Distribution of Pacific Lamprey in Watersheds of Puget Sound Based on Smolt Monitoring Data

Native lamprey play an important role in stream communities; however, endemic populations are declining worldwide. A 2004 petition to list Pacific lamprey (Entosphenus tridentatus) as threatened or endangered under the Endangered Species Act was not reviewed partly because the necessary population data, including simple presence or absence, was lacking. We sampled lamprey captured during salmonid smolt monitoring to determine the current distribution of Pacific lamprey in major watersheds flowing into Puget Sound, Washington. Pacific lamprey were identified in 13 of 18 watersheds and were more common in south Puget Sound watersheds and in watersheds draining western Puget Sound (Hood Canal). Few macrophthalmia (eyed-juveniles) were found, suggesting the majority of juveniles migrated seaward during other time periods. In addition, a “dwarf” adult variant of Pacific lamprey (<300 mm) was observed in several watersheds and may represent an alternate life history for some populations. Using genetic based data we verified that previously described visual techniques to identify Pacific lamprey ammocoetes from other species were successful for 97% (34 of 35) samples.