Considering Pacific Lampreys When Implementing Instream Activities
Abstract.—Efforts to minimize negative effects to fish species during instream activities generally do not consider the life history characteristics of native nongame fish species, particularly lamprey. While there is still much to be learned about Pacific lamprey Entosphenus tridentatus (formerly Lampetra tridentata) distribution, abundance, and status, the need to actively conserve lampreys is evident. Populations of the Pacific lamprey have been reduced in many river drainages along the West Coast of the United States. The purposes of this paper are to raise awareness of the need to consider Pacific lampreys in project implementation and to stimulate development of methods to address instream project impacts.
Projects that alter passage, change flow hydraulics, alter stream substrates, and/or decrease habitat complexity can negatively affect lampreys. Of particular importance to lampreys are low velocity areas where larvae (ammocoetes) live in the substrate as filter feeders for 3–7 years. Since several age-classes of ammocoetes may congregate in high densities, a single dewatering event during construction activities may have a significant effect on a local lamprey population. Methods to reduce effects to the various life history stages of lampreys are just beginning to be investigated and developed. However, basic measures for lamprey conservation will also benefit other aquatic species by providing for a diversity of habitats and stream structure, and complex velocity distributions, while also appropriately modifying the duration and timing of instream actions.