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Monitoring whale sharks requires a reliable method to identify one animal from another and the use of marker ‘tags’ has been common though-out animal monitoring programmes from birds through to whales. As such, it was the first type of identification technique trialed in monitoring whale sharks in Seychelles in the 1996 pilot programme (Sagren vol.1.2).
Marker tags require little equipment and allow the rapid identification of previously encountered sharks; however, they do require in-water observation and are most effective when there are many in-water observers. It also helps if the sharks appear in shallow areas where the observers are!
In the pilot project ‘spaghetti’ type tags were used which were applied by a modified spear-gun into the thick ridge of skin next to the dorsal fin. The tag comprised a hand tooled stainless steel anchor head and a trailing strand of stainless steel wire covered in bright yellow heat shrink tubing with an identification number and contact information printed on it.
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These tags seemed to work adequately but were difficult to read and lack of repeat sightings in subsequent years created concerns as to how quickly they were being ‘shed’ by the sharks, much in the same way as human skin ejects splinters over a period of time.
In 2001, at the outset of the current programme, Rachel Graham joined our project as a consultant and introduced a large reinforced plastic tag she had developed for whale sharks in Belize. These ‘Placard’ tags were indeed much easier to read and were attached with a barbed titanium anchor by a modified pole spear applicator. |
| Plastic
Laminate Placard type tag with tag remnant covered
with fouling after 9 months attached to a whale
shark. Photo David Rowat |
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Placard
tag cleaned remnant recovered after 9 months. Photo David Rowat |
In 2002 six sharks were sighted that were recorded or tagged in 2001, this represents more than 14% of the sharks tagged in 2001, indicating that the sharks have a high affinity or fidelity to this area. Unfortunately the condition of most of the re-sighted tags was not good and accurate animal identification was difficult as the tags were heavily fouled by marine organisms, despite coating with anti-fouling paint. They were also found to have cracked and broken thus loosing large parts of the tag.
This problem prompted a broad search for a suitable alternative which was found in technology associated with the offshore oil industry. Marking underwater pipelines and valves is an important for simplifying underwater operations for divers and Remotely Operated Vehicles (ROVs) and a number of products are used as markers that do not allow growth of fouling organisms. Long term deployment means that traditional biocides like anti-fouling paint are not feasible.
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| Aquasign™
Polymer tag laminate structure |
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One novel technology in use is Aquasign™ developed by Champion
Techologies, a UK Company. The material used is a reinforced silicone rubber polymer through which a non-toxic lubricant is secreted onto the front surface of the marker. Migration of the lubricant is controlled by natural stress relief that leaves the marker face too slippery for marine growth to attach. This leaves the fluorescent background and text characters permanently clear and visible, as such, Aquasign™ replaces a toxic remedial action with a unique environmentally acceptable 'non stick' prevention.
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The new
Aquasign™
'soft' tag. Photo David Rowat |
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A 'soft'
tag deployed. Photo
Udo Engelhardt |
For our application this material has a number of benefits as not only is it fouling free but it is also
inherently flexible and might thus solve both of the current failings of the placard tags. Sample tags were made for us by Aquasign™ and after various in water testing procedures in Seychelles a satisfactory design was achieved. This is a completely new application of the Aquasign™ technology and in order to assist us Champion Technologies and Aquasign™ have offered to sponsor and supply tags made of a material for the coming season.
Already we have a number of sharks tagged with the new ‘Soft tags’. These tags are clearly visible from our micro-light spotting aircraft, making tagging operations significantly easier in areas where many sharks are near the surface at the same time.
Where possible we are also ‘double tagging’ sharks that have older fouled tags already attached as this not only allow us to identify the shark more easily but will allow us to work out how quickly the titanium anchor barbs are shed by the sharks.
We hope that over the coming season we will be able to report further on the application of the Aquasign™ technology in the field of marine animal research.
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