Fig 1.
Map of Palmyra Atoll showing different habitat types and the location of acoustic listening stations (yellow circles).
Black circles around receivers shows approximate detection radius.
Table 1.
Blacktip reef sharks were fitted with acoustic transmitters or data-loggers.
Fig 2.
Effects of time of day and lunar cycle on shark activity, swimming depth and body temperature.
Results of generalized additive mixed models (GAMMs) for telemetry data from blacktip reef sharks. Shown are diel changes in acceleration and body temperature (A), change in activity with lunar cycle (B) and diel changes in swimming depth (C). Dashed lines indicate the 95% confidence interval around each smooth term. Y-axis represents the standardized residuals.
Table 2.
GAMM results showing effects of time of day, tides or lunar cycle on body temperature, acceleration and swimming depth (from telemetry), and ODBA and gastric motility (from data-loggers).
Fig 3.
Effects of time of day on predator and prey activity.
A) GAMM results for changes in Overall Dynamic Body Acceleration (ODBA) as a function of time of day; water temperature (from the data-loggers) has been overlaid (blue points). B) GAM results for change in gastric motility as a function of time of day from a single blacktip reef shark. Dashed lines indicate the 95% confidence interval around each smooth term. Y-axis represents the standardized residuals. C) Foraging rates for three species of herbivorous reef fish, from Palmyra’s backreefs (Acanthurus lineatus, A. nigricans, Ctenochaetus striatus). A quadratic regression has been fit to the bite rate data (with 95% confidence intervals shown in red).
Fig 4.
Images from video camera attached to a blacktip reef shark.
Footage was taken during low tide in the morning and shows the shark using sandflat and inner backreef habitats (A), closely following another blacktip while a giant trevally (Caranx ignobilis) investigates (B), and frequently swimming up into school of mullet (Mugil cephalus, C).
Fig 5.
Diel changes in activity (ODBA, red line), water temperature (blue line) and swimming depth (black line) in blacktip reef sharks # 9 (A) and # 10 (B).
Data are 30 minute running averages. Crepuscular periods are shaded. Note the absence of an activity peak during days without peaks in ambient temperature.