Thursday, May 21, 2009

The Seychelles Whale Shark Encounter Code

After several people have contacted us regarding the 'Whale Shark Encounter Code' we thought it was sensible to have it easily available on our blog, so here it is:

First of all the personal, in-water encounter code:

The following code of conduct has been approved by the Government of Seychelles and was developed through two public workshops; it is based on input from experts and several years of experience of whale shark tourism in Western Australia. The Code is designed to ensure that you have a safe and enjoyable experience when swimming with whale sharks while preventing the animals from being harmed or disturbed.

Swimmers and divers must not :
  • Attempt to touch or ride on a whale shark
  • Restrict the normal movements or behaviour of the whale shark
  • Approach closer than 3 metres from the head or body and 4 metres from the tail
  • Undertake flash photography
  • Use motorised propulsion
A maximum of 8 people are allowed in the water at any time.

For the operators of boats, both private and commercial, the following code also applies:

In recognition of ‘The Wild Animals Protection Regulations 2003’, this encounter policy will enable the wise development of eco-tourism activities based upon the whale shark (Rhincodon typus) while protecting the animal from excessive disturbance by vessels, swimmers and divers.
  • A contact vessel should raise the designated flag.
  • No other vessel is permitted in this zone.
  • A vessel must not exceed 8 knots (14.6 km/hr) in a contact zone and 2 knots (3.6 km/hr) within 50 metres of the contact whale shark.
  • Contact period should not exceed 30 minutes if there are other vessels queuing to view the shark.
  • The shark should be approached head on or from the side whenever possible
  • The vessel must maintain a distance of at least 10m from the nearest whale shark
  • The operator of a vessel shall record the details of the contact on the form provided and return this to the appropriate authority within the time specified.
We hope this is useful to you all and wish you a most memorable experience!

Saturday, May 16, 2009

1240th Indian Ocean whale shark is 400th for Seychelles

On Friday the 15th of May Divemaster intern Kerstin Gillray and instructor Theirry Vandamme from the Underwater Centre / Dive Seychelles captured the identity of the 400th whale shark identified by photo ID in Seychelles... regular readers might wonder about the 400 figure as we have previously reported more sharks identified than this, but read on and all will become clear!

Photo ID has revolutionised the study of whale sharks globally and in Seychelles it has become the main tool for monitoring the population of whale sharks visiting these islands.
Being able to identify individuals allows scientists to establish the make up of the population in terms of numbers of males, females and their age or maturity; this information allows estimates of population size and trends or changes.

For many years researchers had identified individuals
either by tagging them with numbered marker tags or by using prominent features or scars; however, tags do come out and scars do change over time.

The first real attempt at whale shark photo ID was in the early 1980's by Geoff Taylor a medical doctor working at Exmouth near Ningaloo reef in Western Australia. Geoff was able to identify the sharks using the patterns of spots and matching the photos by eye and for many years this was the only way to do this.

A variety of areas were used by different groups, some used dorsal fins, others body markings, but all matched by-eye. After a while it became apparent that the spot pattern behind the gills was like a fingerprint and appeared to remain stable over many years.

Since then two computer based matching programs have been developed, one based on the astronomical pattern matching algorithm used in the space telescope to match star-fields which
was adapted for the EcOcean project. The other was developed by researchers working on ragged tooth sharks called IRIS which was further refined as I3S and made available free of charge to those interested. Using these tools researchers were able to quickly and accurately match whale shark photos.

The I3S computer matching program and the 'target' area for photo identification of whale sharks

So why the discrepancy in the numbers of sharks identified in Seychelles? The key is that just like a human fingerprint, the spot pattern from the right is not the same as on the left. In the early days in Seychelles we used marker tags and only with the advent of affordable digital undwerwater cameras in 2004 did we move into photo ID en masse....

As such, at the end of 2007 we had a total of 512 sharks identified by marker tag and photo ID combined, of which 360 were photo IDs. In 2008 although we added 38 new photo IDs, we also matched together several sharks that were originally identified by just a left or a right hand image...

