Informing the interpretation of dive profiles using animal-borne video: A marine turtle case study

Abstract

It is often of interest to infer the behavior of air-breathing aquatic taxa (i.e., divers) based on the characteristics of dive profiles, which are relatively affordable and easy to obtain. However, dives that appear similar in shape or other attributes can reflect multiple activities, confounding their interpretation. Here, we used animal-borne video and environmental data recorders (AVED) to examine correlations between the dive-surfacing patterns and behavior of green ( Chelonia mydas Linnaeus 1758) and loggerhead turtles ( Caretta caretta Linnaeus 1758) and evaluate our ability to make behavioral inferences from stand-alone dive data. Commonly performed dive types, which have been previously defined, were behaviorally diverse but some generalizations about their function could be made. Furthermore, within Type 1 dives (i.e., square-bottom, U-shaped dives), which are often assumed to reflect benthic resting, dive features (maximum dive depth, duration and variation in depth during the bottom phase) correlated with the proportion of bottom time spent resting versus engaged in other activities. Statistical clustering of Type 1 dives based on these dive metrics identified groups of dives differing in function (i.e., the degree of rest versus traveling or feeding) but some behavioral overlap occurred. The probability of a dive reaching the sea floor varied by dive type, which has important implications if dive profile data are used to infer habitat depth for benthic foragers in the absence of tracking data. Finally, the number of breaths taken while at the surface between dives varied closely with surface interval duration, particularly for loggerhead turtles, suggesting surface times in dive profiles may be useful for estimating oxygen loading prior to a dive. This case study emphasizes the value of AVED technology for increasing the level of ecological insight obtainable from stand-alone dive profiles.