Trincomalee in July: The East Coast Season

Spinner Dolphin Common

Stenella longirostris

A small, slender dolphin that leaps clear of the sea and spins like a top in mid-air.

Where: Offshore on the run out to the whale grounds. Best: May to September.

Blue Whale Occasional Endangered

Balaenoptera musculus

The largest animal that has ever lived, and off Sri Lanka a population that mostly does not migrate, which is why it can be seen almost year round.

Where: Deep water off the east coast. Best: May-Sep. The mirror season to Mirissa, and far fewer boats.

Sperm Whale Occasional Vulnerable

Physeter macrocephalus

The deepest diving mammal on earth, hunting squid two kilometres down, and occasionally gathering off Sri Lanka in pods of hundreds.

Where: Deep water off the east coast. Best: May-Sep. The best chance in Sri Lankan water, and the reason the east coast season is worth the journey.

Black-naped Tern Regular

Sterna sumatrana

Almost pure white apart from a narrow black band across the back of the head, like a headphone cable.

Where: Roosting on Pigeon Island itself, which is a seabird sanctuary as well as a reef. Best: May to September. The island is named for the rock pigeons that breed on it.

Bridled Tern Occasional

Onychoprion anaethetus

Spends most of the year entirely at sea, feeding on fish driven to the surface by tuna hunting below.

Where: Offshore water and the islet itself. Best: May to September.

Green Sea Turtle Regular

Chelonia mydas

The great grazing turtle of the tropics, the only sea turtle that turns vegetarian as an adult.

Where: Shallow reef and seagrass at Pigeon Island and Nilaveli. Best: May to September.

Hawksbill Turtle Regular Critically Endangered

Eretmochelys imbricata

The reef's sponge specialist, its beautiful shell also the reason it was hunted to the edge.

Where: Reef at Pigeon Island and off Nilaveli. Best: May to September. The single best place in Sri Lanka to see one.

Beaked Sea Snake Rare

Hydrophis schistosus

Drop for drop, one of the most venomous snakes in the sea, and it is responsible for most sea snake bites in Asia.

Where: Shallow coastal water and harbour approaches. Best: May to September.

Loggerhead Turtle Rare Vulnerable

Caretta caretta

Jaws powerful enough to crush a queen conch, and it navigates ocean basins by reading the earth's magnetic field.

Where: Coastal water and reef edges, usually juveniles. Best: May to September.

Bluestripe Snapper Common

Lutjanus kasmira

A bright yellow snapper ruled with electric-blue lines, massing in dense, glowing schools around coral heads and wrecks.

Where: Dense yellow shoals holding station over coral heads. Best: May to September.

Powder Blue Surgeonfish Common

Acanthurus leucosternon

A stunning Andaman signature fish, powder blue with a yellow sail and a scalpel-sharp blade at the base of its tail.

Where: Shoaling over the reef top at Pigeon Island. Best: May to September. They graze in loose shoals that pour over the coral like a blue tide.

Black Pyramid Butterflyfish Regular

Hemitaurichthys zoster

They gather in the current in hundreds, and the white wedge on each flank turns the whole shoal into a drifting cloud of triangles.

Where: The drop-off edges off Pigeon Island and the Trincomalee canyon rim. Best: May to September.

Common Lionfish Regular

Pterois volitans

A flamboyant reef hunter fanned out in maroon and white plumes, every graceful spine tipped with venom.

Where: Hanging under ledges on the reef. Best: May to September. The Indian Ocean species, Pterois miles.

Giant Moray Regular

Gymnothorax javanicus

The largest moray on the reef, its gaping, fanged mouth a fearsome look that is really just how it breathes.

Where: Holes and overhangs on the reef at Pigeon Island. Best: May to September.

Indian Sailfin Tang Regular

Zebrasoma desjardinii

It raises a dorsal fin nearly as tall as its own body, and a startled one seems to double in size in front of you.

Where: Reef top and boulder slopes at Pigeon Island. Best: May to September.

Maldives Anemonefish Regular

Amphiprion nigripes

A clownfish found only in Sri Lanka, the Maldives and the Lakshadweep, and nowhere else on earth.

Where: Anemones on the inner reef at Pigeon Island and off Nilaveli. Best: May to September.

Oriental Sweetlips Regular

Plectorhinchus vittatus

A handsome striped reef fish whose fussy juveniles wobble around in polka dots to mimic toxic flatworms.

Where: Under overhangs on the reef by day. Best: May to September.

Sebae Anemonefish Regular

Amphiprion sebae

The big dark anemonefish of the northern Indian Ocean, with a yellow tail that gives it away from a distance.

Where: Sand and rubble margins off Nilaveli and Pigeon Island. Best: May to September.

Titan Triggerfish Regular

Balistoides viridescens

The reef's bad tempered bulldozer, a heavy triggerfish that bites chunks out of coral to get at what is living underneath it.

Where: Reef flat and slope, nesting in the sand patches. Best: May to September. Nests on the sand between coral heads on the shallower sites.

Yellowhead Butterflyfish Regular

Chaetodon xanthocephalus

An Indian Ocean butterflyfish that pairs for life, and you almost never see one without the other close by.

Where: Sheltered coral at Pigeon Island and Nilaveli. Best: May to September.

Blacktip Reef Shark Common Vulnerable

Carcharhinus melanopterus

The neat little reef shark of the shallows, its black-tipped fins often cutting the surface over sun-lit sand flats.

Where: The shallow inner reef at Pigeon Island, in snorkelling depth. Best: May to September. The single most reliable place in Sri Lanka to see a shark, and you do not need to dive. Dozens patrol water barely over head height.

Reef Manta Ray Rare Vulnerable

Mobula alfredi

A four metre wingspan gliding overhead in slow, hypnotic loops that leave divers grinning for days.

Where: Deeper reef edges and cleaning stations. Best: May to September.

Whale Shark Rare Endangered

Rhincodon typus

The biggest fish in the ocean, a spotted, bus sized filter feeder and the undisputed holy grail of tropical diving.

Where: Blue water beyond the reef. Best: May to September.

Small Giant Clam Regular

Tridacna maxima

The electric blue and green lips are not pigment for show. They are farming light, and the clam gets most of its food from algae living in its own flesh.

Where: Reef flat at Pigeon Island, in snorkelling depth. Best: May to September. Close enough to snorkel over, and the mantle closes on contact.

Staghorn Coral Common

Acropora species

The fast-growing branching coral that builds the living thickets of the reef, nursery and shelter for a whole community.

Where: The shallow reef flat inside the island. Best: May to September. Badly hit by bleaching in 2016 and recovering unevenly, and it breaks under a fin or a foot.

Blue Sea Star Common

Linckia laevigata

An almost unreal cobalt blue starfish scattered across the shallows, able to regrow a whole body from a single lost arm.

Where: Reef flat and rubble in snorkelling depth. Best: May to September.

Feather Star (Crinoid) Regular

Comatulida species

A living bouquet of feathery arms that clings to high points on the reef by day and can crawl, or even swim, to a better spot.

Where: Clinging to sea fans and reef edges in the current. Best: May to September.

Christmas Tree Worm Common

Spirobranchus giganteus

Pairs of tiny spiral trees in every colour, studding the coral and vanishing in a flash when a shadow passes.

Where: Embedded in boulder corals on the reef flat. Best: May to September. Wave a hand and the whole colony vanishes at once.