Geology topics

Trevor D. Keyler

Publications and source records attributed to Trevor D. Keyler.

3 recordsLinked to original sources

USGS2026

Light-dependent activity of deepwater sculpin (Myoxocephalus thompsonii) across substrates with and without predation risk

Light availability strongly influences predator–prey interactions in deepwater ecosystems, where visual constraints shape both foraging success and prey behavior. The behavioral response of deepwater sculpin ( Myoxocephalus thompsonii ) to siscowet lake trout ( Salvelinus namaycush siscowet ) was studied under ecologically relevant light intensities spanning several orders of magnitude typical of daytime downwelling light in the 20–100 m depth range of Lake Superior. Trials were conducted over varying substrates (gravel, sand, and black fabric). Deepwater sculpin showed a significant preference for gravel over sand and black fabric. In the absence of siscowet, sculpin movement frequency increased as light intensity decreased. Sculpin reaction distance to siscowet was influenced by both light and substrate. Reaction distance was shortest at low light intensities, peaked at intermediate light intensities (3.05 × 10⁹ to < 6.0 × 10⁹ photons m⁻2 s⁻1), and declined again at the highest light intensities tested. In the presence of siscowet, sculpin activity was suppressed at the upper end of the light range (≥ 6.0 × 10⁹ photons m⁻2 s⁻1). The greatest increase in movement occurred between 6.0 × 10⁹ and 3.05 × 10⁹ photons m⁻2 s⁻1, which corresponded to the range where siscowet prey capture declined, suggesting sculpin exploit this low-light window to move with reduced risk. Reduced activity in the presence of predators is common among cryptic species, and our findings suggest that sculpin restrict movement at higher light levels to avoid detection by siscowet.

Wisconsin↗

USGS2019

Effect of light intensity and substrate type on siscowet lake trout (Salvelinus namaycush siscowet) predation on deepwater sculpin (Myoxocephalus thompsonii)

Foraging characteristics of siscowet lake trout ( Salvelinus namaycush siscowet ) on deepwater sculpin ( Myoxocephalus thompsonii ) were studied under ecologically relevant downwelling light intensities (9.0 × 10 8 to 1.62 × 10 11 photons m −2 s −1 ) and emission spectrum (500–510 nm) on varying substrates (gravel, sand, and black fabric). Siscowet reaction distance within our trials increased with light intensity up to 6.0 × 10 9 photons m −2 s −1 , after which reaction distance remained constant with additional increases in light intensity following the Michaelis–Menten saturation function. Reaction distances were not affected by substrate type under any light intensity. The number of prey captures also increased with increasing light intensity, with most orientations toward prey occurring within the siscowet’s forward sector (± 0°–60°, where 0° represents the tip of the siscowet rostrum). Finally, the overall probability of prey capture was positively related to reaction distance at each light intensity. Results suggest that siscowet can visually forage on benthic prey at great depth in Lake Superior, and reaction distance (≤ 27 cm) to sculpin may not diminish until depths exceed 200 m (6.00 × 10 9 photons m −2 s −1 ).

Lake Superior↗

USGS2015

Foraging mechanisms of siscowet lake trout ( Salvelinus namaycush siscowet ) on pelagic prey

The reaction distance, angle of attack, and foraging success were determined for siscowet lake trout ( Salvelinus namaycush siscowet ) during laboratory trials under lighting conditions that approximated downwelling spectral irradiance and intensity (9.00 × 10 8 –1.06 × 10 14 photons m − 2 s − 1 ) at daytime depths. Siscowet reaction distance in response to golden shiners ( Notemigonus crysoleucas ) was directly correlated with increasing light intensity until saturation at 1.86 × 10 11 photons m − 2 s − 1 , above which reaction distance was constant within the range of tested light intensities. At the lowest tested light intensity, sensory detection was sufficient to locate prey at 25 ± 2 cm, while increasing light intensities increased reaction distance up to 59 ± 2 cm at 1.06 × 10 14 photons m − 2 s − 1 . Larger prey elicited higher reaction distances than smaller prey at all light intensities while moving prey elicited higher reaction distances than stationary prey at the higher light intensities (6.00 × 10 9 to 1.06 × 10 14 photons m − 2 s − 1 ). The capture and consumption of prey similarly increased with increasing light intensity while time to capture decreased with increasing light intensity. The majority of orientations toward prey occurred within 120° of the longitudinal axis of the siscowet's eyes, although reaction distances among 30° increments along the entire axis were not significantly different. The developed predictive model will help determine reaction distances for siscowet in various photic environments and will help identify the mechanisms and behavior that allow for low light intensity foraging within freshwater systems.

Wisconsin↗