Trawling the Depths

Mesopelagic trawl sampling is still going strong on the NOAA Ship Henry B. Bigelow with one more round tomorrow before they finish the cruise with more than two days of acoustic surveys.

Probably the most celebrated animal they've caught so far was a paper nautilus or Argonaut (Argonauta argo) that featured in an earlier post. Argonauts are a rarely encountered pelagic octopus. Only the females create a shell, so they know the one they caught was a girl. Argonauts are fascinating animals with a surprising life history, but they aren't necessarily mesopelagic animals, more epipelagic. The one they caught was in great shape, so they released her after shooting some photos and videos. WHOI biologist and resident fish photographer Paul Caiger has a particular affinity to argonauts, as he published an article on this animal in New Zealand Geographic last year.

One of the recent catches also included a half-naked hatchetfish (Argyropelecus hemigymnus), a species that the team has been seeing in waters influenced by the Gulf Stream. This fish has three forms of camouflage: a very compressed body with silvery mirror-like flanks to reflect any light from an angle and thus make it invisible, bioluminescent photophores on its underside used for counter-illumination to match the down-welling light, and some transparency in the tail region that wiggles making it appear half naked.

Last night, they brought up a strawberry squid (Histioteuthis reversa), which you can see in the slideshow. This is a member of the cock-eye squid group, named for the fact that it has two different-sized eyes (the larger one looks up into the dim light, the smaller one points down, scanning for flashes of bioluminescence). It's also known as the reverse jewel squid due to the complex arrangement of photophores that somewhat resemble jewels stuck in its body and are just another example of the amazing life forms and adaptations we're seeing with each new trawl.