parissayazdi at yahoo.de
Wed May 10 11:17:46 PDT 2006
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:
Please send all requests to: mail at 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.
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%)
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
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