|iSimangaliso’s oceanic heritage by Dr Kerry Sink|
After spending nine months attached to a coelacanth, anArgos Mini-PAT satellite tag was recovered by Triton staff offshore and 16 kilometres south of Jesser Point at the Sodwana Bay node of the iSimangaliso Wetland Park. The coelacanth, the 26th of 32 individuals known from South Africa’s first World Heritage Site was tagged by Trimix Divers on the 13 May 2013 in Jesser Canyon, 12 km south of the site where the tag popped up at 1am on 8 February 2014.
The fish was tagged at a depth of 120 m during the six week international coelacanth research expedition based at Triton in April and May 2013.
The satellite tag was programmed to release to the surface at midnight nine months later. This international expedition is registered under the auspices of the iSimangaliso Wetland Park Authority and is currently being undertaken in South Africa’s sole marine and terrestrial world heritage site. With only 46 marine world heritage sites globally, iSimangaliso is considered one of the ‘Jewels of the Oceans.’ The pop-up Argos satellite tag is designed to continuously collect environmental data that can inform scientists about the depth, position and temperature of the tagged fish. The tag came to the surface 5 days earlier than it was programmed to and emitted signals to the Argos satellite network. Coelacanth researchers requested assistance from Peter Timm, owner of Triton Dive Lodge and who has a long history of involvement in coelacanth discovery and research. The tag transmits summarised data via satellite but much more scientific information is stored on the tag and its retrieval is critical to access the full set of data on coelacanth movement.
Map showing positions where the tagged coelacanth ranged in the 2003 coelacanth telemetry study.
This tagging study, a co-operation between iSimangaliso Authority, French and South African scientists and divers is the first time that longer term data on coelacanth movement has ever been collected. The only previous coelacanth movement study in the iSimangaliso Wetland Park consisted of a ten day acoustic telemetry study of a single fish although a more comprehensive study monitoring several fish was undertaken in the Comoros by a German team of coelacanth researchers. The previous Sodwana study, also facilitated by Triton, involved boat-based tracking of a tagged coelacanth using a directional hydrophone to “listen” for the signals from an acoustic pinger tag that was placed on the flank of coelacanth (individual 15, “Taggi”) using an airgun fired from the submersible Jago. In that study, the coelacanth was tagged in Wright canyon and appeared to remain in caves during the day when no signal could be detected at the surface. The coelacanth was more active at night and was found in two different arms of Wright canyon ranging over a distance of 2.5 km. The depth range of the coelacanth was a surprise with the coelacanth coming into water as shallow as 73m but ranging over only a 60 m range (73-133m) compared to the Comoran coelacanths which usually move into deeper water at night and range over a 500 m depth range. Comoran coelacanths are reported to be most active between the 200 -300 m depth range, mostly below the depth of the caves at 160-250 m where they have been observed during the day. There, coelacanths (particularly larger fish) regularly dive to depths of 400 m with the deepest record at almost 700 m.
Coelacanths seem to have strong site fidelity. For example Individual 4 (known as Grant after Triton’s most experienced Trimix skipper!) has been seen in the same location in Jesser Canyon more than 15 times over a 12 year period. The coelacanth tagged in 2003 moved over an area less than 2.5 km in ten days and tagged fish in the Comoros moved over a maximum distance of 11km although individuals have been observed over a maximum latitudinal range of 35 km there.
The spot where the tag emerged at 01h18 on 8 February 2014 (see orange dot on map) is approximately 12 km north of the known coelacanth distribution in the Park, extending the known range between Chaka and Wright by a few kilometres. Coelacanths are known from only three submarine canyons, Jesser Canyon off Two Mile Reef, Wright Canyon off Five Mile reef and Chaka Canyon near Cape Vidal. In 2004, divers also spotted a coelacanth inshore of Diepgat canyon at a depth of 56 m in the early morning after an upwelling event. The area offshore of 9 mile reef where the tag popped up is not mapped. The presence of the fish here could suggest that there is an unknown underwater feature such as a canyon in the area.
Scientists were very relieved and extremely impressed that the tag was retrieved. Recovery of such a small tag in the Agulhas current is a considerable challenge and many of the experts had warned that finding the tag was a near-impossible task in this part of the Indian Ocean. The tag is only 3.8 cm in diameter,similar to the size of a chicken egg and the dark grey colour is very similar to the blue-grey sea on a Sodwana summer morning.
