[MARMAM] New Publication: Stable isotope trophic discrimination factors for seven pinniped species

Roxanne Beltran roxanne.beltran at gmail.com
Sat Apr 9 15:03:40 PDT 2016

My co-authors and I are pleased to share our new publication “Seals and sea
lions are what they eat, plus what? Determination of trophic discrimination
factors for seven pinniped species” in the journal Rapid Communications in
Mass Spectrometry:


*Abstract: *

*Rationale:* Mixing models are a common method for quantifying the
contribution of prey sources to the diet of an individual using stable
isotope analysis; however, these models rely upon a known trophic
discrimination factor (hereafter, TDF) that results from fractionation
between prey and animal tissues. Quantifying TDFs in captive animals is
ideal, because diet is controlled and the proportional contributions and
isotopic values of all prey items are known.

*Methods: *To calculate TDFs for the Hawaiian monk seal, northern elephant
seal, bearded seal, ringed seal, spotted seal, harbor seal, and California
sea lion, we obtained whiskers, serum, plasma, red blood cells, and prey
items from nine captive individuals. We obtained δ13C and δ15N values using
continuous-flow isotope-ratio mass spectrometry. The average δ13C and δ15N
values from bulk and lipid-corrected prey from the diet were subtracted
from theδ13C and δ15N values of each blood and whisker sample to calculate
tissue-specific TDFs for each individual (∆13C or ∆15N).

*Results: *The ∆13C values ranged from +1.7 to +3.2‰ (bulk prey) and from
+0.8 to +1.9‰ (lipid-corrected prey) for the various blood components, and
from +3.9 to +4.6‰ (bulk prey) or +2.6 to +3.9‰ (lipid-corrected prey) for
whiskers. The ∆15N values ranged from +2.2 to +4.3‰ for blood components
and from +2.6 to +4.0‰ for whiskers. The TDFs tended to group by tissue,
with whiskers having greater ∆13C values than blood components. In
contrast, the ∆15N values were greater in serum and plasma than in red
blood cells and whiskers.

*Conclusions: *By providing the first TDF values for five seal species
(family Phocidae) and one otariid species (family Otariidae), our study
facilitates more accurate mixing models for these species. These values are
particularly important for critically endangered Hawaiian monk seals and
the three Arctic seal species (bearded, ringed, and spotted) that are faced
with a rapidly changing environment.

Please contact me if you have any questions or do not have access to the

Take care,

Roxanne Santina Beltran
NSF Predoctoral Fellow
Ph.D. Student, Burns and Breed Labs
University of Alaska Anchorage/Fairbanks
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