Vibrant Marine Life in the Cook Islands

The vibrant marine life in the Cook Islands is a dream for ocean lovers. But many visitors don’t know which marine animals exactly to expect and what they need to know about them. So, here are all the details.

As a whole, marine life in the Cook Islands hosts humpback whales, sharks, turtles, rays, eels, trevallies, giant clams, pearl oysters, and tons of reef fish and deep-sea fish. There are also venomous or poisonous species, such as stonefish, lionfish, and porcupinefish. 

Get your free Vibrant Marine Life in the Cook Islands Infographic at the end of this article.

Impressive Humpback Whales

One of the most fascinating part of the marine life in the Cook Islands are the Humpback whales.

From July to October is Whale season. The giant mammals make their way from Antarctica to the warmer waters to breed.

They have some favorite playgrounds on Rarotonga, like close to Black Rock or in front of Avarua Harbor. But you can find them on all Cook Islands. On the outer islands, they often swim directly behind the reef, like on Aitutaki, Mangaia, Mauke, Atiu and Mitiaro.

Even if they have young ones, they usually are relaxed and friendly. And you can take a closer look on a whale-watching excursion.

Heaps of Sharks – And Possibly Unknown Species

When it comes to marine creatures, sharks are always in the focus of attention. Due to their reputation of being potentially dangerous to humans, their presence always makes people feel a bit uncomfortable.

The Cook Islands don’t disappoint when it comes to sharks. Here are the species you can come across and their main characteristics.

Commonly spotted:  

• Whitetip reef shark

It is one of the most common sharks in the entire Pacific, with a size of up to 1.6 meters/ 5.5 feet. Its main characteristics are the white spots on the tip of the dorsal and caudal fins. Whitetips are curious but rarely aggressive towards humans.

• Blacktip reef shark

Like the Whitetip reef shark named after the spots on the dorsal and caudal fins, in this case, black. It’s another abundant shark that attains a length of 1.6 meters/ 5.5 feet and prefers shallow, coastal water. There have been rare cases where a Blacktip accidentally bit a person in the calf, who waded through the flat water.

• Grey reef shark

Completely in grey, with a round snout, big eyes, and of medium size with about 2 meters/ 6.6 feet. The shark shows when it feels threatened, swims sideways with its pectoral fins lowered. Keep away and keep your distance.

• Hammerhead shark

The Hammerhead shark uses its unique head to detect and hunt prey. In particular to catch and pin down its favorite dish, the stingray. Usually, Hammerhead sharks are safe for humans, but they defend themselves when attacked. Their size can reach 6 meters/ 19.7 feet.

More rarely seen sharks around the Cook Islands:

• Oceanic Whitetip shark or Brown shark

Long white-tipped rounded fins on a short, stocky body characterize the oceanic whitetip shark. The Cook Islanders often call it a brown shark. It has the reputation to be unpredictable and can become aggressive towards humans.

• Tiger shark

Large female specimens can have a length of 5 meters/ 16.4 feet and about 1 ton of weight. The shark’s skin color ranges from blue to green and shows tiger-like black stripes – this is how it got its name. Tiger sharks are a more dangerous shark species, in second place behind the Great white.

• Bull shark

Coming with a bullnose and aggressive due to a high testosterone level are the main characteristics of the Bull shark. With about 3.5 meters/ 11.5 feet and 300 kilograms, it’s smaller than the Tiger shark but hazardous for humans too. Bull sharks can survive in freshwater, which makes them appear in rivers.

• Dusky shark

It is a giant, fairly stout shark, with a length up to 4 meters/ 13 feet and a weight of about 350 kilograms. Due to its size and occurrence in shallow water, it’s potentially dangerous for humans. Dusky sharks also have one of the strongest bites in the world.

• Silky shark

The Silky shark, named for its skin’s smooth texture, is slim and streamlined and not longer than 2.5 meters / 8.2 feet. It has an aggressive nature, and a specific posture indicates a threat (head raised, back arched and tail lowered).

• Silvertip shark

It tends to rush up from deep water to inspect divers, comes very close, and even encircles and pursues. Aggressive behavior and its power make the silvertip shark dangerous for humans. The silvertip on its fin is characteristic of the bulky and about 3 meters/ 10 feet long predator. 

• Nurse shark

The nurse shark is a slow-moving bottom-dweller, and for the most part, harmless to humans. Still, it has several rows of tiny yet sharp teeth, and with 4 meters/ 13 feet, it can become huge.

