[MARMAM] New article: Juvenile southern elephant seals from Marion Island consume krill: a stable isotope investigation using whisker regrowths

Nico Lubcker nlubcker at zoology.up.ac.za
Mon Aug 21 08:09:09 PDT 2017


Dear colleagues,

My co-authors and I would like to share with you our work recently
published in Marine Ecology Progress Series:

Lübcker N, Reisinger RR, Oosthuizen WC, de Bruyn PJN, van Tonder A,
Pistorius PA, Bester MN. 2017. Low trophic level diet of juvenile southern
elephant seals Mirounga leonina from Marion Island: a stable isotope
investigation using vibrissal regrowths. Mar Ecol Prog Ser 577: 237–250.

Article available at https://doi.org/10.3354/meps12240.

ABSTRACT:
Insight into the trophic ecology of marine predators is vital for
understanding their ecosystem role and predicting their responses to
environmental change. Juvenile southern elephant seals (SES) Mirounga
leonina are considered generalist predators within the Southern Ocean.
Although mesopelagic fish and squid dominate their stomach lavage samples,
the stable isotope profile captured along the length of sampled vibrissae
of young SES at Macquarie Island, southwest Pacific Ocean (54.5° S, 158.9°
E) recently emphasized the contribution of crustaceans to their diet
(likely Euphausia superba). Herein, we used the stable isotope values of
sampled vibrissal regrowths with known growth histories to assess the diet
of juvenile SES at Marion Island, southern Indian Ocean (46.8° S, 37.8° E)
on a temporally integrated basis. We specifically aimed to
quantify the possible contribution of crustaceans to the diet of juvenile
SES. Sequentially (chronologically) sampled vibrissal regrowths of 14
juvenile SES produced fine-scale dietary information spanning up to 9 mo.
The depleted stable isotope signatures of nitrogen (d15N) (8.5 ±
0.6‰) and carbon (d13C) (-20.3 ± 0.1‰) measured during the
period of independent foraging suggested the use of a lower trophic level
diet within the Polar Frontal Zone. A mixing model predicted that up to
76% of juvenile SES diet comprised crustaceans, consisting of 2 crustacean
groups, each contributing 26% (credible interval, CI: 13 - 39%) and 50%
(CI: 35 - 64%) to their diets, presumably representing subantarctic krill
species. This first utilisation of the isotopic signature captured along
the length of vibrissal regrowths confirms the inclusion and importance of
crustaceans in the diet of juvenile SES.

See
(https://www.researchgate.net/project/Low-trophic-level-diet-of-juvenile-southern-elephant-seals-Mirounga-leonina-from-Marion-Island-a-stable-isotope-investigation-using-vibrissal-regrowths/)
for more information regarding this project, or
(http://www.marionseals.com/) for more information regarding our research
group.

Sincerely,
Nico Lubcker
PhD. Zoology Candidate
Mammal Research Institute
Old Botany Building Room 1.16.5
Department of Zoology and Entomology
University of Pretoria
Hatfield
South Africa
0028
Cell: + 27 72 0370130







---------------------------- Original Message ----------------------------
Subject: New article: Vibrissal growth parameters of southern elephant
seals Mirounga leonina
From:    "Nico Lubcker" <nlubcker at zoology.up.ac.za>
Date:    Thu, January 5, 2017 09:35
To:      "marmam at lists.uvic.ca" <marmam at lists.uvic.ca>
--------------------------------------------------------------------------

Dear colleagues,

My co-authors and I would like to share with you our work recently
published in Marine Ecology Progress Series:

Lübcker N, Condit R, Beltran RS, de Bruyn PJN, Bester MN. 2016. Vibrissal
growth parameters of southern elephant seals Mirounga leonina: obtaining
fine-scale, time-based stable isotope data. Marine Ecology Progress Series
559: 243-255. doi: 10.3354/meps11899.

Article available at http://www.int-res.com/abstracts/meps/v559/p243-255/


ABSTRACT: Stable isotopes provide a powerful, indirect approach to assess
the trophic ecology of individuals on a spatial and temporally integrated
basis (especially when combined with telemetry). However, using stable
isotopes requires accurate, species-specific quantification of the period
of biomolecule deposition in the sampled tissue. Sequentially sampled
vibrissae (whiskers) provide a chronology of biogeochemical data, although
knowledge of vibrissal growth is required for temporal interpretations. We
sampled vibrissae from southern elephant seals Mirounga leonina (hereafter
SES) at Marion Island, southern Indian Ocean, to address the following
aims: (1) define the prevalence and timing of their vibrissal replacement,
(2) determine the vibrissal regrowth rate and temporal resolution of
isotopic data captured along the length of sequentially sampled vibrissae,
and (3) explore assumptions regarding their vibrissal growth. Contrary to
the previously described asynchronous vibrissal shedding pattern of SES,
71.1% of individuals displayed vibrissal shedding during the annual pelage
moult. Furthermore, vibrissal growth ceased once the asymptotic length was
reached, and the vibrissae were retained before being replaced. Vibrissae
with known growth histories were resampled at multiple known intervals to
control for unknown growth starting dates. Vibrissae followed a von
Bertalanffy growth function as the growth rate decreased near the
asymptotic length. The resolution of the isotopic data obtainable per 2 mm
section ranged from 3.5 d at the vibrissal tip to >40 d at the base. Using
these defined growth rates and shedding patterns, researchers can
prudently apply timestamps to stable isotope values along vibrissae.


https://www.researchgate.net/publication/310330776_Vibrissal_growth_parameters_of_southern_elephant_seals_Mirounga_leonina_Obtaining_fine-scale_time-based_stable_isotope_data

Sincerely,
Nico Lubcker
nlubcker at zoology.up.ac.za
PhD Zoology Candidate
Mammal Research Institute
Department of Zoology and Entomology
University of Pretoria
South Africa





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