Durban - Fish scientists are hoping a nifty satellite device, about the size of a chicken egg, will throw new light on the mysteries of South Africa’s famous “dinosaur fish”.
The floating satellite tag was recovered last month, drifting in the sea off Lake St Lucia, nearly nine months after it was attached to one of at least 32 coelacanths that live in the deep-water canyons in the Sodwana Bay section of the iSimangaliso Wetland Park.
The existence of coelacanths at Sodwana excited the scientific community nearly 14 years ago because this prehistoric and critically endangered species had never been found living along the South African coastline.
With four extraordinary leg-like fins, this was the fish whose ancestors were believed to have crawled out the sea about 360 million years ago to evolve into the first reptiles, mammals and, eventually, humankind.
As part of a research programme on the Sodwana coelacanths, a specially designed satellite tag was attached to coelacanth No 26 in May. It had been designed to fall off after nine months and float to the surface, so that scientists could retrieve the data about the fish’s movements as well as water temperature, depth, pressure and light intensity.
About 10 years ago researchers tried to gather similar data using an acoustic “pinger” tag, but the venture was hampered by the fact that these fish spent most of their time at great depths. As a result their movements had to be tracked from the surface with a boat-based directional hydrophone.
With the new device, however, nearly nine months of continuous data was logged at much greater depths.
But there was one potentially major snag.
There was a risk that the coelacanth tag would never reach the surface if it fell off inside a cave, where these fish are thought to spend much of their time.
Alternatively, the tag could float to the surface and drift away, never to be recovered.
As things turned out, the floating tag drifted to the surface in the early hours of February 8 and a signal was relayed into space to reveal its re-emergence. But word reached the recovery team only that evening, when it was too late to send out a boat team to search for it.
Coelacanth researcher Dr Kerry Sink, who was visiting the park at the time, said that trying to find the device was like looking for a needle in a haystack.
“The tag is about the size of a chicken egg and the colour is similar to the blue-grey sea on a Sodwana summer morning.”
Nevertheless, diver Peter Timms and colleagues from Triton Dive Charters set out early on February 9 in a rubber duck and, with the aid of laptops, guesswork and sheer luck, retrieved the device.
A spokesperson for the iSimangaliso Wetland Park said the data would now be scrutinised by scientists.
The tag is expected to provide new insights into the movement, activity periods and diving behaviour of coelacanth No 26.
Each coelacanth is uniquely marked and recorded in the 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,” said Sink.
More information on the thermal range and maximum and minimum depth of iSimangaliso’s coelacanths is also expected, and the data can also be used to guide coelacanth searches in the future. - The Mercury