The Catch
On April 25, 1977 the Zuiyo-maru, a fishing vessel for the Taiyo Fishery Company Ltd. Of Japan, was off the coast of New Zealand making the normal fishing rounds, but what turned up in their catch was anything but normal: a 4,000 pound animal carcass had become entangled in the nets.
The smell coming from the carcass was horrible, and because of fear of contaminating the fish the crew decided to dump the carcass over the side of the ship. Just then the line holding the carcass snapped and all the contents of the net came crashing down. This is when the crew noticed how truly unusual the carcass looked; the long, pointy neck and side flippers were unlike any other carcass they had caught before.
Some of the crew said it was just a rotten whale, or perhaps a giant sea turtle with its shell removed, but others, like Michihiko Yano, a graduate from Yamaguchi Oceanological high school, thought it could be something completely different, perhaps an undiscovered species or a prehistoric monster.
Because of Yano’s skepticism he borrowed a camera from a fellow shipmate and took five pictures before the crew threw the carcass overboard. He also cut off several tissue samples from the carcass. Later on these samples would be the most crucial evidence in identifying what exactly the carcass was.
The Return Home
When Yano returned to Japan he developed his photos and immediately began distributing them to local scientists, who all agreed that the carcass was unlike anything they had ever seen before. Some initial testing was done to the tissue samples, but nothing very conclusive was drawn from the results.
Then came the media explosion. The fishing company held a press conference and hyped up the find as a major scientific discovery. They said that the carcass was a prehistoric plesiosaur, or some other never-before-seen monster of the sea.
Newspapers all over Japan picked up the story and the pictures Yano has taken were front-page news. A commemorative stamp was issued with a picture of a plesiosaur on it along with an outline of the Japanese National Science Museum. And, needless to say, an incredible amount of fishing vessels were headed for the coast of New Zealand daily, in search of their own finds.
Across the sea, in Europe and America, the story was picked up, but there was significantly less media hype surrounding the carcass. Publications tended to take a very objective stance on the subject, and the media was very skeptical about the whole thing in general.
The Science
Basically every 10 years a carcass shows up that is proclaimed as some type of new, or lost, creature of the sea. The Zuiyo-maru sea creature is different, though, because there was detailed photographs and, most importantly, tissue samples that testing could be done on.
Testing done on tissue sample gave substantial evidence that the carcass belonged to a basking shark. The horny fibers sampled from the carcass were rigid, needle-like structures that tapered toward both ends and had a translucent light-brown color, exactly like most basking shark fibers. When gross amino acid testing was done the results closely resembled elastoidin from a basking shark.
In recent times the basking shark theory was solidified when another carcass washed up onto the shores of New Zealand. This new carcass looked exactly like the carcass in the pictures from the Zuiyo-maru, making the basking shark theory almost perfect.
There are still some, however, who believe that the Zuiyo-maru is a plesiosaur. Among these believers are die-hard creationists, who suggest that the existence of the plesiosaur would confirm their young-earth theory. But most people have accepted the basking shark stance and have let the issue die.
Sources:
http://www.genesispark.org/genpark/catch/catch.htm
http://members.aol.com/paluxy2/plesios.htm
http://www.angelfire.com/mi/dinosaurs/zuiyomaru.html