Fabian Ritter, Faculty of Biology, University of Bremen
From 1 September until 31 December 1995 a study on the behaviour of cetaceans off La Gomera (Canary Islands) was conducted. The platform for the collection of data were small former fishing boat now being used for commercial whale watching. Behaviours were sampled in 3-min scan samples (Altmann 1974), with emphasis given to the observation of interactive behaviours and the spatial relationship of boat and animals. The sightings were categorised according to their intensity, as defined by the duration of the encounter, the minimum distance between boat and animals, the occurrence of interactive behaviours (e.g. approaches, bowriding, spyhop), and the occurrence of in-water-encounters. Until 1996 swimming with cetaceans was not yet prohibited in the Canary Islands (which is the case now), and tourists were allowed to swim with cetaceans during certain situations. In the case of in-water-encounters the number of swimmers and the time they stayed in the water was recorded. Observations from above and below the surface, as well as qualitative descriptions by the swimmers were used to estimate the animals´ interest in the swimmers.
Six out of seven cetacean species reported during this study were encountered at least once in the water. Only the striped dolphin (Stenella coeruleoalba) could be observed exclusively from the boat. In-water-encounters took place during 24 (52%) of 46 sightings. The number of in-water-encounters varied from 1 to 7 per sighting (mean 1,67). During the 24 sightings with in-water-encounters, 80 swimming attempts were conducted (mean 3,3 per sighting). The number of swimmers per in-water-encounter varied from 1 to 6 (mean 2,06). In-water-encounters lasted between 1 and 14 minutes (mean 3,86 min). Of the 80 in-water-encounters, 14 (17,5%) were characterised by little, 35 (43,8%) by intermediate and 22 (27,5%) by obvious interest of the animals in the swimmers.
During 8 (10%) in-water-encounters a direct interaction between swimmers and cetaceans could be observed. These interactions involved all species except sperm and sei whale and included repeated approaches by the animals, continuous swimming close to or around swimmers and sometimes mutual imitation of movements, postures, etc.
There were inter-species differences concerning the reaction to swimmers. Short-finned pilot whales reacted mostly indifferent, only sometimes interacting with swimmers, while Atlantic spotted dolphins often were very playful, this is also the species which approached closest to swimmers (within 1 metre or less), while there was no instance where a human touched a cetacean. Moreover, in bottlenose dolphins, pilot whales and rough-toothed dolphins there seemed to be a relationship between the affinity to swimmers and the present behavioural state.