Dear Colleagues,
I would like to bring to your
attention two manuscripts that
were recently published on the bioenergetics and body condition
of Pacific
walruses. This research
was undertaken
in an effort to quantify important physiological parameters that
will be
important for incorporating into population models to predict
how loses of sea
ice in the Arctic may affect the sustainability of this species.
I have never posted to MARMAM
before. However, I felt
that it was important to
share these papers because they provide a template that may be
modified and applied
to other marine mammals that are faced with limitations in food
availability. The
abstracts and citations are provided
below. If you are unable to access these journals, please
contact me for a
PDF.
Best Regards,
Shawn
Shawn R. Noren, Ph.D.
Associate Research Scientist
Institute of Marine Science
University of California, Santa
Cruz
Early View for Marine Mammal
Science: DOI:
10.1111/mms.12186
Identifying a reliable blubber measurement site
to assess body
condition in a marine mammal with topographically variable
blubber, the Pacific
walrus
SHAWN R. NOREN,
MARK S. UDEVITZ, LISA TRIGGS, JESSA PASCHKE, LISA OLAND,
CHADWICK V. JAY
Abstract
Pacific walruses
may be unable to meet caloric requirements in the changing
Arctic ecosystem,
which could affect body condition and have population-level
consequences. Body
condition has historically been monitored by measuring blubber
thickness over
the xiphoid process (sternum). This may be an unreliable
condition index
because blubber at other sites along the body may be
preferentially targeted to
balance energetic demands. Animals in aquaria provided an
opportunity for
controlled study of how blubber topography is altered by caloric
intake.
Morphology, body mass, blubber thickness (21 sites), and caloric
intake of five
mature, nonpregnant, nonlactating female walruses were measured
monthly (12 month
minimum). Body condition (mass 9 standard length–1) was
described by a model
that included caloric intake and a seasonal effect, and scaled
positively with
estimates of total blubber mass. Blubber thicknesses (1.91–10.69
cm) varied
topographically and were similar to values reported for
free-ranging female
walruses. Body condition was most closely related to blubber
thickness measured
dorsomedially in the region of the anterior insertion of the
pectoral flippers
(shoulders); sternum blubber thickness was a relatively poor
indicator of
condition. This study demonstrates the importance of validating
condition
metrics before using them to monitor free-ranging populations.
Physiological and
Biochemical Zoology 87(6):837–854. 2014.
Energy
Demands for Maintenance, Growth, Pregnancy, and Lactation of
Female Pacific
Walruses (Odobenus rosmarus divergens)
Shawn R. Noren, Mark S. Udevitz,
Chadwick
V. Jay
ABSTRACT
Decreases in sea ice have altered
habitat use and activity patterns of female Pacific walruses
Odobenus rosmarus
divergens and could affect their energetic demands, reproductive
success, and
population status. However, a lack of physiological data from
walruses has
hampered efforts to develop the bioenergetics models required
for fully
understanding potential population-level impacts. We analyzed
long-term
longitudinal data sets of caloric consumption and body mass from
nine female
Pacific walruses housed at six aquaria using a hierarchical
Bayesian approach
to quantify relative energetic demands for maintenance, growth,
pregnancy, and
lactation. By examining body mass fluctuations in response to
food consumption,
the model explicitly uncoupled caloric demand from caloric
intake. This is
important for pinnipeds because they sequester and deplete large
quantities of
lipids throughout their lifetimes. Model outputs were scaled to
account for activity
levels typical of free-ranging Pacific walruses, averaging 83%
of the time
active in water and 17% of the time hauled-out resting.
Estimated caloric
requirements ranged from 26,900 kcal d21 for 2-yr-olds to 93,370
kcal d21 for
simultaneously lactating and pregnant walruses. Daily
consumption requirements
were higher for pregnancy than lactation, reflecting energetic
demands of increasing
body size and lipid deposition during pregnancy. Although
walruses forage
during lactation, fat sequestered during pregnancy sustained 27%
of caloric
requirements during the first month of lactation, suggesting
that walruses use
a mixed strategy of capital and income breeding. Ultimately,
this model will
aid in our understanding of the energetic and population
consequences of sea
ice loss.