Occupancy and Detection of Larval Pacific Lampreys and Lampetra spp. in a Large River: the Lower Willamette River

Abstract

Pacific lampreys Entosphenus tridentatus (formerly Lampetra tridentata) are declining in the Columbia River basin, and the use of large, main‐stem river habitats by larvae of this species is unknown. We used a deepwater electrofisher to explore occupancy, detection, and habitat use of larval Pacific lampreys and larval Lampetra spp. in the lower Willamette River, Oregon. We used a generalized random tessellation stratified approach to select sampling quadrats (30 × 30 m) in a random, spatially balanced order. Pacific lampreys, Lampetra spp., and unidentified lampreys were found in the Willamette River; larvae were detected in all areas except the Multnomah Channel. We calculated reach‐ and quadrat‐specific detection probabilities and the amount of sampling effort required for 80% confidence that larval lampreys were in fact absent when they were not detected. Lampreys were detected in a variety of areas (although relatively low numbers were collected), including shallow, nearshore areas; midchannel areas (depth up to 16 m); and anthropogenically affected areas. Detection probabilities (i.e., in occupied areas) were 0.07 (reach) and 0.23 (quadrat). The sampling effort required for 80% confidence that lampreys were absent when undetected was 20 quadrats (in the lower Willamette River reach) and 6 subquadrats (within a quadrat). Differences in lamprey detection by depth were not observed. A variety of sizes was collected (20–144 mm total length), indicating the likely occurrence of multiple ages of larvae. Our study identifies how the occurrence of larval Pacific lampreys can be quantified with statistical rigor in a large river (i.e., larger than fourth order [1:100,000 scale]). The effect of channel management activities on larval lampreys should be considered in efforts to conserve these important species.

Evaluation of environmental DNA surveys for identifying occupancy and spatial distribution of Pacific Lamprey (Entosphenus tridentatus) and Lampetra spp. in a Washington coast watershed

“…To empirically evaluate detections by eDNA and electrofishing, we calculated the proportion of survey reaches where lampreys were detected by each method (identified herein as d unit ) for each river basin. This metric (a measure of naïve occupancy) has been used to assess lamprey distributions in other studies (Jolley, Silver, Harris, & Whitesel, 2018;Jolley et al, 2012;Reid & Goodman, 2015).…”

“…To empirically evaluate detections by eDNA and electrofishing, we calculated the proportion of survey reaches where lampreys were detected by each method (identified herein as d unit ) for each river basin. This metric (a measure of naïve occupancy) has been used to assess lamprey distributions in other studies (Jolley, Silver, Harris, & Whitesel, ; Jolley et al, ; Reid & Goodman, ). For Lampetra spp., eDNA and electrofishing d unit estimates did not include one survey reach in the Black River and four survey reaches in the Newaukum River where occupancy status could not be established by electrofishing because electrofishing ceased prior to reaching the upstream terminus (i.e., E. tridentatus were found first).…”

“…Occupancy models yield parameter estimates that are more reliable than estimates of naïve occupancy (the proportion of sites where target taxa is detected) because occupancy models account for imperfect detection, which is common to presence-absence surveys, including eDNA surveys. Furthermore, occupancy assessment may be more important to highly fecund, panmictic species because knowledge of distribution in any given watershed may be more relevant than abundance (Dunham, Chelgren, Heck, & Clark, 2013;Jolley, Silver, & Whitesel, 2012;Reid & Goodman, 2015). Occupancy parameter estimates can also provide information on the efficacy of eDNA sampling protocols (Hunter et al, 2015;Schmelzle & Kinziger, 2016;Schmidt et al, 2013), allowing protocols and/or sampling efficiency to be improved as needed.…”

“…Entosphenus tridentatus are anadromous, semelparous, and exhibit a complex life history that involves larval (i.e., ammocoete), migratory juvenile (i.e., macrophthalmia), and adult marine and freshwater phases. Larvae reside and burrow in fine sediments in small streams (Claire, Cochnauet, & LaBar, 2007;Stone & Barndt, 2005;Torgersen & Close, 2004) and large rivers (Harris & Jolley, 2017;Jolley et al, 2012) for 3-7 years where they filter feed on organic material and detritus (Sutton & Bowen, 1994), after which they metamorphose into migratory juveniles, typically during July-December (McGree, Whitesel, & Stone, 2008). Juveniles migrate to the Pacific Ocean, typically in spring or fall (Beamish & Levings, 1991;Moser, Jackson, Lucas, & Mueller, 2015), where they exhibit a parasitic feeding behavior for 1-2 years prior to sexual maturation, followed by a return to freshwater where they spawn and die.…”

Ammocoetes of Pacific Lamprey Are Not Susceptible to Common Fish Rhabdoviruses of the U.S. Pacific Northwest

“…However, fish transported to captivity from the wild may be vectors of pathogens that can spread to other captive fish. In the wild, the Pacific Lamprey often exists sympatrically with numerous other fish species, including various salmonids (Torgersen and Close 2004;Jolley et al 2012). Therefore, an understanding of the susceptibility of Pacific Lampreys to common fish pathogens in their natural environments is essential for effective conservation and management.…”