Shark Research - Insights into mortality of whale sharks in Atlantic and Indian Ocean tuna fisheries

A recent research article in Biological Conservation has examined mortality rates of whale sharks (Rhincodon typus) as a result of the European tuna purse seine fisheries in the Atlantic Ocean and Indian Ocean.

Tuna often associate with large marine species such as dolphins and whale sharks; tuna fishermen sometimes rely on sightings of these species to indicate the presence of large schools of tuna. Once tuna have been sighted, a net is set to encircle the shoal and the bottom of the net is drawn together, like a purse, to trap the fish. Owing to the fact that there are often large marine fauna close by, these animals can also become trapped along with the tuna.

This study used log book data and observer data to assess the number of whale sharks sighted, caught and killed in purse seine nets in the Atlantic Ocean and the Indian Ocean. The biggest incidence of whale shark mortality occurred in certain hotspots where whale sharks overlapped with the purse seine fishers. Overall the incidence of whale shark mortality in the Atlantic and Indian Oceans was relatively low - from 1995 to 2011, 2 whale sharks were reported to have died out of 186 encircled by the nets. In recent times, the purse seine fisheries have implemented new strategies for ensuring the survival of whale sharks caught in nets, such as the cutting of the net to allow the shark to escape.

This data is in stark contrast to whale shark mortality in the Pacific Ocean provided by the Western and Central Pacific Fisheries Commission (WCPFC). Between 2007-2009, 56 whale sharks died in purse seine nets - the most common reason cited was that the fishermen were not aware of the presence of the shark in the net before mortality occurred. As a result of this, the WCPFC has banned the setting of nets around whale sharks since the beginning of 2014.

Additionally, both the Indian Ocean Tuna Commission (IOTC) and the WCPFC have admitted that accurate data on the number of whale sharks encircled and killed by purse seine fisheries is difficult to obtain. The data for this study relied on the accurate reporting of whale shark mortality by purse seine skippers and observers - which only cover 10% of the European fleet.

More analysis of the tuna purse seine fishery and better observer coverage is needed in order to obtain a better picture of the mortality of large pelagics in the tuna purse seine industry.

Shark travel - whale sharks in the Philippines

For many people, the whale shark (Rhincodon typus) is top of their list to see. Whilst I have had the opportunity to encounter many types of shark on my global wanderings including white sharks, bull sharks, blacktips and grey nurse sharks, it feels as though I almost left the poor whale shark until last!

Capable of attaining lengths of up to 12m, the whale shark is the largest living fish in our oceans. However they are no threat to humans (unless you don't mind out for that powerful tail!) as their diet primarily consists of plankton which they filter out of the water.

Whale sharks are found all over the world in tropical and warm temperate seas, however there are some spots where sightings are quite common. I visited one of those such spots recently: Donsol in the Philippines.
Legazpi airport is the closest dropping off point for Donsol. I flew there from Manilla with Cebu Pacific Air (about 1 hour). Once you are at Legazpi airport a 1 hour drive through hilly, forested terrain will bring you to Donsol. I was pleasantly surprised at the lack of impact by tourism on Donsol - despite having a major tourist draw in the form of the whale shark, the town still feels very local and I didn't encounter too many other tourists there during my stay.

Donsol has plenty of local delicacies available at the market!

The peak time to see whale sharks here is over the Easter period, but the season runs from December to May. I had booked into a hotel in town - Giddy's Place (http://www.giddysplace.com/) and they were able to arrange my trip out with the whale sharks. Once you arrive at Donsol Bay you are assigned a Butanding Interaction Officer (BIO), a guide and a spotter and out you go on your boat for a maximum of 3 hours to try and find some sharks!

The spotters risk it all to get up high and spot whale sharks!

Known locally as butanding, the whale sharks are often found near the surface as they feed on plankton blooms. On our first day out we were incredibly unlucky - no sharks at all - only a pod of dolphins which put on a real show leaping clear out of the water! However on our return for day 2, we had a total of 5 whale sharks show up. The boat does not stop as it positions itself close to the shark - a quick leap from the moving boat and you are in the water with the largest fish in the world. And for anyone who might be worried that the clumsy monkeys in the water are capable of harassing these gentle giants, please rest assured that you will swim with everything you have just to try and keep up with the shark for 30 seconds. A few, slow flicks of their giant tail and the whale sharks had accelerated way past our group.

On one encounter, as the shark began to dive, I was lucky enough that it passed a few meters below me. I simply lay perfectly still in the water as the behemoth cruised past underneath me seemingly not bothered by my presence.  

Whale sharks are currently only legally protected in 10 countries - one of which is the Philippines. There is no doubt that the Philippine government has realised the tourist value of the whale sharks and this has led to them protecting the shark. I am happy to report that the standards of the guides and spotters on the whale shark trip were very high. All participants had to watch a video informing them of correct ethical conduct around the sharks - no touching, no riding, only 6 people maximum around a shark and only for a maximum time of 10 minutes. Once on board the boat and out at sea the crew enforced the rules and made sure that the sharks were not harassed. With such pressure on sharks from the trade for fins (a whale shark fin can fetch up to USD$10,000), tourism is the best chance we have now to encourage governments to really make the effort to protect their sharks from poaching.

To see a video of my time in Donsol, click the link below!