Tañon Strait IMMA

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations

Data on Indo-Pacific bottlenose dolphins presented in Tiongson and Karczmarski (2016) meets the criterion for Criterion B2. In this study, photo-ID data were obtained during 50 encounters between 2014-2015. Individual sighting frequencies ranged from one (n = 21) to ten (n = 1), with the majority of the 121 catalogued individuals (82 %, n = 99) seen more than once. Group sizes ranged from a solitary individual to ~60 dolphins, with a mean of 11 and median of 10 dolphins per group (±10.5 SD). Groups frequently consisted of all age classes, including calves and neonates, although adult-only groups were also seen. Inter- and intra- annual photographic recaptures of Indo-Pacific bottlenose dolphins are reported in the poster presented by Tiongson and Karczmarski at the Society for Marine Mammalogy Conference in 2015. Their data illustrate the site fidelity of this small population.

Criterion C: Key Life Cycle Activities

Sub-criterion C2: Feeding Areas

The IMMA is likely to be a foraging ground for spinner dolphins because it is an important and highly productive area (Tañon Strait – Commission report). Although direct evidence of feeding areas of spinner dolphins are difficult to quantify, indirect evidence from interviews of fisherfolk and uncommon direct observations of daytime foraging activity suggest a likely probability that spinner dolphin foraging areas lie within the strait and perhaps in deeper locations where the mesopelagic layer is likely to occur. Foraging areas of Indo-Pacific bottlenose dolphins have also been identified using kernel density estimation and local convex hull analysis of observed foraging behaviour (Tiongson and Karczmarski, 2017).

Sub-criterion C3: Migration Areas

The Tañon Strait has been assessed as an important area for the resting of spinner dolphins (Stenella longirostris) described in Tiongson and Karczmarski (2017). Resting represented the predominant daytime behaviour for spinner dolphins. Nearly half (48%) of their overall core area function as the core resting area.  Dolphins need to move safely between their resting and foraging areas. A population of approx. 3500 spinner dolphins was estimated in the Strait (Dolar et al. 2006).

Criterion D: Special Attributes  

Sub-criterion D2: Diversity

The Tañon strait hosts a high diversity of odontocetes, with 8 species reported in the latest work from Karczmarski and Tiongson (2016). This included Indo-Pacific bottlenose dolphin (Tursiops aduncus), spinner dolphins (Stenella longirostris longirostris), Risso’s dolphin (Grampus griseus), short-finned pilot whale (Globicephala macrorhynchus), dwarf sperm whale (Kogia sima), melon-headed whale (Peponocephala electra), False killer whale (Pseudorca crassidens) and pantropical spotted dolphin (Stenella attenuata).  From previous studies (Leatherwood et al. 1992, Dolar and Wood 1993, Bautista et al. 2003, Aragones et al. 2010) four additional species were reported, Tursiops truncatus, Lagenodelphis hosei, Feresa attenuata, and Mesoplodon sp. but these have not been sighted during the recent surveys. Survey from Dolar et al. (2006) in the Tañon Strait reported a high abundance of dwarf sperm whale (Kogia sima), the second most abundant species encountered during their study with 27 encounters and an estimated density of 48 schools 1000 km^-1. The most common species was the spinner dolphin with 52 encounters and an estimated density of 117.5 schools per 1000 km surveyed.