AfriOceans M-Sea Programme Scientific Report 2006
The M-Sea Programme Scientific Research Project, an AfriOceans Conservation Alliance initiative, in collaboration with Two Oceans Aquarium (TOA), sponsored by SOSF, involves the release and tagging of captive ragged tooth sharks, including the tagging of wild ragged tooth sharks. It was initiated in 2004 with the release of Maxine. In April 2005 Val was released and the first wild shark tagged under this programme Sam, who was caught and released the day after. (AfriOceans M-Sea Programme Scientific Report 2004/5).
This report summarizes the protocols used in the release of Dee from TOA, and the tagging of a free-ranging female Lesley off Saxon Reef south of Arnison (east of Cape Agulhas) in March 2006. This was third release of a TOA ragged-tooth shark during this programme. The results obtained from the Wildlife Computers Pop-off Archival Tags (PAT) are provided and the movements illustrated in the accompanying figure.
Dee was one of the first sharks introduced to the TOA main display tank. She had been caught on 4 March 1992 at Dynamite Jetty, near the Port Elizabeth harbour in Algoa Bay by the Port Elizabeth Museum, Oceanarium and Snake Park staff (now called Bayworld). She measured 1045 mm total length (TL), 720mm precaudal length (PCL) and weighed 6.4 kg. She was probably a nought-year-old animal that had been born the previous spring/summer. She was injected with 2 cc of oxytetracycline to mark her vertebrae as part of a growth study and was implanted with a passive internal transponder tag (PIT), similar to those used for pet identification, as is standard procedure at Bayworld. This PIT tag was numbered 0021 3E28. It is not visible because it is implanted below the skin near the dorsal fin.
She was held in the Bayworld tank until 28 October 1995 when she was donated to TOA for their display. TOA and Bayworld staff captured her with the use of valium, placed her in a 800 l tank on a truck and she was then successfully transported to TOA in Cape Town. When she left Bayworld, she measured 2160 mm TL, 1530 mm PCL and weighed approximately 72 kg. She was not injected with OTC again prior to her transportation.
Dee remained in the TOA display until Thursday 2 March 2006, when she was removed from the tank and held in the 35 cu m, 8 m diameter holding tank on the roof until 14 March 2006. She was tranquilized with phenoxyethenol prior to transfer to the tank on the transport truck. She measured 2800 mm TL, 2020 mm PCL and weighed 196 kg. She was transported without incident to Struis Bay and held overnight with careful monitoring of her life support systems until 15 March 2006 to allow the release at sea to be done under optimal weather conditions.
On 15 March at approximately 08:15 she was sedated again with phenoxyethenol for her final move. She was fitted with a VEMCO coded pinger numbered 805 that had been coated with medical grade silastic. This was inserted into her body cavity after minor surgery and three stitches were used to close the wound. Approximately 25 cc of OTC was used to reduce any risk of infection. An orange spaghetti tag was inserted into the base of her first dorsal fin. This tag was labeled PEM 3541. The Wildlife Computer PAT 4 popup tag, set up on the afternoon of 13 March, was tested in the harbour on 15 March at 07:54 and attached to her first dorsal fin , as detailed below. All instruments and equipment had been bathed in 97% ethanol to ensure that they were sterile.
Dee was lifted in a stretcher by crane into a holding tank on the TOA semi-rigid inflatable boat Aquarium 1 and taken to the east side of Saxon Reef in approximately 4 m of water. Water temperature was approximately 21° C and a southwest wind of 5-10 knots was blowing. The PAT tag was initiated by pressure and ensured that it was working properly prior to release. Dee was placed in the water at 10:30 am and monitored for about 2 hours. She initially spent time on the bottom but was assisted to the surface where she swam strongly and took about 4 gulps of air before swimming away, after the marker buoy attached to her caudal peduncle had been removed. Air gulping at the sea surface is normal behavior for these sharks. The air is used for buoyancy control and it is stored in the stomach. The coded pinger was working well. The position of release was 34° 41.235′ S, 20° 14.390’E (in decimal degrees: 34.6872° S, 20°.2418E).
Dee’s tag was programmed to release on 10 July 2006 at 21:00. The first reception of the tag through the ARGOS satellite system was 11 July at 07:34. The tag surfaced at 33.425° S 27.317° E, off the Eastern Cape near Madagascar reef, which is almost half way between Port Alfred and East London. The tag drifted in the area and was washed ashore about 3.3 km south-west of the Bira River mouth. John Galway and his wife Jacky kindly searched for it repeatedly using a GPS, but they failed to find it, possibly because it had been buried by sand, or removed by a passerby.
The tag only sent data via the ARGOS satellites over a five-day period, but good quality information was received, even though the complete data set could not be sent before the tag was beached. Once beached, it was no longer able to broadcast information the ARGOS satellites because PAT 4 tags only transmit in a vertical position in water.
