Tourism impact on dolphins populations: linking behavioural responses to energetic costs

SILVANA DANS; ENRIQUE CRESPO; SUSANA PEDRAZA; MARIANA DEGRATI,; GRISELDA GARAFFO

San Sebastián-Donostia, España

Congreso; 21th Annual Conference European Cetacean Society; 2007

European Cetacean Society

Behavioural pattern of dusky dolphins was modelled by matrix models and Markov chains theory, in a way that behavioural changes due to tourism vessels may be translated into changes in the time budget. This approach allows quantifying the response of this budget to changes in behaviour by a perturbation analysis. Behavioural data were gathered from group follows by a research boat in the absence of commercial vessels and denominated as “control”. Follow time was divided in 2-min intervals and predominant activity was assigned in each one by instantaneous sampling. A probability matrix was constructed from transition probabilities from one activity to other. Activity budget, bout length, recurrence time and first passage time were derived from ergodic properties. Also, behavioural data was recorded when commercial boats were present at the same time that the research-boat, and then an “impact” matrix was also constructed. Whatever the preceding behaviour, the most probable succeeding behaviour was the same. In a second place, the activity most probable to succeed whatever the preceding one, was travelling, however, feeding had the highest probability of succeeding a travelling bout. This result suggests a strong relationship between feeding and travelling. There were significant differences in only two transitions between “control” and “impact” probabilities. However, sensitivity analysis showed that the time budget is more sensitive to changes in transitions that did not show significant differences, suggesting that small changes may produce significant differences in time budget. The transition that would mostly alter feeding time budget is travelling®feeding, suggesting that a decrease in this transition would decrease feeding time budget and vice versa, even that this transition did not significantly differ between control and impact. In this sense, perturbation analysis plays an important role in detecting what transitions would produce the major effects on activity budget.