Word of the tag’s emergence only reached Peter on the evening on the 8th of February and so the recovery attempt could only begin on the morning of 9 February. At that stage the tag was off five mile reef and moving south with the initial track suggesting that it may come onshore. During the night, the tag picked up speed and was travelling south in the Agulhas current with the Triton staff staying up late watching developments on Google Earth! The Triton rubberduck launched at 6am the following morning having received an updated position from Dr Angus Paterson, Director of SAIAB, en route to the beach. Peter acquired a new position from his own laptop just before launching and as the rubberduck approached that position, the crew kept a lookout for the tag. Dr Paterson sent an updated position and checking on an onboard laptop the tracking team noted the position was from 45 minutes ago. Peter managed to calculate the speed of the current which was flowing at 2.5 km / hr and when the next position was sent the team realised they were searching approximately 1 km upstream from the tag. Peter used a buoy to calculate the drift and improve the chances of finding the tiny tag in the large area. Peter used his GPS track function to monitor the area searched and plan a grid search. Using dead reckoning the team plotted a point 750 m down current of the last received co-ordinates and initiated a grid search pattern. The team searched in 500 m long transects perpendicular to the current at 50 m intervals. The 500 m was related to the signal strength of the tag as reported to the satellite network. The strongest homing signal transmitted by the tag only has an accuracy of 250 metres. On the third transect, Triton Dive Instructor Darryl Ilsley spotted the tag and by 9am the tag was back on the beach. The tag had travelled 16 km south of Jesser Point and was about 4km offshore when it was retrieved (See map).
Once the full set of data is retrieved detailed information on the behaviour and habitat of this coelacanth over the last month should be available. Scientists and divers are particularly excited to see the depth data to assess whether coelacanths move into deeper water particularly when temperature increases. The multi-disciplinary expedition focuses on population biology, coelacanth behaviour and broader biodiversity surveys of the submarine canyons “This knowledge will be used to inform and enhance the iSimangaliso Authority’s existing conservation and protection strategies for this flagship species” states Andrew Zaloumis, iSimangaliso Authority CEO.
Coelacanths have a relatively small gill surface area for their large body size and their blood physiology is reported to be adapted to cooler water. Their haemoglobin (the oxygen transporting blood protein) is apparently most efficient in the 15- 20°C range, the temperature range where coelacanths have most commonly been found in both iSimangaliso and the Comoros. Warm water may increase the metabolic rate and oxygen demand of coelacanths thereby increasing respiratory demand in water which actually has less oxygen available. In the Sodwana section of the iSimangaliso Wetland Park, coelacanths have however occurred over a 7 degree temperature range and in the Comoros they have been observed in caves in water as high as 25 degrees. Peter Timm’s logbook indicates that all of his coelacanth sightings, and there are more than 40 of them, were in water at or below 20°C and he believes coelacanths may move into undiscovered deep water refuges when the water heats up.
South African researcher, Dr Kerry Sink was passing through the Sodwana Bay section of the Park on 9 Feb and collected the tag. After joining her on a tour of the Zululand game reserves and having data download disrupted by the presence of a hungry hyena, the tag is currently at the South African National Biodiversity Institute in Cape Town and transmitting data from the Kirstenbosch National Botanic Garden. Once the summarised data is sent via satellite, a process that takes a few days, the scientists will arrange for the full set of data to be downloaded directly from the tag. The tag will offer new insights into the movement, activity periods and diving behaviour of this coelacanth. Individual 26 is fondly known as “Eric Eyelashes” after the diver who first photographed this coelacanth and the eyelash- like white markings around its eye. Each coelacanth is uniquely marked and recorded in a Catalogue of Living Coelacanths of the iSimangaliso Wetland Park. Pressure, light intensity and sea temperature data will help determine when the coelacanth entered and left caves, diving behaviour or movement inshore and along shore movements over longer distances. This is the very first time that such data has been collected over such a long period and may reveal tidal, lunar or seasonal patterns in behaviour. More information on the thermal range and maximum and minimum depth of iSimanagaliso’s coelacanths is also expected. This data can be used to guide coelacanth searches in the future. The coelacanth has a history of surprise from its initial discovery after millions of years of presumed extinction through to new insights in reproduction, evolution and distribution. Its very likely that there is at least one new coelacanth secret stored in the little grey tag that lies winking into space.
|Last Updated ( Wednesday, 09 April 2014 10:36 )|