TL: RESULTS OF THE GREENPEACE CETACEAN SURVEY CRUISES DURING THE WESTERN MEDITERRANEAN STRIPED DOLPHIN EPIZOOTIC. SO: Greenpeace International (GP) DT: June 1991 Keywords: greenpeace reports mediterranean russia species marine mammals oceans gp europe / Ricardo Aguilar(1), Xavier Pastor(2) and Jaume Forcada(3) (1) Greenpeace Spain. Rodriguez San Pedro, 58. 28015 Madrid (2) Greenpeace International. Mediterranean Sea Project Ses Rafaletes, 16,9J. 07015 Palma de Mallorca (3)Department of Animal Biology (Vertebrates). Faculty of Biology, University of Barcelona. 08071 Barcelona INTRODUCTION In mid-July 1990, a mass mortality affected the striped dolphin (Stenella coeruleoalba) population in the western Mediterranean Sea. The striped dolphin is a common species in this area, occurring mostly in deep waters. Because of this distribution, the number of animals washed ashore during the epizootic are believed to represent a small proportion of those actually deceased. In order to gather data about the patterns of distribution, abundance and behaviour of striped dolphins in the area during the event , two sighting cruises were carried out on board the Greenpeace ship "Sirius". Survey One took place in an area known to have been affected by the die-off (Gulf of Lions and western Ligurian Sea), while Survey Two covered an apparently unaffected region (south of the Balearic islands and north of Algeria). Although the main purpose of the surveys was to collect information on the striped dolphin populations, data on distribution of other cetacean species were also collected. MATERIAL AND METHODS Survey One (5-11 October 1990) cruised 656 nautical miles across the Gulf of Lions and the western Ligurian Sea, covering an area of approx 16.000 square nautical miles, totalling 64.5 hours of effective searching time. Survey Two (7-9 December 1990) covered the waters South of the Balearic Islands and North of Algeria, totalling 306 nm over an area of 4.000 nm2 during 28.5 hours of effective searching. Both cruises were carried out with the MV "Sirius",a former Dutch pilot boat, 46 m long. Cruise speed during the survey was 10 knots. Track design and data collection followed standard line- transect methodologies. Sightings were made by teams of two trained observers permanently placed above the vessel's bridge, 9 meters above the sea level. Observers were replaced every two hours. Observations were carried out during 12 hours a day (05.30 to 17.30 GMT) during Survey One, and 10/11 hours a day (06.30 to 17.30 GMT) during Survey Two. The "Sirius" interrupted the cruise during night hours returning to position in the morning. Positions were determined by a satellite navigation system Magellan GPS NAV 1000. Water temperatures were measured with a digital thermometer Elektron, which ranges from -25 C to 120§C. For every sighting the following data were recorded: species, group size, direction of swimming, date, hour, position, surface water temperature, chart depth, duration of sighting, angle and distance of sighting, and weather conditions. Observations on behaviour and associated fauna were also recorded. The data on school size obtained were compared between them and also with those available in the data base of the Department of Animal Biology of the Faculty of Biology, University of Barcelona (covering the period 1982 to 1989). Indices of relative abundance of striped dolphins in each of the surveys was calculated as number of individuals and number of schools per hour of searching, and number of individuals and number of schools per mile searched. RESULTS Figures 1 and 2 show the surveys track and the distribution of sightings. In total, 45 sightings of cetacean were made (32 in Survey One and 13 in Survey Two). This included 25 of striped dolphin (19 in Survey One and 6 in Survey Two). Of those, two sightings corresponded to dead individuals found in open waters of the Gulf of Lions. Other species occasionally sighted were fin whales (Balaenoptera physalus), Risso's dolphins (Grampus griseus) and common dolphins (Delphinus delphis). DISCUSSION In the area surveyed, striped dolphins distributed following the pattern commonly observed for the species in the western Mediterranean. Thus, most observations were recorded in waters deeper than 100 m and at temperatures ranging 16.2-22.6§C. The number of schools observed was fairly high in both surveys and, when calculated relative to the time searched, it was similar between the two areas (table 2). However, substantial differences appear when school sizes are compared between surveys and with data obtained previously to the die-off. Thus, the school size in the northern fringe was extremely low, ranging only from 1 to 8 individuals, while in the southern one it ranged 1 to 60, these latter values being more consistent with the size of the st riped dolphin aggregations commonly observed in the region (table 1). These differences can be clearly observed in Figure 3, which compares the striped dolphin school sizes in observations previous to the die-off with those carried out during surveys One and Two. At the time the cruises were carried out, the epizootic had affected severely the area covered by survey One -two dolphins were found floating dead during that cruise-, while it had not reached the southern fringe or, if it did, its effect was less intense. Therefore, the low school size observed in survey One probably reflects the high mortality suffered by the population during the episode. Coupled with the relatively high number of schools observed, these findings suggest that the population had been sev erely decimated in this area and that, at the time of the surveys, the survivers had not aggregated to constitute new groups but, rather, they still maintained the original school segregation. Also, reflecting this severe reduction in school size, the relative abundance of the striped dolphin in survey One was substantially lower than in survey Two, as indicated by the various indices depicted in table 2. ------------------------------------------------ data base Sirius Sirius 1982-89 Survey One Survey Two ------------------------------------------------ 24.90 3.48 19.17 ------------------------------------------------ Table 1.- Mean values of striped dolphin school size ---------------------------------------------------------- Survey One Survey Two Individuals/hour searched 0.93 4.02 Individuals/mile searched 0.09 0.38 Schools/hour searched 0.26 0.21 Schools/mile searched 0.03 0.02 ---------------------------------------------------------- Table 2.- Frequency and relative abundance indices of striped dolphin schools and individuals.