From July 15 – August 2, 2024, 6 CSSF team members supported Dalhousie University, the National Oceanic and Atmospheric Administration (NOAA) and Fisheries and Oceans Canada (DFO) aboard the R/V Henry B. Bigelow for the Cross-border Coral Habitat Exploration (CroCHEt) Expedition in the Gulf of Maine and in submarine canyons on the continental slope, including two in the Northeast Canyons and Seamounts Marine National Monument. The aims of the scientific team were to answer several questions about deep-water corals and to maintain successful collaboration between Canadian and US scientists. Scientists from Dalhousie University, the Delaware Museum of Nature and Science, DFO, and NOAA all participated. The expedition had 8 scientific objectives: 1) conduct video surveys and collect specimens at various locations, 2) explore new areas that may be of interest for protection, 3) evaluate deep-water coral abundance and spatial distribution, 4) collect fauna for taxonomic, reproductive, age, and isotopic analyses, 5) collect data for long-term monitoring in conservation areas, 6) undertake onboard experiments on temperature tolerance of select coral species, 7) collect water samples for eDNA analysis, and 8) collect multibeam data. Work that required the expertise of our team and ROPOS included the collection of imagery, biological samples, and seawater samples.

The CroCHEt expedition had one leg. We performed 11 dives with ROPOS at 9 sites 4 of which were in Canadian waters: 1) Oceanographer Canyon, 2) Gilbert Canyon, 3) Heezen Canyon, 4) Corsair Canyon, 5) Gulf of Maine, 6) Northeast Channel, 7) Jordan Basin, 8) Gulf of Maine Transboundary Transect and 9) Hydrographer Canyon. This expedition summary will, for the most part, contain information from the dives in Canadian waters (Corsair Canyon to Gulf of Maine Transboundary Transect).

At Oceanographer Canyon and within 10 h and 32 min, we collected 25 biological samples, including corals, a sponge, and other marine life. At Gilbert Canyon on July 20, 2024, we and the science team dedicated our dive to the late S. Kim Juniper, who was a dear friend, integral in the establishment of CSSF-ROPOS, Chief Scientist for many ROPOS expeditions, and an avid deep-sea microbial researcher and professor at the University of Victoria. Our Operations Manager, Keith Tamburri, and Co-Chief Scientist, Anna Metaxas, took a moment with a rock that was covered in marine organisms to pay tribute to him and how he would get our team to sit there for hours, just watching sulphide worms battle each other. Our live feed was broadcasted at his celebration of life. At this site (Gilbert Canyon), we collected 23 biological samples, including corals, a sponge, brittle stars, and other sea creatures within our 11-h, 10-min dive. At Heezen Canyon, we collected 32 biological samples, including corals, sponges, brittle stars, worms, a snail and other marine life within 11 h and 43 min. At Corsair Canyon we started at 907 m and ended at 462 m depth. Within 11 h and 50 min, we collected imagery of 6374 marine animals and 18 biological samples, including corals, a sponge, an anemone and other specimens. In the Gulf of Maine, a school of pollock followed ROPOS for most of the dive. We collected 12 biological samples, including sponges, a sea star, brittle stars, a worm and other ocean critters over 11 h and 39 min. At Northeast Channel, we completed 2 dives, the first from 431 m to 860 m depth and the second from 479 m to 772 m depth. For the first dive, we dealt with strong currents and on the second, we came across lost fishing gear near a marine conservation area, the Northeast Channel Marine Refuge. The first dive took 11 h 42 min and the second took 10 h 55 min. Across those dives, we collected imagery of 6589 marine animals and 21 biological samples, including corals, brittle stars and other organisms. At Jordan Basin, the shallowest site, we started at 223 m and ended at 211 m depth. Within 11 h and 38 min, we collected imagery of 17 999 marine animals and collected 36 biological samples, including corals, a sponge, a shrimp, a brittle star, and other specimens. At the Gulf of Maine (Transboundary Transect), we performed 1 dive in Canadian waters, which began at 221 m and ended at 186 m depth and another dive in American waters. We collected imagery of 8927 marine animals and 5 biological samples, including corals and sponges and took footage of old trawl marks within the span of 10 h and 49 min. At Hydrographer Canyon, and within 10 h and 5 min, we collected 19 biological samples, including corals, sponges, worms, a brittle star and other marine specimens.

Highlights for the Science Team included how many types and sizes of corals were present in both fields and on vertical walls, some of which they estimated were several centuries old, as well as the presence of dense forests of coral in the marine conservation areas. They also enjoyed our last dive at Hydrographer Canyon, which was an area that was visually interesting and had a variety of octopuses and squids.

A highlight for the ROPOS Team was how good the high density of corals made the scientists feel. Our Operations Manager, Keith Tamburri, found it fun to check if corals were in the sonar area that the Science Team’s predictive models pointed towards. It was also unusual and exciting for us to see a glass squid.

The main challenge we faced on this expedition was navigating ROPOS through the high current areas, but strong currents are hard to avoid because these places are where the corals tend to thrive. To handle the current, we ran transect lines astern (backwards) at 1 knot. When we do this, we don’t know where we’re going as much, but sometimes we have to, to prevent us from losing control and from having ROPOS being blown away. When there’s a strong current, the launch and recovery vessel also needs to move with it, and both the ship and ROV need to drift at the same rate. It’s possible for the ship to move faster than the ROV, which would pose a safety risk and risk of damaging ROPOS. So, we took care to keep in constant communication with the captain of the ship to keep things under control. Another challenge was the low visibility at Jordan Basin, which made it challenging to collect quality imagery. Despite this, we were able to capture footage of 17 999 marine animals.

As part of public outreach, our Science Team streamed all the dives on YouTube and set up an email account to which other researchers and the public could send questions. On average, 40 people watched our dives per day. The CroCHEt was a Challenger 150 expedition which is a UN Ocean Decade endorsed project. For highlights from the Science Team, please visit the Delaware Museum of Nature and Science website.

For more information on the science, see: Nizinski, M. S., and E. K. Shea. 2025. Observations and preliminary findings from the United States/Canada transboundary cruise to the northwestern Atlantic canyons and Gulf of Maine (CROCHET; HB-24-05). U.S. Dep. Commer., NOAA Tech. Memo. NMFS-F/SPO-263, 45 p.