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

• Main Author: Nicol, Douglas J
• Format: Thesis
• Language: English
• Published: 1991
• Subjects: Cetacea; The Beaches; Killer Whale; Sperm whale; toothed whale
• Online Access: https://eprints.utas.edu.au/21044/; https://eprints.utas.edu.au/21044/1/whole_NicolDouglasJ1993_thesis.pdf

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.