Pacific Lamprey and Western River Lamprey marine ecology: Insight from new ocean collections

Abstract

Little is known about the marine ecology of anadromous Pacific Lamprey Entosphenus tridentatus and Western River Lamprey Lampetra ayresii. This information is needed to determine how marine life regulates adult abundances and identify management actions that may benefit declining populations. To address this deficit, we compiled historic data, collected lamprey from marine stock assessment surveys and commercial fisheries, and documented fish with Pacific Lamprey wounds. Pacific Lamprey were most commonly caught by midwater trawls targeting Pacific Hake Merluccius productus along the continental shelf break from northern California to northern Washington. Pacific Lamprey ranged in size from 115 mm total length (TL) and 2.9 g to 714 mm TL and 655g (n = 1,912), and were expected to represent multiple ocean ages. The vast majority (93%) of Pacific Lamprey were small (< 300 mm TL), likely in their first year in marine waters. Growth for small Pacific Lamprey was estimated as 0.37 mm/d and 0.13 g/d over the summer. Gut fullness for Pacific Lamprey was high (5.5% of body weight [BW]), but highly variable for larger individuals (range 0‐55% BW). Our results suggest there is a positive relationship between calendar day and lamprey length and condition factor in most years, while the effect of latitude varies by life stage. We documented Pacific Lamprey wounds on 240 individual fish, representing 16 species, of which 6 species are new lamprey hosts. We had comparably few records for Western River Lamprey (n = 72; mean length = 285.5 mm TL), which were primarily found in surface waters on the continental shelf from northern California to southern British Columbia. Our results have implications for both fisheries and conservation management, including development of best practices for lamprey caught by net fisheries, and using new marine information to inform conservation actions.

Patterns in distribution and density of larval lampreys in the main‐stem Columbia River, Washington–Oregon

“…include the Western River Lamprey L. ayresii and Western Brook Lamprey L. richardsoni, which are not genetically distinct (Carim et al 2023), and the Pacific Brook Lamprey L. pacifica, which appears to be currently limited to the Willamette River basin (Reid et al 2011;Carim et al 2023) and thus was outside our study area. Like Pacific Lamprey, Western River Lamprey are anadromous (Weitkamp et al 2015(Weitkamp et al , 2023. Tissue was sampled from a subset of larvae for future genetic confirmation of morphological identification.…”

“…Anadromous lampreys transform from larvae into ectoparasitic juveniles and then migrate to the ocean to feed on host fishes and whales (Dawson et al 2015;Clemens et al 2019). Although the duration of ocean residence is not well known and may vary among lamprey species and individuals, it is thought that Pacific Lamprey reside in the ocean for several years (Beamish 1980;Hess et al 2022;Weitkamp et al 2023, this special section). Resident nonparasitic lampreys transform directly from larvae into adults.…”

Evaluation of Pacific Lamprey statoliths for age estimation across their life cycle

“…Freshwater juveniles that were casualties from a screw trap on a tributary (Ahtanum Creek) of the Yakama River were also provided by the YNF. Marine juveniles collected as bycatch from the National Oceanic and Atmospheric Administration's (NOAA) At-Sea Hake Observer Program in the summers of 2017 and 2018 were provided by the Northwest Fisheries Science Center (Weitkamp et al 2023, this special section). Adult samples, the majority of which were collected during the 2016 tribal harvest at Willamette Falls, Oregon, were provided by CRITFC.…”

“…Medland and Beamish (1991) found that temperature affected the growth of larval Sea Lamprey statoliths, which stopped growing at or below 8°C. Pacific Lamprey are known to parasitize Pacific Hake Merluccius productus and other species with relatively deep depth distributions (Weitkamp et al 2023), which could keep them in relatively cool waters, although some variation in thermal exposure would be expected. The sole use of hatchery larvae in this study could have contributed to the strong positive relationship between statolith and body size, as studies of hatchery salmon otoliths indicate that artificial rearing results in wider and more uniform growth rings (Zhang et al 1995;Barnett-Johnson et al 2007;Claiborne et al 2014).…”

Bringing partners together: A symposium on native lampreys and the Pacific Lamprey Conservation Initiative

“…Results from Blanchard et al (2023, this special section) and Liedtke et al (2023, this special section) inform the distribution of larval lampreys in freshwater habitats from small (e.g., sediment distribution) to large scales (basin-wide distribution) and highlight effects of stream management decisions on larval lamprey populations. Weitkamp et al (2023, this special section) is the most comprehensive evaluation to date on the marine ecology of Pacific Lamprey and Western River Lamprey. This research adds much to the little currently known about marine biology of anadromous lampreys of conservation concern (Clemens et al 2019;Shink et al 2019;Quintella et al 2021).…”