Research

Research program

Freshwater invasions rarely happen in isolation. In Oregon rivers, non-native Smallmouth Bass (Micropterus dolomieu) interact with both native Signal Crayfish (Pacifastacus leniusculus) and the expanding non-native Ringed Crayfish (Faxonius neglectus). My dissertation examines these interactions across three linked studies — from diet patterns and prey availability in the field, to predator–prey mechanisms in the laboratory, to how temperature shapes competition between the two crayfish species.

The question running through all three chapters: can interactions among non-native species alter the course of a biological invasion, and what does that mean for the native species caught between them?

Diagram showing Oregon river systems leading to Smallmouth Bass, which interacts with Signal Crayfish and Ringed Crayfish, feeding into three chapters (field diet, predator-prey trials, thermal preference and competition) that converge on understanding species interactions under environmental variation.

Dissertation overview: Oregon river systems host non-native Smallmouth Bass, which interact with native Signal Crayfish and non-native Ringed Crayfish across three chapters — field diet and electivity, predator–prey trials, and thermal preference and competition.

Study species

A Smallmouth Bass held in hand during field sampling on an Oregon river.

Smallmouth Bass held during field sampling

Smallmouth Bass
Micropterus dolomieu

Non-native predator established in the Willamette and Umpqua Rivers, and the focal fish species in the diet and predator–prey research (Chapters 1–2).

Signal Crayfish (Pacifastacus leniusculus) photographed during capture-mark-recapture field sampling in the Umpqua River system, with an external individual marker visible on the carapace.

Signal Crayfish photographed during capture–mark–recapture field sampling in the Umpqua River system.

Signal Crayfish
Pacifastacus leniusculus

Native crayfish of the Pacific Northwest, and the native prey and competitor species examined throughout the dissertation.

Ringed Crayfish (Faxonius neglectus) showing unusual blue coloration, photographed in the Willamette River system near Eugene, Oregon.

Blue-colored Ringed Crayfish observed in the Willamette River system near Eugene, Oregon.

Ringed Crayfish
Faxonius neglectus

Non-native crayfish expanding into Oregon’s Umpqua and Rogue basins, and the focal invader in the predator–prey and competition experiments (Chapters 2–3). This individual shows unusual blue coloration, occasionally observed in this species.

Dissertation chapters

Chapter 1

Trophic ecology of Smallmouth Bass in two Oregon rivers

Research questions.

  • How important are crayfish, relative to fish and invertebrates, in Smallmouth Bass diets in the Willamette and Umpqua Rivers, and does that pattern change across years?
  • In the Umpqua River, where Signal and Ringed Crayfish co-occur, does Smallmouth Bass show species-specific electivity when diet is compared with local crayfish availability?
  • How variable is diet composition among years within each river?

Approach. Diet samples come from the Willamette River Fish Decadal Assessment and the annual Umpqua Bass Bash, paired with a standardized capture–mark–recapture crayfish availability study across five Umpqua sites, sampled over four days each. Comparing stomach contents with local prey availability will allow me to calculate Jacobs’ electivity index (D) and test whether Smallmouth Bass select for Ringed over Signal Crayfish rather than simply consuming whichever is more available. Stomach samples have been collected across the 2023–2026 field seasons; species-level processing of those samples is ongoing.

Study area. The Willamette and Umpqua River basins, Oregon — two systems that differ in geomorphology, thermal regime, and crayfish assemblage, providing a natural contrast for these comparisons.

Map of western Oregon showing the Willamette River basin and the Umpqua River basin, including North Umpqua, South Umpqua, and mainstem Umpqua subbasins, with a generalized focal sampling area and no specific coordinates shown.

Study systems in Oregon showing the Willamette and Umpqua river basins and generalized focal sampling areas. Sensitive collection locations are intentionally not shown.

A researcher wearing waders stands in a river, examining a mesh trap over a sorting tray beside a large boulder.

Field sampling for crayfish availability on an Oregon river

Flowchart showing Smallmouth Bass sampling leading to diet observations, combined with crayfish availability from baited trapping and active hand sampling, and environmental context from temperature and habitat, converging on prey selection and electivity analysis.

Field sampling integrates Smallmouth Bass diet observations with estimates of local crayfish availability.

Chapter 2

Laboratory predator–prey trials: Smallmouth Bass and crayfish

When a Smallmouth Bass is offered one Signal Crayfish and one Ringed Crayfish at matched size, which prey (if either) is consumed first, and how consistent is that outcome across individuals?

Experimental design (current protocol). Each Smallmouth Bass is held in its own opaque tank and pre-conditioned there overnight (about 12 hours) before a trial. One Signal Crayfish and one Ringed Crayfish, size-matched by carapace length, are then introduced together, and the encounter is video-recorded for a standardized observation period under low, standardized lighting with disturbance minimized (visual barriers, remote camera control). Up to six fish are run in parallel across six independent tanks each morning. Individual bass are tracked across repeated standardized trials with appropriate recovery intervals between trials.

Measurements. The primary outcome is which prey item, if either, is consumed first. Secondary behavioral metrics include approach, attack, aborted attacks, capture, latency, escape responses, defensive posture, and handling time, scored from video.

