Beaked Whale Strandings in the Mediterranean Sea

PROCEEDINGS OF THE ECS WORKSHOP BEAKED WHALE RESEARCH Held at the European Cetacean Society’s 21st Annual Conference, The Aquarium, San Sebastián, Spain, 26th April 2007 Editors: Sarah J. Dolman , Colin D. MacLeod and Peter G.H. Evans ECS SPECIAL PUBLICATION SERIES NO. 51 FEB 2009 5. BEAKED WHALE STRANDINGS IN THE MEDITERRANEAN SEA M. Podestà1, A. D’Amico2 and G. Pavan3 1 Museo di Storia Naturale di Milano, Corso Venezia 55, 20121 Milano, Italy michela_podesta@hotmail.com; 2 SPAWAR Systems Center San Diego, 53560 Hull Street, San Diego, CA 92152-5001, USA; 3 Centro Interdisciplinare di Bioacustica e Ricerche Ambientali, University of Pavia, Via Taramelli 24, 27100 Pavia, Italy This paper updates the Mediterranean beaked whale stranding summary that was published in 2006, which covered strandings through 2004 (Podestà et al., 2006). The complete list of papers from which the data were collected is reported in the references listed in Podestà et al., (2006). This article includes new stranding events recorded in 2005 and 2006. Podestà et al. (2006) reviewed and documented primarily Cuvier’s beaked whale (Ziphius cavirostris) stranding events recorded in the Mediterranean Sea, including those that may not have been previously reported in the literature, such as those only available in relatively inaccessible sources (e.g. local museums archives and newspapers). This analysis of the historical literature, together with cross-referencing and examining specimens held by regional museums, clarified a number of inconsistent reports from earlier papers. All of the stranding sites were georeferenced; in many cases the exact latitude and longitude were not known so the georeferenced location of the beach, village or town where the stranding occurred was used. Datasets were transferred to a Geographic Information System (ESRI ArcView 8) for validation of locations and display. The coastline and bathymetric data used for the Mediterranean Sea is the IBCM bathymetric contours distributed by the British Oceanographic Data Centre (BODC, UK). We accumulated data for all beaked whales, however, the most common beaked whale species found in the Mediterranean is the Cuvier’s beaked whale, of which we have documented 327 stranded animals. We have 5 stranded animals of the genus Mesoplodon. The first recorded Cuvier’s beaked whale stranding event was a skull of a single animal in 1803 on the French coastline. We have also collected information on events that were reported as mass strandings (2 or more animals) in the literature, even if the carcasses were found spread over many miles of coast. In some cases, some ‘single’ stranded animals were reclassified into one mass stranding event, based on 2 or more animals being found stranded in a several day period and in close proximity along the coastline. We recorded stranding events from 10 of the 20 Countries that border the Mediterranean Sea. In Fig. 1 the distribution of the stranded animals is illustrated. 18 Figure 1. Beaked whale stranding records in the Mediterranean Sea (1803-2006) The study effort along the Mediterranean coast is extremely variable by area, and this must be taken into account in any analysis. National networks have been operating in France and Italy for many decades, and have stranding records that date back to the beginning of the 19th century. The first record in Spain is nearly one hundred years later. For other countries, records started within the first half of the 20th century. The lack of strandings along the Northwest Adriatic indicates that this area may not be a beaked whale habitat due to the shallow depth, as there has been relatively consistent effort along the Italian coast. The lack of strandings on the coast of northern Africa on the other hand may indicate a lack of effort, since many of these regions have deep water typical of beaked whale habitat. There are little sighting data for these regions as well. As reported in Table 1, we divided the data into three categories: single animals only, events with two animals, and those with three or more animals. Strandings resulting from fishery bycatch were identified, and were not included in those events listed as mass strandings. About 35% of all the animals stranded in Italy and about 40% of those stranded in Greece were included in mass standing events of three or more. Stranding events consisting of three or more animals occurred in four countries out of the ten from which we have data. 19 Table 1 - Number of animals and number of stranding events by Country. Strandings of 1 and 2 animals include bycatch Country Total animals Strandings of 1 Strandings of 2 Strandings of 3+ Italy 129 80 2 6 (45 animals) Greece 88 39 7 Spain 42 36 1 6 (35 animals) 1 (4 animals) France 35 27 2 1 (4 animals) Algeria 13 9 2 Turkey 7 5 1 Israel 6 6 Croatia 5 5 Albania 1 1 Malta 1 1 Total 327 209 15 (30 animals) 14 (88 animals) Figure 2. Strandings of two (yellow dots) and of three or more animals (red dots) Mass strandings of three or more animals have primarily occurred in the two main areas - the Ligurian and the Ionian Seas (Fig. 2). In the Ligurian Sea, there were five events of three or more animals; four of these events occurred on the north-western Italian coastline in the 1960s (three in one year), and one occurred on the northern coast of Corsica about 10 years later. There have been no mass stranding events of three or more in this region since 1974, although there have been many sightings as recorded in surveys conducted in recent years. 20 Figure 3. Strandings distribution and slope gradient It is difficult to use strandings data to determine the distribution of animals. However, geo-referencing of the data coupled with known bathymetric features in a region can give an indication of where there is a probability of finding beaked whales. Fig. 3 shows the slope gradient derived from 1 degree bathymetric contours (GEBCO). The lighter regions indicate high slope gradient; the dark line is the 1000 m contour. The distribution of the stranding locations shows that most strandings of Cuvier’s beaked whales occur near regions with steep slopes, which is consistent with known sightings. Only five Mesoplodon specimens have been reported stranded in the Mediterranean Sea. One animal reported as Sowerby’s beaked whale (M. bidens) stranded in Italy in 1927, but it was not preserved and no clear species description was given. Based on the morphological description provided, it was certainly not a Cuvier’s beaked whale [‘the teeth are not on the tip of the lower jaw’]. A Blainville’s beaked whale (M. densirostris) stranded in Spain in 1980. The first finding of a Gervais’ beaked whale (M. europaeus) stranding in Mediterranean waters occurred on the Italian coastline in 2001. Anecdotal evidence reports the presence of two beaked whales stranded alive and subsequently released along the coasts of the French Riviera. These whales belonged to the genus Mesoplodon, but no further identification was possible based on the collected evidence. These strandings indicate the presence of Mesoplodon in the Mediterranean. However, no sightings data are available for this genus. We have documented 238 Cuvier’s beaked whale stranding events consisting of 327 animals in the Mediterranean Sea over a 204-year period. Of these, 209 events consisted of a single animal, 15 events consisted of two animals and the remaining 14 events consisted of three or more animals for a total of 88 animals, which represents about a quarter (27%) of the total animals. The geo-referenced stranding locations generally occur when regions of steep bathymetry are close to the coast. 21 ACKNOWLEDGEMENTS We thank the national stranding networks that provided the data. A special thanks to A. Drougas, A. Komnenou, N. Portunato, G. Notarbartolo di Sciara, O. Van Canneyt, M. Rosso, D. Holcer, F. Garibaldi, A. Cañadas, and J.A. Raga. REFERENCE Podestà M., D’Amico, A., Pavan, G., Drougas, A., Komnenou, A. and Portunato, N. 2006. A review of Cuvier’s beaked whale strandings in the Mediterranean Sea. J. Cetacean Res. Manage., 7:251-261. 22 View publication stats