Minimizing errors in the analysis of dive recordings from shallow-diving animals

Abstract

Knowledge of the diving behaviour of aquatic animals expanded considerablywith the invention of time–depth recorders (TDRs) in the 1960s. The large volume of data acquired from TDRs can be analyzed using dive analysis software, however, the application of the software has received relatively little attention.We present anempirical procedure to select optimumvalues that are critical to obtaining reliable results: the zero-offset correction (ZOC) and the dive threshold. We used dive data from shallow-diving coastal dugongs (Dugong dugon) and visual observations from an independent study to develop and test a procedure that minimizes errors in characterizing dives.Weinitially corrected the surface level using customsoftware.We then determined the optimumvalues for each parameter by classifying dives identified by an open-source dive analysis software into Plausible and Implausible dives based onthe duration of dives. The Plausible diveswere further classified asUnrecognized dives if theywere not identified by the software butwere of realistic dive duration. The comparison of these dive types indicated that a ZOC of 1 mand a dive threshold of 0.75 mwere the optimumvalues for our dugong data as they gave the largest number of Plausible dives and smaller numbers of other dive types. Frequency distributions of dive durations fromTDRs and independent visual observations supported the selection. Our procedure could be applied to other shallow-diving animals such as coastal dolphins and turtles.