And so it is that we have now achieved 400 photo IDs from Seychelles with Kerstin's new shark, which was in fact her very first whale shark!

This is also the 1240th photo identified whale shark in the Indian Ocean regional database shared between Seychelles, Western Australia, Djibouti, Mozambique, Madagascar and the Red Sea!

But Kerstin didn't care... it was Number One for her!!!

Monday, May 11, 2009

2009 Djibouti expedition …. First results…

After several months of very hard behind-the-scenes work by Katie, Morgane and David the results from the two weeks of survey expedition in Djibouti are beginning to crystalise and some intriguing trends are emerging.

To summarise the overall sighting results, a total 812 encounters were recorded from which a total of 187 sharks were identified using I3S photo identification software.

Of these 170 were new sharks while 17 had been recorded from Djibouti in previous years.
Of the 187 sharks 141 were male, 27 were female and for 19 the sex was not determined. This higher ratio of males to female is found in Seychelles and in most other aggregations sites.

A total of 163 of the identified sharks were sized with the average length being 3.69 m (largest 7.0m, smallest 2.0m) which was also found on the previous expedition, making this group of sharks much smaller in size than those found in any other whale shark aggregation world-wide.

74 of the identified sharks were seen on only one occasion, while two sharks were see 9 times, 3 seven times and 3 six times; the average number of sightings was 2.4 per shark.

Data from the plankton tows has also been completed courtesy of Dr. Dave Conway of the Marine Biological Association, Plymouth, and as expected there were some high levels of plankton biomass recorded of up to 12.7 g /m3 compared to the highest biomass recorded in Seychelles of 1.25 g /m3.

Zooplankton recorded: Lucifer (left) are most abundant in Seychelles, while Copepods (centre) and Larvaceans (right) predominate in Djibouti

In terms of what zooplankton was around the three most abundant forms were all families of Copepod shrimps, one being parasitic copepods of the Oncaea genus. The fourth most abundant group were the free-swimming tunicates (Larvaceans) of the class Appendicularia; these are filter feeders that resemble tadpoles or the larvae of other zooplankton. There were also large arrow worms (Chaetognaths) and although there numbers were not as high as the other groups their individual size meant they comprised a good proportion of the biomass.

This was a different plankton demographic compared to Seychelles where the mysid Lucifer shrimps are the most abundant followed by two groups of calanoid shrimps, arrow worms and then the free swimming tunicates. The whale sharks seemed to enjoy both the menus though!

The data from the two pop-up satellite tags was also interesting. One shark left the bay of Tadjoura and was moving off towards the Somali coast when the tag detached, having made dives to depths of 832 m. By comparison the other shark stayed in the protected Gulf and in fact moved further in to the almost enclosed Ghoubet al Kharab or Devil’s Goblet; this tag recorded depths of up to 144 m.

An interesting if somewhat disappointing finding was that there was almost no difference in water temperature from the surface down to 50 m as recorded by the conductivity-temperature-depth instrument. Even when it was attached to the deeper diving ROV of the BBC film crew (see photo left) the temperature at 60m remained at 26.6°C; similarly the deeper dives of the tags on the whale shark that stayed in the Gulf showed a drop to 24.4°C at 144m. The deep dives of the other shark as it moved out of the Gulf of Tadjoura indicated that there was a rapid drop in temperature from 26.4°C at 72 m with 20.0°C being recorded at around 150 m with the lowest temperature recorded being 14.4°C. This indicates that the waters inside the Gulf were a very stable and ‘well mixed’ body of water while the more oceanic waters towards the ‘Horn of Africa’ exhibit layering or stratification.

So all in all some intriguing information is beginning to be revealed about this population of very young whale sharks off Djibouti, which will doubtless require a future expedition to follow it up….. in fact, plans are already being made for a trip either at the end of this year or in early January 2010.... if you are interested in joining us drop us a line!