Sunday, April 19, 2009

Shark tagging workshop held in Seychelles

Dr Kim Holland from the Institute of Marine Biology, University of Hawaii recently held a shark tagging workshop during his visit to Seychelles under the MADE (Mitigating Adverse Ecological impacts of open ocean fisheries) programme being implemented in Seychelles by IRD and local partners.

Within Seychelles, the objective was to place pop-up satellite relayed tags (PATs) on a number of pelagic shark species found on the offshore fishing grounds, as had been done on tuna, to help define their movement and behaviour patterns. It was also planned to deploy a number of the new ‘mini-PATs’ developed by Wildlife Computers especially for smaller marine animals.

Unfortunately previous studies had encountered high failure rates of tag attachment and so prior to the deployment it was felt appropriate to hold a practical tagging workshop to test how well different tag-anchors held in real conditions, using a number of dead sharks previously caught in local fishing activities.

When attaching PATs to small sharks (below 3 m in length) the usual method has been to place the anchor dart through the base of the dorsal fin so that it passes between the cartilaginous ‘fin-rays’ and then uses them like a picket fence for the anchor to wedge behind. On larger sharks the tags are often placed into the muscle or dermal layers, as on whale sharks, and so the anchors require a somewhat greater holding ability.

The first day of the workshop was an introduction to the theory of anchor design where Dr. Holland passed on information from veterinarians regarding how tissue deals with foreign objects such as tag-anchors or darts… generally, rounded surfaces without sharp edges were better at promoting tissue adhesion, while sharp edges would tends to cut through tissue adhesions if the anchor or dart moved in any way.

A variety of tag darts and anchors were available for testing the following day; this included the titanium PAT or 'M-dart used by many research teams, a new plastic toggle anchor under development by Wildlife Computers, a modified nylon ‘slip-tip’ dart with two large wings from Dr. Mike Musyl (NOAA), an umbrella dart designed by Dr. Mike Domier (Pfleger Institute of Environmental Research ) and a new design being developed by Dr. Holland himself.

The three good muscle/tissue anchors, from the top the new Wildlife Computers toggle design on its stainless steel applicator, middle is the titanium PAT or M dart, and at the bottom the nylon 'slip-tip' design from Mike Musyl.

The first three of these tags did well in pull tests using ballistic foam, a good substitute for muscle or skin tissue, but the last two darts did poorly in this medium. In experiments on the shark carcasses to test how well each tag performed in being inserted between the fin rays and locking behind them, the latter two tags, the Domier umbrella and the ‘Holland’ dart worked well if the anchor was inserted fully between the fin-rays.

Of the three other attachments, the new Wildlife Computers design faired well but was found to be harder to push through the fin rays while the Titanium anchor dart tended to cut through the fin rays and thus weaken their supporting ability to help retain the tag; the big winged anchor was too large to test on smaller sharks.

The two effective intra-fin-ray tags: top is the 'Holland' anchor with the tether attached at right angles to the shaft, below is the umbrella dart from Mike Domier on its applicator tool.

The ‘Holland’ dart was very unusual as the tag was attached at right angles to the shaft of the tag, a design that it was hoped would reduce movement of the anchor itself.

After the practise session it was out to sea for a week for the tagging team to try to put out the first batch of tags…. But first you have to catch your sharks... here's Kim hard at work trying to do just that!

We wait to see how they got on and look forward to the coming whale shark season to try out some of the new anchors...

Friday, April 10, 2009

First whale sharks of 2009 on April Fools day!

Regular visitor to Seychelles Frank Eichler thought that he was having his leg pulled when on a dive trip to Marianne and Felicite islands the crew shouted whale shark…. It was April 1st and the season for ‘Poisson D’Avril’ after all!

However, on getting closer there was not just one whale shark but four! The sharks were circling and feeding occasionally on the patchy plankton in the area.

Frank and fellow divers were soon in the water and frank knew which areas he needed to photograph to get an ID shot, having been out with MCSS in previous seasons.

