Mystery of Strange Marks on Sea Floor Solved by Scientists

A decades-long conundrum of what could be behind markings in the seabed has now been solved. Researchers first spotted these horseshoe-shaped imprints on the ocean floor in 2013 off the coast of New Zealand, at a depth of around 1,600 feet. For years, they've wondered what was behind them. Research has now revealed that the marks were caused by a strange creature called the deep-sea rattail. This mystery was solved by Sadie Mills, an invertebrate collection manager at New Zealand's National Institute of Water and Atmospheric Research (NIWA) and her colleague Darren Stevens, a NIWA fisheries scientist.

"Sadie sent me a bunch of images from the survey and asked whether they had been caused by a deepsea rattail, also known as a grenadier," Stevens said in a NIWA statement. "She suspected that what we were seeing was lebensspuren – which is a German word meaning 'life traces,' referring to physical evidence of life that is left behind in the environment. We wondered if these markings could be traces of a rattail foraging in the sediment for its next meal." The researchers compared the profiles of heads of specific species of rattail—long, thin deep-sea fish—to the marks on the seabed. The images fit together nearly perfectly. "I noticed that some Coelorinchus rattails (there are 23 Coelorinchus species in New Zealand waters) have a unique shape to the underside of their head," Stevens told Newsweek. "This is because they have a long snout, a mouth on the underside of their head, and each species has a slightly different head shape. Given the size of the imprints (the DTIS towed imaging system has two lasers on it mounted 20 cm apart) and the depths in which these unique marks were seen we believe that there were only three Coelorinchus rattail species that were likely to have made the marks. "By using images of the underside of the head of these three species we were able to match the two most clearly defined imprints to two of these species: a two saddle rattail (Coelorinchus biclinozonalis) and a oblique banded rattail (Coelorinchus aspercephalus). We did not match any images to the third species, Bollons' rattail (Coelorinchus bollonsi), but it is likely to make similar imprints."

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The exact reason they make these marks on the seabed is unknown. "We believe that the rattails that likely create these bite marks are doing so to capture prey that live in or on the sediment, such as small crabs or large polychaetes (marine worms) that live in tubes in the soft sediment," Stevens told Newsweek. This finding was published in the journal Deep Sea Research Part I: Oceanographic Research Papers.

Rattails are found at depths of between 600 and 13,100 feet and have huge blue eyes evolved to detect traces of light from bioluminescence. These fish feed on a variety of creatures, from smaller fish to crustaceans. "This new discovery could allow future surveys to identify soft sediment feeding areas and critical fish habitats for these species, which are a key part of the ecosystem," Stevens said. The researchers are excited by their finding, as it may pave the way to figuring out the origins of other mysterious clues left by deep-sea creatures.

"NIWA uses a technology called the Deep Towed Imaging System (DTIS) to allow us to see the seafloor in stunning detail. When our people review this footage, they often see markings in the sediment, but unfortunately most of them are unknown to science and we can only guess what might have made them, let alone find convincing proof," Mills said in the statement. "It is so cool to finally have the validation that what we saw on the video was actually rattails feeding in the mud. It's like getting a nice reward at the end of many years of watching DTIS footage." They also hope to learn more about the rattail and its behavior. "It would be interesting if seafloor video analysts went back and did a study on the prevalence of these in historical seafloor video footage," Mills told Newsweek. "The seafloor sediment consistency probably has to be just right for the marks to stay there long enough for us to see them, and for the marks not be disturbed by current or other seafloor animal activity. So perhaps we were very lucky to see these!" Do you have a tip on a science story that Newsweek should be covering? Do you have a question about rattails? Let us know via science@newsweek.com.