Largemouth Bass Research

Largemouth bass are native to the Mississippi drainage but were

to California in the late 1890s as a game fish and probably expan

the Delta in the early 1900s. While they have been residing in the

at least 100 years, it is only in the last few decades that they hav

extremely abundant, now supporting a renowned recreational fish

Largemouth bass are notoriously voracious predators, but their n

history in the Delta (distribution, habitat preferences, food habits)

reasons for their increasing populations have not been well docu

One major hypothesis for their rise in population numbers is that 

weeds (such as Brazilian waterweed, Egeria densa) have also expanded in the Delta over the same time period, and might prov

excellent habitat for bass. The increases in bass and aquatic weeds are part of major changes in the entire biological community

shorelines of the Delta that have occurred since the mid 1980s.

Our recent studies have examined the largemouth bass distribution, diet, association with aquatic weeds and other environment

variables in the Delta, as well as investigations of their movement patterns using acoustic telemetry. This work has been done b

researchers in the Aquatic Ecology Section of DWR and the University of California, Davis (Dr. Andrew Sih in the Department of

Environmental Science and Policy, and Dr. Peter Klimley’s Biotelemetry Laboratory). Resulting analyses will provide information

seasonal movement patterns, patterns of abundance and growth with respect to abiotic and biotic conditions, and diet compositi

bioenergetics for the largemouth bass population in the Delta. The results from this research will provide insights that managers

assess whether largemouth bass are important predators for native fishes and understand the reason for their recent expansion

Delta.

Recent Results

Ferrari, M.C.O, L. Ranåker, K.L. Weinersmith, M.J. Young, A. Sih, and J.L. Conrad. 2013. Effects of turbidity and an invas

waterweed on predation by introduced largemouth bass. Environmental Biology of Fishes. Published online March 2013:

http://link.springer.com/article/10.1007/s10641-013-0125-7.

Conrad, J.L., K.L. Weinersmith, M.J. Young, D. de Carion, E. Hestir, M. Santos, P. Crain, S. Ustin, P.B. Moyle, and A. Sih.

More big bass: Understanding the role of largemouth bass as top predators in the littoral zone (PDF, 1 KB). Delta Science

Conference, Sacramento, CA. September 2010.

Vella, M., C. Nelson, and J.L. Conrad. 2010. Patterns in largemouth bass diet composition in the Sacramento-San Joaqui

(PDF, 1.20 MB). DWR Environmental Scientist Workshop, Sacramento, CA. September 2010.

Conrad, J.L., K.L. Weinersmith, M. J. Young, D.de Carion, P. Crain, E. L. Hestir, M. J. Santos, S.L. Ustin, P. B. Moyle, and

2010. Rising abundance of largemouth bass in the littoral zone of the Sacramento-San Joaquin Delta: the role of Egeria d

(PDF, 1.40 MB). Interagency Ecological Program 2010 Workshop, California State University, Sacramento, May, 2010.

Conrad, J.L. , K.L. Smith, E. Hestir, M. Santos, A. Sih, and S. Ustin. Largemouth bass abundance and diet in the Sacrame

Joaquin Delta: investigating temporal and spatial variation with respect to submerged aquatic vegetation. State of the Estu

Conference, Oakland, CA, September 2009.

Aquatic Ecology Section http://www.water.ca.gov/aes/predators/largemouthbass.cfm

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Aquatic Ecology Section http://www.water.ca.gov/aes/predators/largemouthbass.cfm

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