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

ACKNOWLEDGMENTS

Field sampling was in part led by K. Siitari, M. Wagner, A. Shick, J. Pierce, and B. Johnson of the U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, and by B. Knutzen, D. Looney, and S. Hamrick of the Cow Creek Umpqua Tribe of Indians. We are also grateful for sampling assistance from the Bureau of Land Management (S. Clark, S. Lightcap, J. McEnroe, C. Sipher), Oregon Department of Fish and Wildlife (B. Bangs, J. Brandt, H. Huchko, L. Jackson), and S. Lewis of SK Consulting. W. Gerth of Oregon State University assisted with identification of prey in Smallmouth Bass diets. An enthusiastic thanks to M. Fincel for an excellent review and great discussions about this work and M.A. Eggleton for information about prey energy densities. We also extend our appreciation to the associate editor and three anonymous reviewers for their comments and assistance in improving this submission. Funding for the study was provided by the U.S. Fish and Wildlife Service’s Tribal Wildlife Grant Program, awarded to Amy Amoroso of the Cow Creek Band of the Umpqua Tribe of Indians. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.