A few times recently when I’ve been out collecting sediment, I’ve had the feeling that I’m being followed. Each time, I turn around and find one of these little guys in tow, hovering over the areas of sea floor that I’ve just disturbed by my sampling. They’re called spotted ratfish (Hydrolagus colliei) and I’ve grown quite fond of them, despite their funny looks. They’re like my little underwater sidekicks, always interested in what I’m doing and standing by patiently as I do my work. If the name weren’t already taken, I’d suggest we call them “dogfish” for their loyal underwater companionship. But given their genus name, Hydrolagus (lagos means hare in Greek), I might instead just take to calling them water bunnies.
Spotted ratfish are part of an ancient group of fish called Chimaeras, which are cartilaginous and most closely related to sharks. Their tails are long and skinny, providing limited propulsion. To swim, they instead flap their pectoral fins like a bird. They’re generally thought to favor crunchy foods like crabs and clams, but may also eat worms and other invertebrates in soft sediment. Similar to dogs, what keeps them hovering nearby is probably the hope that I’ll uncover something delicious as I’m sampling. Dog-like or not, though, I ignore the urge to reach out and pat them on the head. They have a venomous spine in front of their dorsal fin that can deliver a painful sting.
If ratfish look to you like weird mythological creatures concocted by the likes of Napoleon Dynamite, you wouldn’t be alone. The name Chimaera is, of course, borrowed from the Chimera in Greek mythology, a fire-breathing beast composed of parts from a snake, a lion, and a goat. As wikipedia reports: “The term chimera has come to describe any mythical or fictional animal with parts taken from various animals, or to describe anything perceived as wildly imaginative or implausible.” I love that. Ratfish indeed look like the result of some wildly imaginative experiment, and it makes me love them all the more.
As I dive at sites around Seattle, even when I’m not collecting sediment, I’m amazed at how many spotted ratfish I see (at least 2-3 per dive). An article in the Seattle Times a few years ago highlighted the success of spotted ratfish in Puget Sound (article). Their population here is estimated at 200 million. As Sandi Doughton, the author of the article, states, “that’s more than 30 [ratfish] for every woman, man and child in the state [of Washington].” Spotted ratfish have been a dominant species in bottom trawl surveys in Puget Sound for some time, particularly as other fish populations have plummeted. Information about their population trajectory is limited, but many believe that something about the changes we have made to the marine environment has provided this species with the conditions it needs to flourish and proliferate. Precisely what conditions these might be is unclear.