The search for the coelacanth
By Sue Matthews. Published in Marine Scientist (2004)
The Jago - built in Germany in 1989 – is synonymous with the coelacanth, having played an instrumental role in helping Prof Hans Fricke and his team from the Max Planck Institute for Behavioural Physiology to unravel the secrets of the 'fossil fish'.
The team were the first to observe a living coelacanth in its natural environment, and can be credited with most of what we know about the fish today. Regular expeditions to the Comores revealed that the coelacanths there shelter in caves below 150 m depth during the day, and venture into deeper water at night to hunt for prey items such as squid and bottom-dwelling fish.
The Comores were widely considered the last stronghold of the coelacanth, with a population size estimated at less than 600 individuals. However, in 1997 a dead coelacanth was photographed in a fish market in Indonesia, and a year later a live specimen was caught off the island of Sulawesi. In November 1999 the Jago team embarked on a survey of the island's north coast, and after a long search found two coelacanths in a cave at a depth of 155 metres.
Most recently, the Jago team has been participating in the multidisciplinary African Coelacanth Ecosystem Programme, based in South Africa. In October 2000 a group of recreational divers exploring a deep canyon off Sodwana Bay stumbled upon three coelacanths in a cave at 108 metres. This was the first time the species had been seen in South African waters since its initial discovery in 1938. The Jago team returned to the spot during the programme's inaugural research cruise in March 2002 - and found a coelacanth on the very first dive!
So far, 18 different fish have been recorded (each can be identified by its unique pattern of white spots), all in Jesser and Wright canyons. In April the Jago team extended the survey to other canyons in the area, in the hope of adding to this tally.
The Jago is also contributing to other components of the research programme. Its video footage is proving useful in documenting the biodiversity of the canyons, which cannot be surveyed through trawling. Tissue samples are being collected from coelacanths using a small dart fired from the Jago through a compressed air tube, allowing the harmless removal of a scale or two. The thin layer of cells on the scales is enough to establish a tissue culture for genetic analysis, which can be used to assess kin relationships and the degree of genetic variability between the coelacanths. The latter will indicate whether the Sodwana population is an isolated founder population - perhaps derived from a single pregnant female that might have been swept southward in the Mozambique Current - or a relatively well established population descended from a more widespread community.
The Jago has also been used to tag a coelacanth with a small acoustic pinger, allowing the fish to be tracked with a directional hydrophone from an inflatable boat. This was of limited success, because rough seas made working in a small boat at night too dangerous, but tracking on three occasions revealed that the fish moved in a depth range of 70 to 130 m. Future plans for the programme include the deployment of a number of acoustic arrays along the edge of the continental shelf, so that the coelacanths' movements can be tracked remotely. Of particular interest is how these weak swimmers manage to move between canyons, given that the Agulhas Current flows at velocities of up to 2 m per second at the surface.
A similar canyon system occurs in the north of Mozambique, and it is now considered highly possible that a new coelacanth population will be found there. The Jago team hope to explore this area in the near future.