• Lemon shark

Its yellow-brown skin helps to camouflage itself in a sandy home environment – and is its namesake. The Lemon shark can grow up to 3.5 meters/ 11.5 feet but is not considered a significant threat to humans. 

Penrhyn, one of the northern atolls of the Cook Islands, hosts a majority of these sharks species. Thus, it is also known as Shark Island. Its lagoon is very remote, untouched, and open to the ocean via three passages. The plenty of marine life there is impressive – and so are the sharks. They pop up everywhere, in knee-deep water as well as in the deep lagoon areas. 

Marine life in the Cook Islands might also surprise in the future, because Marine biologists assume that there are even unknown shark species in Penrhyn’s waters.

One of them, Jessica Cramp, is located in the Cook Islands and founded the sharks pacific program to research and preserve sharks throughout the Pacific communities.

Endangered Sea Turtles

Marine life in the Cook Islands also includes the Green turtle and the Hawksbill turtle. Both species show up regularly, in the lagoons, in the passages, and behind the reef. They are shy and dive down if people come too close.

The Green turtle can grow up to a size 1.5 meter / 4.9 feet and weigh up to 190 kilograms.

It got its name from the green fat under the carapace, not the color of the shell itself, which is rather olive to brown.

While the Hawksbill turtle is named after its pointed beak, which resembles a Hawk.

It is smaller than the green turtle with 1 meter/ 3.3 feet in size and about 80 kilograms.

The Hawksbill turtle is a critically endangered species.

Majestic Eagle Rays & Manta Rays

The majority of Eagle rays on the Cook Islands are spotted eagle rays. White dots and circles on the dark dorsal surface, and the eagle-like head profile, gave this ray its name.

They are a main part of the marine life in the Cook Islands and meander through lagoons, passages, and next to the reef. You can see them as singles or in large groups.

Eagle rays are excellent swimmers; they fly through the water. A mature Eagle ray can be up to 5 meters in length and 3 meters in width and heavyweight (more than 200 kilograms). Their long tail holds a couple of venomous spines, so keep a safe distance. Eagle rays are friendly to swim with. 

While the Manta ray is much rarer and can be found in deep water only. The gentle giant can reach a width up to 7 meters/ 23 feet and get a weight of more than a ton. It’s beautiful and safe to swim with this majestical marine animal. 

Patterned Eels, but No Snakes

Marine life in the Cook Islands hosts a couple of eels.

The most common one is the Moray eel, which can grow up to 2,5 meters / 8.2 feet. Usually, it hides under rocks with only the head being visible, looking for prey. From time to time, you can see them swimming freely around to change their location. Or to chase competitors away that invade their residential area. Do not get too close to a Moray eel. He will defend his territory, and a bite can be pretty harmful.

There are no snakes in the Cook Island, neither on land nor in the water.

But there are also smaller eels around, with a size of only 1 meter / 3.3 feet. Like the spotted, banded, or crocodile snake eel, which refers to the patterns on their skins.

Although they look like snakes, they are still fish. Which you can tell from their dorsal fins that snakes do not have.

Mesmerizing Reef Fish

Like many tropical islands, the Cook Islands’ lagoons and reef areas appear like an aquarium. They are colorful, lively, and full of surprises. The most common groups of fish you come across here are

• Butterflyfish (BFF):

Pacific Double-saddled BFF, Teardrop BFF, Long-nosed BFF, Threadfin BFF, Speckled BFF, Saddled BFF, Racoon BFF, Reticulated BFF, Redfin BFF, Ornate BFF, Dot-and-Dash BFF, Chevron BFF, Tahiti BFF and Pyramid BFF.

With three primary colors, white, yellow, and black, the Butterflyfish comes in so many different patterns and is beautiful to watch.

• Wrasses:

Floral Wrasse, Bird Wrasse, Checkerboard Wrasse, Three-spot Wrasse, Bluestreak cleaner Wrasse, Sixbar Wrasse, and Sunset Wrasse. 
The most iconic one is the Humphead wrasse, also known as Napoleon fish. In Aitutaki’s lagoon and some of Rarotonga’s passages, you meet it often.

• Triggerfish: 

Lagoon Triggerfish (Picasso), Orangelined Triggerfish, Blue Triggerfish, Titan Triggerfish.
During breeding time, the triggerfish is very defensive and picks people that come too close. This happens a lot on the Cook Islands and can end with a blue mark.

