Results of the California Assessment under the Pacific Lamprey Conservation Initiative This assessment indicates that Pacific Lamprey populations in California had been extirpated from at least 55% of their historical habitat north of Point Conception by 1985. The primary threat responsible for extirpations was large impassible dams, which excluded migrating adults from access to high quality spawning and rearing habitat in the foothills and higher elevations. In southern California, recent surveys and review of available information also indicate that no viable populations of Pacific Lamprey currently occupy drainages south of the Big Sur River on the central coast. Some populations have been lost due to drainage-specific threats, however,
there is also evidence for a general northward range contraction, perhaps caused by regional metapopulation dynamics.
Most of the remaining occupied California watersheds are rated at ‘imperiled’ or 'vulnerable' in the NatureServe rankings. This result suggests both the urgency for action and opportunities for recovery with implementation of appropriate conservation measures. The principal threats affecting many populations include passage barriers (mainstem and tributary), dewatering or flow management, and water quality/habitat issues associated with high water temperatures, low flow and nutrient loading. Additional threats, generally low to moderate in scope or severity, included stream habitat degradation, possible predation (varying by sub-region), and “small population” effects in the south. Ongoing actions such as distribution and habitat surveys, barrier
removals, fish screening, and habitat restoration projects are assisting Pacific Lamprey restoration in all sub-regions. However, due to a focus on salmonid conservation in the region, there is a general lack of awareness or consideration for lamprey requirements in many projects, which can and has led to unintentional adverse effects.