ECOLOGY AND FEEDING OF FIN WHALE

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Fin whale (Balaenoptera physalus) is the commonest species in the canyon (based on data collected between 1996-2000).

With the help of local fishermen, we concentrated our efforts in the waters surrounding the island of Ischia throughout 1996.

In the following years it was possible to ascertain the presence of a large amount of fin whales in the zone between the islands of Ischia and Procida and the mainland coast in a comparatively small area (about 35 square miles) roughly corresponding to the submarine canyon of Cuma (Pennetta et al. 1998). It was possible to repeatedly observe the fin whale's feeding behaviour.

Between 1996-1998 we recorded 66 sightings of fin whale for a total amount of 94 individuals and 52,4 hours of direct observation.

In the summertime the surface water temperature varied between 26.5°C and 24.2°C with an average temperature of 25.6°C. The  average depth of the sighting point was 280 m (±193.8 SD; range 25/900); the average distance from the nearest coast was 5.6Km (±3.2 SD; range 0.6/13.1).

The mean group size of fin whale was 1.5, with a highest number of 6 individuals observed at once; 69% of the sightings included a single individual, in the 8% of the sightings young individuals (length below 11m) were together with adults; on six occasions young isolated individuals were detected. During the month of July 1998, 12 individuals were photo-identified, 2 of which detected twice.

The analysis of faecal material, according to what had been already observed, has revealed the presence of crustacean exoskeletons belonging to the euphasiacean Meganyctiphanes norvegica.

Space connections, as a consequence of a high concentration of shared prey or of trophic levels, have been observed with several other species. Odontocetes like striped dolphins and common dolphins have been frequently observed in the area, along with a large number of some pelagic fishes as Mobula mobular, Thunnus sp. and sea birds as Calonectris diomedea, Puffinus puffinus and Larus ridibundus.

The fishery resources of the area are daily exploited by 20 trawling nets, 12 bottom gill nets for Merluccius merluccius, 10 encircling nets for Scombersox saurus, 8 small mesh drift nets for Scombridae, 5 bottom long lines and one purse seine.

In 41% of feeding sightings the whales were involved in opportunistic feeding from fishermen's gears: encircling nets and trawling nets.

This research has enabled us to point up a significant presence of fin whale in the coastal waters of Ischia. The specific geomorphological characteristics of the area have been described by Pennetta (1998) who explain how the continental slope appears to be incised by submarine canyons, of which the deeper one is that of Cuma. These canyons seem to be the main reason of this concentration of fin whales in such a small area (35 square miles) so close to the island.

The production enhancement is apparently projected into the food chain down to sea birds and mammals. The presence of big pelagic predators (whales, common and striped dolphins, tuna), along with the daily taking made by a remarkable quantity of commercial fisheries, suggest a big concentration of food resources.

We point up the huge importance of the role played by submarine canyons at least in distribution and abundance of trophic resources of these marine mammals, as submarine canyons are an important habitat, were a particular pelagic assemblage can be found.