Dolphin Research Institute (DRI)
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Other Research Projects

Impacts of Boat Traffic on Acoustic Behaviour

Moonraker approaching web.jpg Port Phillip Bay is subject to high levels of boat traffic. A major shipping port is situated at Port Melbourne, in the northern part of the Bay but there is also a significant amount of traffic associated with recreation, fishing, diving and other marine-based industries.

This high usage by watercraft may present a number of problems for dolphins. As part of recent research DRI researchers have investigated the impact of boat traffic on the acoustic behaviour of bottlenose (Tursiops sp.) and short beaked common dolphins (Delphinus delphis) in Port Phillip Bay and Gippsland Lakes.

Dolphins use their highly developed senses especially vocal and hearing to communicate and synchronise with each other. It is thought that the presence of watercraft may potentially mask the sound of these whistles and disrupt the dolphins' behaviour.

This study recorded and analysed the whistles and behaviours of the two species of dolphins at both sites before, during and after experimental boat approaches. Analysis revealed an increase in whistling rate for both species of dolphins and at both locations during travelling and feeding behaviour.

Results from this study demonstrate an apparent impact of boats on acoustic communication in dolphins. However further research is needed to fully address the implications and thus future management practices.

Contaminants in our Water - How do they affect our Dolphins?

Common Dolphin 12 April07 008 web210x158.jpg Contaminants and pollutants can enter our waterways in a number of ways. No matter how they end up in our water it is inevitable that they will also affect our marine life.

There are certain contaminants that can magnify in concentration through food chains. If organisms low in the food chain become contaminated and are then eaten by animals higher on the food chain, contaminates will accumulate in these 'higher food chain' animals this process is known as bioaccumulation.

Dolphins are part of these 'higher food chain' animals and if the concentration of contaminants reaches certain levels in their systems there can be serious health implications.

Recently researchers from DRI have been conducting studies to identify contaminants that may be of concern to bottlenose dolphins (Tursiops sp.) in inland coastal Victorian waters.

Blubber samples from both living and deceased dolphins in two populations were assessed for contaminants to enable a comparison of levels between live and dead animals. Contaminant levels in sediment and fish samples were also assessed to identify potential sources of contamination.

As a result of these assessments a range of contaminants were detected including mercury, PCB's and zinc.

This study has found strong evidence that the concentration of mercury could compromise the health and survival of these dolphins. This is shown through the significantly higher concentrations of mercury found in dead animals compared to live dolphins. However there was no one obvious food source found to be contributing to contaminant levels present in the dolphins.

Where do Dolphins Live?

Common dolphins Mt Eliza web210x158.jpg In order to affectively protect and conserve the dolphins that live in Port Phillip Bay we must understand what parts of the Bay they inhabit. Port Phillip,

Victoria is home to a small, unique population of bottlenose dolphins (Tursiops sp.) which currently share the bay with a recently 'discovered' short-beaked common dolphin (Delphinius delphis) pod.

As part of our current research program, researchers at DRI have been investigating the distribution of dolphins between Mornington and Observatory Point.

One particular study was conducted during winter where environmental variables such as sea surface temperature, depth, and presence of gannets, fur seals and penguins as well as fish density were recorded.

It was found that common dolphins preferred areas from Mornington to Mt Marta whilst the bottlenose dolphins were mush more widespread throughout the entire study area and were randomly distributed. However the environmental variables measured did not seem to have any impact on dolphin distribution.

Overall it was suggested that dolphins may move seasonally in Port Phillip.

What do Dolphins Eat?

fish in mouth web 210x95.jpg As well as knowing where dolphins live in order to protect them, we must also know what they eat.

Dolphins found in different areas will have different food available to them and therefore may have different diets to dolphins of other areas. With this in mind, it is therefore important to research what dolphins in each area eat so we know what to protect.

Researchers from DRI have been studying the two different species of bottlenose dolphins (inshore and offshore) found in Victorian waters. The inshore species of bottlenose dolphins can be divided into two distinct populations, one in Port Phillip Bay and the other in the Gippsland Lakes.

In this study dolphin teeth were collected from recently stranded animals in Victoria and from specimens in museum collections. These teeth were analysed and it was found that the two species consumed different prey.

Within the inshore species it was implied that the Port Phillip population may be feeding on animals higher in the food chain than the population from the Gippsland Lakes.

Results also suggest that within these inshore species there may be differences in diet between males and females. These results relating to sex-based diets, however did not apply to the offshore population of dolphins.

When researchers compared results from the offshore population with other published data they were able to suggest that the energy for dolphins in this population comes from food chains that are based on seagrass and phytoplankton.

Although this study did not define exactly what dolphins in the Port Phillip Bay and Gippsland Lake area feed on, important discoveries about differing diets between populations and sexes were made.

We now know that in order to protect the offshore population of dolphins we need to protect seagrass and phytoplankton so that their food chains and thus what the dolphins feed on will also be protected. Further study will need to be done for inshore populations to determine exact differences between diets and how to protect them.

Our Dolphins are Unique

2 side by side web.jpg Little is known about the genetic structure of dolphin populations worldwide and it is largely unknown how many different species of bottlenose dolphins there really are.

It is important when managing dolphin populations that we know what species they are because different species will be locally adapted and have different requirements.

The aim of one study conducted by researchers at DRI was to clarify two populations (Port Phillip Bay and Gippsland Lakes) of coastal bottlenose dolphins along Victoria's coast.

Samples of genetic data were collected from various locations across coastal Victoria, including Port Phillip Bay, Western Port Bay and the Gippsland Lakes. These samples were analysed and results showed that there were two distinct clusters, representing 'coastal' and 'offshore' locations.

This strongly supports the Southern Australian bottlenose dolphin 'new species' concept.

Overall the data collected suggests that Victorian coastal dolphins, similar to other world-wide coastal populations, are genetically unique, been isolated from other populations and therefore locally adapted. As mentioned above, this has important implications for management and conservation and we must tailor our techniques to suit different species.