Rapid development of larval Pacific lamprey Entosphenus tridentatus in southern populations provides adaptive benefits for uncertain flow regimes

The duration of the ammocoete life stage in Pacific lamprey (Entosphenus tridentatus) is not well understood, particularly in southern latitudes, hampering the development of conservation strategies. We studied the development of anadromous Pacific lamprey from hatchling to transformation into macrophthalmia near the southern extent of their range. Lampreys were absent from San Luis Obispo drainage in Southern California for over 6 years, but the drainage was naturally recolonized, with ammocoetes first detected again in 2017. This provided an opportunity to examine in-river growth and development using repeated sampling. We estimated ammocoetes transformed into macrophthalmia in as little as 2.6 years, one of the shortest larval durations documented for the species and at least half that assumed in studies of other wild populations. This is the first estimate of time-to-transformation for Pacific lamprey in its southern range and provides insights into adaptive strategies and refinement of recovery approaches for lamprey species worldwide.

Automated summary

This study examines the development of Pacific lamprey in the southern extent of their range and estimates the time it takes for their larval transformation. The findings provide insights into conservation strategies and recovery approaches for lamprey species worldwide.