Not so long ago, a sailor sailing across the cold waters of the northern Pacific Ocean might have had every chance of being confronted by a sea cow. This cow would have measured 10 meters long, and weighed between five and ten tones. And it would spend most of its day cruising the seas, eating grass growing underwater. The cow in question was known as Steller's sea cow, which is now extinct. Today, many people are unaware that such an extraordinary creature once existed, or don't know its incredible story. But scientists have discovered many fundamental facts about this mystical animal. Surprisingly, the first recorded sighting of a Steller's sea cow didn't happen until 1741, when a sailing expedition was stuck on an uninhabited island, later named Bering Island. The sailor survived by hunting and eating the huge sea cow. Like its modern relatives, the sea cow lived in herds. _ and its slow-moving behaviour made it easy to be caught. Those sailors that escaped Bering Island spread word of the bounty  of meat to be found off its shores. As a result, more and more expeditions came to hunt the animals. One report stated that one sea cow could feed 33 men for a month. Incredibly, just 27 years after the island and species had been discovered by modern man, the last sea cow was reported killed. That makes the Steller's sea cow one of the few truly large mammals known to have been driven extinct in the modern age. What is the main idea of the passage?
Why did expeditions hunt the Steller's sea cow? When did the Steller's sea cow become extinct? How did the Steller's sea cow become extinct? What do we know about the Steller's sea cow?