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The life history of sperm whales, Physeter macrocephalus, from southern Australian waters

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Evans, Karen J.(Karen Jennifer) (2003) The life history of sperm whales, Physeter macrocephalus, from southern Australian waters. PhD thesis, University of Tasmania.

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Abstract

One hundred and fifteen sperm whales (97 female, 15 male, 3 unknown gender) were
involved in three mass stranding events during the month of February 1998 along the
west and north-west coastlines of Tasmania, Australia. Sixty six of these whales stranded
at Ocean Beach, Strahan, 35 at Greens Beach, Marrawah and 11 at Black River Beach,
Stanley. The remaining three whales stranded singly along the coastline. Three mass
strandings of this species in such close temporal proximity have not been reported in this
area before, and this is the first time that samples have been systematically collected from
complete or near-complete groups of sperm whales from Tasmanian waters. The broad
aim of this project was to examine the life history of complete or near complete female
groups of sperm whales in an effort to contribute to the paucity of knowledge on two key
areas of research identified for sperm whales in the Australian Government's Action Plan
on Australian Cetaceans: the basic biology of this species and pollutant impacts on this
species.
This study is made up of three components: (i) by developing modifications to current
methods of age determination, an assessment of the demographics and growth of the
female component of these groups was undertaken; (ii) by collecting stomach contents
and blubber samples, an investigation into energy acquisition and storage was undertaken
and (iii) concentrations of organochlorines were determined from blubber samples and
concentrations and interpreted in light of ecological factors such as diet and demography.
The three stranding groups were composed primarily of adult females. Total lengths of
all animals ranged from 417-1200 cm and ages ranged from 0.75-64 years. Female sperm
whales, unlike many other mammals, demonstrate high, relatively stable survival
throughout their entire life span. Overall, growth is prolonged in female sperm whales,
not reaching asymptotic length until around 20 years. The longevity, low fecundity, slow
growth, delayed sexual maturation and high input of resources into young over a
protracted period define sperm whales as extreme K-selected animals. Survival in mature
female sperm whales in this study was higher than those observed in mature females from
Japanese waters and similar to that observed in female sperm whales deriven from
Western Australian whaling operations. This suggests survival in female sperm whales
from Australian waters may have undertaken little change post whaling. However, there
appear to have been some changes in the age structure of female sperm whale groups and
additionally increases in the total lengths of individuals, which indicate some postwhaling
demographic changes. The diet of southern Australian sperm whales in late summer was dominated by oceanic
cephalopods. Cephalopod beaks from stomach contents represented 48 species from 14
families of Teuthids, two species from two families of Octopods and the single
Vampyromorph species. Subtropical and muscular species of cephalopods dominated the
diet of southern Australian sperm whales, but a high level of both inter- and intra-group
variability in the diet was apparent. Common cephalopod prey species were similar to
that of sperm whales elsewhere in the Southern Hemisphere and included members of the
Histioteuthidae, Onychoteuthidae, Ommastrephidae, Architeuthidae, Cranchiidae and
Pholidoteuthidae families. While smaller species (<300 mm dorsal mantle length) were
numerically abundant, larger species (>1,000 gm) were clearly important to sperm whales
(comprising 78.6 % of the total estimated wet mass) and are likely to provide an efficient
means of acquiring energy for this species. Differences in diet composition and prey size
between sperm whales reflect individual variability in foraging success and perhaps also
foraging groups related to the social structure of this species.
Individual variability in foraging success and therefore, in the acquisition of energy will
be reflected in an individuals energy stores. High individual variability characterised
both blubber thickness and blubber lipid content in the sperm whales in this study, which
suggests both deposition (acquisition) and mobilisation (utilization) of energy stores
differed between individuals. The social structure and foraging ecology of this species
may serve to minimize the need to rely on stored energy reserves to meet reproductive
energy requirements. Continual foraging of lactating mothers facilitated by communal
care of young by other members of a pod would aid in facilitating flexibility in the
acquisition of energy in an effort to meet energetic costs associated with reproduction,
minimising the need to draw on energy reserves to meet those demands. Additionally,
the broader role of blubber for structural, buoyancy and insulative functions coupled with
high individual variability may cause a lack of obvious relationships between these
variables and body size, age, sex and reproductive state in this species. Organochlorines were present in the blubber of all sperm whales sampled in this study.
The relationships between organochlorines, sexes, age and reproductive groups were
marked by high individual variability and highlight the complexity of organochlorine
accumulation in this species. Differences in organochlorine concentrations were
observed between two stranding groups and are likely to be the result of differences in the
dietary composition and foraging areas of the groups. As a result of this smaller
geographic scale of variation, it is therefore difficult to determine temporal changes in organochlorine concentrations positively in highly mobile species across large regions.
Organochlorine concentrations were on the whole lower than those observed to be linked
with deleterious effects in cetacean species elsewhere. However, it is difficult to draw
clear conclusions from this due to species-specific intake, differences in metabolism and
differences in physiological reactions to pollutant concentrations.
A life history involving low fecundity, high longevity, slow growth rates and delayed ,
attainment of sexual maturity, a high input of resources into young, and high sociality
involving communal care of young and communal defense all under-pin the aspects of the
life history sperm whales observed in this study. Yet despite the high dependence on life
as a social "unit" this study highlighted the influence of individuality on the life history of
female sperm whales. The sociality of female sperm whale groups allows for flexibility
in life history traits providing these animals with individual means to sustain their fitness
in an aquatic environment and allows them to ride out temporal and geographical
fluctuations in the environment. The identification of present day threats and their
impacts on sperm whale populations (e.g. chemical and noise pollution, competition with
fisheries), moreover establishing the identity and interactions between sperm whale
populations in the Australian region, are essential for determining current pressures on
populations and should be a high priority for environmental managers in ensuring the
conservation of this species.

Item Type: Thesis (PhD)
Keywords: Sperm whale
Copyright Holders: The Author
Copyright Information:

Copyright 2003 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

For consultation only. No loan or photocopying until 11/06/2005. Thesis (Ph.D.)--University of Tasmania, 2003. Includes bibliographical references

Date Deposited: 09 Dec 2014 00:07
Last Modified: 11 Mar 2016 05:54
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