Dolphin collection critical to conservation

Indo-Pacific bottlenose dolphins-430W

Indo-Pacific bottlenose dolphins in north Spencer Gulf, South Australia are under threat from many human activities.

Australia’s largest and most comprehensive whale and dolphin (cetacean) collection is held at the South Australian Museum and has become a vital part of dolphin conservation efforts in Australia. The collection of over 1200 cetacean specimens includes approximately 350 specimens of Indo-Pacific bottlenose dolphins (Tursiops aduncus) and 400 short-beaked common dolphins (Delphinus delphis). These specimens of South Australia’s most numerous dolphin species have primarily been amassed over the last 25 years under the direction of Dr Catherine Kemper, Senior Research Scientist, Mammals.

The dolphin collection is much more than just skulls and skeletons. It includes reproductive organs, stomach contents, tissues for toxic contaminant and genetic studies as well as parasites. The impacts of human activity on animals can be slow and insidious and often it is almost too late when serious problems are detected. One of the aims of the collection and associated research is to record extensive life history information that will help researchers assess the impacts of human activity on the common dolphin species and conserve populations.

As with any animal population, ongoing monitoring is critical to tracking changes and this relies in part, on predictions that include comprehensive life history information. The Museum’s marine mammalogy group provides essential data on growth, sexual maturity and mortality of dolphins in South Australia by studying the carcasses of dead animals. It is the only group doing this type of research in Australia. Determining the age of dolphins is essential to this research and more accurate age estimates have been possible since the Museum’s Marine Mammal Ageing Facility was established in 2007.

The age of a dolphin is estimated using tooth structure. Thin longitudinal sections of teeth are stained with haematoxylin and highly trained personnel count groups of ‘lines’ within the dentine. Each group is equivalent to one year. A neonatal line is laid down in a tooth around the time of birth and forms the baseline from which counts are taken. To make sure the estimates are accurate, at least two teeth are taken from each animal and each tooth section is examined independently by three people.

Tooth section.

The stained thin-section from a tooth of a 19-year-old Indo-Pacific bottlenose dolphin from South Australia. Each yellow dot marks a year of age. 

Estimating the age of Indo-Pacific bottlenose dolphins has been a particular focus at the Museum, as this species is more likely to be affected by human activity. The dolphin life history research program has also uncovered some reproductive abnormalities that may be associated with heavy metal exposure. Research on heavy metal toxicity has been a focus of the Mammal team’s investigations. One of its students, Trish Lavery, discovered kidney and bone disease in South Australian dolphins with high concentrations of heavy metals. As dolphins are benthic feeders and long-lived, they are particularly vulnerable to contaminants, including heavy metals, deposited in ocean sediments.

The comprehensive collection of South Australia’s dolphins helps researchers to determine what is ‘normal’ within a population. This means that the Museum’s pathologists, taxonomists and zoologists are well-equipped to detect any problems at an early stage — a vital aspect of any conservation program.