Society Archipelago IMMA

Criterion A – Species or Population Vulnerability

The Megaptera novaeangliae Oceania subpopulation is assessed as Endangered on the IUCN Red List of threatened species.  Models for the recovery of the Oceania sub-populations suggest stocks likely remain below 30% of K and are recovering at a slower rate that other humpback whale populations (Jackson et al. 2007).

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations

Combined demographic and genetic data were used to describe the isolation and interchange of insular spinner dolphins among island communities of the Society Archipelago (Oremus et al. 2007). Dorsal fin photographs for individual identification and biopsy samples for genetic analyses (n = 154) were collected from 6 island communities during 189 small-boat surveys over 3 years. Capture–recapture analyses at Moorea (the primary study site), based on long-term observations of distinctively marked individuals and microsatellite genotypes (12 loci), indicated a local community of about 150 dolphins. This community appeared relatively closed on an intra-generational scale, as confirmed by re-sightings of individuals over 15 years. Surveys around neighbouring islands indicated the presence of similar distinct communities with relatively low levels of interchange, likely to follow demographic patterns similar to Moorea. Overall, significant differentiation at both mitochondrial and nuclear levels indicated restricted gene flow among neighbouring communities, although some individual movement was documented.

At least two small resident populations of rough-toothed dolphins have been described in the IMMA on the basis of photo-ID and genetic data (Oremus et al. 2012, Albertson et al. 2016). Oremus et al. (2012) collected photographs for individual identification (n = 108 unique individuals) and biopsy samples (n = 64) to assess genetic diversity, population structure and abundance of rough-toothed dolphins around Moorea and Raiatea (170 km apart). Genotype (14 microsatellite loci) and photo-identification recaptures over two to 12 years indicated long-term site fidelity around Moorea and a high probability of demographic partitioning between Moorea and Raiatea. There was also a marked genetic differentiation between the two islands for both control region mitochondrial haplotypes (450 base pairs, FST = 0.58, pST = 0.07, p < 0.001), a pattern confirmed by Bayesian clustering analysis. Around Moorea, estimates of abundance and current effective population size support a population size in the low hundreds. These results suggest a pattern of small, resident community structure. Sub-criterion B2: Aggregations

Megaptera novaeangliae – The nearshore waters of the IMMA in the Society Archipelago are critical places where humpback whales aggregate for breeding during the winter months. This habitat is important for all sex- and age-class groups of whales (Poole 2002, Gannier 2004). Gannier (2004) reported that although his survey effort included offshore waters, humpback whales in French Polynesia were mostly (83%) found less than 2 km from the shoreline. Furthermore, the sighting rate for individuals were estimated for inshore waters of different archipelagos from visual data; although the density of humpback whales in the IMMA are not homogenous (different rates between Windward and Leeward Islands), it does include the area of highest relative density in French Polynesia. Toothed whale sightings in the Society Archipelago show an aggregation pattern for these species in nearshore waters (Gannier 2000, Laran et al. 2012).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

Megaptera novaeangliae – The Society islands form critical annual winter calving and mating habitat for humpback whales (Poole 2002, Gannier 2004). The evidence supporting this sub-criterion Ci is undisputed and given the social and behavioural tendency for humpback whales to aggregate, these findings are consistent with other populations.

Criterion D: Special Attributes  

Sub-criterion D1: Distinctiveness

Population structure analysis of spinner dolphins across the Pacific shows that samples from the Society Archipelago IMMA are genetically differentiated from other regions (Baker, unpublished report). Albertson et al. (2016) using the most extensive dataset to date, assessed the isolation and interchange of rough-toothed dolphins at the regional and oceanic scale within the central Pacific Ocean. Using mtDNA and microsatellite genotyping (nDNA), they analyzed samples of insular communities from the main Hawaiian (Kaua‘i n = 93, O‘ahu n = 9, Hawai‘i n = 57), French Polynesian (n = 70) and Samoan (n = 16) archipelagos, and pelagic samples off the Northwestern Hawaiian Islands (n = 18). An overall AMOVA indicated strong genetic differentiation among islands (mtDNA FST = 0.265; p 0.001; nDNA FST = 0.038; p 0.001), as well as among archipelagos (mtDNA FST = 0.299; p 0.001; nDNA FST = 0.055; p 0.001).

Sub-criterion D2: Diversity

A total of 16 cetacean species have been identified in the IMMA indicating a high level of species diversity in this area (Poole 1993, Gannier 2000, Laran et al. 2012).  Several other species of cetacean are confirmed in the area, including dwarf sperm whale, Blainville’s and Cuvier’s beaked whale, melon-headed whale, Fraser’s dolphin, killer whale, short-finned pilot whale, false killer whale, pygmy killer whale, Risso’s dolphin, pantropical spotted dolphin, sperm whale, bottlenose dolphins.