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Vassar College

Publication Date

Fall 2018

Program Name

Australia: Rainforest, Reef, and Cultural Ecology

Abstract

Australian fur seals (AFS), Arctocephalus pusillus doriferus, are upper trophic predators endemic to the Bass Strait of south-eastern Australia. Their populations have been monitored since the mid-1900s to assess ecosystem health and the continual recovery of the species from extensive hunting in the early 19th century. The best way to track the environmental conditions and recovery of AFS populations is by monitoring the pups that are confined to the breeding colonies. This study looked particularly at the mortality rates of AFS pups because mortality of the young is a good indicator of population dynamics. The aim of this study was to determine unusual versus usual mortality rates and the factors affecting them for AFS pups. Mortality and total pup population data was obtained from the pup database which contains all the AFS pup data collected since the 1980s up to the 2017-2018 breeding season. Two pup estimates, Capture-Mark-Resight (CMR) and Direct count total, were used in conjunction with the dead pup count for Deen Maar Island, Seal Rocks, The Skerries, and Cape Bridgewater breeding colonies. Data were analyzed in RStudio. A Generalized Linear Model (GLM) was developed to determine differences between breeding site and season on pup mortality rates. Body condition of live pups was also studied to examine whether health of the AFS pups provide insight into mortality rates. This was investigated by calculating a Body Condition Index (BCI) and developing a GLM to determine whether breeding season, site, and pup sex affect this variable. Pup mortality rates generally fell under 15%. Although Cape Bridgewater and the 2013-2014 season at Seal Rocks showed unusually high mortality rates than other locations and seasons, there were no significant differences between breeding locations nor seasons. However, due to the limited data on dead pup numbers, these results were not entirely conclusive. Furthermore, the calculated BCI did not align well with veterinarian observed body conditions of pups and the GLM results were highly variable. For this reason, the BCI results could not provide insight on mortality rate trends. Given the results of this study, it will be necessary in the future to use more accurate 4 and frequent methods for acquiring dead and live AFS pup numbers to better understand ecosystem health and population recovery.

Disciplines

Animal Sciences | Biology | Marine Biology

 

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