Uncover the fascinating relationship between age and lactation duration in northern elephant seals, and its implications on their reproductive dynamics and pup survival. This study sheds light on the critical role of age in understanding marine mammal lactation patterns Northern Elephant Seals Lactation Dynamics Marine Mammal Reproduction Age-Dependent Lactation Mirounga angustirostris Marine Biology Wildlife Conservation Mammalian Lactation Reproductive Strategies Marine Mammals Pup Growth and Survival Breeding Season Dynamics Animal Behavior Evolutionary Biology Ecological Research

1. Age dependent lactation dynamics
in northern elephant seals
(Mirounga angustirostris)
Presented by Elise Baugh | June 2023
Research Authors: Elise Baugh and Mimi Chavez

2. Introduction:
Research Background
Lactation duration is a driver for population dynamics
Lactation Life History strategies
Northern elephant seals are amazing

3. Lactation is the defining characteristic of all mammals.
The Duration and efficiency of lactation impacts
offspring’s growth and survival
There is an Inverse relationship between fertility and lactation
Lactation the most energetically expensive period of reproduction
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Lactation is a driver for population dynamics
Introduction

4. Capitol provisioning : phocids
• High calorie, energy-rich milk
• Hi efficiency of Energy transfer
• Short lactation duration
• Mothers fast during lactation,
• low metabolic overhead
• No weaning period
Income provisioning: most mammals
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Tactics for ’financing’ the energetic cost of lactation:
Two life history strategies
• Low calorie energy milk
• Energy transfer inefficient
• Long Lactation period
• Mothers forage during lactation
• High metabolic overhead
• Gradual Weaning period (i.e.: length of 3- 4 years in
bottlenose whales)
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Introduction

5. Research Questions
• How do we investigate reproductive senescence in
marine mammals?
• How does reproductive senescence in aging elephant
seals impact the duration of the lactation period?
We hypothesized that older females will have shorter lactation
periods while younger breeding females will have longer lactation
period

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• Highly efficient energy transfer during abbreviated lactation period
Provide a unique opportunity to study marine
mammals
• Northern Elephant seals are semi-terrestrial
• Reproductive events occur on land
Site Fidelity
• Northern Elephant Seals return to Año Nuevo Marine Reserve biannually,
• Enables research on major life histories events over an individual’s lifespan
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Why northern elephant seals are amazing organisms to
study….
Concentrated lactation period
Introduction

7. Methods
Research site
Flipper tags and lifetime ID numbers
Marking with a wooden stamp
Resights

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Research site +
BioE-128 Classroom:
Año Nuevo
Marine
Reserve
Methods

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Flipper tag Identifications remain
on the seal to identify the
individual year after year
Flipper tags :
Methods

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Unique ID is marked on
seals with hair die and
wooden stamps
Methods
Marking with wooden stamps:

11. Field observations for the breeding
season begins annually on the first
day of December.
We record:
• Date of sighting
• Location on beach
• Pup Status, date of birth
• Molt
• Comments
• Photos
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Methods
Field re-sights:

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Females with a pup are
classified as ‘breeders’
While those present without a
pup during the season are
recorded as ‘non-breeders’
Age of pup at first sighting
date of wean
Methods
Field resights:

13. Results:

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Results:
Our analysis revealed :
• A significant positive
relationship between age
and the mean lactation
duration of breeding
females:
• And a negative linear
correlation between the
age of females (of
reproductive age) present
at Ano Nuevo that were
not breeding

15. Discussion:
We hypothesized that older females will have shorter lactation periods
while younger breeding females will have longer lactation period
• We based this hypothesis on previous studies that indicate the energy content of milk
increases with age.
• sample size : 27 breeding females
• Age range incorporated reproductive females 3-13 years old.
Result of this study revealed the opposite:
• Older females have longer lactation periods
• younger breeding females will have shorter lactation period
What does this Mean ?
As Elephant seals age their lactation period becomes less efficient , more time is required

16. Professors, Teachers and
team at BIO 128L
Mimi Chavez: co-author in
this study:
The Año Nuevo Marine
Reserve Seal Colony
Acknowledgements
Thank you to:
Bruce Lyon: elephant seals and research site photography within this presentation:
Evolutionary Biology Advising