An experimental study to evaluate predation threats on two native larval lampreys in the Columbia River Basin, USA

Abstract

Experimental predation studies were conducted to evaluate and compare the predation threats of 10 species of native and non‐native fishes on larvae of Pacific Lamprey, Entosphenus tridentatus, and Western Brook Lamprey, Lampetra richardsoni. The relative predatory threats were examined over four sets of binary factors, including the following: (a) short (2‐day) or long (7‐day) duration, (b) presence/absence of fine sediment, (c) live or dead larvae and (d) species of lampreys. Our short‐term results showed a positive correlation with the sizes of predator fishes and consumed lamprey larvae. Also, most predator fishes had a significantly higher propensity to prey on lamprey larvae when sediment was absent. Conversely, this demonstrated the importance of sediment in protecting lamprey larvae from predation. Based on the predatory behaviour for live and dead larvae, predator fishes were classified into four groups using principal component analysis. Predation rates of larvae in sediment by piscivorous predators including Northern Pikeminnow Ptychocheilus oregonensis and Smallmouth Bass Micropterus dolomieu were lower and showed no differences even when the study duration was extended. In contrast, predation rates by benthic predators including White Sturgeon Acipenser transmontanus and Common Carp Cyprinus carpio, increased when we extended the study duration. This suggests that when given longer duration, benthic predators are more adept at consuming larvae within the sediment. These results provide important context for assessing the potential threat of predation on lampreys in streams, which is a key knowledge gap for lampreys.

Effects of dewatering on behavior, distribution, and abundance of larval lampreys

“…Our laboratory results suggest the observed changes in distribution and abundance at Leaburg Reservoir were at least partially due to mortality associated with dewatering. However, changes in distribution and abundance may also result from predation (Arakawa & Lampman, 2020; Beamish, 1980; Merrell, 1959), larval emergence and re‐burrowing elsewhere within the study area (i.e., individuals could re‐burrow in areas not yet dewatered), and escapement to watered habitat outside the study area (Liedtke et al, 2015). Regardless of larval fate, our research indicates dewatering can have substantial effects on abundance and spatial distribution of larval lampreys in freshwater habitats.…”

Whose Kids Did You Eat? Genetic Identification of Species and Parents of Larval Lampreys in Fish Predator Guts

“…Each of the groups of predator fishes were tested separately and held with eight larvae per predator fish for either two or seven nights (short-and long-term studies). The short-term studies took place between December 5, 2016 and February 15, 2017 552 and the long-term studies took place between December 28, 2016 and February 20, 2017 (see Arakawa and Lampman 2020).…”

“…Hence, the true numbers of larval/juvenile lampreys contained in the stomach of predator fishes may be substantially underestimated due to their rapid degradation in the predators' stomach. Lampreys in the digestive system of predators are often fully digested and decomposed prior to stomach content analysis, making ID to genus or life stage (larval versus juvenile) extremely difficult (Schultz et al 2017;Arakawa and Lampman 2020).…”

“…Molecular techniques, such as parentage-based tagging, have the potential to vastly improve our understanding of lampreys as prey species. We conducted an experimental predation study in the laboratory using a variety of commonly observed native and nonnative fish species from the Columbia Basin that had a high likelihood of consuming larval lampreys (Arakawa and Lampman 2020). As part of this study, in addition to visual examination of morphological structures in the gut contents, genetic analysis of deteriorated and decomposed tissues from the gastrointestinal tracts of predator fishes were conducted to evaluate whether the lamprey genera/species and their parents could be determined.…”

River Network and Reach‐Scale Controls on Habitat for Lamprey Larvae in the Umpqua River Basin, Oregon

“…After identifying PBH in the Umpqua River network, we assessed the potential overlap of PBH with water temperatures suitable for Smallmouth Bass Micropterus dolomieu , a nonnative predator. Lamprey larvae moving to find suitable burrowing habitat (Smith et al 2012) and lamprey transformers and juveniles migrating downstream may be consumed by Smallmouth Bass (Schultz et al 2017) and other nonnative warmwater species, such as Largemouth Bass M. salmoides (Arakawa and Lampman 2020), Bluegill Lepomis macrochirus , and Brown Bullhead Ameiurus nebulosus . Smallmouth Bass was introduced to the basin in 1964 (Simon and Markle 1999) and is now found throughout the Umpqua River basin and lower portions on most tributaries (Simon 2008).…”