NADIA AMALINA DANIEL, DANIELLE KREB & HARFIANDRI DAMANHURI

Abstract. Cetacean studies in Indonesia are rare, especially those pertaining to population abundance. This is in spite of the fact that cetaceans are considered priority biodiversity by the Ministry of Marine Affairs and Fisheries that must be protected and managed sustainably. The purpose of this study was to examine the species and habitat characteristics of cetacean species within the Pieh Marine Protected Area (MPA) and the surrounding seas, West Sumatra Province and provide recommendations for their management. 25 days of non-consecutive vessel-based surveys were conducted between 2019 and 2022, covering a total distance of 1,567 km. Species diversity, spatial distribution, frequency of occurrence of less frequently observed species, population abundance for species with highest occurrences, and environmental parameters were analysed. Eight species of cetaceans were identified during on-effort surveys in decreasing order of encounter frequency: Stenella longirostris longirostris (Gray’s spinner dolphin; 44 encounters), Stenella longirostris roseiventris (dwarf spinner dolphin; seven encounters), Stenella attenuata (pantropical spotted dolphin; seven encounters), Tursiops aduncus (Indo-Pacific bottlenose dolphin; six encounters), Balaenoptera omurai (Omura’s whale; five encounters (three on-effort and two off-effort)), Grampus griseus (Risso’s dolphin; two encounters), Lagenodelphis hosei (Fraser’s dolphin; one encounter), and Peponocephala electra (melon-headed whale; one encounter). Cetaceans were found in the waters around four islands, namely Bando, Pieh, Pandan, and Toran Islands with water temperatures ranging between 28.0–31.8°C and a depth of 5–360 m. No significant differences in temperature and depth preferences were found between cetacean species inside the MPA but all species except for Omura’s whale were encountered at lower mean depth than other studies in the region or elsewhere. The first abundance and density estimates for populations of Stenella dolphins in Indonesia were obtained from this study in Pieh Marine Protected Area and the surrounding seas, covering an area of 399.2 km², with 2,997 individuals and 3.8 individuals/km² (CV = 25.2%). The highest density of S. l. longirostris was 2.4 individuals/km² with a total population estimate of 1,921 individuals (CV = 30.2%). This baseline information about cetaceans is relevant in the management of Pieh Marine Protected Area and the surrounding seas. The methods used in this study may be replicated in other marine protected areas as part of routine patrols by trained observers to conduct marine mammal studies to narrow the knowledge gap regarding cetacean diversity, distribution and relative abundance in the vast marine environment of Indonesian waters. The high density of spinner dolphins, the presence of calves, the near year-round presence of cetaceans, frequent occurrence of Omura’s whales, and the observation of two near-threatened species (T. aduncus and P. electra), identifies the area as an important habitat for at least eight cetacean species on the west coast of Sumatra and qualifies a nomination of the Pieh Marine Protected Area as an Important Marine Mammal Area.

Key words. spinner dolphins, Indonesia, population, density and abundance, marine mammal conservation, Important Marine Mammal Area (IMMA)

Read article here: RBZ-2025-0029