Millions of strange-looking glowing sea creatures called pyrosomes have started to “bloom” off the coast of the Pacific Northwest of the US and Canada, filling up fishing nets, clogging hooks and research gear, and befuddling scientists who have no idea why populations of the tube-like organisms are exploding, flooding the water column.

“Call it the invasion of the pyrosomes,” writes Michael Milstein in a post on the National Oceanic and Atmospheric Administration’s (NOAA) Northwest Fisheries Science Center website.

They started to show up in the spring and in the past month or two, swarms of the animals been spotted all over the region.

Pyrosomes are odd creatures — they’re technically tunicates, colonies of individual organisms known as zooids that feed off of plankton and other small organisms. They have little bumps, are about as firm as a cucumber or pickle, and are gelatinous like jellyfish. They’re translucent and bioluminescent, which gives them a glow (the word pyrosome means “fire body”).

And while they can occasionally be found further north, they typically inhabit tropical waters, which makes the appearance of these massive quantities strange and disturbing to fishermen who worry that they could devastate a fragile food network.

“We have a lot of questions and not many answers,” Ric Brodeur of the Northwest Fisheries Science Center’s research station in Newport, Oregon explained in a post on the center’s site. “We’re trying to collect as much information as we can to try to understand what is happening, and why.”

Pyrosomes can grow to massive sizes, potentially to more than 60 feet long, though the ones currently flooding the seas off the coast of British Columbia and Alaska are more cucumber-sized.

It’s the numbers that are troubling. Salmon and halibut fishermen haven’t been able to access their normal catch, with long lines catching pyrosomes instead of fish on basically every hook, according to reports by the CBC and National Geographic.

One five-minute trawl of a research net off the coast of Oregon dragged in about 60,000 of the creatures. Researchers from Ocean Networks Canada at the University of Victoria released a video showing just how thick the water was with these cucumber-like bodies.

Some think that these populations might come from an anomalous huge “blob” of warm water that hovered in the Pacific from 2014 to 2016, though that warm mass has dissipated.

“It’s really weird,” Jennifer Fisher, a faculty research assistant with Oregon State University’s Hatfield Marine Science Center, told National Geographic. “I’ve never seen anything like it.”

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Typically found in the tropics, we’re seeing huge numbers of #pyrosomes in the eastern Pacific. Read more https://t.co/pZ8aQHhc2A #ONCabyss pic.twitter.com/18RnlIJWmW

— Ocean Networks ???????? (@Ocean_Networks) June 14, 2017

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