Pinniped diving behaviour in geographic and oceanographic space
Abstract
Southern elephant seals (SES) are far-ranging top predators and sentinels of the Southern Ocean ecosystem
status. Their well-being depends on the resources available in different oceanographic habitats. This study
presents methods for long-term monitoring of SES movements and body condition within the Atlantic sector.
Collecting information on SES, who spend months at sea, is often only possible using telemetry. I thus
present a method designed for detecting buoyancy changes from low-resolution dive data. Detected buoyancy
changes, which reflect body condition changes (i.e. lipid gain or loss), are examined in relation to when and
where they geographically occur. For replenishing resources SES rely on macroscale latitudinal fronts, which
provide favourable foraging conditions through aggregating prey and enhancing productivity. Generally, SES
associate more frequently with higher latitude fronts/zones. Body condition improvements associated with a
given frontal system vary strongly according to year, season and month. The variability in body condition improvements
is higher in some frontal systems than in others, likely due to shifts in the Subantarctic and Polar
Front. During a migration, some individuals stay within ≤3 frontal systems, whilst others change between
several frontal systems and primarily improve their body condition in upper ocean waters. Body condition
improvements, related to particular water masses, differ between the sexes and seasons. SES do not trace
particular water masses across different frontal systems. Large inter-individual variability exists in how fast,
when and where successful resource acquisition occurs. Conclusions drawn from track-based behavioural
metrics regarding foraging activity are biased by the influence of currents on the horizontal movements of
SES. The presented current-correction methods reveal that movements in geographic and hydrographic space
differ. Currents primarily alter the horizontal travel direction, and SES show an ability to compensate for such
deflections. However, even after current-correcting trajectories, track-based behavioural metrics fail to reflect
body condition improvements, but rather display different foraging strategies. Individuals are flexible in using
different foraging and movement strategies, depending on which oceanographic habitat they exploit. They exhibit
large plasticity towards spatio-temporal variability. This could indicate resilience against environmental
changes. However, long-term monitoring is necessary to fully capture the vulnerability of SES towards climate
change.
Type
Thesis, PhD Doctor of Philosophy
Rights
Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Embargo Date: 2021-04-17
Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 17th April 2021
Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 17th April 2021
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