Telling the Cocos Sharks Apart

Approach

How to look

~2 min · read first

Most shark sightings at Cocos are brief: the animal is passing a cleaning station, cruising the edge of a reef, or already turning away into the blue. Colour changes with light and depth, so rely on fin shape and body shape, and check the same things in the same order every time.

Size and build. Is it slim or stocky, small or very large?
Head and snout. Long and rounded, short and blunt, or square?
First dorsal fin. Tall or low, upright or swept back, and where it starts compared with the pectoral fins.
Second dorsal fin. Tiny, ordinary, or almost as big as the first. This one fin settles several questions.
Pectoral fins and tail. Dark tips, white edges, and the length of the upper tail lobe.
Only then, colour and behaviour. Is it resting, patrolling a wall, or circling in open water?

Let the site do some of the work

Whitetips are on almost every dive, and are the sharks resting on the sand. A grey shark at a hammerhead cleaning station is most often a Galápagos. Silvertips are most likely at Silverado and Small Dos Amigos, and tiger sharks along the sandy edge of the reef at Manuelita. The Sharks & rays page has where each one is reported.

Anatomy

The parts to know

One diagram · ten parts

A generic shark seen from the side, for naming the parts. It is not any one species.

Parts of the shark and what to check on each
No.	Part	What to check
1	Head and snout	Long and rounded, short and pointed, or blunt and square. Teeth showing with the mouth closed.
2	First dorsal fin	Height, how far it leans back, tip shape, and white edges. Also where its front edge starts compared with the pectoral fins.
3	Interdorsal ridge	A low ridge of skin along the back between the two dorsal fins. Present in some sharks and not obvious in others.
4	Second dorsal fin	Tiny, ordinary, or almost as big as the first. Look for a long thin trailing tip.
5	Pectoral fins	Long and narrow or broad. Dark tips on the underside, or white edges.
6	Pelvic fins	Small paired fins under the rear of the body. Useful mainly for judging where the first dorsal sits.
7	Anal fin	A single small fin under the tail end. Not needed for these species.
8	Upper tail lobe	Short and ordinary, or very long. A white tip.
9	Lower tail lobe	Usually much shorter than the upper lobe. Check for a white tip.
10	Gill slits	Five slits on each side for these sharks. They help you tell the head end from the body.

Quick key

Five questions

Work down the list

Is it a big, heavy shark with a blunt, square snout and faint dark bars on the flanks? It is a tiger shark.
Do the fins have clean white tips or edges? A slim, smallish shark with white only on the dorsal fins and tail tips, often resting on the bottom, is a whitetip reef shark. A larger shark with white edges on nearly every fin, including the pectorals, is a silvertip.
Do the fins have crisp black tips, on the dorsal, the pectorals and the lower tail lobe? It is a blacktip shark.
Otherwise it is grey, with no white or black on the fins. Look at the second dorsal fin. A tiny second dorsal with a long thin trailing tip points to a silky shark.
A small, ordinary second dorsal and a tall, upright first dorsal, on a stocky shark near the reef? It is a Galápagos shark.

Checkpoint — if you can answer these five questions about a shark in a photo, you can name every shark on this page.

Profiles

The six sharks

What to look for · what it gets confused with

Silky shark Carcharhinus falciformis

Look for: a slim, tapering body, a small head with a long rounded snout, and a low rounded first dorsal that starts behind the tips of the pectoral fins. The second dorsal is tiny, with a very long thin trailing tip, which is the best single mark. The pectoral fins are long and narrow and have dark tips underneath. Bronze-grey above, white below.
Easily mistaken for: the Galápagos shark.
At Cocos: Reported at Manuelita, Dirty Rock and Bajo Alcyone (DAN). Described as an occasional sighting on a 2024 expedition (SEE Turtles 2024).

Galápagos shark Carcharhinus galapagensis

Look for: a stocky body, a broad rounded snout, and a tall upright first dorsal that starts roughly over the tips of the pectoral fins. The second dorsal is an ordinary small fin with a short tip, and there is a low ridge on the back between the dorsals. The pectoral fins are broad and have no strong dark tips. Plain grey-bronze.
Easily mistaken for: the silky shark.
At Cocos: Visits the cleaning stations at Dirty Rock and Punta María, where close passes are common (DAN; SEE Turtles 2024). One stayed with a group for a whole night dive at Manuelita Shallows (Blue Water Dive Travel).

