Detection of Sea Turtle’s Pushing-up Behaviour with Acceleration Data Logger

When sea turtles accidently enter into a fully-submerged bag net, they tend to push up the upper net in need of fresh air. In this study, we tried to detect pushing-up behaviours of green turtles in an experimental bag net (8m*8m*2.1m) with a tri-axial acceleration data logger. Four green turtles (SSCL: 58.1-71.2cm) were applied. Behaviour of each green turtle in the net was recorded by an underwater video camera, and the number and duration of successive pushing-up behaviours were confirmed. Detection of pushing-up behaviour was attempted by filtering the time series attitude angle and the ODBA (Overall Dynamic Body Acceleration) of the turtle which were converted from the static surge acceleration or the tri-axial dynamic acceleration. The total number of pushing-up behaviours was 38 times and the total duration was 284 seconds. The most accurate threshold of 35 degrees in attitude angle and 2.0 m/s2 in ODBA detected 82 % of all the pushing-up behaviours although it contained non pushing-up behaviours such as quick changes in swimming direction. It also detected 54 % out of the whole duration time. Data from geomagnetic direction and depth sensor would improve precision of the detection in a field experiment