As they approached Mizushima harbor, the tanker crew apparently didn't know that the whale was there.
Ship strikes are a leading cause of death in endangered whale populations.
Insider was told by an expert that the ship struck the whale's center.
This shocking photo shows a 39-foot dead whale suspended limply above the bow of a Japanese tanker at Mizushima in Japan.
Insider was confirmed by the Mizushima Coast Guard's Office that the whale that was found dead was a male Bryde Whale, weighing five tonnes.
Locals saw the whale when the tanker arrived at the port in Kurashiki's western city. These images were published for the first time in Yomiuri Shimbun (one of Japan's five national newspapers).
According to the Daily Mail, a witness who saw the tanker stated that "I have lived for over 80 years, but this is my first time seeing a whale."
According to Yomiuri Shimbun, the ship's crew didn't know they were carrying the whale along with them while they cruised through the Pacific.
A Bryde whale is stranded on the bow a Japanese Mizushima Coast Guard Office ship.
Mizushima Coast Guard Department spokesperson said that this was the first time they had seen anything like it. They will be looking into how they can prevent such incidents in the future.
Coast Guard photos did not show the name of the ship.
Photo of a healthy Bryde whale swimming in Mirs Bay, Shenzhen, China Photo taken by Shi Lei/Nanfang Daily/VCG via Getty Images
According to World Wide Fund for Nature, ship strikes are one of the most common causes of death for vulnerable and endangered whale populations.
Michael Fishbach, executive director, and cofounder of the Great Whale Conservancy (an environmental NGO based out North Carolina), told Insider that for every record, a dozen whales die from being harmed by ships.
"Because they have negative buoyancy, the whales sink straight to the bottom when they die. Except for rare instances like this one where they are struck in their center, you will see a situation such as the one shown in the above image.
Fishbach stated to Insider that there is no doubt that whales are being killed each year by ships in their 1000s.
Fishbach stated that the industry has designated a body to approach shipping companies to discuss what changes are needed to save the whales.
According to the whale specialist, approximately 60% of ships involved in whale strikes were container vessels.