text: It was due to be a routine mission to examine the depths of the Gulf of Mexico. However, researchers were stunned when their underwater robosub had an unexpected encounter almost 2,000 feet under the ocean. Rather than the deep sea squid and corals they expected to see, a giant sperm whale swam to inspect their sub - causing gasps and shouts of 'holy cow' from the sub's operators. Scroll down for video . The robot sub was examining the depths of the Gulf of Mexico when the sperm whale suddenly appeared . The sperm whale is the largest toothed whale. Adult males reach 16-20 meters (50-65 feet) in length, although most are less than 18 meters (60 ft). Females are much smaller than males, reaching only 11 meters (36 feet) on average. The sperm whale's life is based on sound. It finds food and navigates using sound and it communicates and stays in touch with its family using sound. Sperm whales are listed as an endangered species under the U.S. Endangered Species Act. The global population size is estimated as somewhere between 100,000-300,000 animals. 'What the heck is that?' says one of the crew, when all of a sudden a massive object begins to appear on the screen.'Hello baby,' says another. 'At 598 meters (1,962 ft) below the Gulf of Mexico off the coast of Louisiana, ROV Hercules encountered a magnificent sperm whale,' 'The whale circled several times and gave our cameras the chance to capture some incredible footage of this beautiful creature. 'Encounters between sperm whales and ROV's are quite rare.' Footage shows the curious leviathan swimming in and out of the camera lights, at times spinning and looking directly into the camera.'You can see its eye,' one of the crew says. 'According to biologists we've consulted, the animal on the video is likely a juvenile, especially if it's a male,' they say. 'General consensus among the experts who have examined the video is that it is a male, though the video of the underside of the whale is grainy so it is difficult to know with 100% certainty.' It was difficult to tell the actual size of the whale, the team say, but the ROV is 6 feet wide in the front. Using this as a guide, and how close he was to the vehicle, it is estimated the whale was between 35-40 feet in length. The team also investigated the scarring visible on the whale. 'It could be a number of things, including squid tentacles and suckers, especially the scars around the efface and mouth; but likely not propeller scars like the comments made in the video. This neutrally buoyant yellow remotely operated vehicle (ROV) is the workhorse of the Nautilus Exploration Program, and it always used in tandem with Argus, it's mothership. Hercules is equipped with six thrusters that allow the pilots to 'fly' it in any direction. It has two manipulator arms designed for collecting samples and recovering artifacts. Video from Hercules' high-definition main camera is streamed up a fiber-optic cable to the control van on Nautilus, then out to the world. It is capable of operating down to 4,000 meters. 'It could also be from other sperm whales. 'They often jaw each other when playing or socializing. 'Sperm whales are identified with the scars on the trailing edge of their tails.' The whale can be seen inspecting the robosub in the video . The researchers were piloting the Hercules sub when the encounter occured. This neutrally buoyant yellow remotely operated vehicle (ROV) is the workhorse of the Nautilus Exploration Program, and it always used in tandem with Argus, it's mothership. Hercules is equipped with six thrusters that allow the pilots to 'fly' it in any direction. It has two manipulator arms designed for collecting samples and recovering artifacts. Video from Hercules' high-definition main camera is streamed up a fiber-optic cable to the control van on Nautilus, then out to the world. It is capable of operating down to 4,000 meters. Dr. Robert Ballard’s Exploration Vessel E/V are on their most ambitious expedition season yet, exploring sites ranging from the Gulf of Mexico to British Columbia through late September. Over six weeks of the six-month expedition will be dedicated to exploration and mapping of the Galapagos Rift and the site of the first hydrothermal vent discovery in 1977. The six-month-long 2015 season marks the transition of the vessel and operations of the Ocean Exploration Trust (OET) to the west coast of the United States and the Pacific Ocean, concluding over two years of research in the Gulf and Caribbean regions. E/V Nautilus is owned and operated by the Ocean Exploration Trust (OET), a nonprofit founded in 2008 by Dr. Robert Ballard.
target: Robosub was exploring the Gulf of Mexico off the coast of Louisiana .
  At 598 meters the sperm whale appeared in the robosub's cameras .