Travelling light: white sharks (Carcharodon carcharias) rely on body lipid stores to power ocean-basin scale migration

Kira Krumhansl,Gen Del Raye,Barbara A. Block,Salvador J. Jorgensen,Juan M. Ezcurra

doi:10.1098/rspb.2013.0836

Abstract

Many species undertake long-distance annual migrations between foraging and reproductive areas. Such migrants depend on the efficient packaging, storage and utilization of energy to succeed. A diverse assemblage of organisms accomplishes this through the use of lipid reserves; yet, it remains unclear whether the migrations of elasmobranchs, which include the largest gill breathers on Earth, depend on such a mechanism. We examine depth records from pop-up satellite archival tags to discern changes in buoyancy as a proxy for energy storage in Eastern Pacific white sharks, and assess whether lipid depletion fuels long-distance (approx. 4000 km) migrations. We develop new algorithms to assess body condition, buoyancy and drift rate during drift dives and validate the techniques using a captive white shark. In the wild, we document a consistent increase in drift rate over the course of all migrations, indicating a decrease in buoyancy caused by the depletion of lipid reserves. These results comprise, to our knowledge, the first assessment of energy storage and budgeting in migrating sharks. The methods provide a basis for further insights into using electronic tags to reveal the energetic strategies of a wide range of elasmobranchs.

Highlights

Migration optimizes resource availability by allowing migrants to take advantage of seasonal changes in distant environments [1]
White sharks, which undertake distant seasonal migrations and whose buoyancy is dominated by liver lipids [22], are ideal candidates for this approach, given the recent application of satellite tags
The objectives of this study were to use time-series data collected on electronic tags and video monitoring of captive animals: (i) to validate the use of drift rate as a proxy for buoyancy and lipid storage in white sharks, (ii) to track changes in drift rate during long-distance migratory transits, and (iii) to determine whether white sharks rely on body energy stores rather than opportunistic foraging to fuel their migrations

Summary

Introduction

Migration optimizes resource availability by allowing migrants to take advantage of seasonal changes in distant environments [1]. White sharks, which undertake distant seasonal migrations and whose buoyancy is dominated by liver lipids [22], are ideal candidates for this approach, given the recent application of satellite tags.

Objectives

Results

Conclusion