• Parrotfish:

Bullethead Parrotfish, Red lip Parrotfish, Pacific Longnose Parrotfish, Bicolor Parrotfish.
The Parrotfish feeds on algae, growing on corals. To do so, it bites off pieces of coral and grinds it. Then digests the edible portions from the rock and excretes them as sand. Very helpful for nature as one Parrotfish produces up to 90 kg of sand each year. But – never eat Parrotfish from inside the lagoon. It may have ingested the Cigua toxin while eating corals.  

And there are also heaps of bright and shiny

• Angelfish: Lemonpeel Angelfish, Emperor Angelfish, Flame Angelfish, Regal Angelfish

• Goatfish: Yellowstripe Goatfish, Mutlibarred Goatfish, Longbarbel Goatfish

• Bannerfish: Pennant Bannerfish, Masked Bannerfish

• Groupers: Peacock Grouper, Hexagon Grouper 

• Unicornfish: Bluespine Unicornfish, Orangespine Unicornfish

• Damsel: Grey Damsel, Blue Damsel
  

Another big part of the crowd of the vibrant marine life in the Cook Islands are:

Convict Surgeonfish, Squirrelfish, Yellowspot Emperor, Flametail Snapper, Bannerfish, Bluebox fish, and more.
All these fish are fantastic to look at. They are not shy and often appear in schools, where you can simply float with them.

Starry Pufferfish and Porcupine (puffer)fish:
Pufferfish are slow-moving since they do not have fully developed fins. To compensate for this, they can inflate up to three times their body size to scare predators. Most importantly, they carry a strong toxin to defend themselves. More about the Porcupinefish in the following chapter.

Close to the surface, some translucent fish species are floating along like Cornetfish, Trumpetfish, or Needlefish.

While on the bottom of the ocean floor, you come across Peacock flounders, the Blue sea star, and Sea cucumbers. The latter can become annoying when they cover entire lagoon areas. But they help to regenerate their environment by removing excess organics out of the water – like a vacuum cleaner. 

Around the rocks, there are Sea urchins and the venomous Crown-Of-Thorns starfish (COT). Stay away from them because they have harmful stings.  

And finally, keep this rule in mind: Do not eat reef fish because they can carry the Cigua-toxin, which causes Ciguatera Food Poisoning (CFP). Find out more about CPT, what it is and what to do if you have eaten toxic fish.

Highly Venomous and Poisonous Stonefish, Lionfish & Porcupinefish

It’s essential to know facts about these species of marine life in the Cook Islands because they can be very harmful and even lethal to humans. Find more information about dangerous animals in the Cook Islands, precautions and what to do if one has harmed you.

Meanwhile, the Stonefish is present on the Cook Islands all year round. It’s the world’s most venomous fish.

It adapts perfectly to its surroundings and appears like a stone. It’s easy to step on its sharp and venomous spikes because it hides well in the shallow water and close to rocks. A sting is excruciatingly painful and requires medical treatment, including an antivenom.

Another part of marine life in the Cook Islands is the Lionfish. Due to a lack of natural enemies, its population is increasing worldwide. This makes it a threat for its environment as it is a top predator that kills native plants and animals in a battle for limited food resources. The Lionfish comes with a dozen venomous spines that can sting painfully and make medical help necessary.

While the Porcupinefish is the world’s most poisonous fish. It carries a potent neurotoxin, which is 1.200 times stronger than cyanide. The fish is lethal to humans if ingested.

Crazy enough, in Japan, it is a delicacy to eat after qualified chefs have removed the toxic components. But still, people die from it.

Under certain circumstances, a porcupinefish is not only poisonous but also venomous. For example, if parts of the toxin on the fish skin make their way into the human bloodstream through an open injury.

Bottom line: Do not eat and do not touch or step on a Porcupinefish!

Beautiful Corals, Anemones, Giant Clams, Black-Lipped Pearl Oysters

As in all oceans, also in the waters of the Cook Islands, corals die but luckily also regenerate again.

Here are the types of corals you come across as part of the marine life in the Cook Islands: 

• Massive corals, which are ball- or boulder-shaped and slow-growing. Most of them are of green and brown color. They are solid and resist storms and swells.
  
  
• The Blue coral consists of a strong skeleton with blue-colored polyps living in its tubes. On the ocean floor, it appears like a jagged medium-size block.
  
  
• While the Razor coral or Mushroom coral got its name from the oval shape with radiating walls, making it appear mushroom-like. Its color ranges between yellow, orange, purple, and green.
  
  
• The fan-like Fire corals that grow in many areas are stunning with their green-yellow to orange coloring. 

