A New Method to Calibrate Attachment Angles of Data Loggers in Swimming Sharks

Shizuka Kawatsu,Jason P Breves,E Gordon Grau,Susumu Hyodo,Katsufumi Sato,Nobuyuki Miyazaki,Yuuki Watanabe,Bradley K Fox

doi:10.1155/2010/732586

Abstract

Recently, animal-borne accelerometers have been used to record the pitch angle of aquatic animals during swimming. When evaluating pitch angle, it is necessary to consider a discrepancy between the angle of an accelerometer and the long axis of an animal. In this study, we attached accelerometers to 17 free-ranging scalloped hammerhead shark (Sphyrna lewini) pups from Kaneohe Bay, Hawaii. Although there are methods to calibrate attachment angles of accelerometers, we confirmed that previous methods were not applicable for hammerhead pups. According to raw data, some sharks ascended with a negative angle, which differs from tank observations of captive sharks. In turn, we developed a new method to account for this discrepancy in swimming sharks by estimating the attachment angle from the relationship between vertical speed (m/s) and pitch angle obtained by each accelerometer. The new method can be utilized for field observation of a wide range of species.

Highlights

An accurate determination of pitch angle is critical to gain detailed information about the diving and foraging strategies of aquatic animals
Pitch angle is significantly correlated with time spent at the bottom-phase of the dive [2]
When we analyzed the relationships between raw pitch angle and vertical speed per second, we found a linear regression from each pup

Summary

Introduction

An accurate determination of pitch angle is critical to gain detailed information about the diving and foraging strategies of aquatic animals. Air-breathing aquatic animals that forage underwater control pitch angle and allocate their submerged time. Pitch angle is significantly correlated with time spent at the bottom-phase of the dive [2]. Based on the observation of swimming behavior, it is apparent that sharks make a sharp dorsal turn at the bottom, consume food items, and swim away along the bottom [3]. In this sequence, pitch angle is an important indicator of a feeding event

Methods

Results

Conclusion