The Risso’s Dolphin (Grampus griseus) is a large marine mammal belonging to the order Cetacea and the family Delphinidae. It is easily recognized by its rounded head, tall sickle-shaped dorsal fin, and the numerous white scars covering its body. Distributed throughout temperate and tropical oceans around the world, Risso’s Dolphins are most commonly found in deep offshore waters and along the edges of continental shelves. They are highly intelligent marine mammals with a unique diet that consists primarily of squid.

In this article, we’ll explore the Risso’s Dolphin’s characteristics, habitat, behavior, diet, reproduction, and ecological importance.

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What Is the Risso’s Dolphin?

The Risso’s Dolphin belongs to the order Cetacea and the family Delphinidae.

It is widely distributed throughout the Pacific, Atlantic, and Indian Oceans, inhabiting temperate and tropical waters. Around the Korean Peninsula, it is occasionally observed in the waters surrounding Jeju Island and the southern coast.

Adult Risso’s Dolphins typically measure:

• Body Length: Approximately 2.6–4 m (8.5–13.1 ft)
• Weight: Approximately 300–500 kg (660–1,100 lb)
• Dorsal Fin Height: Approximately 20–50 cm (8–20 in)

Their average lifespan is 30–40 years, although some individuals are known to live even longer.

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Characteristics of the Risso’s Dolphin

1. Body Covered with White Scars

One of the most distinctive features of the Risso’s Dolphin is the large number of white scars covering its body.

These scars are believed to result from interactions with other dolphins and the suction cups of squid, their primary prey. As individuals age, the number of scars typically increases, giving older dolphins a noticeably lighter appearance.

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2. Rounded Head and Sickle-Shaped Dorsal Fin

Unlike many dolphin species, the Risso’s Dolphin has almost no pronounced beak, instead featuring a large, rounded forehead.

Its tall, backward-curving dorsal fin resembles the shape of a sickle, making the species relatively easy to identify at sea.

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3. Exceptional Diving Ability

The Risso’s Dolphin is an accomplished deep diver, adapted to hunting squid in offshore waters.

It can dive to depths of several hundred meters and remain underwater for approximately 20–30 minutes during a single dive.

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Behavior

The Risso’s Dolphin is a highly social marine mammal.

Its typical behaviors include:

• Living in social groups
• Diving in deep offshore waters
• Communicating through whistles and clicks
• Using echolocation to locate prey
• Traveling long distances
• Cooperatively hunting for food

Groups typically consist of 10–30 individuals, although much larger aggregations may form in areas where food is abundant.

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Diet and Habitat

The Risso’s Dolphin is a carnivorous marine mammal.

Its primary food sources include:

• Squid
• Pencil squid
• Octopuses
• Cuttlefish
• Small fish
• Crustaceans

It shows a particularly strong preference for cephalopods, often hunting squid that migrate toward the ocean surface during the night.

Preferred habitats include:

• Deep offshore waters
• Continental shelf edges
• Oceanic trenches
• Temperate seas
• Tropical seas

The species favors deep-water environments where squid and other prey are plentiful.

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Ecological Importance

The Risso’s Dolphin is an important apex predator in marine ecosystems.

By feeding on squid and small fish, it helps regulate their populations and contributes to maintaining the balance of the marine food web.

In turn, it may occasionally become prey for killer whales (orcas) and large sharks, making it an important link in the transfer of energy throughout ocean ecosystems.

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Relationship with Humans

The Risso’s Dolphin is generally gentle and poses little threat to humans.

Its high intelligence and curious nature have made it an important subject of marine research, and in some regions it is also a popular species for whale-watching tourism.

However, marine pollution, accidental entanglement in fishing gear (bycatch), plastic waste, and underwater noise pollution remain significant threats to its survival.

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The Risso’s Dolphin is one of the world’s most distinctive dolphin species, admired for its scar-covered body, rounded head, and remarkable diving abilities. By hunting squid in deep offshore waters, it plays a vital role in maintaining the balance of marine ecosystems.

With continued efforts to reduce marine pollution, prevent bycatch, and protect offshore habitats, the Risso’s Dolphin will continue to thrive as one of the ocean’s most fascinating and ecologically important marine mammals for generations to come.