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The basking shark was still target fished and taken as by- catch in EU waters until 2008 when a moratorium was brought in by the EU. Their liver oil is still valuable as it is extremely stable at high temperatures and pressures and the demand for shark fins to make shark-fin soup has led to a huge increase in landings of many shark species in recent years. The basking shark was added to Appendix of CITES (Convention on International Trade in Endangered Species) in 2002 which means that they products from them only be exported, re-exported or introduced from the high seas if a permit has been issued by the relevant national authorities. Such a permit may only be issued when the management authorities are satisfied that such trade will not be detrimental to the survival of the species. It is considered Vulnerable in the IUCN red List of Threatened Animals. The basking shark was given legal protection in UK waters in 1998. UK legislation (Schedule 5 of the Wildlife and Countryside Act of 1981) specifies that no basking sharks can be caught within 12 miles of the coast and none landed even if caught outside territorial limits. They are also protected in UK (Isle of Man) waters. There has been some interest in providing similar protection within the Irish 12 nml limit but no legislation has been enacted to date.
Basking Shark Survey 2009
The aims of the Basking Shark Survey in 2009 were to extend the basking shark tagging program started in 2008 including deployment of satellite tags. Secondary aims include collecting images useful for photoidentification and tissue samples for genetic analysis. It is hoped the increase in knowledge and interest in basking sharks will ultimately provide support for the legal protection of this species in Irish waters.
A total of 600 basking shark tags, all with a unique numbers, in four different colours were made for this study by Floy Tags, Seattle in the US. Colours were allocated to specific counties with YELLOW for Co Donegal, GREEN for Co Kerry, RED for Co Cork and WHITE for other counties. This was to facilitate tracking movements as even if only the colour of a tag was recorded we can allocate the shark to a county.
Tags were deployed using two different types of tagging poles. Four extendable painter’s poles measuring 3m in length were modified for attaching basking shark tags. An applicator supplied by Floy Tag was attached at the end of each pole using epoxy resin. Four 4m extendable fishing rods were also modified in the same way after the eyes and the last 0.25m of the rod were removed.
An underwater pole camera (SCUBAR-PRO) was used to try and determine the gender or to film sharks.
Male sharks can be identified by the presence of claspers and the absence of claspers, were therefore female. This is especially important when deploying the satellite tags.
Example of basking shark tag Tag mounted on tagging pole Preparing to tag basking shark Shark length was estimated to the nearest meter compared to the 6m research vessel. Length categories were consistent with those used by the MCS Sighting Schemes and other research groups namely: Category 1 = 2m, Category 2 = 3-4m, Category 3 = 5-6m, Category 4 = 7-8m, Category 5 = 8+m.
Two satellite tags were available for this study, one each purchased by Crossing-the-Line Films and the Galway-Mayo Institute of Technology. Both were MK10 Archival Tags manufactured by Wildlife Computers. They were supplied by Mauvis Gore of Marine Conservation International, who is a collaborator on this project.
The satellite tags were deployed with an extendable pole at the base of the sharks’ dorsal fin. Each tag was held in the shark with an anchor similar (but a little larger) to the coloured tags. The satellite tag was attached to the anchor with a short tether and programmed to detach from the shark after 215 days (7 months) at 1300 GMT. The tag also records time at temperature: 3, 4, 7, 9, 10, 11, 12, 13, 14, 15, 16, 18, 20, 20+ ºC and time at depth: 0, 20, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1000+ m. This will produce 60 sec histogram sampling interval summarised into 12 hour histograms that begin at 0500 GMT.
These settings were the same as tags used for deployment in the Isle of Man and southwest Scotland in 2009 to facilitate direct comparison of data.
Photo-identification Images of the sharks dorsal fin and adjacent back were obtained for photo-identification purposes. Most sharks are not well marked with only small nicks occurring on the dorsal fin. These can be very useful for short-term recognition for example when tagging to determine whether an individual has already been tagged during a session. Occasionally an individual has received significant damage and is very useful as these could possibly be re-sighted between locations or over time, which is a very useful method of determining the longevity of coloured tags.
