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ISRA FACTSHEETS

AUSTRALIA AND SOUTHEAST INDIAN OCEAN

ISRA FACTSHEETS

AUSTRALIA AND SOUTHEAST INDIAN OCEAN

Amphitheatre Caves ISRA

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Amphitheatre Caves ISRA

Amphitheatre Caves

Summary

Amphitheatre Caves is located in western Shark Bay, Western Australia, Australia. This area is situated off Steep Point in South Passage which is the westernmost point of mainland Australia. It encompasses multiple limestone caves and crevasses. This area overlaps with Shark Bay Marine Park. Within this area there are: threatened species and resting areas (Sand Tiger Shark Carcharias taurus).

Amphitheatre Caves

Amphitheatre Caves

DESCRIPTION OF HABITAT

Amphitheatre Caves is located in western Shark Bay, Western Australia, Australia. This area sits off Steep Point in South Passage which is the westernmost point of mainland Australia. South Passage is a deep, narrow, high-energy channel bordered by rugged limestone cliffs and rocky shores with a benthic sediment composed of turf rubble (Sutton & Shaw 2020). It serves as one of the main conduits for oceanic water exchange between the open Indian Ocean and the semi-enclosed Shark Bay (Sutton & Shaw 2020). This area encompasses multiple limestone caves and crevasses in a site known by recreational divers as Amphitheatre and Purple Rain (Shark Bay Eco Tours unpubl. data 2016–2024; E Gosden pers. obs. 2025).

This area has a semi-arid climate characterised by two main seasons: warm to hot summers (October–March) and mild winters (April–September). The bay’s waters are warmer than adjacent oceanic waters in summer and cooler in winter (Nahas et al. 2005). Average sea surface temperatures are higher in summer (mean = 24.6 ± 1.0°C) than in winter (mean = 20.8 ± 1.7°C). Water circulation is influenced by the Leeuwin Current, which brings warm, low-salinity tropical water southward, mixing with the bay’s hypersaline inner waters.

This area overlaps with Shark Bay Marine Park (WA DBCA 2025).

This Important Shark and Ray Area is benthic and pelagic and is delineated from inshore and surface waters (0 m) to 22 m based on the bathymetry of the area.

CRITERION A

VULNERABILITY

One Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occurs in the area. This is the Critically Endangered Sand Tiger Shark (Rigby et al. 2025).

CRITERION C

SUB-CRITERION C3 – RESTING AREAS

Amphitheatre Caves is an important resting area for one shark species.

Between late September and mid-November from 2016–2024, dives were regularly conducted once a week within the area. Sand Tiger Sharks were observed on ~90% of the dives with an average of three animals observed per dive (range, 1–8 individuals) generally resting in caves (Shark Bay Eco Tours unpubl. data 2016–2024; E Gosden pers. obs. 2025). During this period, individuals observed were mainly mature females with body sizes visually estimated at 220–320 cm total length (TL).  Size-at-maturity for this species is 220–230 cm TL for females (Ebert et al. 2021). Between late October and mid-November, more than half of the females recorded were either visibly pregnant (determined from their distended abdomens) or with relatively fresh mating scars. At the beginning of the season (late September), few females show scars, but their prevalence increases as the season progresses (mid-November). Adult male sharks were rarely observed with a proportion of one out of 10 individuals. This area might function as a reproductive area where females in early pregnancy rest after mating.

Compared to eastern Australia, critical habitat for Sand Tiger Sharks has been poorly studied in western Australia, with most known aggregations occurring near Perth (Hoschke et al. 2023). This area represents the only naturally occurring, regularly used aggregation site for the species in central and northern Western Australia.

Amphitheatre Caves

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