Bohol Sea IMMA
Size in Square Kilometres
29 517 km2
Qualifying Species and Criteria
Sperm whale – Physeter macrocephalus
Blue whale – Balaenoptera musculus
Melon-headed whale – Peponocephala electra
Criterion B (2)
Fraser’s dolphin – Lagenodelphis hosei
Criterion B (2)
Marine Mammal Diversity
Criterion D (2)
Balaenoptera edeni, Balaenoptera omurai, Feresa attenuata, Grampus griseus, Globicephala macrorhynchus, Kogia sima, Kogia breviceps, Mesoplodon densirostris, Orcinus orca, Pseudorca crassidens, Stenella attenuata, Stenella longirostris, Steno bredanensis, Tursiops truncatus
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The Bohol Sea represents a biodiversity hotspot for cetaceans in the Philippines, and South East Asia where 19 species of cetaceans are known to occur, including the blue whale (Balaenoptera musculus). The Bohol Sea is the only known area in the country where blue whales have been positively identified. Balaenoptera edeni and Balaenoptera omurai are also known to occur here and were hunted until the late 1990s. Sperm whales have also been historically hunted in this area and sightings have been reported during dedicated surveys, public reports and strandings. Highly productive and deep waters support large populations of small resident teuthophagous odontocetes, including melon-headed whales, short-finned pilot whales, Risso’s dolphins and Fraser’s dolphins. The deep waters also host beaked whales and several encounters with Blainville’s beaked whale have been reported.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
Based on logbook and museum records available from the whaling era, blue whales were historically present in the Philippines. Surveys conducted between 2000 and 2004 in the area by WWF-Philippines and Silliman University, did not report any baleen whales. However, informal reports from fishermen and dolphin watching tour operators in Pamilacan Island in the North Bohol Sea, describe the sporadic presence of large whales, locally known as bongkaras, between January and June. The first confirmed sighting of a blue whale (Balaenoptera musculus) in the Bohol Sea occurred in 2004 but it was not until 2010 that the species was properly documented and photo-identified. There have been 33 blue whale sightings recorded between 2004 and 2019, in the Bohol Sea (Acebes et al., 2021). One single individual blue whale, recognized through photo-identification, was re-sighted in the Bohol Sea during eight different years: 2010, 2011, 2012, 2015, 2016, 2017, 2018 and 2019 (Acebes et al., 2021). The geographic location and time of year—all sightings occurred between January and July—suggest that blue whales in the Philippines may extend the outer range edge of the Indo-Australian population that migrate between Western Australia, Indonesia, and East Timor (Acebes et al., 2021). Although blue whale sightings in the Bohol Sea coincide with times of high ocean productivity, further investigation is needed to determine if the whales are coming to the region to feed. Similarly, sightings of sperm whales have been uncommon but regular for the last fifteen years with reports from early WWF surveys, surveys carried out from Silliman University and BALYENA.ORG on the north-western Bohol Sea and from sightings of tourists.
Criterion B: Distribution and Abundance
Sub-criterion B2: Aggregations
During 84 surveys conducted by Ponzo and colleagues in the Northern Bohol Sea from 2010 to 2013, the melon-headed whale was the most encountered species 41.8% (n= 121), followed by Fraser’s dolphin and spinner dolphins. This shows similar findings as earlier surveys conducted by Sabater (2005) from 2002-2004 wherein the most frequently sighted species were the spinner dolphins, melon-headed whales and Fraser’s dolphins, and Tiongson and Sabater (2013) from 2010-2012 with the melon-headed whales and Fraser’s dolphins as the two most commonly encountered species. Based on dorsal fin markings, 415 unique individual melon-headed whales have been identified in this area with 59 individuals recaptured across years (from 2010 to 2013) and some individuals photographed in all 4 years, suggesting some degree of residency. Group size ranged from 1 to 70 individuals (median= 20; μ= 21) and on occasions, several groups converge in a 1km area and form mega pod of up to 400 individuals. Encounters with Fraser’s dolphins were in numbers of more than 18 animals and in mixed species group, the most frequent association was with melon-headed whales (Sabater 2005).
Sub-criterion D2: Diversity
The Bohol Sea hosts a diversity of cetaceans, with 19 species confirmed from sightings during survey, strandings or verified reports from tourists. From March 2010 to June 2013, a total of 12 species were encountered in the Bohol Sea (n= 291 sightings) by Ponzo and colleagues, with melon-headed whales was the most encountered species 41.8% (Peponocephala electra, n= 121) followed by Fraser’s dolphin 21.6 % (Lagenodelphis hosei, n= 63), spinner dolphins (Stenella longirostris, n= 41), pantropical spotted dolphins (Stenella attenuata, n= 2), bottlenose dolphins (Tursiops sp., n= 1), short-finned pilot whales (Globicephala macrorhynchus, n= 9), Risso’s dolphin (Grampus griseus, n= 8), dwarf sperm whale (Kogia sima, n= 5), Blainville beaked whales (Mesoplodon densirostris , n= 3), rough-toothed dolphin (Steno bredanensis, n= 1), Bryde’s whale (Balaenoptera edeni, n= 4), blue whale (Balaenoptera musculus, n= 2). Other species were encountered off effort, including pygmy killer whales (Feresa attenuata) and sperm whale (Physeter macrocephalus). Systematic boat surveys conducted by the Institute of Environmental and Marine Sciences, Silliman University between 2010-2012, recorded 11 cetacean species in which, five were seen in mixed-species groups of two or more species (Tiongson & Sabater 2014). Eight species were encountered, in decreasing frequency: melon-headed whale (Peponocephala electra), Fraser’s dolphin (Lagenodelphis hosei), spinner dolphin (Stenella longirostris), Risso’s dolphin (Grampus griseus), Indo-pacific bottlenose dolphin (Tursiops aduncus), dwarf sperm whale (Kogia sima), short-finned pilot whale (Globicephala macrorhynchus), and Pantropical spotted dolphin (Stenella attenuata). Mixed-species encounters were observed to be most frequent between the melon-headed whale and Fraser’s dolphin (i.e. 66% of the time) followed by Fraser’s and Risso’s dolphin mixed-groups.
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