Size in Square Kilometres
Qualifying Species and Criteria
Dugong – Dugong dugon
Criterion A; B (1); C (2)
Australian humpback dolphin – Sousa sahulensis
Criterion A; B (1)
Humpback whale – Megaptera novaeangliae
Criterion C (1)
Marine Mammal Diversity
Tursiops aduncus, Balaenoptera musculus, Orcaella heinsohni, Balaenoptera acutorostrata, Orcinus orca, Eubalaena australis, Balaenoptera omurai,, Balaenoptera physalus, Pseudorca crassidens
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The Pilbara region of Western Australia encompasses a diverse array of marine habitats including coral reef, coastal islands, subterranean karst limestone waterways, extensive mangroves, seagrass beds, high intertidal cyanobacterial mats, macroalgae-dominated reef flats, intertidal sand flats, soft coral and sponge beds. This area has been recognized at a national and international level through designation of State and Commonwealth marine protected areas including Ningaloo Marine Park and Murion Islands Management Area, Barrow Island Marine Park and Montebello Islands Marine Park as well as the Ningaloo Coast World Heritage Area. Ningaloo reef is one of the world’s longest fringing coral reefs and a biodiversity hotspot that includes resident populations of Australian humpback dolphins (Sousa sahulensis) (Hunt et al., 2017), Indo-Pacific bottlenose dolphins (Tursiops aduncus) (Haughey et al., 2020, Hanf 2015, Raudion et al., in review) and dugongs (Dugong dugon) (Bayliss et al 2018, Sobztik et al 2014) and seasonally present humpback whales (Megaptera novaeangliae) (Chittleborough 1953, Jenner et al., 2001, Irvine et al., 2018). The sheltered waters of Exmouth Gulf are an important feeding and nursing/calving habitat for Australian humpback dolphin, dugongs, and Indo-Pacific bottlenose dolphins as well as an important nursery for humpback whales. Key habitat prevalent throughout the region, including coastal waters out to nearshore islands, includes sand flats, seagrass beds, sponge gardens and coral communities. A large variety of marine mammal species have been recorded in this area, some seen regularly such as minke whales, blue whales and false killer whales while others are present seasonally such as killer whales as they follow migrating humpback whales (Pitman et al 2015), and southern right whales, present in very low numbers during their annual migration. Still others are sighted more opportunistically including Omura’s whales (Ottewell et al 2016, Cerchio et al 2019) and snubfin dolphins (Allen et al 2012). The boundary for the IMMA follows the 100m bathymetry contour and aligns with existing marine protected area boundaries for the Commonwealth Ningaloo and Montebello Islands Marine Parks and the Ningaloo World Heritage Area.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
Dugongs and Australian humpback dolphins are both listed as Vulnerable by the IUCN and are resident to the region (Hunt 2018, Hunt et al., 2017, Allen et al., 2012, Hodgson 2007, Sobtzick et al., 2014, Bayliss et al., 2018, Marsh and Sobtzick 2019). Furthermore, this area has been recognized at a national and international level through designation of State and Commonwealth marine protected areas including Ningaloo Marine Park and Murion Islands Management Area, Barrow Island Marine Park and Montebello Islands Marine Park as well as the Ningaloo Coast World Heritage Area.
Criterion B: Distribution and Abundance
Sub-criterion B1: Small and Resident Populations
The coastal waters of the North West Cape and Exmouth Gulf support resident populations of Vulnerable Australian humpback dolphins and Near Threatened Indo-Pacific bottlenose dolphins. Australian humpback dolphins inhabit the area with the highest density recorded for this species around North West Cape, with a population size estimated at 129 individuals within a 130 km2 area (Hunt et al 2017). Haughey et al. (2020) estimated a resident population of 141 (95% CI 121-161) Indo-Pacific bottlenose dolphins at the North West Cape, highlighting the importance of these coastal waters. Resident populations have also been recorded along the Pilbara coast and islands (Hanf 2015, Raudino et al 2018a) though no abundance estimates have been made. There are early indications that the dolphins inhabiting island habitat may be geographically separate from the mainland coastal population (Raudino et al 2018b). In particular high levels of female residency in humpback dolphins (Hunt et al., 2019) suggest that these waters are important for breeding and nursing for this species and dolphin calves were sighted during this study (Hunt 2017). Exmouth Gulf also contains a significant population of Vulnerable dugongs with estimates fluctuating over the years; 1062 (±321) individuals in 1989, 95 (±62) individuals in 2000, 1411 (±561) in 2007 and 4,599 ( 1,959) in 2018 (Preen et al 1997, Prince 2001, Hodgson 2007, RPS 2010, Bayliss et al 2019). Variation in dugong abundance and use of the Exmouth Gulf is likely a result of the seagrass loss following tropical cyclones and marine heatwaves and movement of dugongs to areas supporting seagrass (Bayliss et al 2019, Gales et al 2004). Aerial surveys of dugongs between 1989 and 2018 consistently identify the nearshore eastern waters of the Gulf as critical feeding and nursing habitat (Preen et al 1997, Bayliss et al 2019). Local-scale drone surveys coupled with in-situ assessments of the benthic habitat have shown that seagrass, particularly Halophila and Halodule species, are significant factors influencing dugong presence in south-eastern Exmouth Gulf (Christophe Cleguer pers comm).
Criterion C: Key Life Cycle Activities
Sub-criterion C1: Reproductive Areas
The sheltered waters of Exmouth Gulf have been suggested to have contributed to the recovery of the Breeding Stock D humpback whale population. The Gulf is the largest known resting area for this population, initially from 1950’s whaling data (Chittleborough, 1953) and more recently from boat-based and aerial surveys that report resting behaviour occurring from a few hours to a few weeks (Jenner et al., 2001, Jenner and Jenner 2005, Braithwaite et al., 2012, Irvine and Salgado Kent 2019), where mothers and calves can spend up to 3 weeks (Jenner & Jenner, 2005) resting and gaining size and strength. In addition, the area represents a southward extension of the breeding grounds for calving and mating (Irvine et al., 2018).
Sub-criterion C2: Feeding Areas
The seagrass habitat of Exmouth Gulf is an important feeding ground for dugongs. Aerial surveys of dugongs between 1989 and 2018 consistently identify the nearshore eastern waters of the Gulf, Pilbara coastal waters and nearshore Pilbara islands as critical feeding and nursing habitat (Sobztick et al 2014, RPS 2010). Local-scale drone surveys coupled with in-situ assessments of the benthic habitat have shown that seagrass species such as Halophila and Halodule are good predictors of dugong presence and abundance in the south-east Gulf (Christophe Cleguer pers. comm.). Variation in dugong abundance and use of Exmouth Gulf and the broader Pilbara Region is likely a result of the seagrass loss following tropical cyclones and marine heatwaves and movement of dugongs to areas supporting seagrass (Gales et al 2004, Sobztick et al 2014). Safeguarding the seagrass in the Gulf will protect a feeding ground and allow dugongs to migrate from alternative feeding grounds when required.
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