Tracking Gentle Giants

Rhincodon typus can grow up to 18 metres in length and is the world’s largest fish! Despite this, little is known about these gentle giants of the sea.

They may not venture near the surface for months or even years on end – only frequenting a few locations around the world to feast on seasonal abundances of plankton, krill or coral and fish spawn.

One such location is Cenderawasih Bay in West Papua. Although whale sharks are generally thought to be migratory – here predominantly juvenile and young adult males can be found lingering in the bay, sometimes year round, feeding on small baitfish attracted by the local fishermen.

The fishermen suspend lights from small rafts called ‘bagans’ to attract silverside baitfish. The whale sharks share in the spoils and often up to a dozen sharks can be found swimming around the bagans. This unique relationship has caught the attention of tourists from around the world who desire close encounters with the biggest fish in the sea! The number of visitors to the area has increased and as a result, in 2013 the Indonesia government declared whale sharks to be a protected species.

Conservational International (CI) then began working with the Indonesian Ministry of Fisheries and other local agencies to discover more about the Cenderawasih sharks and in particular, it became important to try and work out where the sharks went when they left the bay and, if they needed any additional measures of protection.

To solve the mystery marine biologists began tagging the sharks with satellite tags. Previously satellite tags were tethered to dorsal fins from a distance as it was not often possible to affix more secure ‘fin-mounted’ tags to swimming sharks. However the shark would simply shed the tethered tags within weeks, giving only perhaps a brief insight into their mysterious lives.

In 2015 Mark Erdmann, CI’s vice president for Asia-Pacific Marine Programs, began a tagging program designed to take specific advantage of the Cenderawasih sharks. Here the shark’s more sedentary behaviour allowed Mark and his team to deploy the more secure fin-mounted tags. With the help of the local fishermen and guests from the TRUE NORTH, Mark and his team were now able to quickly affix fin-mounted tags before gently releasing the tagged animal. Closely monitoring the reaction of the sharks, Mark and his colleagues were pleased to note that the exceptionally docile Cenderawasih sharks appeared to suffer little or no stress as a result of the fin-mounting process. And once attached, the tags immediately started to ping back vital information!  Each time the whale shark came near the surface the tag would transmit the animal’s location, dive depth, light levels and water temperature and, with a battery life of 2 years, the tags have been providing ground breaking insight into how to better protect the whale sharks of Cenderawasih Bay.

True North Adventure Cruises has formed a close collaboration with Conservation International and we are especially proud to be supporting Dr Erdmann’s efforts in Cenderawasih Bay. A total of 14 tags have been deployed to date and a remarkable amount of data has been collected.

Stay tuned for more details about what we have discovered about these mysterious giants of the sea!