Role of large‐ and fine‐scale variables in predicting catch rates of larval Pacific lamprey in the Willamette Basin, Oregon

Abstract

Pacific lamprey Entosphenus tridentatus is an anadromous fish native to the Pacific Northwest of the USA. That has declined substantially over the last 40 years. Effective conservation of this species will require an understanding of the habitat requirements for each life history stage. Because its life cycle contains extended freshwater rearing (3-8 years), the larval stage may be a critical factor limiting abundance of Pacific lamprey. The objective of our study was to estimate the influence of barriers and habitat characteristics on the catch-per-uniteffort (CPUE) of larval Pacific lamprey in the Willamette River Basin, Oregon, USA. We sampled lampreys at multiple locations in wadeable streams throughout the basin in 2011-13 and used an information theoretic approach to examine the relative influence of fine-and large-scale predictors of CPUE. Pacific lamprey was observed across the basin, but its relative abundance appeared to be limited by the presence of natural and artificial barriers in some sub-basins. Lower velocity habitats such as off-channel areas and pools contained higher densities of larval lamprey; mean Pacific lamprey CPUE in off-channel habitats was 4 and 32 times greater than in pools and riffles respectively. Restoration and conservation strategies that improve fish passage, enhance natural hydrologic and depositional processes and increase habitat heterogeneity will likely benefit larval Pacific lamprey.

Bioenergetics Models to Estimate Numbers of Larval Lampreys Consumed by Smallmouth Bass in Elk Creek, Oregon

“…Although precision of our consumption estimates was relatively low (i.e., confidence intervals around consumption estimates varied by two orders of magnitude), our findings indicate that over a 2-month period potential consumption in a single pool approached 1,000 larvae, distributed just among the individuals we handled (not the estimated population abundance). We were not able to differentiate lamprey species in diet samples, but local studies suggest the majority of the lampreys in these habitats were probably Pacific Lampreys (Gonzalez 2014;Schultz et al 2016). It is also important to recognize that prior to Smallmouth Bass establishment the entire Umpqua River basin represented the leading edge of the invasion front for this nonnative species.…”

Sample Sizes Needed to Describe Length-Frequency of Small-Bodied Fishes: An Example Using Larval Pacific Lamprey

“…To do so, we calculated the percentage of resamples from each subsample size that contained at least one individual .110 mm. This length has meaning specific to Pacific lamprey monitoring because it is the approximate length at which larvae are likely to begin metamorphosis (Schultz et al 2016). In this case, designers of monitoring plans would be interested in the sample size needed to document the presence (or quantify the abundance) of individuals in this life stage.…”

“…We sampled larval lampreys from wadeable locations in 14 tributary subbasins of the Willamette River, Oregon, from July to October of 2011-2013 (Schultz et al 2016; Figure 1). Each of our sample reaches consisted of two entire pool and riffle channel units to capture fish from all available habitat.…”

“…Conservation of Pacific lamprey across its range will require the development of monitoring efforts that effectively characterize the status of individual populations (Luzier et al 2011). Larval lampreys are also of interest to researchers because they have a unique life history with a relatively long larval phase (i.e., 3-7þ y; Potter 1980), typically exhibit slow growth relative to other small-bodied fishes (Meeuwig and Bayer 2005), and rarely exceed 160 mm total length (TL; Schultz et al 2016). Our analyses will aid in the development of these monitoring programs and have further utility for assessments of other lamprey species (e.g., sea lamprey) and small-bodied fishes that attain similar maximum lengths.…”

Growth and annual survival estimates to examine the ecology of larval lamprey and the implications of ageing error in fitting models

“…Although L . richardsoni also metamorphose into adults, metamorphosis appears to occur later in the year (Schultz et al , ) and they are less likely to migrate substantial distances. Because the two forms of lamprey have similar ecology during the larval stage (Schultz et al , ), this analysis assumed that inferences drawn from L .…”