By Steve Ross, Research Professor - University of North Carolina-Wilmington, Center for Marine Science
May 19, 2013
Our surveys last year of Baltimore Canyon revealed a high diversity of fishes using a wide variety of habitats. Last year we collected over 73 species by trawling and observed and collected many more using the remotely operated vehicle (ROV). We used the data from last year to help guide our fish investigations this year where most of our sampling is in Norfolk Canyon.
Although visibility in the canyons is often poor due to high nutrient loads and suspended sediments, this year we experienced particularly bad visibility, which made fish observations difficult. On our last of 12 dives in this cruise leg, the dives covered a huge range of depths (about 280 meters to 1,400 meters), two canyons, mud and rocky walls, methane seeps, open muddy bottom, and steep slopes. This wide array of habitats services a similarly wide array of fishes, many specific to certain types of conditions.
The deep vertical walls of the canyon hosted abundant cutthroat eels, duckbill eels, and a fish of the family called "oreos." This oreo species was thought to be rare but now that we are gathering better data, it appears to be more common. This points out the value of exploring ecosystems that are difficult to access except by vehicles like ROVs and manned submersibles.
In one area, there were abundant deepwater sharks swimming around the canyon walls. We also spotted a shark that still had a fishing hook in its mouth.
An interesting discovery was that, while examining a coral in the ship’s lab, we discovered several clutches of fish eggs. We are uncertain of the species, but we do know that fishes have not been reported to lay eggs in these corals. We have some of the eggs developing in our cold room and hope they may hatch. A small, pale fish called a bythidid is very closely associated with some of the corals.
On soft muddy bottoms, we have seen about the same kinds of fishes observed in Baltimore Canyon last year. Goosefish, witch flounder, several hake species, and eels are abundant roaming over the open slope. There appear to be good food resources in almost every area, as we see swarms of krill and amphipods in dense aggregations near the bottom.
On the deep methane seep site, fishes were particularly abundant over and around the dense mussel beds. One species of rockling seemed very tightly associated with the mussels, laying on the mussels and in crevices created by the mussels.
On the shallow seep site in Baltimore Canyon, a cutthroat eel of the genus Dysommina was very abundant. This eel at times was also entwined in coral branches.
It will take many months to digest all of the fish data. But these cruises have added a lot to our knowledge of what fishes occur in these canyons and how they use the habitats.