The deep sea is full of strange things, from bacteria and other exotic microbes that sense magnetic fields to giant squids and even "potatoes". There's a particularly strange thing that hosts in the depths of the ocean off the coast of New Zealand, at least until recent research has revealed its origins: the unexplained "hoof prints" scattered on the ocean floor are actually the work of some clever fish.
The mysterious markers, first discovered in 2013, have puzzled scientists ever since. Researchers at New Zealand's National Institute of Hydrology and Atmospheric Research (NIWA) found them at depths of more than 450 metres (1,476 feet) in New Zealand waters.
The team has now analyzed their original footage, and after a long period of pondering, they have finally come up with an explanation for the traces of these mysteries, which, sadly, does not involve small underwater horses.
They believe the culprit is the deep-sea dog fish, also known as Coelorinchus – some of these species have long snouts that look very much like these peculiar traces of the seabed.
"We wanted to know if these marks could be traces of dog fish feeding in the sediment," NIWA's Darren Stevens said in a statement.
"These types of dogfish have a long snout and a retractable mouth located under the head, allowing them to forage on the ocean floor in a way that other fish cannot. ”
Stevens overlaid images of the dogfish's uniquely shaped heads and seabed imprints, and to his surprise, they fit together perfectly.
"I had a hunch that this might work, but I was really surprised that the head contour image and imprint fit so perfectly. We were able to provide fairly good evidence that the imprints were made by two species of bigeye fish," Stevens added, before going on to explain that the findings by identifying foraging areas and critical habitats could be critical to our understanding of the dog fish species.
The team believes that this is the first time that their natural foraging behaviour has been documented, revealing valuable information about how they hunt. According to a paper in which they published their findings, dogfish may have come into contact with the seafloor in a head-down position, which may have involved "a short period of sudden velocity drops" before sucking up the sediment and filtering the prey within.
Observing such puzzling patterns in the deep ocean is no easy task, let alone trying to figure out what causes it. In this case, study author Sadie Mills explained that they were able to use the Deep Sea Traction Imaging System (DTIS) to allow them to observe the seafloor in extreme detail. However, most of the time, it is impossible to determine the cause of any anomaly.
"It's cool to be able to finally verify that what we see on the video is indeed bigeye fish feeding in the mud. It's like a beautiful reward after years of watching DTIS footage," Mills said.
This isn't the first time that deep-sea creatures have sparked a sea mystery: hungry crustaceans have been discovered to be the architects of strange caves in the Bering Seabed, and strange octagonal patterns covering the seabed of the Fram Strait are the result of octopuses foraging.
The study was published in Deep Sea Research Part I: Papers on Marine Research.