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  • Sex ratios of migrating southern hemisphere humpback whales: A new sentinel parameter of ecosystem health

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    Author(s)
    Druskat, Alison
    Ghosh, Ruma
    Castrillon, Juliana
    Nash, Susan M Bengtson
    Griffith University Author(s)
    Bengtson Nash, Susan M.
    Druskat, Alison
    Year published
    2019
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    Abstract
    Southern hemisphere humpback whales have evolved energetically demanding capital breeding and migratory life-history behaviours. It has been hypothesised that not all individuals of a population participate in the seasonal migration each year, or only undertake partial migrations. Given the cost of migration and reproduction, we explored the possibility that specifically, not all mature females participate in the seasonal migration every year, or significantly delay or shorten their migration, in response to poor feeding conditions. That is, females must attain a minimum threshold of accumulated energy reserves to commit to ...
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    Southern hemisphere humpback whales have evolved energetically demanding capital breeding and migratory life-history behaviours. It has been hypothesised that not all individuals of a population participate in the seasonal migration each year, or only undertake partial migrations. Given the cost of migration and reproduction, we explored the possibility that specifically, not all mature females participate in the seasonal migration every year, or significantly delay or shorten their migration, in response to poor feeding conditions. That is, females must attain a minimum threshold of accumulated energy reserves to commit to a reproductive event that likely occurs as a product of mating during migration. With a 1:1 male to female birth ratio, yet a male bias observed along the main migratory corridor; this study utilised inter-annual migratory cohort sex ratios to explore their potential to serve as measures of population fecundity, as a function of ecosystem health. The sex ratios of randomly biopsied adult humpback whales, sampled at a defined location and set time-points along the main migratory corridor from 2008 to 2016 were investigated. Northward migration sex ratios in 2009, 2014 and 2016 revealed a lower male bias suggesting good female participation in the migration and therefore apparent optimal provisioning during the two preceding summers. By contrast, the 2011 southward migration, revealed the highest male bias recorded of 5.75:1. Southward migration sex ratios were found to oscillate closely with measures of population adiposity, a sentinel parameter employed for long-term surveillance of the Antarctic sea-ice ecosystems under the Southern Ocean Observing System-endorsed Humpback Whale Sentinel Program. Anomalously poor humpback whale body condition recorded in 2011 was attributed to poor Antarctic feeding conditions during the extreme La Niña event of 2010/11. These findings lend support for the application of migratory cohort sex ratios, standardised by time and location, as a measure of relative inter-annual population fecundity. This work therefore contributes a new non-lethal tool for the study of population health, as a function of ecosystem productivity, and facilitates the inclusion of fecundity as a sentinel parameter into long-term Antarctic ecosystem surveillance under the Humpback Whale Sentinel Program.
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    Journal Title
    Marine Environmental Research
    DOI
    https://doi.org/10.1016/j.marenvres.2019.104749
    Copyright Statement
    © 2019 Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence (http://creativecommons.org/licenses/by-nc-nd/4.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, providing that the work is properly cited.
    Note
    This publication has been entered into Griffith Research Online as an Advanced Online Version
    Subject
    Chemical sciences
    Environmental sciences
    Biological sciences
    Antarctic sea-ice ecosystem
    Climate
    Energetic health
    Fecundity
    Migration
    Publication URI
    http://hdl.handle.net/10072/386726
    Collection
    • Journal articles

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