Dive 15: Pourtales Terrace Sinkhole
May 2, 2018
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Dive 15: Swimming Squid Serenade

On a more shallow Dive 15, several squid (Illex sp.) were observed. Most were seen on the sediment, but others – like this individual observed at ~455 meters (~1,490 feet) – lifted off the bottom and was seen swimming. It was quite mesmerising to watch. Download larger version (mp4, 23.4 MB).

Today’s dive surveyed a large, unexplored sinkhole off the Pourtales Terrace to a depth of ~490 meters (~1,610 feet). The bottom was covered with a lot of sediment and swarming with small fishes, shrimp, squid, and crabs. Several patches of Sargassum seaweed and various pieces of human-made debris were encountered, including balloons, cans, and fishing gear. On the northern side of the sinkhole, fish became less abundant and a rock outcrop was observed. Going upslope towards the rim of the sinkhole, larger rock outcrops with isolated corals and sponges were observed. Climbing the sinkhole wall, the substrate changed to limestone covered by a thin layer of sediment. Glass sponges were occasionally seen on the substrate, as well as tube worms, anemones, crinoids, urchins, and bryozoans.

Moving away from the sinkhole and towards the terrace, the terrain became flatter. Brittle star arms protruded from the numerous holes in the flat terrain. Demosponges (Phakellia sp.) became common, as did snowshoe urchins (family Echinothuriidae). Other invertebrates recorded included glass sponges, crabs, squat lobsters, anemones, lace corals, sea stars, squid, hermit crabs, byozoans, and hydroids. Fish included short-bearded codling, blackbelly rosefish, armored searobin, roughy, rattails, hake, herring smelt, cardinalfish, duckbill flathead, toadfish, shallowtail bass, hatchetfish, barracudina, bristle mouth, shortnose greeneye, a slope dragonet, and flatfishes. Only five colonies of stylasterid corals were seen throughout the dive.