Spatial Distribution and Habitat Use of Pacific Lamprey (Lampetra tridentata) Ammocoetes in a Western Washington Stream

Abstract

ABSTRACT We investigated the spatial distribution and habitat associations of Pacific lamprey (Lampetra tridentata) ammocoetes in a southwest Washington stream. The ammocoetes exhibited a highly aggregated, non-random spatial distribution pattern. Conductivity, dissolved oxygen, and gradient influenced ammocoete distribution at the large scale (across 50 m reaches), whereas wetted width, percent fines, canopy density, and velocity influenced distribution at the small scale (1 m2 quadrats). We observed optimum water depths of 70 cm and current velocities of 0 to 10 cm/sec. In general, ammocoetes preferred fine substrates though larger ammocoetes were found at low densities in large gravel substrates. Our findings illustrate the importance of slow water environments for the rearing stage of Pacific lamprey. Restoration activities should be designed to restore watershed function and process in a way that naturally allows systems to retain these critical habitats. Additionally, when considering ammocoete habitat use and distribution, it is important to take into account the scale of the observations.