Natural Recolonization by Pacific Lampreys in a Southern California Coastal Drainage: Implications for Their Biology and Conservation

Abstract

The historical range of anadromous Pacific LampreyEntosphenus tridentatus includes coastal drainages from Alaska south to northern Baja California. However, there has been a widespread loss of distribution inland due to the construction of dams that form impassable barriers as well as a loss of Pacific Lampreys from some historically occupied drainages in the south. These losses have prompted the consideration of suitable approaches to reestablishing Pacific Lamprey populations through either active intervention or natural processes. While Pacific Lampreys apparently do not home to natal streams, they are thought to use cues that are related to such factors as flow patterns or the presence of ammocoete (larval lamprey) pheromones in offshore river plumes to identify suitable rivers for spawning and rearing. In this report, we present documentation of natural recolonization of the San Luis Obispo drainage by Pacific Lampreys on the central California coast, located 130 km south of the nearest freshwater population of Pacific Lampreys and with no existing ammocoete population. We also review recent observations of adult Pacific Lampreys in other southern rivers, recolonization of the Carmel River following dam removal, and indications that Pacific Lampreys are still using oceanic habitat off southern California. The results of our investigation demonstrate that Pacific Lampreys are fully capable of returning to an isolated drainage from which they have been extirpated and then rapidly reestablishing a viable population of ammocoetes, contradicting the hypothesis that they are dependent on existing ammocoete pheromones or adult sex pheromones to attract adults. These results indicate the importance of proactive management for Pacific Lampreys in drainages within their historical range, even if they are not currently present. The results also demonstrate that recolonization does not necessarily require active reintroduction efforts. Rather, conservation efforts should focus on identifying factors that may have led to the loss of Pacific Lamprey and removing potential impediments in order to facilitate natural recolonization.

Six years of fluvial response to a large dam removal on the Carmel River, California, USA

“…Endangered Species Act, and other biota. Although data on steelhead response to dam removal on the Carmel River are not yet published, Pacific lamprey ( Entosphenus tridentatus ) have successfully recolonized the Carmel River after dam removal and are spawning there (Reid & Goodman, 2020), indicating some ecosystem benefit. Our grain‐size analyses (Figure 9) show that by 2021, 6 years after dam removal, all reaches had average bed‐material size within the 5–75 mm range necessary for salmonid spawning (Kondolf & Wolman, 1993) and with less than 10% sand, consistent with appropriate salmonid spawning habitat.…”

Robust Recolonization of Pacific Lamprey Following Dam Removals

“…When habitat becomes accessible after dam removal or habitat improvements, it is useful to assess the relative merits of taking a passive approach to lamprey recolonization (relying only on volitional migrants) versus actively translocating lamprey to repopulate the newly available habitat (Reid and Goodman 2020). Due to the modest numbers of adults translocated in our study and the limited years available to monitor any translocation production, we could not fully assess the relative merits of these alternative approaches.…”

“…In smaller coastal systems, the species may need just an opportunity to access appropriate habitat to naturally re‐establish because these areas have fewer passage impediments and greater proximity to oceanic sources of Pacific Lamprey spawners. For small coastal rivers with dams that prevent passage of Pacific Lamprey, dam removal could be the only requisite for restoration of robust and self‐sustaining Pacific Lamprey abundance via natural recolonization (Reid and Goodman 2020; Moser et al., in press).…”

“…Lampreys apparently are not philopatric, and they use pheromonal cues to find watersheds for spawning (reviewed by Moser et al 2015). The relative rates of population recovery following natural recolonization compared to production resulting from translocated adults likely depend on the system and the sources of lamprey (Reid and Goodman 2020).…”

Seascape genomics reveals limited dispersal and suggest spatially varying selection among European populations of sea lamprey (Petromyzon marinus)

“…Spawning migration towards freshwater, however, is not philopatric regarding spawning locations; contrary to other anadromous fishes, sea lampreys do not return to the natal rivers to spawn (Almada et al, 2008; Bergstedt & Seelye, 1995; Spice, Goodman, Reid, & Docker, 2012). Instead, it has been suggested that sea lampreys are steered by a migratory pheromone released by stream-resident larvae (Sorensen et al, 2005; Vrieze, Bergstedt, & Sorensen, 2011), although natural recolonization of freshwater locations without ammocoete presence has been recently noted (Reid & Goodman, 2020). Less understood is how selection acts across the sea lamprey life cycle, despite its numerous life history events (such as the transition to parasitism linked to adulthood, onset of anadromous and catadromous migrations) providing substantial opportunities for selection to act.…”