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ISRA FACTSHEETS

ASIA REGION

ISRA FACTSHEETS

ASIA REGION

Dampier Strait ISRA

109/122

Dampier Strait ISRA

Dampier Strait

Summary

Dampier Strait is located in West Papua, Indonesia. The area is situated in the Raja Ampat archipelago and composed of several islands, bays, and the strait that separates Waigeo from Batanta Island. The area has an extended shelf characterised by the presence of coral reefs. This area overlaps with the Raja Ampat and Northern Bird’s Head Ecologically or Biologically Significant Marine Area, Waigeo Barat Key Biodiversity Area, and one marine protected area. Within this area there are: threatened species (e.g., Snaggletooth Shark Hemipristis elongata); range-restricted species (e.g., Spotted-belly Catshark Atelomycterus erdmanni); reproductive areas (e.g., Blacktip Reef Shark Carcharhinus melanopterus); feeding areas (e.g., Reef Manta Ray Mobula alfredi); undefined aggregations (e.g., Oceanic Manta Ray Mobula birostris); and the area sustains a high diversity of sharks (32 species).

Dampier Strait

Dampier Strait

DESCRIPTION OF HABITAT

Dampier Strait is located in West Papua, Indonesia and is part of the Raja Ampat archipelago. It sits within the Bird’s Head Seascape and includes several islands (including the southern side of Gam), bays, and the strait that separates Waigeo, the largest island in the area, from Batanta Island (Allen & Erdmann 2009, 2024; Veron et al. 2009; Mangubhai et al. 2012). The area has an extended shelf characterised by the presence of coral reefs, mangroves, and seagrass beds.

Dampier Strait is strongly influenced by monsoon seasons. The northwest monsoon occurring from November to April is characterised by warm sea surface temperatures. In contrast, the southeast monsoon (May to October) is characterised by strong and continuous southeast winds that produce upwellings, resulting in an increase in primary productivity in coastal areas (Mangubhai et al. 2012).

The area overlaps with the Raja Ampat and Northern Bird’s Head Ecologically or Biologically Significant Marine Area (EBSA; CBD 2024) and with Waigeo Barat Key Biodiversity Area (KBA 2024). In addition, it overlaps with the Taman Wisata Perairan Kepulauan Raja Ampat marine protected area.

This Important Shark and Ray Area is benthopelagic and is delineated from inshore and surface waters (0 m) to 100 m based on the bathymetry of the area.

CRITERION A

VULNERABILITY

Thirty Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occur in the area. Threatened sharks comprise one Critically Endangered species, four Endangered species, and eight Vulnerable species; threatened rays comprise four Critically Endangered species, nine Endangered species, and four Vulnerable species (IUCN 2024).

CRITERION B

RANGE RESTRICTED

Dampier Strait holds the regular presence of Raja Ampat Epaulette Shark and Spotted-belly Catshark as resident range-restricted species. These species occur year-round in the area and are regularly encountered during underwater visual census and reported by local artisanal fishers (based upon observations and data from 2001–2023).

Raja Ampat Epaulette Shark has been reported continuously in the area between 2001–2023 based on underwater visual census, dive operator surveys, and artisanal fisher interviews and is found predominantly on shallow reef flats with seagrass beds and scattered coral bommies, though it is also found in mangroves and on coral reefs (Allen et al. 2016). Though the species is found throughout Raja Ampat, Dampier Strait holds an exceptionally high abundance of Raja Ampat Epaulette Shark due to the well-developed reef flats typical in this area, particularly around Gam, Arborek, Mansuar, Saonek, Kri, and the Fam Islands (E Setyawan pers. obs. 2023; Konservasi Indonesia unpubl. data 2021). Previously, estimated abundances in Raja Ampat were ~200 individuals/km2 across Raja Ampat (VanderWright et al. 2021), but recent surveys in 2023–2024 in Dampier Strait have revealed abundances of 1,030–2,340 individuals/km2, which is 5–10 times higher than the average abundance in Raja Ampat (Elasmobranch Project Indonesia unpubl. data 2023; Konservasi Indonesia unpubl. data 2024).

Spotted-belly Catshark has been regularly reported in the area between 2001–2023 based on underwater visual census, dive operator surveys, and artisanal fisher interviews, and is found on shallow reefs in Dampier Strait. This species has been observed four times in the past five years based upon a total of seven 1-hr night dive surveys (M Erdmann unpubl. data 2024). It has also been reported by artisanal fishers from 13 of 15 villages surveyed in Dampier Strait in 2018 (M Erdmann unpubl. data 2018).

These two species are restricted to the Indonesian Seas Large Marine Ecosystem.

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Dampier Strait is an important reproductive area for two shark and one ray species.

At the Papua Diving Resorts at Cape Kri in the central Dampier Strait, the regular presence of aggregations of ~20 (50 maximum) neonate/young-of-the-year (YOY) and juvenile Blacktip Reef Sharks (based on their small size) has been observed since 1995 on the reef flat year-round (M Ammer pers. comm. 2024). In addition, these sharks are also observed in Sorido Bay in Kri Island where pregnant females are regularly observed (M Erdmann per. obs. 2023). All seven of the major dive resorts operating in Dampier Strait also report continuous year-round presence of 10–50 neonate and juvenile Blacktip Reef Sharks under their jetties and around their water bungalows on sandy substrates or near coral reefs and seagrass beds (M Erdmann unpubl. data 2024).

