Age and reproduction in Northern Elephant Seals

Maternal age can influence reproductive success and offspring fitness, but the timing, magnitude, and direction of those impacts are not well understood. Evolutionary theory predicts that selection on fertility senescence is stronger than maternal effect senescence, and therefore the rate of maternal effect senescence will be faster than fertility senescence.We used a 36-year study of northern elephant seals (Mirounga angustirostris) to investigate reproductive senescence. Our dataset included 103,746 sightings of 1,203 known-age female northern elephant seals.We hypothesized that fertility (maternal reproductive success), offspring survival and recruitment into the breeding population, and male offspring production would decline with advanced maternal age. Furthermore, we hypothesized that older females would shorten their molting haul out to allow for more time spent foraging. We found evidence for both fertility and maternal effect senescence, but no evidence for senescence impacting..., Seals are tagged with alphanumeric flipper tags at the time of weaning (approximately one month old), allowing for a demographic database of known-age individuals. We made daily attempts to observe tagged individuals during the breeding and molting seasons, approximately January through June of each year, from 1987 to 2023. When observing a tagged breeding female, we collected information about her pup status (present or absent) and pup sex (male or female). Pup sex was determined in the field by visual inspection based on the presence or absence of a penile opening. When possible, we used hair bleach to mark pup fur with a temporary unique identifier. After weaning, this identifier allowed us to find pups, attach permanent unique flipper tags, and link the pups to their mothers in the database. This analysis includes adult female seals observed on four or more days during the breeding season (December 1 - March 15). The threshold number of days was chosen to minimize observation errors..., , # Age and Reproduction in Northern Elephant Seals

[https://doi.org/10.5061/dryad.pg4f4qrx1](https://doi.org/10.5061/dryad.pg4f4qrx1)

The .csv file contains processed data (each row is a year-seal combination), the .r file contains the code to create formatting functions, and the .qmd file contains the code to fit the models and reproduce the figures.

## Description of the data and file structure

**Headers in the \"128L pull 2023_12_05.csv\" file are as follows:**

animalID: a unique identifier for an individual seal, consistent across years and linked to an alphanumeric flipper tag.

year: the calendar year of the observation

observed: A binary variable indicating whether an animal was seen with a pup (\"B\") or not (\"1\").

firstobsmolt: A date in format YYYY-MM-DD indicating the first time in a given year an animal was observed during the molting season, used as a proxy for molting haulout arrival. NA (not available) indicates that phenological observations were not made for that sea...