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Blue triggerfish with maze-like yellow markings hovering over pale coral rubble — Nosy Be

Nosy Be · Madagascar · Seamount · Reef · Pelagic & blue water

Banc du Petit Castor

A 500 m dome where grey reef and leopard sharks patrol the slopes

Area photo: Diego Delso · CC BY-SA 4.0

Banc du Petit Castor is a bank in the Mitsio Archipelago that forms a dome about 500 m across, its top at 9 m and its flanks falling to 60 m. Giant sea fans, crevices and cavities cover the deeper slopes. Divers make the trip for sharks and passing pelagics on a reef that sees few boats.

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Where it is and how deep

Depth profile of Banc du Petit Castor: typical dive 9–60 m (30–197 ft) 18 m · Open Water30 m · Advanced40 m · Recreational limit9 m60 mtypical dive
Depths on a shared scale to 70 m (230 ft); dashed lines mark common certification limits.

No published position for this site — the map shows Nosy Be and its other sites; operators know the mooring.

The dive

The bank rises as a broad dome, 500 m in diameter, with its crest at 9 m and its sides falling away to 60 m. Deeper down, the slope opens into crevices and cavities among giant sea fans and good coral.

Along the drop-off, jacks and tuna pass in the open water, and whitetip, grey reef and leopard sharks are regular sightings. Manta rays appear on some dives.

Marine life and season

  • Reef sharks
  • Trevally & jacks
  • Tuna
  • Manta rays
Month-by-month season rating for Banc du Petit Castor
JanFebMarAprMayJunJulAugSepOctNovDec
Off-seasonOff-seasonFairGoodGoodGoodGoodGoodGoodPrimePrimeGood

Season follows Nosy Be: Cyclone season (Jan-Mar) shuts down most diving; whale sharks aggregate Oct-Dec and humpback whales pass offshore during the austral winter.

Sources

  1. Mitsio Archipelago - Diving Cattitude — Diving Cattitude

More dive sites in Nosy Be

Reef

Banc d'Ankaréa

Coral plateau with fusilier shoals, turtles and passing grey sharks

12–25 mintermediate

Wall

Four Brothers

Sheer walls where barracuda, mobulas and whitetips pass

0–30 mintermediate

Wall

Gaby Rock

A deep drop-off off Nosy Iranja with a fair chance of big fish

40–70 madvanced

Wall

Greg's Wall

A tunnel and arches cut through a gorgonian wall below 30 m

13–38 m · max 70 madvanced

Reef

Kassimo

A long soft-coral reef thick with reef fish, kept for the third dive

5–15 mintermediate

Pinnacle

Les Tétons

Two rock peaks breaking the surface, cut through with arches and caves

5–20 mintermediate

Artificial reef

Mahaveluma

A scuttled trawler at 28.5 m off Nosy Sakatia

to 28.5 madvanced

Reef

South Canyon

Leopard, grey and whitetip sharks on a hand-shaped reef

to 26 madvanced

Similar dives elsewhere

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Blue soft corals and dense fish life on a swim-through thila

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Three coral blocks from 10 m, the biggest 80–100 m long

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The park's only offshore seamount, 8 m to 60 m

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An isolated seamount that pulls in barracuda and trevally schools

20–27 madvanced