Dear colleagues, I have finished my PhD thesis with the title: "Impact of tour boats on the behaviour and energetic of bottlenose dolphins (Tursiops truncatus) off Choros Island, Chile." The dissertation is written in german, but an english summary is included (see below). My thesis can be downloaded as pdf-file under: http://e-diss.uni-kiel.de/diss_1579/ Please send all requests to: mail@parissa-yazdi.de Yazdi, P. (2005): Einfluss der Tourismusboote auf das Verhalten und die Energetik der Großen Tümmler (Tursiops truncatus) vor der Insel Choros, Chile. Dissertation. Christian-Albrechts-Universität, Kiel. Summary: Watching whales and dolphins in their natural habitat has increased throughout the world. Since bottlenose dolphins are common in coastal regions, they are visited frequently by tour boats. Boats can affect the behaviour of dolphins. To what degree their presence changes the dolphins' energy budget was still unknown. Therefore, the aim of the present work was to examine how the activities and energetics of bottlenose dolphins are affected by boats. Furthermore, the focus was on the different reactions of dolphins to boats far away and nearby as well as on the dolphins' strategies to avoid boats. Observations were conducted in Chile off Choros Island in the summer months of 2000/2001. Swimming speeds and movements of the dolphins were recorded via theodolite tracking. The results of this study show that close boats (<100 m) affect the behaviour of bottlenose dolphins more strongly than boats further away (>100 m). Whereas dolphins reacted to distant boats in 44% (n=23) of observations, they responded to close boats 95% (n=82) of the time. Their activity budget did not change significantly with distant boats compared to controls. Close boats, however, induced a decrease of feeding (from 6% to 0%), resting (from 15% to 5%) and social behaviour (from 15% to 5%). The proportions of high-speed swimming (from 5% to 11%) and slow swimming (from 20% to 38%) increased. Close boats caused behavioural changes 3.5 times more often than controls. With a constant number of close boats, resting changed to diving and social behaviour to slow swimming (p<0.05). In addition, dolphins reacted with frequent speed changes: slow swimming changed to high-speed swimming and vice versa. As a result of an increasing number of boats in the proximity, the transitions of slow swimming to high-speed swimming and slow swimming to diving showed an increase. If the animals were diving, they most often maintained this activity. However, dive time decreased with the presence of close boats by 45% (without boats: = 108 s; with close boats: = 59 s), while the duration at the surface remained unchanged (without boats: = 35.8 s, with boats: = 39.0 s). Off Choros Island, all types of diving behaviour strongly associated with feeding constituted 53% of the controls. With close boats, however, these kinds of submergings were not observed. In the presence of close boats, dolphins were observed 6 times more frequently to leap (when swimming at the surface between dives) and 3.6 times more frequently to tail-slap (when swimming slowly) than under control conditions - an indication of disturbance. Bottlenose dolphins off Choros Island responded to close boats with evasive manoeuvres similar to techniques used for avoiding predators. They mostly showed horizontal avoidance in 37% (n=82) of the cases. This also includes weak reactions such as changes of movement patterns during slow swimming. In the absence of boats, dolphins swam slowly often in a zigzag-pattern (59%; n=27) usually within their preferred residence area. With boats, however, movements predominantly followed (71%; n=51) a direct path - most frequently to the west or northwest of Choros Island as boats always approached from the east. Primarily dolphins left their preferred residence area, when many boats stayed for a longer time in their surroundings. The number of close tour boats had a significant influence on the mean swim speed of the dolphins. With more than two close boats, animals swam approx. 37% faster (3-5 close boats: = 2.6 m s-1) than without close boats (without/ distant boats: = 1.9 m s-1). Without boats, dolphins swam long distances and straight at high speed. With boats the distances (without boats: = 842 m; with boats: = 501 m) and the durations (without boats: = 3.0 min; with boats: = 1.5 min) of the high-speed tracks were significantly shorter. There was a trend to movements in zigzag pattern. Here a second strategy of horizontal avoidance was displayed: escape. Bottlenose dolphins off Choros Island showed an increase of group dispersion or a tendency to split into subgroups, when exposed to more than two boats. Possibly group dispersion is a further avoidance strategy of dolphins: scattered emerging positions make movements more unpredictable. Furthermore, individuals or subgroups could follow different avoidance strategies, causing the splitting of a group. Diving as a vertical avoidance strategy constituted 16% of dolphin reactions (n=82) towards close boats. In 14% of the cases, there was a simultaneous occurrence of horizontal and vertical avoidance behaviour, for example when dolphins dove and swam westward, in order to leave the boat traffic area. That was mostly the case, when several boats stayed a long time in the proximity of the dolphins. Based on activity budget, average swim speeds, and leap frequencies of the bottlenose dolphins off Choros Island, an energy consumption of 2.93 W kg-1 was calculated. This corresponds to a daily energy demand of 50.6 MJ per dolphin with 200 kg body weight. Animals utilized 36% of their energy for the execution of their daily activities. A leap to a height of 9 m costs a dolphin 79.5 KJ, corresponds to approximately 0.25% of its daily resting metabolism. If the power of leaps is averaged over all group members, they constituted only 1% of the total energy consumption. With boats at close range, the mean power requirement of dolphins was around 15.4% higher than during controls. The quantifiable additional momentary costs amounted to 324 kJ per hour, which corresponds to the energy content of approximately 65 g fish. With close boats, dolphins used a third of their energy budget to avoid boats by swimming at high speed. Whether additional energetic costs could be induced by tour boats and which long-term consequences might have to be expected is discussed. In the light of these findings, recommendations for dolphin-watching guidelines are given. These contain among others the restriction of the number of boats in the proximity of dolphins (<100 m) to a maximum of two boats. Boats should keep a minimum distance of 30 meters or 50 meters, respectively, if bottlenose dolphins show resting or social behaviour. Guidelines would not only provide for the protection of the animals on a long-term basis, they would also increase the probability of satisfying encounters between tourists and these small cetaceans. Dr. Parissa Yazdi Marine Biologist ___________________________________________________________ Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos - Hier anmelden: http://mail.yahoo.de