River Lamprey (Lampetra ayresii) Outmigrant Upstream of the John Day Dam in the Mid-Columbia River

Abstract

The anadromous River Lamprey (Lampetra ayresii) is known to occur in North America from Alaska to central California, generally in association with larger estuarine systems (such as the Fraser River in British Columbia, the Sacramento River in California, and the Columbia River in Washington-Oregon; Vladykov and Follett 1958; Weitkamp and others 2015). Its occurrence in the Columbia River basin, however, has not been well documented. Although small numbers of juvenile (feeding phase) River Lamprey have been captured incidentally in the Columbia River Estuary (Bond and others 1983; Weitkamp and others 2012, 2015), there are few records of this species in freshwater (Kostow 2002). The farthest upriver report in the Columbia River basin is a March 1940 record at Bonneville (presumably at Bonneville Dam), 235 river kilometers (rkm) from the Pacific Ocean (Vladykov and Follett 1958). However, adult River Lamprey (117to 324-mm total length; Vladykov and Follett 1958; Bond and others 1983; Wydoski and Whitney 2003; Weitkamp and others 2015) are less noticeable than the larger Pacific Lamprey (Entosphenus tridentatus) (700to 800-mm total length; Clemens and others 2010) and might spawn in deep water in large river systems similar to other lamprey species (Dawson and others 2015). Thus, even when abundant, they are rarely observed in freshwater (Beamish 1980; Beamish and Youson 1987). Furthermore, during its prolonged freshwater larval stage, it is difficult or impossible to distinguish River Lamprey, either morphologically or genetically, from the closely related and widely distributed Western Brook Lamprey (Lampetra richardsoni) (Docker 2009). The nonmigratory, non-trophic adult Western Brook Lamprey (90to 180-mm total length) can be distinguished from adult River Lamprey by morphological and dentition characters (Wydoski and Whitney 2003; Docker 2009). There is a growing conservation concern for lampreys worldwide. Like other species, the River Lamprey is susceptible to various freshwater threats such as dredging and barriers to migration (Maitland and others 2015). The Columbia River Basin is currently fragmented by many mainstem hydropower, navigation, and flood-control dams, as well as numerous additional dams and irrigation diversions in tributary systems. Many of these dams do not provide fish passage and those that do are likely problematic for migratory adult lampreys (Moser and others 2015). Documentation of River Lamprey in the Columbia River basin would help inform management of this highly regulated system, as well as elucidate distribution patterns to aid conservation. A current effort is underway to increase the monitoring of outmigrating juvenile lampreys through the operation of salmonid smolt monitoring systems at mainstem Columbia River dams (Fish Passage Center 2014). Subsamples of juvenile (metamorphosed to outmigrating phase) and larval (unmetamorphosed) lampreys are collected, anesthetized, identified (to species for juvenile lampreys and to genus for larval lampreys), measured, and assessed for body condition. A putative juvenile (recently metamorphosed) River Lamprey was collected at the John Day Dam smolt bypass facility on 28 May 2013 from a sample time frame of 13:00 to 07:00. The fish was 144-mm total length and weighed 3.1 g. Its dentition pattern clearly distinguished it from the relatively more common Pacific Lamprey (Fig. 1). Pacific Lamprey have 3 large cusps on the supra-oral lamina, 4 pairs of lateral teeth, and 1 row of posterior teeth; whereas the River Lamprey has 2 cusps on the supra-oral lamina, 3 pairs of lateral teeth, and no posterior teeth (Wydoski and Whitney 2003). Its caudal pigmentation was likewise consistent with Lampetra spp. (Fig. 2, Fig. 3); lampreys in the Entosphenus genus possess a lighter caudal ridge, whereas the caudal ridge of Lampetra spp. is uniformly dark (Goodman and others GENERAL NOTES