A hundred and six individuals were identified by means of natural, permanent marks on their dorsal fin. The initially high rate of recruiting of new individuals in the photoidentification catalogue showed a progressive decrease after May 1992, indicating that most members of the dolphin community have been already identified.

Most individuals were continuously sighted during the course of the study, showing a high degree of site fidelity. Four dolphins (3.8%) were sighted only once. Dolphins seem to range within an area which is larger than the one selected for this study (covering approximately 900 Km 2 ), and because of their movements - likely to be determined by variations in food resources as well as by social and environmental factors - in some periods only a few animals can be found within the limits of the study area. This assumption seems to be confirmed by the large variation in the time spent searching for the dolphins (1 minute to 19 hours), also indicating their highly variable density and distribution.
At least 23 out of 106 individuals catalogued calved during 1990-94. At least three newborns were reported in 1990, one in 1991, seven in 1992 (one died), none in 1993, and nine in 1994 (one died), showing remarkable differences in the reproductive rate among years. The overall increase in the number of calves across years can be related to the progressive increase in the number of dolphins catalogued across time, with less opportunities to detect maternities during the first years of the study.

Peak calving season, based on 11 observations, was summer (82%), with only one birth occurring in spring and one in fall.

Mean group size was 7.4, most groups being composed of less than 15 individuals. The modal group size (= most frequent observation) was only two dolphins. Group size was strongly correlated with group composition, with groups composed by adults only being the smallest (mean = 4.3), and groups with calves being the largest (mean = 9.2 with one calf, 14.8 with two calves).

The group size changed significantly with time of day, with smaller groups in the morning and late afternoon.

Behavioural data showed a clear predominance of activities considered to be feeding-related (covering up to 80% of the behavioural budget) over non feeding-related activities such as travelling and socializing.

Group size was significantly related to behaviour, with a mean group size of about 6-7 dolphins during feeding-related activities, 8-9 during travelling, and 10-11 during socializing. The occasional occurrence of large groups, composed by up to 65 dolphins, could be determined by the presence of concentrated food resources, but the significant relation between group size and behaviour showed that social factors may have an important rule in determining such aggregations. The low group size during feeding-related activities indicates that looking for food in small groups represents an efficent strategy in an area where the food resources are probably scattered.

The high fluidity of the dolphin groups, with frequent changes in group size and composition, could also represent an ecological adaptation to an unpredictable and variable distribution of the food resources.

About 10% of the working trawling boats opportunistically inspected were followed by dolphins. Despite these "antagonistic" interactions, local fishermen show tolerance towards the dolphins.

Based on photoidentification data, the movements of selected individual dolphins were plotted in order to outline their movement patterns, assess mean speed of travel and area coverage.

Despite remarkable individual differences, most individuals often frequented a few particular areas. Some of these areas have particular bottom features such as slopes, rocky shallows, or submarine mountains, although a large percentage of time was spent on merely flat muddy bottoms. Observations often showed that dolphin movements roughly corresponded to the 50m-isobath. Movement plotting also indicated that the selected individuals, although showing a high level of residency in the study area, often moved out of it.

Local dolphins cover relatively wide areas per unit time. A rough estimate of the daily geographic range indicated that the "average" dolphin could cover an area of 543 km 2 in 24 hours.

Females seem to cover comparatively smaller areas than males during a given period of time.

Cetaceans . . . Conservation