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The dog(fish) days of diving…

September 30, 2012

Unlike the Ostfriesland, which sank ‘turtle’ (bottom up), the German light cruiser we dove on today was oriented upright. Normally this would facilitate exploration, but the Frankfurt was the victim of systematic rounds of increasingly powerful bombs, leading up to the first use of 600lb bombs, and the ship sank as a tangled mass of bent metal in many places. In fact, it sank so quickly after the last round of bombs that the usual inspection parties assessing and documenting damage in between raids were unable to board her for a last time. In addition to the tangle of fishing nets and gear that wrapped large portions of the ship, we found an abundance of dogfish (chain catsharks), literally in ‘dogpiles’ on almost every available ledge. Their mermaid purse eggcases draped the nets and wires like living curtains that swayed in the wake of the ROV. Every frame of the live video-feed contained at least one life-stage  and many different behaviors of the dogfish, and it was these prolific wreck residents that sought retribution for our bright interruption into their private lives. Near the end of the dive, having successfully avoided fishing gear and longlines across many transects of the ship, the ROV mysteriously lost some of its mobility.

Dogfish

K2 suffers the dog(fish) days of diving. The tough skin of the dogfish prevented the sharp thruster blades from cutting the body (which it is normally capable of with squid and fish), and both sharks remained in one piece, successfully stopping the motion of the thrusters and frying their motors. Lateral thruster shown here.

The Nancy Foster strategically moved in order to extract the ROV safely without risking entangling the depressor on any parts of the wreck; the ROV crew in the van scratched their heads as K2 was reeled up to the surface. Once on deck, Rudy’s keen eyes noticed two sacrificial acts of sabotage by the wreck residents.

Two unfortunate dogfish (with their incredibly tough skin) died in the ROV’s thrusters (one lateral and one top), completely frying the internal magnetized motors. As one of the voucher specimens, we collected a small cluster of dogfish eggcases (the sabotaging dogfish also became voucher specimens). Once in the lab we put one of the cases on the bright light of the dissecting scope and were amazed to be able to see the developing embryo inside.

developing embryo inside the dogfish eggcase

A developing embryo inside the dogfish eggcase. The large circle is the yolk.

The dog(fish) days continued through the next morning as the ROV crew worked to repair the thrusters so the Kraken II could return to the water. Unfortunately they only had enough spare parts to repair one of the thrusters (doggone those dogfish!), but they determined the Kraken would still be safely mobile with only one lateral thruster, and so by lunchtime we were ready for a launch.

The previous night, a curiously smooth, large riverstone had turned up in one of the four boxcore samples from the deepest part of the canyon, and in the morning the archaeologists were thrilled by this unexpected find. First, they were intrigued by the idea of it being a riverstone (worn smooth by tumbling water) potentially washed down the canyon long ago when this part of the continental shelf was exposed and the shore of a river. Second, they were intrigued by the idea that riverstones were once used as ballasts on ships during transatlantic voyages.

large clay deposit

A large clay deposit with geometric edges seemed out of place on the smooth ocean floor. The clay provided structure and shelter for lots of species, including crabs.

Could this stone be a clue to an unknown shipwreck somewhere beneath the waves? Geological and archaeological curiosities were satisfied by returning to the site to launch the newly fixed K2.

The topography of the bottom was relatively flat and uniform at first, but several hours of exploration revealed what appeared to be small cliffs of layered rock worn smooth by water (or wind?), strange geometric chunks of clay larger than K2 itself, and a plethora of wildlife (but no shipwreck).

A tongue fish

A tongue fish, a relative of the flounder.

Here is a sample of my running species list that I made while watching the ROV video during the dive:

–          A small octopus

–          Myctophids

–          Conger eels (hiding in holes in the cliffs)

–          Box crabs

–          Spider crabs

–          Large pink anemones (>10cm)

–          Pinkhead shrimp

–          Red Hake

–          Fourbeard rockling

–          Hermit crabs

–          Galatheid crabs

–          Polychaete worms

–          Tongue fish

–          Flounder

–          Batstars  (>10cm)

–          Scorpion fish

–          Sponge (>10 cm)

–          Squid

–          Acanthogorgia

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