Delphis 98's cetaceans

101 observations of cetaceans were realized with boats participating in the operation Delphis 98 and placed on a square of the railing of sampling

Even though it is evident that one or several groups of Dolphins can have been identified correctly by the observers during Delphis 98, it seems that the immense majority of registered observations as " common Dolphin " are in fact " blue and white Dolphin ", as well as probably a good part of the small "non-become identified" cetaceans. Proportions relatively raised by Dolphin of Risso and by black Globicéphale are explicable on one hand because of the distribution of the effort of search during Delphis 98 (effort concentrated in the band of 0-30 miles), and on the other hand because of an important presence this year of black Globicéphale. The strong presence of the Big dolphin in Delphis's 98 statements can also be due to the big number of observers in the coastal band, although several errors of identification are possible. Finally percentages obtained for Sperm whale and common whale during Delphis 98 are close to usual values found in the pond ligure.

Actual average statements by the observers of Delphis 98 are the following ones: common Dolphin (13,4 individuals by group), blue and white Dolphin (15,5 individuals by group), Dolphin of Risso (15,5 individuals by group), black Globicéphale (26,8 individuals by group), Big dolphin (10,4 individuals by group), Sperm whale (1 individual by group), common whale (10,4 individuals by group) and non-identified (19 individuals by group).

One notes that actual average registered or the two sorts of small delphinidés are close one of the other and rather typical of mean value raised in the pond for the blue and white Dolphin. Also, actual average found during Delphis 98 for the Dolphin of Risso, black Globicéphale, Big dolphin, the Sperm whale and common whale can be considered as representative of these sorts in the Occidental north Mediterranean Sea, account held with the weak number of observations registered in certain cases. If one looks now at the cards of distribution, one raises the following elements: the geographic distribution of common whale is typical of this sort; within the canvassed zone. The mysticète frequents especially the waters of depth superior to 2000 metres. The two observations of Very sperm whale are so situated in the usual domain of this sort, as well as those of black Globicéphale. About this sort, one notices very interesting spatial structure revealed by Delphis's 98 observations: most of the groups are seen on the same sector of about fifty kilometres of area in the Southeast of the island of the east. This organization of the large-scale animals could not show through of a conventional sampling realized with a single boat. For the Dolphin of Risso, distribution is also typical of this sort, in spite of two observations situated enough in the wide, in the South - southeast of the island of the East. Distributions obtained for the blue and white Dolphin and the indicated cetaceans as " common Dolphin " are completely similar, still confirming the problems of identification met for Delphis. Finally, the Big dolphin would have been observed very in the wide three times: One remembers himself that this sort is usually very coastal in the Mediterranean Sea, so it is advisable to look with caution at these observations in deep waters.

The potentialities of the operation Delphis 98 being more and more evident, it is advisable for the future publishing to strengthen the forming of the participants and the used methods, to obtain quickly excellent results in term of identification of cetaceans. So, it will be possible completely to take advantage of data to obtain new results on the distribution of cetaceans in the sanctuary.

	The correct identification of the small delphinidés is always problematic for a part of the observers, in spite of efforts granted by the organizers.
	The actual of groups of cetaceans are estimated well generally rather by the participants.
	The principle of the operation allows to obtain a very good image of the distribution of sorts, particularly considerable fact for black Globicéphale and Dolphin of Risso.

Copyright - manon.org - 02/01/2000 - - Mise à jour le dimanche 21 janvier 2001