Dampier Strait is an important mating and egg-laying area for Raja Ampat Epaulette Shark. Mating is observed regularly by dive operators in shallow seagrass beds at night (M Ammer pers. comm. 2023), and targeted surveys in 2015 and 2023 recorded neonates and juveniles on all 10 reef sites surveyed (M Erdmann unpubl. data 2015; Elasmobranch Project Indonesia unpubl. data 2023). Though the home range of individuals has not yet been formally investigated, it seems that all nine species of epaulette sharks have limited home ranges and likely mate and lay eggs on the same reefs where they hatched (Allen et al. 2016; M Erdmann pers. obs. 2002–2024). Preliminary results from an ongoing acoustic tagging study of Raja Ampat Epaulette Sharks seem to support this as tagged individuals have remained on the same reef flat for the three-month period between January and March 2024 (E Setyawan unpubl. data 2024).

Long-term monitoring of the Reef Manta Ray population in the area documented 71 pregnant females from 2004 to 2019 based on the presence of extended abdomens (Setyawan et al. 2020, 2022). One of the females was observed with four consecutive pregnancies between 2013–2016, and five pregnancies in seven years. In addition, 15 females presented at least two consecutive-year pregnancies. Other females were observed with recent mating scars (Setyawan et al. 2020). Courtship behaviour (mating trains) has also been reported in the area between November–March with a peak in January and February (Setyawan et al. 2020). Potential Reef Manta Ray nursery areas have been identified in two sites in Dampier Strait: Hol Gam lagoon and Fam Islands. One to three YOY were observed in Hol Gam lagoon in 2005 during three different trips (E Setyawan pers. obs. 2024). YOY were defined as individuals <200 cm disc width (DW) as previously reported for other sites in Indonesia (Germanov et al. 2019) which is close to the known size-at-birth for this species (130–150 cm DW; Last et al. 2016).  Between 2008–2018, 14 YOY (160–200 cm DW) were observed in Hol Gam lagoon based on aerial surveys, underwater visual census, and video footage from underwater cameras (Setyawan et al. 2020). Some of these individuals were recorded repeatedly in the lagoon and moving back and forth to feeding areas and cleaning stations in the area (Setyawan et al. 2020). For Fam Islands, 40 YOY (160–200 cm DW) were identified in reef areas between 2016–2019 with these small individuals observed in all the surveys during that period (Setyawan et al. 2020). These YOY represented 32% of individuals identified in Fam Islands. In addition, 42 juveniles (210–240 cm DW) were also identified. YOY and juvenile Reef Manta Rays represented ~60% of the total number of individuals identified in Dampier Strait (Setyawan et al. unpubl. data. 2023).

CRITERION C

SUB-CRITERION C2 – FEEDING AREAS

Dampier Strait is an important feeding area for two ray species.

Aggregations of Reef Manta Rays were regularly documented feeding on the surface between 2004–2019 (Setyawan et al. 2020). These feeding aggregations were commonly composed of 25–50 individuals with a larger aggregation of 112 individuals recorded on one occasion (Setyawan et al. 2020). Feeding aggregations occur from December to March at five sites around Arborek (Manta Ridge, Irwor Inbekya, Mambarayup, Hol Gam, and Arborek Island) while in Fam Islands (Andau Besar, Andau Kecil, Meos Ba, Meoskor, Fam, and Nafsi) they occur year-round with a peak between June–October (Setyawan et al. 2020). This seasonality is related to upwelling events produced by seasonal monsoons that increase primary productivity in the waters of Dampier Strait (Setyawan et al. 2018).

Feeding aggregations of Oceanic Manta Rays (10–15 individuals) were regularly observed around Arborek Island between 2019–2022, mostly in February and March, and frequently in association with feeding Omura’s Whales Balaenoptera omurai (M Izuan pers. comm. 2022). Additionally, feeding aggregations of Oceanic Manta Rays (10–20 individuals) have been regularly observed around Batanta Island from 2015–2023, generally during December–April (M Erdmann pers. obs. 2015–2023). For both aggregations observed at Arborek and Batanta islands, Oceanic Manta Rays feed on dense patches of ‘krill’ (not identified to species, but larger, pink-colored crustacean zooplankton measuring 5–10 mm TL) that are abundant during the northwest monsoon (M Erdmann pers. obs. 2015–2023).

CRITERION C

SUB-CRITERION C5 – UNDEFINED AGGREGATIONS

Dampier Strait is an important area for undefined aggregations of two ray species.

Regular monitoring between 2011–2022 in Dampier Strait revealed that this area hosts eight cleaning stations for Reef Manta Rays and three for Oceanic Manta Rays. Within the Dampier Strait, aggregations of both species can be found at cleaning stations year-round, with a peak from December to March (Setyawan et al. 2020). The majority of the cleaning stations also serve as feeding sites and both species constantly switch between cleaning and feeding. For Reef Manta Rays, 515 individuals have been identified (Setyawan et al. 2022). Aggregations range from 3 to 30 individuals and are found at depths of 5–15 m (E Setyawan pers. obs. 2020). For Oceanic Manta Rays, aggregations range from 3 to 15 individuals and are found at depths of 15–20 m (E Setyawan pers. obs. 2020).

CRITERION D

SUB-CRITERION D2 – DIVERSITY

Dampier Strait sustains a high diversity of Qualifying Species (32 species). This exceeds the regional diversity threshold (31 species) for the Asia Region. The regular presence of Qualifying Species has been documented by frequent observations in diving operations and visual census by scientists and through citizen science (Allen & Erdmann 2009, 2024; M Erdmann et al. unpubl. data 2002–2024).

Dampier Strait

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