Researchers explore ocean dolphins

Catching a lift: A common dolphin leaping with a remora holding onto its side. Photo: supplied.
Catching a lift: A common dolphin leaping with a remora holding onto its side. Photo: supplied.

The dolphins in the Peel-Harvey and adjacent coastal waters are bottlenose dolphins, Tursiops aduncus by their scientific name.

When going further offshore, perhaps somewhere at the 50 metre depth contour, the bottlenose dolphins are another subspecies called Tursiops truncatus. These animals look similar but are generally bigger than their coastal counterparts. The two subspecies can interbreed, and in some cases we may not be able to tell conclusively which species an animal belongs to.

As part of our research we have collected tissue samples for genetic analyses from dolphins encountered up to 20 nautical miles offshore. We only choose the calmest days to venture further out on our small boat.

During our offshore trips it has become apparent that we do not see dolphins as frequently as we do near the coast, or in the estuary. The groups we have encountered mainly consist of individuals that are new to us, although we have also made a few matches to individuals encountered in our dedicated study area within WA waters.

Although bottlenose dolphins are the most commonly encountered dolphins on our coastline, the further offshore waters are used by other dolphin species. In June we had the privilege of encountering a group of approximately 15 common dolphins, which are a species associated with deeper and warmer waters. They approached our boat and were leaping out of the air in what is thought to be an attempt of removing fish called remoras attached to their body.

Remoras use one of their fins which has developed into being able to grip a surface to attach onto a passing dolphin. By attaching to a dolphin the fish gets a free ride, feed, escape from predators and may even have an increased opportunity for reproduction if there are other remoras attached to the same individual dolphin. It is not well understood whether dolphins benefit from having a remoras attached to them. Some benefits may be that the remora clears external parasites, cleans wounds or removes dead skin. We have never seen a remora on the estuary resident or near coastal dolphins.