On his return to Mahe he visited Dive Seychelles with his camera to download his images for Katie and the MCSS team to analyse and straightaway Katie recognised one of the sharks as being a ‘regular’.

The I3S analysis confirmed that one was indeed an old regular UT06-063 ( a 7 m male) who has been sighted every year since 2006; one of the other sharks was definitely new while the other two we are working on the videos for a suitable frame for identification.

April 1st is very early for whale sharks to be seen around Seychelles and so the team are wondering if the sharks are going to be coming in early this year?

Saturday, April 4, 2009

Whale sharks in ancient mythology

Whale sharks, the worlds largest living fish, seem to have affected people in ancient times just as much as they inspire them today.

Dr. Bruce Carlson, Chief Science Officer at the Georgia Aquarium, and Dr. Rebecca Stone, Curator of the Art of the Ancient Americas at the Carlos at the Michael C. Carlos Museum at Emory University, recently made a presentation about linkages between zoology and ancient Latin American shamanism, particularly about whale sharks.

Contrary to previous understanding, including her own, Dr. Stone now believes that a centuries-old statue of a female shaman (Mayan priestess) is modeled after whale shark anatomy.

Ceramic female shaman statue, photo courtesy Michael C. Carlos Museum

Recent research and conversation with Dr. Carlson has led Dr. Stone to re-evaluate the imagery on the ceramic female shaman effigy in the collection, and to interpret her shape and markings as representing a whale shark. The statue was originally thought to represent a jaguar, a “power animal” commonly revered in Mayan and Aztec art. This idea is supported to some extent by the annual aggregations of whale sharks off the Yucatan peninsula in the Mexican Caribbean and off the coast of South America.

However, this is not the only inclusion of whale sharks in spiritual or traditional art.
From central India comes the Timingila Jataka Medallion from among the Bharut reliefs of Buddhist origin which date back to the second century BC. The medallion depicts three men in a boat being swallowed by a large fish (the Timingila) which on its interpretation in 1956, by Sunder Lal Hora, was likened to a whale shark:

When the fish inhales water for oxygenating its gills, the power of suction is so great that a small boat with three occupants could be sucked into its cave-like mouth as is so clearly shown on the medallion.”
A rubbing of the Timingila Jataka Medallion from the Buddhist Bharut reliefs, courtesy British library

The likelihood of whale sharks being known from India is also very high as they have long been associated with the Gujarat coast and so are likely to have been encountered by the Indian fishermen and were probably thus woven into such ancient legends and beliefs.
Scholarly translations of the texts from these reliefs vary in their interpretation of the medallion, but a Chinese Buddhist translation is the shortest and most simple:

Five hundred merchants start on a sea-voyage. The ship comes near a giant fish which swallows the waves together with all living animals contained in them. With an irresistible force the ship also is drawn into the throat of the gigantic fish. In vain the merchants pray to the different gods, whom they worship, then the captain of the boat says to them that he knows of a great god called Buddha. They should pray to him in place of other gods. There- upon all the merchants together shout ' namo Buddhdya ' In this way the fish learns that a Buddha has again appeared in the world. It realizes that it would be improper to do any harm to the living beings; it therefore shuts the mouth so that the water begins to flow back and the ship is saved. The fish really has been a monk in its former birth. The name of the Buddha reminds it of its former existence and this led it to the decision to spare the life of the beings.

Most translations agree on the continuation of the story where the gigantic fish starves itself to death and is reborn once again as a Buddhist monk (Dharmaruchi) who is revered through out Buddhism.

While I’m not completely sold on the idea that whale sharks are re-incarnated Buddhist monks it certainly seems that the monks were aware of whale sharks many, many centuries ago.

Quotations on the translations of the Timingila Jataka Medallion courtesy of the ‘Corpus Inscription Indicarum, vol. II, part II, Bharhut Inscriptions edited by H. Luders’ and image of the Medallion courtesy of the British Library.