The Zuiyo Maru was a Japanese trawler that caught a creature initially claimed to be a prehistoric plesiosaur off the coast of New Zealand in 1977. Although Japanese scientists insisted it was "not a fish, whale, or any other mammal", others argued that it was most likely the carcass of a basking shark.
On the 25th of April 1977, the Japanese trawler Zuiyo Maru, east of Christchurch, New Zealand, caught a strange, unknown creature in the trawl. The crew was convinced it was an unidentified animal (Bord, 1990), but despite the potential biological significance of the curious discovery, the captain, Akira Tanaka, decided to dump the carcass into the ocean again so not to risk spoiling the caught fish. However, before that, some photos and sketches were taken of the creature, nick-named "Nessie" by the crew, measurements were taken and some samples of skeleton, skin and fins were collected for further analysis by experts in Japan. The discovery resulted in immense commotion and "plesiosaur-craze" in Japan, and the shipping company ordered all its boats to try to relocate the dumped corpse again, but with no apparent success. (Sjögren, 1980).
The foul-smelling, decomposing corpse weighed two tons and was about 10 m long. According to the crew, the creature had a one and a half meter long neck, four large, reddish fins and a tail about two meters long. It lacked a dorsal fin. No internal organs remained, but flesh and fat was somewhat intact (Sjögren, 1980 and Welfare & Fairley, 1981).
Professor Tokio Shimaka from Yokohama university was convinced that the remains was of a supposedly extinct plesiousaur. Dr Fujiro Yasuda from Tokyo university agreed with Shimaka that "the photographs show the remains of a prehistoric animal" (Sjögren, 1980).
However, other scientists were more skeptical. According to Bengt Sjögren (1980), the Swedish paleontologist Hans-Christian Bjerring was soon interviewed by Swedish TT, and said: "If it's true that the Japanese collected samples of fins and skin, it would be possible to conclude from a microscope what it is. If it would be shown to be a hitherto unknown animal from the sea, it is as big of a sensation as the discovery of the coelacanth in 1938... but there is reason to be suspicious of the claims of plesiosaurs, for example, as the marine environment and fauna changed drastically since the age of the plesiosaurs on earth."
Another Swedish scientist, Ove Persson, was also critical of the plesiosaur interpretation. He recalled other discoveries of similar dead marine creatures resembling plesiosaurs that on closer inspection revealed them to be just decomposed, unusually large sharks. He also added, according to Sjögren (1980): "The discovery of the coelacanth was not as strange as if a plesiosaur would be discovered. The plesiosaur is much bigger and breathes with lungs. It seems incredible that it would manage to remain hidden."
A basking shark?
On the 28th of July 1977 the Zuiyo Maru carcass was commented upon in New Scientist. A scientist from the British Natural History Museum in London, had the same opinion as Bjerring and Persson: that the remains were not from a plesiosaur. The decomposition pattern of a basking shark, whose spine and braincase is relatively highly ossified for a cartilaginous fish, can be expected to produce a similar shape to a plesiosaur; the first parts that fall off during decomposition are the lower jaw, the gill area, and the dorsal and caudal fins. Bengt Sjögren (1980) concluded: "It was the infamous old ´Stronsay beast´ that once again haunted like on innumerable other occasions. The scholars in Japan went into the same easy trap as the Scot naturalists did in the 19th century."
However, some Japanese scientists criticised the shark hypothesis. Professor Yoshinori Imaizumi of the Japanese National Science Museum said, "It's not a fish, whale, or any other mammal." and professor Toshio Kasuya agreed, "If it was a shark, the spine would be smaller, and the neck itself is too long as shown in the picture. I think we can exclude the fish theory.".
The above mentioned Fujiro Yasuda ruled out a mammalian origin and claimed: "No animal of that size has such an elongated body" (Welfare & Fairley, 1981). He concluded that the stretching of the body and positions of fins were totally different from that of any known shark, and added: "We can't find any known species of fish that correspond with the animal caught outside New Zealand. If it is a shark, it is a species unknown to science." Two other Japanese scientists, Obata and Tomata from Tokyo National Museum of Science also agreed that no known species or genus of animal fit the appearance of the Zuiyo Maru creature.
Also, when the carcass samples were tested for amino acid levels, variances occurred from the levels expected in a basking shark. However, this could be explained by the fact that the carcass had been decomposing in and leached by seawater for some time.
In popular culture
This incident was mentioned briefly in the 1991 film Godzilla vs. King Ghidorah.