be healthy and near the carrying capacity of about 3,000 adults. ODFW also documented multiple age-classes and the presence of young-of-the-year fish, which suggested successful recruitment.
However, the population has fallen by approximately 90 percent since 1997. We attribute this decline to a substantial reduction of open water habitat due to encroachment by macrophytes, plants that grow in or near the water. ODFW has worked with the U.S. Fish and Wildlife Service to increase the quantity of open water habitat at Foskett Spring and create an additional population of the fish at Dace Spring.
In 2009, a collaborative project between the Service, BLM, and ODFW was implemented to complete a restoration project at Dace Spring and create two permanent pools. The following year, 50 dace from Foskett Spring were transferred into these new pools.
ODFW biologists will monitor both the donor and the introduced populations to obtain population estimates, describe the population size structures, and look for evidence of recruitment. Once we are confident that the introduced population is well established, and have documented successful spawning and increasing abundance, ODFW will plan a similar habitat restoration project for Foskett Spring. Ideally, this will result in a stable or increasing population and contribute towards recovery.
In 2009, the Service completed a 5-year status review for the Foskett Spring speckled dace. Among the recommendations in the review was the collection of demographic information on age structure, age at reproduction, and longevity. In partnership with Oregon State University, ODFW initiated a project in 2010 to gather this information. Validation is the first step in assessing the age structure of a population. In this case, validation involves verifying that growth patterns on ageing structures of individual fish are discernable and deposited annually. Examples of fish ageing structures include scales, otoliths (ear bones), and rays of the pectoral fins.
Annular growth rings, or annuli, are typically deposited on hard structures of the fish, much like annular rings form in trees. In the summer, rapid growth creates widely spaced rings, but the rings become more closely spaced when growth slows down for the winter. In springs, where water temperatures are fairly constant, these differences in fish growth may not be as evident.
In 2010, ODFW biologists marked all of the dace introduced into Dace Spring by exposing them to the antibiotic oxytetracycline (OTC) for six hours. When OTC is incorporated into the dace's hard structures, it forms marks that are visible under ultraviolet light.
ODFW will sample 50 dace to characterize the annual growth patterns since the time of their initial marking. This will allow biologists to validate growth patterns and assign accurate ages. If the patterns are regular and discernable, samples will be collected again in 2012 to describe the age structure, the age and size at reproduction, and the longevity of individuals. This information will be critical to assess the health of these populations and their responses to habitat restoration.
Paul Scheerer; a fish and wildlife biologist with the Oregon Department of Fish and Wildlife, can be reached at firstname.lastname@example.org or 541-757-5147. Mark Terwilliger, a, senior faculty research assistant at Oregon State University, Department of Fisheries and Wildlife, can be reached at email@example.com or 541-737-2407.
Editor's note: In 2006, Paul Scheerer was recognized by the Service as a Recovery Champion for his work on the Foskett Spring speckled dace and a variety of Oregon's other endangered and threatened fish species.