Temperature. The standardized protocol targets a stable working temperature; pilot testing has explored trial temperatures across roughly 16–25 °C while the protocol was being refined, rather than comparing fixed “warm” and “cool” treatments as a manipulated factor in this chapter.

Current status. Pilot-phase trials are underway to finalize the protocol; the full dataset under the standardized design has not yet been collected, and no prey-choice outcome should be treated as a result at this stage.

A rack of blue opaque experimental tanks used for predator-prey trials, stacked in rows in a laboratory.

Experimental system used for controlled Smallmouth Bass–crayfish predator–prey trials.

Flowchart showing a Smallmouth Bass pre-conditioned overnight in its tank, then one Signal Crayfish and one Ringed Crayfish introduced together, followed by a video-recorded observation period, an outcome of which prey is consumed first plus secondary behavioral metrics, and repeated standardized trials across six independent opaque tanks.

Chapter 2 trial design: overnight pre-conditioning, paired prey introduction, video-recorded observation, and repeated standardized trials across six independent tanks

A researcher assembling a custom blue rectangular experimental tank with a center divider on a workbench.

Constructing the experimental tank system used in the predator–prey and thermal trials

Once published, this chapter will carry: publication · dataset · R code · conference presentation · DOI.

Chapter 3

Thermal preference and shelter competition between native and non-native crayfish

Research questions.

  • How does interspecific shelter competition between Signal and Ringed Crayfish vary with relative body size and sex?
  • How does thermal context change activity levels, encounter rates, and the strength of competitive asymmetry between the two species?
  • Does displacement from shelter measurably increase a crayfish’s behavioral exposure?

This chapter has two experimental components at different stages, plus a planned field component.

Thermal-choice pilot trials (active). Individual crayfish are placed in a two-channel tank with a warm channel, a cool channel, and a shared central junction. After a 3-minute acclimation period (not analyzed), a 20-minute recording period is scored for time spent in each zone, latency to first choice, and number of channel switches, examined across four 5-minute windows. This is designed as a short-term behavioral-response assay — it measures immediate zone choice after a controlled warm/cool input, not a long-term equilibrium preferred temperature. Each individual is tested once and then moved to a labeled recovery tank. Pilot thermal-choice trials are underway to refine the behavioral assay and analysis workflow before final analysis; this is pilot/protocol-testing data, not yet a basis for conclusions about species differences.

Overhead photo of an empty blue tank divided by a center partition that stops short of one end, with two probes positioned near the far end of each channel.

Experimental apparatus used for short-term crayfish thermal-choice behavioral trials.

Top-view schematic of a two-channel thermal-choice tank with a warm channel on one side, a cool channel on the other, a shared junction where a crayfish is released, and temperature loggers in each channel.

Thermal-choice apparatus (top view): warm and cool channels sharing a central junction, with a crayfish released at the junction after acclimation

A handheld FLIR thermal-imaging camera held up to a blue divided tank, showing a warm-to-cool color gradient on its screen.

Verifying the thermal gradient in the apparatus with a handheld thermal-imaging camera

Shelter-competition experiment (planned, not yet started). The approved design crosses two temperatures (cool 17 °C, warm 23 °C) with two shelter levels — one refuge, forcing direct competition, versus two refuges — for size-matched Signal and Ringed Crayfish pairs, with 9 replicates per combination. Planned 60-minute video-recorded trials would record shelter dominance, aggression, and displacement, analyzed afterward with tools such as ToxTrac, Fiji/TrackMate, and DeepLabCut. As of this update, no trials have been run under this design.

Diagram of a planned 2 by 2 factorial design crossing cool and warm temperatures with limited and equal shelter, for size-matched Signal and Ringed Crayfish pairs, marked as not yet started.

Conceptual design for the planned Signal Crayfish–Ringed Crayfish shelter-competition experiment.

Field thermal context (planned, not yet conducted). The design would classify Umpqua Basin reaches into cold (≤18 °C), transitional (18–21 °C), and warm (≥21 °C) categories using a modeled stream-temperature dataset (Siegel et al. 2023), validated with in-situ loggers, then sample them with standardized baited traps to characterize crayfish coexistence. This basin-wide field sampling has not yet been carried out.

Map of the Umpqua River basin with a legend of planned cold, transitional, and warm reach classifications, marked as not yet sampled, with no specific coordinates shown.

Planned reach classification for the Umpqua Basin thermal-context field survey — not yet conducted.

Methods and tools

Area Methods and tools
Field ecology Smallmouth Bass diet sampling, crayfish trapping and hand sampling, habitat and substrate surveys
Environmental monitoring Modeled stream temperature (Siegel et al. 2023), in-situ temperature loggers (HOBO/Hydromath)
Experimental ecology Predator–prey trials (active pilot testing), thermal-choice trials (active pilot testing), shelter-competition trials (planned)
Behavioral ecology Video recording; BORIS behavioral coding (thermal-choice trials); ToxTrac, Fiji/TrackMate, and DeepLabCut (planned, for the shelter-competition experiment)
Quantitative ecology R, generalized and mixed-effects models, Jacobs’ electivity index
Reproducible science Quarto, Git and GitHub, Zotero with Better BibTeX