Steller sea
lion research > Open
water project > Past Present Future of project
Past, Present and Future of Open Water Project
PAST:
Two completed studies determined the metabolic cost of diving to
different depths. The first showed surprising results — the rate
with which sea lions used oxygen (O2)
decreased as they went to deeper and deeper depths. The second study
advanced these results by evaluating the foraging decisions that sea
lions make at different depths and for different densities of food. Results
from this study showed that sea lions increased the duration of their
dives with increasing depth when food was abundant.
PRESENT:
The effect of changes in buoyancy on foraging energetics
The cost of foraging (or rate of oxygen consumption)
is of prime importance for animals that have a finite amount of O2 available
during their dives. The relationship between body condition (or level
of subcutaneous fat) and the cost of foraging may play a significant
role in whether or not a sea lion will successfully capture prey. Thus,
changes in subcutaneous fat can affect buoyancy and the cost of foraging
depending on how well an animal can manage its available O2.
Seasonal changes in body composition in wild seals and sea lions have
been well documented. In Steller sea lions, the amount of subcutaneous
fat varies between 8 and 15 % of their total body mass, and may affect
the cost of foraging. However, it is not currently known what effect
this may have on dive behavior, foraging cost or prey capture rates.
We are therefore assessing how simulated changes in buoyancy affect
behavior and foraging energetics.
The results from this project will provide important information on
the influence of body condition on the energetic costs and foraging
success of seals that dive to different depths. This will form an important
component of our larger goal to determine the food requirements of
wild populations, and assess how changes in the type or distribution
of their prey can impact wild populations. This, in turn, informs larger-scale
research on the underlying causes behind the decline of sea lions in
western Alaska.
Equipment testing and calibration
Although many studies use remote electronic devices tags to
study the behavior of animals, the accuracy of resulting data may be
limited because few tags are calibrated before deployment. They are
also limited by a poor understanding of the associated behavioral and
physiological costs to the tagged animal. We are therefore testing,
calibrating and evaluating the behavioural and physiological effects
of various electronic instruments. These include heart rate data loggers,
and instruments that measure flipper beat frequency and swim speed.
FUTURE:
An animal’s buoyancy and the
increased drag close to the water surface may affect an animal’s
swimming efficiency. We
will therefore compare the metabolic cost of shallow (almost horizontal)
dives as compared to deeper vertical (V shaped) diving.
It has been proposed that diving mammals are particularly resistant
to hypoxia (low O2) and hypercapnia
(high Carbon Dioxide - CO2). However,
the ventilatory effects of O2 and CO2 are
difficult to study and are different in animals on land or submerged
in water. We therefore plan to quantify how sensitive sea lions are
to this tradeoff to fully understand the foraging decisions that
sea lions make while diving.
