Nautical charts indicated there was nothing in the area that could have caused the accident. But the ferry, travelling at about 40 to 45 knots, had struck something -- and that something turned out to be a minke whale.

Collisions between whales and ships have become a fact of life in areas around Japan's main southwest island of Kyushu as well as the sea that separates South Korea and Kyushu, with about a dozen incidents reported in the past two and a half years.

What is happening in Japan and South Korea is a microcosm for what is going on in other parts of the world. Whales are migrating or have found a home in high-traffic shipping lanes, increasing the risk of collisions.

From 1975 to 2002 there were nearly 300 documented cases, with the actual number of strikes much higher because most go undocumented or unreported, according to a US National Oceanic and Atmospheric Administration (NOAA) study.

In 68 percent of documented cases, the whales were killed, with smaller vessels suffering significant damage, it said.

The collisions are a threat to the endangered North Atlantic right whale, which is too slow to swim away from big ships, at times too oblivious to know a ship is coming and too buoyant to dive quickly to get out of the way, experts said.

NOAA said there are about 300-350 North Atlantic right whales in the world. The species can grow to about 18 metres (60 ft) and weigh up to 100 tonnes. They are the most endangered large whale off the US East Coast, the agency said.

"Ship collisions are responsible for more right whale deaths than any other single human impact," NOAA said in a 2004 paper.

DEATH ON THE HIGH SEAS

Whales, ships and the high seas have been a deadly combination since about the time the fictional Captain Ahab tried to chase down the white whale in "Moby Dick", Herman Melville's mid-19th-century classic.

Scholars have said the plot was inspired by the 1820 voyage of the Essex, which hit, or was rammed by, a whale and sank.

"Historical records suggest that ship strikes fatal to whales first occurred late in the 1800s as ships began to reach speeds of 13 to 15 knots, remained infrequent until about 1950, and then increased during the 1950s-1970s as the number and speed of ships increased," said Nina Jensen, a marine expert for the leading conservation group WWF International.

Ship strikes mostly affect 11 species of whales, with the fin, humpback and northern right being hit the most often, Jensen said in an email from Norway.

Whale calves, which typically spend more time at the surface than adult whales, are more vulnerable.

No one is sure why whales cannot spot and avoid ships.

Some say the biggest creatures in the sea did not develop avoidance behaviour as they evolved.

When whales do notice a ship is coming, they may try to out-swim it but lose out to the faster vessel. Whales can get trapped by a ship's water forces or can be confused by the sonar signals they receive at the surface from large vessels and their engines, experts said.

CROWDED SHIPPING LANES

Crews of large container ships might not even know if they have collided with a whale because of the ship's size and blind spots from the command cabin.

Even ships that in theory should be cautious about protecting the marine mammals, such as whale-watching cruises, are responsible for 14 percent of known collisions, NOAA said.

South Korea said last month it would exchange information with Japan on ferries crossing the Korea Strait to prevent collisions with whales.

Experts said that slowing ships and redirecting them past seas where whales congregate would cut the number of collisions.

Some shipping companies have said there is little evidence that cutting speed would reduce the risk of collision, NOAA said.

Some in the industry have backed tagging whales with transmitters so ships can receive real-time information on their location.

The Toppy 4 ferry had a high-tech system to prevent collisions, but to no avail. It was equipped with underwater speakers designed to emit sounds that whales dislike.

All of this is a far cry from Melville's day.