Devil rays surviving in the Mediterranean.
Credit: © Elio Filidei, Jr
Giuseppe Notarbartolo di Sciara of the Italian Tethys Research Institute and his colleagues, Giancarlo Lauriano, Nino Pierantonio, Ana Cañadas, Greg Donovan and Simone Panigada , have turned up superb results on one of the largest non-bony fish. The 1.5 tonne animals have been estimated in this research to number more than 12,700 individuals in their study area in Summer between Tuscany and Sardinia. Winter survey produced a total zero of sightings, indicating the migration possibilities for the ray. Aerial surveys, especially in such a specialised plane, have improved enough recently to enable such detailed analysis and we can only hope it is accurate. Rays in the Med are rarely fished, but they are caught in bycatch. As they operate alone in most situations, it is likely they are surviving quite well, compared to our worst fears for their future well-being!
The authors’ paper in PLOS ONE is entitled The Devil We Don't Know: Investigating Habitat and Abundance of Endangered Giant Devil Rays in the North-Western Mediterranean Sea.
The scatter of the sightings did not hide the summer efforts at congregation in the preferred area at a wide range of depths. The ray dives to several thousand metres and probably ranges quite widely, given its powerful swimming ability. Gaza is a proposed destination for winter gatherings, in the SE Mediterranean. They were observed to travel up to 337km in 120 days.
Feeding is often on their favourite Meganyctiphanes norvegica, the common Northern krill, which itself dives deep to 1000m in its daily behaviour patterns. As far as breeding is concerned, as is often the case, we know nothing. 90% of the Gaza observations were of males, but where the ladies had disappeared to is a mystery. Sexual segregation seems to be a likely habit for the species. The quantity of animals having been measured in a favoured reserve, it now remains to discover how much the species is affected by habitat degradation and the driftnets that plague them. The species is supposedly protected, but if we could only discover how common they used to be before driftnets appeared, then a true picture of population trends could be established. The endangered species of the ocean deserve even more attention than those we can clearly see.
It is a great challenge to study a non-food species, even of such a size, and produce such interesting insights into the unknown ecosystem that has accompanied civilisation since its beginnings. Who knows what influence these majestic giants have had on our ancestors, and us on them. Here is an example of the ridiculous gill raker trade, both in mantas and these mobulids, in one of our many conservation stories
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