Processing of acceleration and dive data on-board satellite relay tags to investigate diving and foraging behaviour in free-ranging marine predators
Résumé
1. Biologging technologies are changing the way in which the marine environment is
observed and monitored. However, because device retrieval is typically required to
access the high-resolution data they collect, their use is generally restricted to
those animals that predictably return to land. Data abstraction and transmission
techniques aim to address this, although currently these are limited in scope and do
not incorporate, for example, acceleration measurements which can quantify
animal
behaviours and movement patterns over fine-scales.
2. In this study, we present a new method for the collection, abstraction and transmission
of accelerometer data from free-ranging marine predators via the Argos satellite
system. We test run the technique on 20 juvenile southern elephant seals
Mirounga leonina from the Kerguelen Islands during their first months at sea following
weaning. Using retrieved archival data from nine individuals that returned to
the colony, we compare and validate abstracted transmissions against outputs from
established accelerometer processing procedures.
3. Abstracted transmissions included estimates, across five segments of a dive profile, of
time spent in prey catch attempt (PrCA) behaviours, swimming effort and pitch. These
were then summarised and compared to archival outputs across three dive phases:
descent, bottom and ascent. Correlations between the two datasets were variable
but generally good (dependent on dive phase, marginal R2 values of between
.45 and
.6 to >.9) and consistent between individuals. Transmitted estimates of PrCA behaviours
and swimming effort were positively biased to those from archival processing.
4. Data from this study represent some of the first remotely transmitted quantifications
from accelerometers. The methods presented and analysed can be used to
provide novel insight towards the behaviours and movements of free-ranging marine
predators, such as juvenile southern elephant seals, from whom logger retrieval
is challenging. Future applications could however benefit from some adaption,
particularly
to reduce positive bias in transmitted PrCA behaviours and swimming
effort, for which this study provides useful insight.