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ISRA FACTSHEETS

AUSTRALIA AND SOUTHEAST INDIAN OCEAN

ISRA FACTSHEETS

AUSTRALIA AND SOUTHEAST INDIAN OCEAN

Agincourt Reef No. 3 ISRA

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Agincourt Reef No. 3 ISRA

Agincourt Reef No. 3

Summary

Agincourt Reef No. 3 is located on the Great Barrier Reef, ~40 km off Cape Tribulation, Queensland, Australia. The area is characterised by a reef lagoon on the leeward side of the reef, with rubble substrate and a complex coral community. The area is influenced by severe weather systems and cyclones but is sheltered from wind and wave activity. The area overlaps with the Great Barrier Reef Marine Park. Within this area there are: threatened species and undefined aggregations (Grey Reef Shark Carcharhinus amblyrhynchos).

Agincourt Reef No. 3

Agincourt Reef No. 3

DESCRIPTION OF HABITAT

Agincourt Reef No. 3 is located on the Great Barrier Reef, ~40 km off Cape Tribulation, Queensland, Australia. It encompasses the northwestern portion of Agincourt Reef No. 3, located at the southernmost end of the ribbon reefs along the outer edge of Australia’s continental shelf. The area is characterised by a reef lagoon on the leeward side of the reef, with rubble substrates and a complex coral community of branching Acropora spp., large Porites spp., and Montipora spp. colonies (Cook et al. 2023).

The area is influenced by severe weather systems and cyclones but is sheltered from wind and wave activity (Cook et al. 2023). During the austral summer monsoon (November–February), productivity is enhanced in the area due to upwelling events on the outer shelf (Wolanski & Hammer 1988).

Agincourt Reef No. 3 overlaps with the Great Barrier Reef Marine Park – Marine National Park Zone (UNEP-WCMC & IUCN 2025).

This Important Shark and Ray Area is benthic and pelagic and is delineated from 0–30 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 Endangered Grey Reef Shark (Simpfendorfer et al. 2020).

CRITERION C

SUB-CRITERION C5 – UNDEFINED AGGREGATIONS

Agincourt Reef No. 3 is an important aggregation area for one shark species.

Adult female Grey Reef Sharks aggregate seasonally in the area. Observations were collected by snorkel guides working in the area year-round between 2022–2025, with in-water observations lasting up to two hours daily (H Platt pers. obs. 2025). In 2022, 2024, and 2025, aggregations of up to 10 adults, larger than 150 cm total length (TL), visually estimated, were observed daily during a two-week period in early July each year (H Platt pers. obs. 2025). Size-at-maturity ranges between 120–145 cm TL (Ebert et al. 2021). Seasonal aggregations were typically observed swimming in line formations or semi-tight groups of 4–10 individuals, composed mainly of females, many of which had relatively fresh mating scars on their bodies (H Platt pers. obs. 2025). Additionally, observations of solitary juveniles (~100 cm TL) were common in the area during the same season when aggregations occurred (H Platt pers. obs. 2025). Grey Reef Shark females may display a higher residency and a different habitat use than adult males at certain reefs within the Great Barrier Reef (Espinoza et al. 2015). Further information is required to understand the nature and function of these aggregations.

Agincourt Reef No. 3

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