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

Abstract

AbstractObjectiveLittle 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 to identify management actions that may benefit declining populations.MethodsTo address this deficit, we compiled historic data, collected lamprey from marine stock assessment surveys and commercial fisheries, and documented fish with Pacific Lamprey wounds.ResultPacific 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 655 g (n = 1912) and were expected to represent multiple ocean ages. The vast majority (93%) of Pacific Lamprey were small (≤300 mm TL) and thus were likely in their first year in marine waters. Growth for small Pacific Lamprey was estimated as 0.37 mm/day and 0.13 g/day over the summer. Gut fullness for Pacific Lamprey was high (5.5% of body weight [BW]), but it was highly variable for larger individuals (range = 0–55% BW). Our results suggest that 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 six species are newly identified as 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.ConclusionOur results have implications for both fisheries and conservation management, including development of best practices for lamprey caught by net fisheries and the use of new marine information to inform conservation actions.