Arcangeli, A., Crosti, R., Marini, L., Poggi, A., Poldi, A., Pulcini, M., Safontas, C., Sdringola, S., Ukmar, E. (2008). Monitoring cetacean populations over 15 years in Central Tyrrhenian Sea using a non-dedicated ferry as an observation platform

Monitoring cetacean presence, distribution and migration timing is an effective indicator to detect environmental changes and habitat degradation. The geographical and ecological characteristics of the Central Tyrrhenian Sea makes it strategic for monitoring the presence of animals, also because intercepts the marine corridor that connects the Northern-Pelagos Sanctuary to the Southern-Mediterranean Sea. From 1989 to 1991 weekly observation on cetacean were undertaken from non-dedicated ferries along the “transect” from Civitavecchia (Rome district) to G.Aranci (Sardinia). In 2007 research restarted with same protocol and under supervision of same investigators. We compared summer data of the three years in the 1990’s (87 ferry runs-590 hours of observations) with the study conducted from May to September 2007 (31 runs-160h). Each transect was considered as an independent statistical unit and we primarily analysed frequency of occurrence (f.o.), mean group size (g.s.) and distribution. Results showed that in 2007 f.o. of Balaenoptera sp. was 0,18h^-1±0,06 with g.s. of 1,3±0,11 while, for Stenella coeruleoalba, was 0,51h^-1±0,08 with 5,4±0,57 g.s. There was a significant difference of monthly f.o. of Balaenoptera sp. (P<0.05), with higher values at beginning of summer, strengthening the migratory behaviour trend recorded for the first time in the 1990’s. Monthly f.o. of S.coeruleoalba, instead, was similar during the summer period in 2007 (P=0.36) as it was in the 1990’ study. Compared with 1990’s there was an increase of f.o. of Balaenoptera sp. (78%) and of S.striata (29%), for the latter g.s. decreased (18%). Most of the sightings occurred towards the Sardinian coast. No ferry-whale collision was recorded in the investigated periods(n=139). Re-surveying confirmed how effective and cost efficient is such a programme for monitoring cetacean distribution and consequently environment quality. Increase abundance of animals and strengthening of migration pattern could be related to the Pelagos Cetacean Sanctuary supporting the need of the proposed new Sanctuary in the Southern-Mediterranean.

Per approfondimenti e/o articolo scrivi a: Antonella Arcangeli

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