Acoustic accelerometry reveals diel activity patterns in premigratory Port Jackson sharks.

Julianna Kadar,Culum Brown,Monique Ladds,Johann Mourier,Joanna Day

doi:10.1002/ece3.5323

Abstract

Distinguishing the factors that influence activity within a species advances understanding of their behavior and ecology. Continuous observation in the marine environment is not feasible but biotelemetry devices provide an opportunity for detailed analysis of movements and activity patterns. This study investigated the detail that calibration of accelerometers measuring root mean square (RMS) acceleration with video footage can add to understanding the activity patterns of male and female Port Jackson sharks (Heterodontus portusjacksoni) in a captive environment. Linear regression was used to relate RMS acceleration output to time‐matched behavior captured on video to quantify diel activity patterns. To validate captive data, diel patterns from captive sharks were compared with diel movement data from free‐ranging sharks using passive acoustic tracking. The RMS acceleration data showed captive sharks exhibited nocturnal diel patterns peaking during the late evening before midnight and decreasing before sunrise. Correlation analysis revealed that captive animals displayed similar activity patterns to free‐ranging sharks. The timing of wild shark departures for migration in the late breeding season corresponded with elevated diel activity at night within the captive individuals, suggesting a form of migratory restlessness in captivity. By directly relating RMS acceleration output to activity level, we show that sex, time of day, and sex‐specific seasonal behavior all influenced activity levels. This study contributes to a growing body of evidence that RMS acceleration data are a promising method to determine activity patterns of cryptic marine animals and can provide more detailed information when validated in captivity.

Highlights

Activity patterns are a key component of animal fitness shaped by endogenous and exogenous factors that dictate behavior and deter‐ mine species movement patterns (Helfman, 1986)
We found that the overall increase in activity patterns in captive sharks between the two periods corresponded to a drop in the proportion of sharks detected by the network of receivers (Figure 7)
The use of accelerometers deployed on Port Jackson sharks in captivity showed correlations between observed behav‐ ior and acceleration data

Summary

Introduction

Activity patterns are a key component of animal fitness shaped by endogenous and exogenous factors that dictate behavior and deter‐ mine species movement patterns (Helfman, 1986). Changes in light intensity and temperature, for example, are associated with changes in season and shifts from night to day (Cohen & Forward, 2016; McNamara, Mace, & Houston, 1987; Thiem et al, 2018). Both of these factors are key stimuli that drive patterns of animal behavior such as breeding and migration. For ex‐ ample, remain inactive during daylight hours in shallower, warmer caves to avoid sexual harassment from males which are frequently active during the day and position themselves to intercept females upon their returns from nocturnal foraging trips into deeper wa‐ ters (Wearmouth et al, 2012)

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