DOI: 10.5061/dryad.nzs7h44ng
title: Risk exposure trade-offs in the ontogeny of sexual segregation in Antarctic fur seal pups

description: Sexual segregation has important ecological implications, but its initial
 development in early life stages is poorly understood. We investigated the
 roles of size dimorphism, social behavior and predation risk on the
 ontogeny of sexual segregation in Antarctic fur seal, Arctocephalus
 gazella, pups at South Georgia. Beaches and water provide opportunities
 for pup social interaction and learning (through play and swimming), but
 increased risk of injury and death (from other seals, predatory birds, and
 harsh weather), whereas tussock grass provides shelter from these risks
 but less developmental opportunities. One hundred pups were sexed and
 weighed, 50 on the beach and 50 in tussock grass, in January, February and
 March annually from 1989 – 2018. Additionally, 19 male and 16 female pups
 were GPS-tracked during lactation from December 2012. Analysis of pup
 counts and habitat use of GPS-tracked pups suggested females had a
 slightly higher association with tussock grass habitats and males with
 beach habitats. GPS-tracked pups travelled progressively further at sea as
 they developed, and males travelled further than females towards the end
 of lactation. These sex differences may reflect contrasting drivers of pup
 behavior: males being more risk prone to gain social skills and lean
 muscle mass and females being more risk averse to improve chances of
 survival, ultimately driven by their different reproductive roles. We
 conclude that sex differences in habitat use can develop in a highly
 polygynous species prior to onset of major sexual size dimorphism, which
 hints that these sex differences will increasingly diverge in later life.
description: Antarctic fur seal pup
 monitoring: Antarctic fur seal pups were captured annually at Main Bay,
 Bird Island, South Georgia (54.010° S, 38.059° W)
 as part of a long-term monitoring programme. One hundred pups were
 selected (by convenience sampling), 50 on the beach and 50 in the tussock
 grass, each month in January, February and March annually from 1989 –
 2018. Each pup was captured by hand, measured, sexed (by examination of
 genitalia), and weighed to the nearest 100 g (using a hand-held spring
 balance). Antarctic fur seal pup
 GPS-tracking: Thirty-five Antarctic fur seal pups, 19 males and 16
 females, were GPS-tracked from the beach habitat at Freshwater beach, Bird
 Island, South Georgia (54.009° S, 38.052° W)
 between December 2012 and April 2013. Pups were sexed, measured, weighed,
 and equipped with a GPS logger (i-gotU GT-600; 37 g; 46 x 41.5 x 14 mm)
 and a radio transmitter (Sirtrack V2G-152A; 16g, 40 x 20 x 10 mm). GPS
 loggers were programmed to record locations every five minutes and pups
 were re-captured and weighed every 3.74 ± 0.076 days until pups weaned or
 died. Six pups died during the study period (atp 10, 11, 13, 18, 29 and
 38).  
      
description: Data file 'Antarctic fur seal pup monitoring data'
 contains data for monitored pups from 1989 – 2018. Data
 file 'Antarctic fur seal pup GPS tracking data' contains the raw
 GPS data for all 35 GPS-tracked Antarctic fur seal pups.
 Data file 'Mass of GPS tracked Antarctic fur seal pups'
 contains the pup measurements (in cm) and masses (in kg).