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The Tasmanian cetacean stranding record : a review of the cetacean strandings in Tasmanian waters and an examination of possible causes

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Nicol, Douglas J (1991) The Tasmanian cetacean stranding record : a review of the cetacean strandings in Tasmanian waters and an examination of possible causes. Research Master thesis, University of Tasmania.

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Abstract

Tasmanian cetacean stranding reports are examined and reviewed to establish the composition
of the record and identify possible causes of the strandings. The record, to the end of February
1986, comprises 213 stranding events (152 single and 61 herd strandings) dating from 1825.
These events involve 22 species and over 3000 animals. Five species (the pygmy right whale,
sperm whale, long-finned pilot whale, common dolphin and bottle-nosed dolphin) have each
stranded on more than 20 occasions, and represent 66% of the events. Four species (the false
killer whale, strap-toothed whale, Cuvier's beaked whale, and Gray's beaked whale) have each
stranded between nine and 13 times. The remaining 13 species have stranded on less than five
occasions, usually only once each, and there are nine strandings in the record for which the
species involved is not known.
In general, areas with high numbers of strandings have complex oceanographic conditions. It
is proposed that the high number of strandings on the western section of the north coast of
Tasmania, and the Storm Bay - southeast area are due to cetaceans experiencing difficulties with
the combination of the areas' oceanographic conditions and extensive shoaling waters, while the
low number of strandings in the central section of the north coast is due to the low number of
cetaceans that enter the shallow central region of Bass Strait
Active strandings are shown to occur predominantly on shelving coasts, the frequency of which
is significantly higher than that expected from the proportion of these topographies along the
coast as a whole. This relationship does not exist on the north coast because of the high
proportion of beaches in this area, indicating that steep coasts may prevent strandings rather
than shelving coasts causing them. Active stranding sites tended to occur at or near local
minima in the geomagnetic field intensity but they were not characterised by having intensity
contours running perpendicular to the coast's alignment.
The stranding record shows a strong seasonality with most events being reported during the
summer months. It is proposed that a major influence is that the summer months are the peak
period of human activity on the beaches, thus a period of high observer effort. Long-finned
pilot whale strandings are significantly correlated with sea surface temperature, possibly
indicating that part of the seasonal pattern is induced by seasonal variations in the physical
environment.
The overall long-term trend are of more strandings being reported each year, and it is proposed
that the increase is due to greater scientific interest and public awareness of cetacean strandings
rather than changes in the actual rate of strandings. The annual fluctuations in the number of
stranding reports, however, can not be explained by variations in observer effort. Several
environmental factors were investigated including aspects of the Tasmanian weather, variations
of, and disruptions to, Tasmania's oceanography, and the disruption of the navigation systems
of cetaceans. Only strandings of two species and two species groups were significantly
correlated with some of these features, at varying time lags (-1, 0, + 1 years), which indicates
that either the availability or susceptibility of cetaceans to strand is affected by some features of
the physical environment around and to the south of Tasmania.

Item Type: Thesis (Research Master)
Keywords: Cetacea
Copyright Holders: The Author
Copyright Information:

Copyright 1991 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:

Includes bibliographical references (p. 163-185). Thesis (M.Env.St.)--University of Tasmania, 1993

Date Deposited: 03 Feb 2015 03:07
Last Modified: 11 Mar 2016 05:55
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