Coelacanth slowly reveals its secrets

[Knight-Dragon]

http://www.bbc.co.uk/blogs/wondermonkey/2011/06/slow-reveal-of-the-coelacanths.shtml

The scientists used remote operated vehicles to descend into the sea and survey an 8km-long stretch of coastline around Grand Comore inhabited by coelacanths. The ROVs followed the fish into the caves in which they live, filming and photographing individuals, which are recognisable by the pattern of white spots on their blue bodies.

They have made some wonderful discoveries.

Coelacanths, it seems, are peaceful animals that do not act antagonistically to one another, even when groups of up to 16 fish share the same cave.

Females are markedly larger than males but there doesn’t appear to be any sexual content to their gatherings.

During the day, the fish live at a depth of 170-240m along a steep volcanic landscape of caves, and at night they drift down to depths of 500m to feed, coming back to their caves in the morning to rest.

The survey reinforces the impression that perhaps just 300-400 coelacanths live at Grand Comore and that the fish do not tolerate waters above 22 degrees Centigrade particularly well, as many fish disappeared from the study area in 1994 when the water warmed, returning later.

But the study by Fricke’s team, published in this month’s issue of Marine Biology, also gives away how much more we still don’t know.

For example, during the entire survey period, the team did not record a single subadult, juvenile, or baby coelacanth. They didn’t spot one in the Comoros, and have never spotted one in separate expeditions to study the fish off Indonesia, South Africa or Tanzania.

Only a single baby coelacanth has ever been sighted, filmed by different researchers in 2009 at a depth of 160m.

So we do not know where coelacanths give birth, where the young go, or why they don’t live with the adults. Such information is vital to preserve species of such rarity.

We still have little idea about how long these ancient-looking fish live for.

The survey by Fricke’s team confirms that coelacanths can live for at least 21 years; they resighted the same fish at the start and end of the survey, while 17 fish were sighted 19 years apart. That confirms that it is unexceptional for a coelacanth to live for two decades at least – the first real evidence of a coelacanth’s minimum age.