true

ISRA FACTSHEETS

NEW ZEALAND & PACIFIC ISLANDS REGION

ISRA FACTSHEETS

NEW ZEALAND & PACIFIC ISLANDS REGION

Tinian Grotto & Valhalla Caves ISRA

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Tinian Grotto & Valhalla Caves ISRA

Tinian Grotto & Valhalla Caves

Summary

Tinian Grotto & Valhalla Caves is located on the western side of Tinian Island in the northwestern Pacific Ocean. This area is situated in the Commonwealth of the Northern Mariana Islands, a self-governing commonwealth in association with the United States of America. This area is characterised by sinkholes, caves, and subterranean passages. Within this area there are:  threatened species and reproductive areas (Whitetip Reef Shark Triaenodon obesus).

Tinian Grotto & Valhalla Caves

Tinian Grotto & Valhalla Caves

DESCRIPTION OF HABITAT

Tinian Grotto & Valhalla Caves is located on the western side of Tinian Island in the northwestern Pacific Ocean. This area is situated in the Commonwealth of the Northern Mariana Islands, a self-governing commonwealth in association with the United States of America.

The island of Tinian and Tatsumi Reef are adjacent volcanic structures that are mostly overlain by uplifted carbonate rock (Brainard et al. 2012). Much of the limestone on Tinian is covered by thin to moderately thick soils, but some limestone areas exhibit karst topography, which is formed by dissolution of carbonate rocks and characterised by sinkholes, caves, and subterranean passages (Brainard et al. 2012). There are two known dives sites within the area. ‘Tinian Grotto’ is found in a large sinkhole that connects to the ocean through several subterranean passages (Brainard et al. 2012). ‘Tinian Grotto’ starts at the surface and reaches a maximum depth of 22 m. The deeper ‘Valhalla Caves’ site has a depth between 25–55 m. These two caves are 32 m away.

This Important Shark and Ray Area is benthopelagic and is delineated from inshore and surface waters (0 m) to 60 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 Vulnerable Whitetip Reef Shark (Simpfendorfer et al. 2020).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Tinian Grotto & Valhalla Caves is an important reproductive area for one shark species.

Between 2019–2021, recreational divers visited Tinian Grotto regularly (~3/month) year-around and frequently observed aggregations of up to five neonate and young-of-the-year (YOY) Whitetip Reef Sharks (J Wolfe pers. obs. 2019–2024). Sharks observed in the caves were visually estimated to measure ~40–50 cm total length (TL), with the largest individuals observed measuring up to ~120 cm TL. The size-at-birth for the Whitetip Reef Shark is 52–60 cm TL (Ebert et al. 2021). Neonates and YOY were present in the area year-round with no life-stage seasonality observed. Recreational divers that frequently visit the Tinian Grotto have observed multiple life stages of Whitetip Reef Sharks in this area (J Wolfe pers. obs. 2019–2024). Since 2021, neonates and YOY Whitetip Reef Sharks have been less frequently observed in Tinian Grotto, probably due to increased dive activity. Generally, YOY Whitetip Reef Sharks have been frequently reported from the deeper caves in the area at the site known as ‘Valhalla Caves’, with aggregations of up to three individuals. Divers suggest that sharks have moved to this deeper cavern, as this area is less frequently visited (J Wolfe pers. obs. 2019–2024).

Tinian Grotto & Valhalla Caves

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