Monitoring Winter and Summer Abundance of Cetaceans in the Pelagos Sanctuary (Northwestern Mediterranean Sea) Through Aerial Surveys

TLDR

Systematic long‑term monitoring of abundance is essential to inform conservation measures and evaluate their effectiveness. The study aimed to initiate systematic monitoring in the Pelagos Sanctuary via two aerial surveys in 2009 and to assess the impact of ship strikes on Mediterranean fin whales. Two aerial surveys were conducted in winter and summer 2009 to collect abundance data. The surveys recorded 467 sightings of seven species, found higher cetacean numbers in summer, estimated fin whale abundance in summer and striped dolphin abundance in both seasons, revealed a decline in fin whales and an increase in striped dolphins relative to past surveys, and showed that aerial surveys yield more efficient, robust estimates than ship surveys.

Abstract

Systematic long-term monitoring of abundance is essential to inform conservation measures and evaluate their effectiveness. To instigate such work in the Pelagos Sanctuary in the Mediterranean, two aerial surveys were conducted in winter and summer 2009. A total of 467 (131 in winter, 336 in summer) sightings of 7 species was made. Sample sizes were sufficient to estimate abundance of fin whales in summer (148; 95% CI = 87–254) and striped dolphins in winter (19,462; 95% CI = 12 939–29 273) and in summer (38 488; 95% CI = 27 447–53 968). Numbers of animals within the Sanctuary are significantly higher in summer, when human activities and thus potential population level impacts are highest. Comparisons with data from past shipboard surveys suggest an appreciable decrease in fin whales within the Sanctuary area and an appreciable increase in striped dolphins. Aerial surveys proved to be more efficient than ship surveys, allowing more robust estimates, with smaller CIs and CVs. These results provide essential baseline data for this marine protected area and continued regular surveys will allow the effectiveness of the MPA in terms of cetacean conservation to be evaluated and inform future management measures. The collected data may also be crucial in assessing whether ship strikes, one of the main causes of death for fin whales in the Mediterranean, are affecting the Mediterranean population.