The distance between Dee’s release site at Saxon Reef south of Arniston and Madagascar Reef, the locality of the pop-off, is approximately 700 km and this was covered in 118 days, giving a minimum swimming speed of 6 km/day or 0.07 m/sec.
The position estimating software inside the tag (which estimates position based on times of sunrise and sunset at the GMT compared with those recorded by the light sensor aboard the tag) showed that Dee stayed on the western part of the Agulhas bank until about 21 April. She moved rapidly eastwards and by 8 May had moved 623 km eastwards. This was a very large migratory movement of 36.7 km per day at 1.5 km per hour.
The global position estimator provides rough positions that suggest that she may have reached the Transkei coast before returning to the position where her tag released. Unfortunately, these positions are not very accurate and attempts will be made at a later stage to match her estimated position with sea surface temperature plots to provide more precise estimate of her route.
The water depths she inhabited varied from 10-29 m in April, from 10-64 m in May and 10-49 m in June. The maximum depth recorded by her tag was 68 m on 24 May. The temperature range she moved through was between 11-24° C, but she stayed mainly within a temperature range of 16-20° C.
Lesley was caught on the west side of Saxon reef from the ski-boat Awesome shortly after Dee had been released. This wild shark was caught at approximately 13:30 using fishing tackle. Named Lesley in honor of Lesley Rochat, executive director of AOCA and project originator, she was brought aboard for tagging using a stretcher and placed upside down to induce tonic immobility. She measured 2610 mm TL, 1950 mm PCL and was estimated to weigh 138 kg using a length/weight regression curve. A VEMCO coded pinger was inserted into her abdominal cavity. This tag was numbered 826. A spaghetti tag numbered PEM 3537 was inserted into the base of her dorsal fin. A Wildlife Computer PAT 4 popup tag numbered 56095 was attached to her dorsal fin, and she was released after approximately 20 minutes and swam away strongly. The position of her release was 34° 41.858′ S, 20° 14.510′ E.
Lesley’s tag was programmed to release on 12 July 06 at 21:00 and the first data was picked up by the ARGOS satellite on 14 July 06 at 08:04, but the first position was obtained on 15 July 06 at 14:44 at a 31° 57.6’S, 29° 18.6′ E, just north of Coffee Bay, Transkei. She had traveled approximately 970 km from Saxon Reef in 120 days, giving an overall speed of 8 km per day. The positioning software in the tag showed that she, too, had stayed around the eastern part of the Agulhas Bank until about 3 May. By 6 May she had moved 342 km in nearly 3 days giving a speed of 114 km per day and 4.7 km per hour. Some 9 days later she had moved a further 293 km eastward at 32.5 km per day or 1.4 km per hour. The overall migration between 3 and 15 May was 634 km and this works out at a movement rate of 52 km per day or 2.2 km per hour.
She traveled between the surface and 40 m water depth in the first two months after release. From about 17 April until 18 May she spent most of her time in less than 40m. After 20 May she spent more time in deeper water, mostly less than 80m, but she did get as deep as 108 m on 30 June. On that day, she swam between 28 and 108 m, demonstrating the large depth range these sharks are able to cover. She moved through waters of 12.2-22.4° C, the cooler waters being at the deeper depths of her swimming range.
The PAT tagging was very successful this year, with both PAT tags broadcasting large amounts of data through to the satellites. Clearly the sharks are surviving and doing well post release from captivity and post tagging of wild-caught animals. The movement patterns are similar, suggesting that the formerly captive-held animals are adjusting well to release and are fitting in to the expected behavior patterns of this species during late autumn. The tags this year provided the first solid evidence of a rapid movement from the western Agulhas Bank, which shows a strong eastward migration, as has been suggested by fishers in the area who report a rapid decline in raggedtooth shark captures after April. Earlier information was not as complete as we obtained this year, although the overall pattern of eastward movement was the same.
The depth ranges and temperatures covered by these two sharks are similar to those recorded in 2005 with Sam’s movements. Clearly this species frequently inhabits waters deeper than normal SCUBA diving depths and can readily move from shallow waters less than 10m to greater than 50m deep.
A new approach to tagging this year was the insertion of a coded ultrasonic VEMCO tag into the abdominal cavities of both sharks. The advantage of this is that the tags will not attract marine growth and will be detectable for the lifetime of the tag (approximately 3 years). This provides the potential for detection over multiple years at any VEMCO receiver station.
This year the listening station array was expanded with a station being deployed at Protea Banks (deployed on 25 May 2006) and one near Cathedral, Aliwal shoal (on 28 August 2006) on the KwaZulu-Natal coast. Hopefully these additional stations will provide more information on these two sharks, as well as any other sharks with tags of the same technology. The stations will be downloaded after 6-12 months.
Malcolm J. Smale