Survival rates of different age classes of short-finned pilot whales (Globicephala macrorhynchus) in the archipelago of Madeira

Jordi Tarrassó Toscano

Cetacean life-history parameters estimates are key to assess population status and the implementation of conservation measures. In Madeira, short-finned pilot whales are organized in stable social clusters that use the area frequently, which would expose them to local anthropogenic pressures. Based on photo-identification data of all the individuals composing five social clusters, multi-state capture-mark-recapture models were built to estimate the survival rates of different age classes from 2008 to 2018. Overall, survival rates were 0.794 (95%Cl: 0.691-0.869) for calves and juveniles, and 0.996 (95%CI: 0.950-1.000) for adults. However, two social clusters had low calf survival rates (0.471; 95%CI: 0.229-0.727) compared to the other 3 social clusters (0.942; 95%CI: 0.295-0.999). Another social cluster had low juvenile survival rates (0.476; 95%CI: 0.263- 0.697) compared to the other four that had values above 0.895. Although possible biases in the photo-identification analysis could partly explain those results, an increase in local pressures, such as marine traffic and whale-watching activities in the area where these cetaceans reside, was observed during the study period. The high capture probabilities found for those clusters with low survival rates suggest that they spend more time in the surveyed area and therefore are more exposed to anthropogenic disturbances, which might end up affecting their survival.