Habitat Enhancement in Headwater Springs

Extensive field data from the early 1990s suggests that the two largest remaining Shasta crayfish populations are limited in size by the availability of usable substrate. This has implications on both the overall size of the population and the growth rate of the individuals in the population. Many life history traits are strongly associated with size. A lower growth rate can translate into a later age at first reproduction; a smaller size at reproduction can result in lower fecundity (i.e., fewer offspring being produced) and decreased survivorship.

The purpose of this project is to make additional habitat available to the Thousand Springs and Spring Creek populations of Shasta crayfish. The amount of usable habitat for Shasta crayfish could easily be doubled or even tripled by adding flat lava boulders to these headwater springs, opening the possibility for substantial population growth. Decreased intraspecific competition would likely result in increased individual growth rate, which would provide dividends in terms of increased fecundity and survivorship. Surveys are planned approximately six months and one year following the placement of the habitat rock to assess the effectiveness of the project by determining whether Shasta crayfish are utilizing the new habitat. Longer term monitoring with surveys every five years will be used to determine changes in population size and composition.