Images of basking sharks were obtained using a Canon D20 Digital camera with 70-200mm and x2 converter. Images of both sides of the dorsal fin were obtained if possible and any other features which may be useful in recognizing individual sharks.
Table 1. Categories for quality of images and marks used in this study (after Ingram, 2000).
Images were sorted and the best images of each side of the dorsal fin saved. The marks were scored using similar criteria used for dolphins (Table 1).
Genetics and Biopsy sampling There is great interest in exploring the genetics of basking sharks in the North Atlantic and beyond. We have had requests for samples from two research groups (University of Aberdeen and University of Illinois at Chicago). Prior to this study only three archived tissue samples from basking sharks in Ireland were available.
Samples were taken from basking sharks stranded during the course of this study and attempts were made to biopsy sample sharks. Two methods of biopsy sampling were tested. A biopsy tip was mounted at the end of a 3m extendable painters pole with the aim of striking a shark if close enough to the research vessel.
A standard crossbow (Barnett Panzer) with 150lb production with Fin Larsen arrows and biopsy tips, was also used. This crossbow has been successfully by SB for sampling large whales in Ireland.
A new method of obtaining samples for genetic analysis was developed during this project. This involves the recovery of slime from the sharks body. Basking sharks are covered in a thin black slime, which is often deposited on nets and ropes when captured. We developed a technique of scraping slime from the body with a coarse dish-cloth wrappred around a mop handle. The cloth is removed from the handle and ethanol added to preserve the DNA.
An important objective of this project was to raise awareness and interest in basking sharks in Ireland. This was achieved by responding to enquiries from the public and journalists. The project is also facilitating a three part programme on animal migration in Ireland in Ireland produced by Crossing-the-Line films. This series is due for broadcast on RTE in October 2009.
Determining gender with a pole camera The new shark slime sampling system !
Fieldwork was carried out between 20 May and 11 September 2009. Six sites were visited two in Co Donegal (Inishowen and Donegal Bay), two in Co Kerry (Blasket Islands and Tralee Bay) and two in Co Cork (Roaringwater Bay and South Cork) (Fig 2). Three of these locations were consistent with the proposed study sites, with the addition of Donegal and Tralee Bays and the South Cork coast, which were visited after reports of sharks in these areas.
Table 2. List of fieldwork carried out during the Basking Shark Survey 2009
Basking Shark Tagging A total of 104 tags were deployed during 2009. Most of these (58%) were in Co Donegal, with 43 (41%) in Co Kerry and only one (1%) in Co Cork (Table 3) (see Appendix I for full details of tagged sharks). This brings the total number of basking sharks tagged in Ireland to 112 as eight sharks were tagged in 2008.
Table 3. Total number of basking shark tags deployed during 2009 and the total deployed in Ireland
It was observed during a pre-tagging line transect survey in Trawbreaga Bay carried out by EJ that the surfacing patterns of the sharks tended to coincide with slack tidal conditions. By looking at both 2008 and 2009 data from Donegal we noted that 92 % of sharks tagged in Donegal were tagged within approximately one hour either side of slack tide. This information could enable future tagging teams to concentrate their efforts in a limited coastal area.
The length categories of tagged sharks are shown in Fig 3. Most sharks tagged were between 5-8m. There was a tendency for the larger sharks (8+m) to be recorded in July compared to June but this may also reflect location as most sharks in June were tagged in North Donegal while most sharks in July were tagged in west Kerry.
A sample of zoo-plankton was obtained during the feeding aggregation observed of Slea Head on 14 July (52º 06’N/10º 25’W). This swarm of plankton had concentrated at the surface, close to the cliffs and were being fed upon by at least three and up to six basking sharks. The species were identified by Dr Cilian Roden as Calanus (most likely Calanus finmarchicus) with larval Euphausiids present too. Calanus are considered one of the most favoured prey of basking sharks in the British Isles due to their high protein concentrations and valuable omega-3 fatty acids.
