Bigfin Reef Squid in Mauritius (Sepioteuthis lessoniana)

The bigfin reef squid, known in French as the Calmar de récif and scientifically as Sepioteuthis lessoniana, is one of the most visually striking cephalopods found in Indo-Pacific waters. In Mauritius, this species is a common sight along reef edges, in sandy lagoons, and in the open water just beyond the fringing reef. Divers and snorkellers alike are regularly treated to breathtaking displays of bioluminescent-like skin patterns and effortless jet-propelled movement.

Identification & Physical Features

What makes the bigfin reef squid immediately recognisable is its unusually large, oval-shaped fin that runs almost the entire length of its mantle — a feature that gives the species its common name. Unlike many squid whose fins occupy only part of the body, Sepioteuthis lessoniana uses these broad fins to hover, manoeuvre and make subtle positional adjustments with remarkable precision.

Adults typically reach a mantle length of 20 to 33 cm, though some individuals can grow larger. Their skin is equipped with thousands of chromatophores — pigment cells that allow them to produce rapid, flowing waves of colour ranging from translucent white and gold through to deep amber and iridescent blue-green. This chromatic display is used for communication, camouflage, and attracting mates.

Behaviour & Ecology

Bigfin reef squid are highly social animals, often observed in loose schools or small groups hovering near reef structures or drifting above seagrass beds. They are active predators, feeding primarily on small fish, crustaceans, and other invertebrates. Hunting typically intensifies at dusk and dawn, when they use their stealth, speed, and camouflage to ambush prey.

One of the most fascinating aspects of their behaviour is their communication system. Groups engage in complex visual signalling, with individuals displaying different patterns on each side of their body simultaneously — a feat that hints at a surprisingly advanced nervous system. During mating seasons, males engage in elaborate courtship displays, and egg clusters can sometimes be spotted attached to coral rubble or rocky substrates on the reef.

Snorkelling & Diving with Bigfin Reef Squid in Mauritius

In Mauritius, encountering bigfin reef squid is relatively straightforward due to their abundance and tendency to hold their position when approached slowly and calmly. They are curious but cautious — a diver who moves deliberately and avoids sudden gestures can often get within a metre or two, observing their colour changes up close.

The best encounters typically occur during early morning or late afternoon dives, when squid are most active near the reef edge. Night snorkelling and night diving also offer exceptional sightings, as squid are drawn to light and become particularly active after dark. Sites around the west and north coasts of Mauritius, where water clarity is high and reef health is good, consistently produce sightings.

Role in the Reef Ecosystem

As both predator and prey, bigfin reef squid play an important role in the reef food web. They are a key food source for larger reef fish, dolphins, and seabirds. Their short lifespan — typically under one year — means populations turn over rapidly, making them sensitive indicators of reef and water quality. In Mauritius, healthy squid populations are a positive sign of a functioning reef ecosystem.

Photography Tips

Bigfin reef squid make exceptional underwater photography subjects thanks to their size, their habit of holding position, and their dramatic colour displays. Use a wide-angle or macro lens depending on how close you can approach. Shoot during the golden hours of early morning or late afternoon for the best natural light, and be patient — the longer you hover quietly, the more relaxed and expressive the squid will become.