Computer models are all the rage in ecology. But using remote sensors on satellites, daily updates have recently shown the situation with endangered species in real time. Many species could be protected this way including several important rare fish species that have been exploited for hundreds of years. Illegal fishing for Bluefin tuna is so rife in the Mediterranean Sea that adult stocks are now at their lowest ever recorded, despite quota restrictions, non-fishing periods and some heavy enforcement. Most believe the numbers have now sunk below 40% of the tuna levels found in the Med. during the 1950s. It originally had the largest distribution of any Atlantic tuna species and is unique in having its permanent habitat in temperate water.
Jean-Noel Druon1, Jean-Marc Fromentin, Florian Aulanier and Jukka Heikkonen are the four authors of a paper in the Marine Ecology Progress Series. As the fish can traverse 100 km per day, NASA's satellite coverage of the whole of the Mediterranean is entirely appropriate. The sensor is known as the MODIS-Aqua and has been in commission since 2002, with a horizontal resolution of 4-6 km.
The EC Joint Research Centre Maritime Affairs Unit in Ispra, Italy has prepared the feeding habitat model for "chlorophyll fronts":
And the spawning habitat model using "temperature fronts":
Feeding and spawning potential habitats are mapped accurately with the help of data over the last ten years. The novelty is that the data is downloaded from satellites on chlorophyll concentrations on the sea surface and temperature. The chlorophyll shows feeding areas that could contain tuna while the temperatures are crucial in determining spawning sites. Tunaspawning grounds were mostly in: the central parts of the western Mediterranean Sea (around the Balearic Islands and Sardinia as well as north of the Algerian and Sicilian coasts); the Gulf of Syrta, east of Sicily; the central Aegean Sea and the northern Levantine Sea.
This data tracks the oceanographic features indicating tuna distribution. Atlantic blue fin is a visual hunter that loves to predate shoals of fish feeding on the plankton (chlorophyll - rich area), and also visits various temperature "fronts" specifically when breeding. Over the seven years shown in the first map, northern areas and the zone east of the Straits of Gibraltar seem likely hot-spots (red/yellow). That's only if you recognise southern Europe and North Africa in this beautiful but almost negative image!
Spawning starts in May in the warmer east and lasts in the cooler west until July. The ability to illustrate seasonality of location and size of the habitats and annual variations due to weather is the key to the value of the mapping method.
When all is computed, of course, then data from surveys, both aerial and through tagging, and fishing returns was compared to the potential habitat survey. Most of data in the Gulf of Lions came from scientific surveys and are related to the feeding behaviour (see the maps) while most purse-seiner data located in the Balearic Islands area and south of Malta is related to the spawning behaviour (large fish do aggregate when spawning and fishermen look for that type of behaviour preferably). The result was a resounding success rate of 80% of potential habitats that fell within approximately 11 km of the actual (either feeding or spawning) sites.
European Commissioner for Research and Innovation, Maire Geoghegan-Quinn, said: "This model will help to ensure sustainable management of bluefin tuna, actively contributing to two of the most pressing challenges for the future: food security and protection of the environment. Another good example of how science and research provide support to European Union policies." Together with vessel detection systems, the way ahead seems to be much tighter regulation of certain countries and surveillance of all, before we bemoan the loss of yet another much-appreciated species.