Do not touch the corals, as they are breaking easily. It is also harmful to humans because skin cuts from living corals can end in severe infections. Especially the polyps that are sitting on the top ends of a fire coral sting painfully.

Nearshore, there are also Magnificent sea anemones. They got their name from the magnificent colorful body that ranges from blue to purple, red, and brown. Plenty of beige and green tentacles sit on their top ends to catch and consume prey.

A very pretty part of the marine life in the Cook Islands are the Giant clams.

You find them in the shallow and sandy water of the lagoons and just behind the reef. The world’s largest mussel can reach a weight of 200 kilograms and an average size of up to 1.2 meters/ 3.9 feet.

It comes in beautiful colors like green, purple, and blue. Unfortunately, their population decreased for years until a conservation program banned clams from harvesting.

While the Black-Lipped Pearl Oysters are essential for an entire industry. The locals use it to raise the rare black pearls, mainly on one of the northern atolls, Manihiki. Local artists create unique pieces of jewelry with these pearls but also their radiant shells.

Brilliant Deep Water Fish

Offshore is the place where the Cook Islanders hunt their favorite fish to eat: 

• Number one is the Yellowfin tuna. The largest specimens can be more than 2 meters/ 6.6 feet long with a weight exceeding 180 kilograms. Its name comes from the bright yellow fins between the dorsal fin down to the tail. In contrast, the main body is electric blue and silver. The Tuna’s dark red meat is great for sashimi and the national dish Ika Mata. 
  
  
• Followed by Flying fish. The Maroro (in Maori) is part of many traditional meals; the locals eat it also dried or raw marinated. Thus, the Cook Islanders catch it daily. The Flying fish does not fly but it propellers out of the water and then glides with wing-like fins over the water. 
  
  
• A smaller type of tuna is the Albacore. Often found in the Cook Islands waters and as food on the table. Its meat is light red or rose and delicious. Albacores have a streamlined body, are dark blue on the back, and silver towards the belly.
  
  
• Often seen is also the Mahimahi, which has a tight body and one single fin from the head almost to the tail. The skin colors are bright blue and green on its back and sides, running over into golden towards the belly. A Mahimahi has a weight of up to 12 kilograms and 1 meter/ 3.3 feet in size.
  
  
• Widespread and a favorite is also the Wahoo. It looks like a typical mackerel, with an elongated silverish body and blue vertical stripes. It’s a powerful and agile swimmer and popular for game fishing. But keep an eye on its razor-sharp teeth.
  
  
• The rare Moonfish is a fantastic part of marine life in the Cook Islands. Weird looking, with its moon-like disc-shaped body, in dark red-orange and silver. The large ones can be 2 meters/ 6.6 feet long and more than 200 kilograms heavy. 
  
  
• Last but not least, you also often come across the Swordfish or Broadbill. It is long, flat, and with a sword-like snout, and can grow more than 4 meters/ 13 feet and a weight of up to 650 kilograms.
  

Plenty of fishing tour operators can take you out for deep-sea fishing. Our Travel Guide of the entire Cook Islands gives you all details.

Plenty of Hard- and Soft-Shell Marine Animals

And here are some participants in the marine life in the Cook Islands.

Crustaceans are present on all Cook Islands.

Be it a tiny Crab, Crayfish, or a Lobster. On some of the southern islands, like Mitiaro, there are lots of Crayfish. You can literally pick them from the reef rocks. 

Note: The Coconut crab is the largest land crab on earth, not a marine animal. But you find them on the Cook Islands; even you do not see them often. They prefer rainforest areas and hide in deep holes in the ground or under the roots of trees. 

Soft-tissue marine life includes Octopus and now and then jellyfish. You have to be aware of the Bluebottle, also called Portuguese Man O War, a floating polyp with venomous tentacles. Luckily, they are rarely found in the lagoons, where they can hit swimmers. 

You Might Also Be Interested In …

We hope that you find these explanations about the dazzling marine life in the Cook Islands helpful.

If you are interested in finding out more about this country and its wildlife, have a look at these related questions:

Are There Any Dangerous Animals in the Cook Islands?
If you are interested in these facts, look at our post about 10 Dangerous Animals in the Cook Islands.

What Do I Need To Know About Animals in the Cook Islands in General?
Have a look at the 9 important facts about animals in the Cook Islands.

Are There Any Sharks in Rarotonga?
We’ll give you an insight where in Rarotonga you find which types of sharks.