Antarctic
Fur seal (Arctocephalus gazella) breeding success in the context of
climate change.
The project
of Individual based modelling of
the project MyctO-3D-map (supported by the French National Research
Agency) concentrated on the success of the breeding period (from birth
to weaning) of large marine predators of the Subantarctic zones.
More
exactly, we were interested, among others, in the fur seals of
Kerguelen (or the Antarctic fur seal: Arctocephalus
gazella) who come to reproduce in
colonies in the archipelago of the same name. These animals are
carnivores and feed very preferentially, in this region, on lantern
fishes (Myctophideae) which migrate towards the surface at
night. After having given birth by the beginning of December, females
proceed to their first feeding and then
alternate stays at sea (5 in 7 days on average) to feed with short
stays in the colony. This phase lasts
approximately 4 months at the end of which the pups
are weaned and start their autonomous life.
MarCPFS is a simulator
which attempt to reproduce these phases including a prenatal period
of exploration of the neighborhood of the Kerguelen Islands during
which fur seals will memorize the richest zones which they discover, so
as to begin the period of breeding in the best conditions to feed. The time step of the
simulator is the hour.
The simulator involves stochastic
elements, in
particular in the decision-making problems of the seals: the decision
to leave the island or to return there, to dive and fish or to continue
foraging somewhere else, the return with fidelity to the memorized
zone, etc.
For each fur seal, bio-energetic parameters are regularly updated
according to the fishing success, the lactation, the hourly metabolic
loss... Are also calculated in the initialization some parameters which
characterize the animal. So, according to her size are calculated the
drag force the mother seal has to face (for an average speed of travel
of 2 ms-1) and the maximal energy she can potentially
acquire.
The seals move in a 2 dimensional and fixed environment (a map of
density of the resources). The resource is distributed in a radius of
500 km around the island. Three parameters are taken into account in
their creation: the average density (from 90 to 360 g of capturables
prey in one hour of dive), the aggregation of the resource (from
scattered to highly aggregated) and the distance island-resource, that
is the distance in which the probability to find zones of maximal
density is 1. Maps thus present a positive gradient of density of the
resource when moving away from the island.
Environmental conditions and characteristic traits of the fur seals
(body size, memorization ability, type of movements) condition the
breeding success. However, environmental conditions and traits can
counterbalance partially and so reveal emergent phenomena in the
results.
For further details, please refer to the following publication and the Supplementary Information attached to the paper:
Massardier-Galatà
L, Morinay J, Bailleul F, Wajnberg E, Guinet C, Coquillard P (2017)
Breeding success of a marine central place forager in the context of
climate change: A modeling approach. PLoS ONE 12(3): e0173797.
doi:10.1371/journal.pone.0173797
Results of simulations can be freely viewed and dowloaded through the
The MarCPFS database :
http://www2.sophia.inra.fr/MarCPFS_Database/index.php