Flipper strokes can predict energy expenditure and locomotion costs in free-ranging northern and Antarctic fur seals.

Christophe Guinet,John P Y Arnould,Tiphaine Jeanniard-Du-Dot,Andrew W Trites,John R Speakman

doi:10.1038/srep33912

Abstract

Flipper strokes have been proposed as proxies to estimate the energy expended by marine vertebrates while foraging at sea, but this has never been validated on free-ranging otariids (fur seals and sea lions). Our goal was to investigate how well flipper strokes correlate with energy expenditure in 33 foraging northern and Antarctic fur seals equipped with accelerometers, GPS, and time-depth recorders. We concomitantly measured field metabolic rates with the doubly-labelled water method and derived activity-specific energy expenditures using fine-scale time-activity budgets for each seal. Flipper strokes were detected while diving or surface transiting using dynamic acceleration. Despite some inter-species differences in flipper stroke dynamics or frequencies, both species of fur seals spent 3.79 ± 0.39 J/kg per stroke and had a cost of transport of ~1.6–1.9 J/kg/m while diving. Also, flipper stroke counts were good predictors of energy spent while diving (R2 = 0.76) and to a lesser extent while transiting (R2 = 0.63). However, flipper stroke count was a poor predictor overall of total energy spent during a full foraging trip (R2 = 0.50). Amplitude of flipper strokes (i.e., acceleration amplitude × number of strokes) predicted total energy expenditure (R2 = 0.63) better than flipper stroke counts, but was not as accurate as other acceleration-based proxies, i.e. Overall Dynamic Body Acceleration.

Highlights

Flipper strokes have been proposed as proxies to estimate the energy expended by marine vertebrates while foraging at sea, but this has never been validated on free-ranging otariids
Of the 40 fur seals instrumented with biologging tags and injected with doubly-labelled water, we removed 7 animals that had inaccurate metabolic rate measurements from further analyses
The 4 partial acceleration datasets were included in analyses at the activity level as energetics and flipper strokes could be assessed over the same timeframe of existing data

Summary

Introduction

Flipper strokes have been proposed as proxies to estimate the energy expended by marine vertebrates while foraging at sea, but this has never been validated on free-ranging otariids (fur seals and sea lions). As most of the metabolic cost of foraging comes from the cost of transport[6] (i.e., the energy needed to move a unit of mass over a distance, usually expressed in J/m or in J/kg/m), count and amplitude of ‘stride’, ‘wingbeats’, and ‘stroke’ rates (in the case of marine animals) have been proposed as proxies of energy expenditure in a wide range of species[7,8,9,10] Several methods such as video images[7,11,12] or acoustic recordings[13] can be used to record these stroke rates in aquatic animals, but they do not allow the intensity or amplitude of strokes to be estimated. The relative paucity of stroking data for marine mammals likely reflects the difficulty of collecting — and of energetically quantifying — such information for large diving animals

Objectives

Methods

Results

Discussion

Conclusion