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

Abstract

Nonnative fishes have been increasingly implicated in the decline of native fishes in the Pacific Northwest. Smallmouth Bass Micropterus dolomieu were introduced into the Umpqua River in southwest Oregon in the early 1960s. The spread of Smallmouth Bass throughout the basin coincided with a decline in counts of upstream‐migrating Pacific Lampreys Entosphenus tridentatus. This suggested the potential for ecological interactions between Smallmouth Bass and Pacific Lampreys, as well as freshwater‐resident Western Brook Lampreys Lampetra richardsoni. To evaluate the potential effects of Smallmouth Bass on lampreys, we sampled diets of Smallmouth Bass and used bioenergetics models to estimate consumption of larval lampreys in a segment of Elk Creek, a tributary to the lower Umpqua River. We captured 303 unique Smallmouth Bass (mean: 197 mm and 136 g) via angling in July and September. We combined information on Smallmouth Bass diet and energy density with other variables (temperature, body size, growth, prey energy density) in a bioenergetics model to estimate consumption of larval lampreys. Larval lampreys were found in 6.2% of diet samples, and model estimates indicated that the Smallmouth Bass we captured consumed 925 larval lampreys in this 2‐month study period. When extrapolated to a population estimate of Smallmouth Bass in this segment, we estimated 1,911 larval lampreys were consumed between July and September. Although the precision of these estimates was low, this magnitude of consumption suggests that Smallmouth Bass may negatively affect larval lamprey populations. Received September 20, 2016; accepted March 31, 2017Published online June 6, 2017

Modeling Brook Trout Carrying Capacity in Owhi Lake, Washington, Using Bioenergetics

“…Changing the proportion of an individual prey item alters the proportions of all other prey; therefore, we altered the counts of each prey item in the diet by ±25%, which redistributed proportions to all other prey (e.g., Schultz et al. ). Energy densities of major prey items were varied by ±20%. Mortality and population size based on estimated lower and upper 95% CIs were modeled; for age‐0 and age‐1 fish, we allowed values to vary by a coefficient of variation of 20% (maximum annual mortality was set to 0.99). Temperature experience was modeled by using the behavioral thermoregulation scenario.…”

“…Consumption of prey items (e.g., Amphipoda, Decapoda, and zooplankton) was altered by ±25%. Changing the proportion of an individual prey item alters the proportions of all other prey; therefore, we altered the counts of each prey item in the diet by ±25%, which redistributed proportions to all other prey (e.g., Schultz et al 2017). 14.3 10.9 9.3 11.0 11.5 275 5.0 5.0 5.0 5.0 5.0 90 2.…”

What to do when invaders are out of control?

“…In fact, direct control of Smallmouth Bass may only exacerbate its impacts on receiving ecosystems due to strong compensatory responses to many forms of removal (Zipkin et al, 2008). This case emphasizes exogenous factors as important interaction modifiers, although less research has been dedicated to endogenous factors that could affect impacts (e.g., body size; Lawrence et al, 2015;Schultz et al, 2017).…”

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

“…In the Columbia River near Richland (WA, USA), each Smallmouth Bass and Northern Pikeminnow (Ptychocheilus oregonensis) were estimated to consume 1.0-1.4 and 0.3-0.6 salmonids daily respectively (Tabor, Shively, & Poe, 1993). A recent research from Southern Oregon suggested that Smallmouth Bass poses a high predation threat to lamprey larvae and negatively impacts the lamprey population (Schultz et al, 2017). However, information on the extent and magnitude of larvae predation by various fishes is still very limited.…”