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 had a hunch this might work but I was really surprised how well the head profile images matched the impressions. We were able to provide fairly good evidence that these impressions were made by two grenadier species,” Stevens said.
“The reason we could point to a specific species is because of their unique head features – these types of rattails have a long snout and an extendable mouth on the underside of their head that allow them to feed off the seafloor, something that other species do not.”
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. The exact reason they make these marks on the seabed is unknown.
“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.
“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.”
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