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ISRA FACTSHEETS

AUSTRALIA AND SOUTHEAST INDIAN OCEAN

ISRA FACTSHEETS

AUSTRALIA AND SOUTHEAST INDIAN OCEAN

Huon Seamounts ISRA

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Huon Seamounts ISRA

Huon Seamounts

Summary

Huon Seamounts is located on the continental slope south of Tasmania, Australia. This cluster of three deep seamounts (Hill K1, Hill U, and z16) is characterised by live hard corals, coral rubble, and rocky and sandy substrates. This area overlaps with the Huon Marine Park. Within this area there are: reproductive areas (Arctic Skate Amblyraja hyperborea).

Huon Seamounts

Huon Seamounts

DESCRIPTION OF HABITAT

Huon Seamounts is located south of Tasmania, Australia. It is part of a deepsea seamount chain extending along the continental slope off Tasmania and includes three seamounts each separated by ~10 km: Hill K1, Hill U, and z16. The area is characterised by live hard corals (the stony coral Solenosmilia variabilis) around the top of the seamount and coral rubble and rocky and sandy substrates around the edge of the seamounts (Maguire et al. 2023). Mean annual bottom temperature is ~3.94°C (Maguire et al. 2023).

This area partially overlaps with the Huon Marine Park (Parks Australia 2025).

This Important Shark and Ray Area is benthic and subsurface and is delineated from 890–2,100 m based on the bathymetry of the area.

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Huon Seamounts is an important reproductive area for one ray species.

During November–December 2018, 99 transects (2 km in length) using a towed camera platform were conducted across seamounts (n = 35) and the continental slope off Tasmania at depths of ~500–1,900 m (Maguire et al. 2023). Stereo-still images were taken every five seconds resulting in 50,928 paired images of which 240 (0.5%) showed skate egg cases.

Within the area, 8,235 images were recorded, of which 187 (2.3%) had egg cases with a maximum of five egg cases counted in a single image. After z110 Seamount (located outside this area), Huon Seamounts held the single seamounts with the largest number of egg cases (n = 190) recorded across all the seamounts surveyed, with the majority being associated with the stony coral Solenosmilia variabilis (Maguire et al. 2023). Of the 113 egg cases identified to species level, more than half (n = 63, 55.8%) were recorded in this area. Of these, 35 (55.6%) were from Arctic Skates (Maguire et al. 2023). Records of egg cases in this area included ‘recently laid’ eggs (n = 66, 34.7%), which are those which have not darkened and had a partially/completely golden colour, and ‘aged’ egg cases, which are darkened egg cases that have been in the substrate long enough to be degraded. Despite only one year of survey data, the presence of both types of egg cases confirms that this area is regularly used by this species to lay eggs (Maguire et al. 2023). These three seamounts were proposed as potential nursery areas for Arctic Skate due to the large number (>40 per seamount) and densities (>0.24 egg cases/m2) of egg cases. Deposition of egg cases among living corals around seamount peaks may provide energetic advantages due to the higher water flow in these areas (Maguire et al. 2023).

Huon Seamounts

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