Nearly 90 years after a strange marine carcass was discovered inside the stomach of a sperm whale off the coast of Canada, scientists, cryptozoologists and marine historians remain divided over whether the remains represented an unknown species or a decomposed basking shark, one of the Pacific Ocean’s most elusive and heavily persecuted marine animals.

The mystery dates back to October 1937, when workers at a whaling station in Haida Gwaii recovered a 3-metre carcass from a sperm whale caught in waters off the Pacific coast. Witnesses described the creature as having a dog-like head, a camel-shaped nose, a reptilian body and a horse-like tail. The remains were reportedly coated in a thin white layer.

The carcass was placed on a platform assembled from wooden crates and photographed before an image appeared on the front page of a regional newspaper on 31 October 1937. The discovery quickly became linked to local stories about “Cadborosaurus,” a legendary marine cryptid said to inhabit the waters of the Salish Sea and the Pacific Northwest.

No biological samples from the carcass survive today, leaving researchers to rely entirely on a small number of black-and-white photographs and eyewitness testimony. The absence of physical evidence has allowed competing interpretations of the discovery to persist for decades.

John Kirk, president of the British Columbia Scientific Cryptozoology Club, argues that the remains belonged to an unidentified marine species rather than a known shark. Kirk has cited interviews with whaling station workers, including one flenser involved in removing the carcass from the whale.Kirk contends that scientific institutions prematurely dismissed the discovery.

He has also pointed to a second alleged Cadborosaurus specimen discovered in 1968 near Naden Harbour, southeast of Haida Gwaii, which was later discarded after museum officials identified it as a fetal baleen whale.“We lost a massive discovery here because of misidentification,” Kirk said in interviews discussing the case.

He has maintained that the 1937 remains possessed hair-like structures inconsistent with shark anatomy and argued the carcass more closely resembled a marine mammal than a reptile or fish.Most marine biologists, however, reject the theory that the remains represented an unknown species. They instead identify the carcass as a decomposing basking shark, a species once common off the coast of British Columbia before government eradication campaigns sharply reduced its population.

Basking shark are the second-largest fish species in the world and can exceed 10 metres in length. Unlike most sharks, they feed passively on plankton near the water’s surface. Because their skeletons are composed primarily of cartilage rather than bone, their bodies undergo dramatic transformations during decomposition.

Ben Speers-Roesch, a marine biologist at the University of New Brunswick, said decomposing basking sharks often create what scientists call the “pseudo-plesiosaur carcass” phenomenon. As the shark’s gill structures collapse and soft tissue deteriorates, the remains can appear to have a long neck, small head and paddle-like appendages resembling extinct marine reptiles.

“With a long spinal cord and a small head at the end, it looks like a mythological sea serpent,” Speers-Roesch said, noting that unfamiliarity with shark decomposition can lead observers to misidentify carcasses.Marine scientists have cited similar cases elsewhere.

In 1977, the Japanese fishing vessel Zuiyō Maru recovered a decomposed carcass off the coast of New Zealand that some initially believed represented a surviving plesiosaur. Subsequent amino acid analysis determined the remains belonged to a basking shark.Speers-Roesch acknowledged that the 1937 Canadian photographs differ slightly from typical basking shark carcasses because of how the remains were displayed after recovery.

He also noted that juvenile basking sharks have occasionally been found inside sperm whales, making the scenario biologically plausible.“The mystery has persisted because it has elements that are not as easily identifiable as a basking shark,” he said. “But so much of the carcass captures what we know about basking sharks and how they decompose.”

The debate over the Cadborosaurus photographs has increasingly intersected with renewed scientific attention on basking sharks themselves. Once abundant in Pacific waters near Vancouver Island, the species became the target of official eradication programs during the mid-20th century.

In 1955, the Canadian federal government launched a campaign to eliminate basking sharks after the animals were blamed for damaging salmon fishing nets. Authorities equipped patrol vessels with large blades mounted on their bows, devices locally described as “razor-billed shark slashers.”Scott Wallace, a former fisheries scientist who authored a 2007 federal report classifying the species as endangered in British Columbia waters, said the vessels intentionally rammed sharks at the surface.

“They simply cut them in half,” Wallace said in accounts describing the program.Government estimates indicate at least 413 basking sharks were deliberately killed during the following 14 years, while another 1,500 may have died through fishing-net entanglements. Additional mortality occurred through a short-lived commercial fishery targeting shark liver oil. Scientists estimate that as many as 2,600 sharks, representing more than 90% of the regional population, were eliminated.

The eradication campaign formed part of broader marine predator control policies implemented during the period. Fisheries authorities also targeted seals, sea lions and orcas around salmon fishing grounds. In the early 1960s, officials installed a .50-calibre machine gun on a coastal island for use against killer whales, although records indicate the weapon was never deployed.

Today, basking sharks are protected under Canadian federal law. It is illegal to kill, harm or capture the species in British Columbia waters, and federal recovery plans remain in place. Fisheries officials have nevertheless stated that recovery of the population could take up to 200 years.

Interest in the species resurfaced after a rare basking shark sighting off the British Columbia coast in 2024 renewed scientific and public attention on the animals and the history of their decline.For cryptozoologists such as Kirk, the absence of definitive proof continues to sustain theories that unknown marine species may still inhabit the Pacific depths.

Marine scientists, however, argue the case ultimately demonstrates how limited human understanding remains when interpreting rare ocean phenomena, especially when decomposition dramatically alters the appearance of marine animals.