Behaviour of bottlenose dolphins : inference for dolphin tourism off Durban, South Africa.

Abstract

During long-term studies of dolphins, the number of individuals in the population being studied are

constantly monitored using the technique of photo-identification. This constant monitoring makes use

of different researchers over time. Therefore, measurement of photographic quality and individual

distinctiveness for photo-identification analyses was incorporated in this dissertation to provide an

additional data set for analysis. Researchers with differing levels of experiences did not obtain the

same information from the same photograph and were unable to reliably quantify variables of photo

quality and individual distinctiveness, but experienced researchers were found to be more adept than

inexperienced researchers in counting notches on the dorsal fin of bottlenose dolphins. These results

highlight the necessity for researchers to be trained in photo-identification techniques prior to carrying

out their study. This study theodolite tracked dolphins off Durban from June 2004 to Feb 2005 to

assess habitat utilization of bottlenose dolphins (Tursiops aduncus) in the Durban bay region.

Dolphins were seen in all months surveyed and throughout the survey area. Temporal distribution of

dolphins was skewed with 91% of dolphins seen before midday and 98% of sightings observed in

water depths less than 30m. Six behavioural categories were recorded, including: social, fast travel,

slow travel, feeding, resting and milling. The most dominant behaviour exhibited by dolphins was

slow travel (46%) followed by feeding (27%). Resting was not observed at all. Of the feeding

behaviour 88% occurred in the southern end of the bay whereas other behaviours occurred randomly

throughout the survey area. Additional theodolite tracks were conducted during experimental boat

approaches (before, during and after boat approaches) to determine potential short-term reactions of

dolphins to dolphin watching boats. Two speeds of approach (slow ~ < 5 km/hr and fast ~ > 40 km/hr)

and two distances of approach (20m and 80 m) were tested. The bottlenose dolphin groups did not

change their behaviour in response to boat approaches during any of the periods of experimentation.

Short-term changes in group speed, group size and spread were not statistically significant. Dolphin

groups continued with their ‘normal’ behaviour and spent the same amount of time in the bay when

compared to their distribution and behaviour in the absence of the experimental boat. These findings

indicate that the experimental boat did not affect the behaviour of dolphins at either a slow or fast

approach and even at a close distance. This is interpreted as being as a result of habituation of the

dolphins due to their residency in a busy port. This work is crucial in developing guidelines for the

development of a sustainable dolphin watching industry off Durban.