Silvertip shark Carcharhinus albimarginatus

Look for: a larger, bulkier grey shark with a clean white edge on the tips and rear edges of nearly every fin, the pectoral fins included. The first dorsal is tall and curved. It swims actively and does not rest on the bottom.
Easily mistaken for: the whitetip reef shark. Check whether the pectoral fins have white.
At Cocos: Sometimes seen at Silverado, the site named after it (DAN), and at Small Dos Amigos (Blue Water Dive Travel). An occasional sighting (SEE Turtles 2024).

Whitetip reef shark Triaenodon obesus

Look for: a slim, smallish body and a short, blunt snout. The first and second dorsal fins both have white tips, and so does the upper tail lobe, often the lower lobe as well. The pectoral fins are plain, with no white.
Easily mistaken for: the silvertip, because both show white on the fins.
At Cocos: The most common shark at Cocos (SEE Turtles 2024). By day it rests on sand and in crevices, for example in the swim-through at Submerged Rock (DAN). At night dozens to hundreds hunt together over the reef at Manuelita and in Chatham Bay (DAN; Blue Water Dive Travel).

Blacktip shark Carcharhinus limbatus

Look for: a slim, fast shark with a long pointed snout and crisp black tips on the first dorsal fin, the pectoral fins and the lower lobe of the tail. The anal fin tip stays pale.
Easily mistaken for: the silky shark, which has only dusky tips on the underside of the pectorals and a tiny second dorsal with a long trailing tip.
At Cocos: Visits the cleaning stations, but it is the shyest shark here and usually leaves soon after divers arrive (SEE Turtles 2024).

Tiger shark Galeocerdo cuvier

Look for: a large, heavy body with a very blunt, square snout and a broad head. Dark vertical bars or spots show on the flanks, and they fade on big adults. The upper tail lobe is long. The pectoral fins are long and broad.
Easily mistaken for: little else at Malpelo. Size and the square snout settle it.
At Cocos: Reported more often in recent years. Two were seen at Manuelita in November 2016, the larger about 4.5 m long (Blue Water Dive Travel). In 2024 they were seen cruising the sandy edge of the reefs, including a juvenile in the Coral Garden (SEE Turtles 2024).

Lookalikes

Pairs that get confused

Four pairs

Silky or Galápagos?

Both are grey, torpedo-shaped sharks of similar size, and divers often mix them up. Ignore the colour and look at the fins.

Silky: slim, a low and rounded first dorsal, a tiny second dorsal with a long trailing tip, and long narrow pectoral fins with dark tips below. Usually in open water; in groups only when attacking bait balls.

Galápagos: stocky, a tall and upright first dorsal, an ordinary-looking second dorsal, and broad pectorals. Usually near the walls and reef, and often bold around divers.

Whitetip or silvertip?

Both have white on their fins, and both show up as small white flashes at a distance. Look at where the white is.

Whitetip reef shark: white only on the tips of the dorsal fins and the tail. The pectoral fins are plain. It is slim, smallish, and often lying on the bottom.

Silvertip: white edging on nearly every fin, pectorals included. It is larger and bulkier and swims in the open instead of resting.

Blacktip or silky?

Both are slim grey requiem sharks of open water. Look at the fin tips and the second dorsal.

Blacktip: crisp black tips on the first dorsal, the pectorals and the lower tail lobe, and a long pointed snout.

Silky: no black on the dorsal fin; the pectoral tips are only dusky, and only underneath. A tiny second dorsal with a long trailing tip.

Scalloped or great hammerhead?

The hammerheads at Cocos are scalloped hammerheads. To rule out a great hammerhead, look at the front edge of the head. The scalloped hammerhead's is scalloped, with a notch in the middle and a gentle notch on each side. The great hammerhead's is nearly straight with one notch in the middle, and its first dorsal fin is much taller.

After the dive

Getting a shark identified later

What to photograph and what to note

Shoot the whole animal from the side if you can, with both dorsal fins and the tail in the frame.
If the animal turns, try to get the underside of the pectoral fins, which shows dark tips or white edges.
Get the head from the front or the side if it comes close, to show the snout shape.
Write down the depth, the site and the time of year, and note whether it was resting, patrolling or in a group.
Ask your guide at the next briefing. They see these sharks every week.

Treat these as guides, not guarantees

Individual sharks vary and juveniles look different from adults. The marks on this page come from standard shark field guides and general references, and not every one has been checked against a source specific to Cocos. Confirm against a field guide or your dive guide's briefing.

Telling the sharks apart