Native Population Characteristics of Pacifastacus leniusclus (Dana, 1852) in Tryon Creek, Oregon

Abstract Pacifastacus leniusculus (Dana 1852), the signal crayfish, is a freshwater astacid native to the Pacific Northwest and introduced in western Europe and Japan. Though P. leniusculus populations have been well-studied abroad, where they degrade local habitat and biodiversity, their ecology and natural history are less understood within their native range, where they fill key roles and risk out-competition by exotic crayfish. The present study describes density, morphology, and behavior of resident crayfish in a fourthorder Oregon stream, Tryon Creek, via surveys of nine sites from June–September 2022. Across sites, there was an estimated average P. leniusculus population density of 0.08 m-2, and no exotic crayfish were detected. Amongst crayfish collected (n = 162), total body length (TL) ranged from 13–90 mm, μ = 53 mm. Branchiobdellidans colonized one in four crayfish throughout Tryon Creek, damage to appendages occurred at a rate of 0.45, and the likelihood of both increased with TL. In a case study of Tryon’s Hwy- 43 Culvert, crayfish showed potential signs of stress; across numerous sites, young juveniles resided gregariously. Despite the present study’s novel strides toward native-range P. leniusculus population characterization, further research is encouraged to establish a well-rounded regional baseline.