Mauro says:

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The stranded specimen has always been hotly debated, though now "skeptics" usually liquidate everything with the usual basking shark (Cetorhinus maximus) explanation. You see, when basking sharks decompose they take a "saurian" appearance: the gills rot away taking away the jaws and the minuscule skull on top of the spine seems an awful lot like a dinosaur head, the tail fins rot away etc.
Problem is this generated more problems than it solved.
For example the Stromsay Beast in the Orkney was reliably identified as a basking shark by that great anayomist, Sir Everard Home, because he bothered to ask the locals for a few samples to analyze.
Too bad the Beast length was 55 ft, when the longest confirmed basking sharks are around 40.
In 1942 at Gourock, Inverclyde, Mr Charles Rankin found a strange 28 ft carcass on the beach. The description would seem to indicate a large shark of some sort. Dimensions are again a problem: Mr Rankin was adamant that it has large pointed teeth and this would rule out a basking shark: the largest living shark with that kind of dentition is the Great White (Carcharodon carcharias), an exceptional visitor to British Islands, though it never reaches 20 ft.
Also there are a number of whales (mainly Ziphidae) only known to science from the occasional stranded specimen: for example Longman’s beaked whale (Mesoplodon bahamondi), Bahamonde’s beaked whale (Mesoplodon bahamondi) and the Lesser beaked whale (Mesoplodon peruvianus) have never been observed (or reliably identified) in the wild are only known from stranded carcasses.
The funny thing is that until recently nobody bothered asking fishermen for help in the study of large sea animals. The whale Berardius bairdii was deemed so rare and little known until the ’60s that it didn’t even have a common name. Then it was discovered that Japanese and Russian fishermen had been hunting them for centuries. It’s ironic to think that the two countries involved have always been known for the excellency of their scientific institutions…
Anyway, back to sea monsters now.
Gary Mangiacopra, a marine biologist who tried to follow up Heuvelmans’ work in the ’80s, observed that after WWII sightings seem to have become less abundant and to show a less marked variety. This could be to a number of causes: for example better access to scientific literature may have reduced misidentification, though I would personally trust much more a XIX century illitterate Norwegian whaler than a present day whalespotter with full Internet access, sea routes have become more restricted, despite the immense increase in commercial traffic, and modern vessels with their powerful diesel and turbine engines may be scaring away the shiest inhabitants of the sea.
Also remember that if a marine biologist or an interested person isn’t around many fishermen will discard or eat any unusual catch without bothering too much about classification or anatomy. The Indonesian Coelacanth (Latimeria menandoensis) was discovered by an extraordinary chance of luck by a marine biologist who was taking a vacation with his Indonesian wife at Sulawesi. They were strolling through the local market when they saw a large fish being carted to a fishmonger’s stall… and the rest is history as they say. Ivan Sanderson was told by fishermen of the Arafura Sea about the habits of the creature that Heuvelmans later called "Merhorse" but, as far as I know, no biologist or other researcher outside of Sanderson and, to a lesser degree, Heuvelmans, took interest into it despite the wealth of details given by native fishermen and the report of the French authorities of Noumea of a Merhorse fighting a colossal squid in 1923 off that island.
Perhaps we should apply the methods which allowed Marc Van Roosmalen to become one of the most succesful zoologists of all times: instead of probing the sea at random just talk to fishermen and other tollers of the sea and "if you happen to catch anything unusual, keep the bones and the skin, thanks".