Basking Shark Re-sightings We had a total of seven confirmed re-sightings of tagged sharks and two unconfirmed records.
1. One shark tagged on 11 June off Clear Island, Co Cork was re-sighted four days later off Castle Point in Roaringwater Bay, Co Cork a distance of 10km. Given that there was only one shark tagged in County Cork, this re-sighting is remarkable and suggests the population is very small.
2. A yellow tagged shark was observed amongst a group of 20 sharks off Coll in the Inner Hebrides on 25 or 26th June. This was most likely one of the sharks tagged in north Donegal on 1-3 June, which equates to a distance of around 140km in 22 days. This was the first international resighting Yellow tag was re-sighted by members of Inishowen sub aqua club on 14th 06 2009 in Trawbreaga 3.
bay, a minimum of 11 days after tagging.
4. A green tagged shark was observed off Slea Head on 20 July, six days after it was tagged approximately 3.5km away
5. Green 173 was re-sighted on 8 August off the Blasket Islands, 10 days after tagging, 4 km away
6. A yellow tag was recorded by Colin Speedie on 10 August off Ardnamurchan Point, Isle of Mull a distance of 140km. It is not known when this tag was deployed but it was at least one month later Yellow tag 063 tagged on 12th September and re-sighted 13th September by diving group on 7.
submarine U-681 off Malin head giving a total distance of approx. 20 km in one day.
8. White tag (could be yellow) by Hebridean Whale and Dolphin Trust (unconfirmed)
9. White tag (could be yellow) Mauvis Gore off inner Hebrides (unconfirmed) During three days fieldwork in Co Donegal from 1-3 June we tagged 50 individual sharks. Twenty-three were tagged on 1 June, 17 on the 2 June and 12 on the 3 June (Table 2). Of those tagged on 1 June four resighted on the 2 June. A very crude mark-recapture model would estimate that the abundance of sharks in Trawbreaga Bay during 1-2 June 2009 was around 135.
Preparing to tag Tagged shark Tagged shark The shark tagged off Cape Clear Island on 11 June was re-sighted four days later on 15 June off Castle Point a distance of 10 km. Given that there was only one shark tagged in County Cork, this re-sighting is remarkable and suggests the population is very small. Also a tagged shark was re-sighted off Dunaff Head, Co Donegal on 16 June by divers. The tag was yellow but no number could be determined. This shark was tagged during 1-3 June. These re-sightings are remarkable and demonstrate the value of shark tagging and also suggest a small population.
Basking Shark Tracking
Two satellite tags were deployed on 14 July off Slea Head in Co Kerry. Both satellite-tags were deployed on sharks in the same feeding group. The first shark was 8m but gender could not be determined and the second shark measured 7m and was thought to be a male as claspers could be seen through the water (Table 4). Both tagged sharks were observed after the satellite tags were deployed and coloured numbered tags were also attached which be invaluable to explore the impact of tagging on these individual sharks should these tags be re-sighted.
Table 4. Details of satellite-tags deployed during Basking Shark Survey 2009
The ARGOS satellite system has been advised on this deployment. They are now scanning the two relevant identifiers and will receive a signal from the tags once detached. It is hoped that the tags will remain on the sharks for the full deployment period of 215 days.
Photo-identification We have obtained 71 photo-identification images, which form the basis of an Irish Basking Shark Photo-ID Catalogue (Appendix II). Over one-half (56%) were considered good quality images but only 21% had marks useful for photo-identification. Most sharks are not well marked but the occasional well-marked individual can be used to check the longevity of tags as there is a chance this shark will be identified again from these wounds and thus it can be checked for the presence of tags.
Photo-id can also provide information on interactions with humans as determined from the presence of damage attributed to propeller damage and cues about migration such as the presence of external parasites (e.g. Penella), which are associated with warm tropical waters. Two sharks were recorded with propeller damage and Penella was recorded on three individual sharks.