A peninsula in Argentina is the only place in the world where killer whales deliberately strand themselves to get food. Jerry Callow watches the spectacle

Bumping along the dusty track in the back of Dino's car we were a world away from the smoky tango bars of downtown Buenos Aires. This was the wild Argentina of windswept pampas, fossilised mammoths and endless, barren vistas - the northern edge of Patagonia, and one of the world's last great wildernesses.

Bumping along the dusty track in the back of Dino's car we were a world away from the smoky tango bars of downtown Buenos Aires. This was the wild Argentina of windswept pampas, fossilised mammoths and endless, barren vistas - the northern edge of Patagonia, and one of the world's last great wildernesses.

We were driving across the Valdez Peninsula and, even though the landscape was dry and desolate, there was a surprising amount of wildlife. Small groups of startled rhea careered along the road in front of us. Guanaco were silhouetted against the clear blue sky, and armadillos scuttled around in the scrub.

But our gaze was firmly fixed out across the icy blue of the Southern Atlantic because it is what lives in the waters surrounding this peninsula that makes it such a special place. Valdez is the Serengeti of the marine world. The peninsula plays host to some of the world's greatest gatherings of marine mammals. It is a haven and breeding ground for sea lions, elephant seals and southern right whales, but this was March and we were hoping to see its most breathtaking visitor of all: the Orca.

At this time of year the Orcas around the peninsula exhibit behaviour seen nowhere else in the world. These massive animals perform an act known as "intentional stranding". They deliberately launch themselves on to the beaches to hunt young sea lions, and the northern corner of the peninsula, Punta Norte, was the place they were most likely to do this.

The Orcas are only able to attack during a short time either side of high tide (when the water is deep enough for them to swim over the reefs that surround the peninsula). This has become quite a tourist attraction, and a specially built wooden viewing platform offers a panoramic view of the whole beach. Below us three groups of sea lions lay on the sand basking in the sun. Dozens of small, black pups scampered around soporific parents.

At the southern end of the beach a wide channel cut through the reef. This was the underwater "corridor" that becomes deep enough for the Orcas to swim through at high tide. It is a place they know well and directly opposite was the largest group of sea lions. With easy access and plenty of food it was, not surprisingly, the most popular place for an attack anywhere on the peninsula.

Suddenly an Orca announced its arrival with a plume of spray from its blowhole. It's easy to identify individuals by the distinctive shape of their dorsal fins, and one of the researchers recognised the Orca as "Mel". At 38 years old, 33 feet long and over 10 tons in weight he was the oldest and largest male in the area.

The tall, black fin sliced through the water and he sped through the channel until he was opposite a handful of pups playing at the water's edge. He was menacingly close now but the youngsters were totally oblivious of the danger. Checking on the position of the pups one last time he swam out to sea, turned around and accelerated towards the beach. A wall of water surged up as his enormous bulk cut through the surf and he exploded on to the beach until he was completely out of the water. The baby sea lion he was aiming at bounced off his head and landed upside down on the sand. The chance had gone.

Thrashing around from side to side it took several seconds before he manoeuvred his massive bulk back into the sea. Frustrated and too tired to try again, he disappeared. Activity on the beach returned to normal. But he'd be back.

Getting there

The best time to see Orca whales at Valdez is from late February until the end of March. The fastest route to Buenos Aires is on British Airways' non-stop flights from Gatwick; the cheapest is usually on Avianca via Bogota. From the Argentine capital, the national carrier Aerolineas Argentinas flies onwards to Trelew , from where there are bus connections. Specialist agents such as Journey Latin America (020-8747 3108) and South American Experience (020-7976 5511) can provide many possibilities

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