By John Rooney
Our seafloor mapping mission began in early May with underwater video and photographic surveys of coral reef habitats along the shores of West Maui, as documented in Seafloor Mapping Mission: Maui. The second part of this mission, led by a team of scientists from the NOAA PIFSC Coral Reef Ecosystem Division (CRED), was to conduct these underwater mapping surveys along the coast of West Hawai‘i.
This specific region off the coast of Hawai‘i Island has been identified as priority site for research and management by the State of Hawai‘i Division of Aquatic Resources, and the NOAA Coral Reef Conservation Program (CRCP), and is within the boundaries of the Hawaiian Islands Humpback Whale National Marine Sanctuary. It is also a NOAA Habitat Blueprint focus area and funding for this work was provided by both the Habitat Blueprint program and CRCP.
The original plan was to transit directly from Maui to Hawai‘i Island, however, rough and dangerous conditions in the Alenuihaha Channel between the two islands made it impossible. Once weather conditions improved, the team returned to the Big Island to continue the mission. The Hawai‘i Division of Boating and Ocean Recreation graciously provided a slip for us in Kawaihae Harbor on the northwest side of Hawai‘i Island.
The first day, CRED team members John Rooney, Rhonda Suka, and LTJG Kristin Golmon set up and tested gear to prepare for an early start the next day. The following morning, we started towing the underwater camera sled system to survey coral reef ecosystems along the approximately 18 miles of coastline stretching from Kawaihae to the southwest. The photographs and videos revealed reefs growing on basalt (volcanic rock) often with dense and diverse coral communities. Toward the northern end of the survey area, we discovered reefs with an abundance of Porities compressa or “finger coral” forming reefs that are more porous than most in the Hawaiian Archipelago. The Porities compressa reefs appear to be a preferred habitat for numerous reef fish that shelter within their branches.
One highlight of our trip was an unexpected visit from a juvenile whale shark that swam up to side of the ship while we were towing the camera sled. We estimated that she was about 11 feet long and, apparently, very curious. She circled around the boat, checking out our camera set-up and the people onboard. She also enjoyed hanging out behind the starboard engine to bask in the wash of water coming off the propeller. We were concerned that she might swim into it, but the winds and seas were calm and she never got too close.
Despite being a shark, whale sharks are actually filter feeders like whales, gulping in water and filtering it out, to feed on plankton, macro-algae, larvae, small squids, and fishes. We assume that, being a filter feeder, she was positioning herself in areas of strong current, in this case created by the propeller wash, to draw in the most seawater for feeding. Never having seen a whale shark in the wild before, those of us on the M/V Koholā felt lucky to be aboard that day.
The next portion of our mission continued aboard a smaller vessel, the M/V Kākū, a 21 ft workskiff that was generously provided by The Nature Conservancy (TNC) Hawai‘i. This aluminum vessel is well-designed for coastal work and suited our needs admirably. TNC was also kind enough to provide expert captains Hank Lynch and Chad Wiggins, who not only operated the boat, but helped maintain our logbooks and assisted throughout each survey day.
Because the Kākū lacked the enclosed cabin space required to protect topside electronics, we were unable to use our standard Towed Optical Assessment Device (“TOAD”) camera sled. Fortunately, colleagues from NOAA PIFSC were kind enough to loan us another camera system. Rhonda Suka rigged together a Deep Blue SplashCam system with a GoPro camera in a waterproof housing, two LED lights in their own housings, and a pair of lasers mounted in parallel to provide scaling information.
The SplashCam provided a real-time video feed from the seafloor and the GoPro collected still photos that will be used to classify the different types of seafloor and variety organisms growing on it. Although lacking many of the capabilities of the larger TOAD camera sled system, the SpashCam/GoPro combination allowed us to continue to operate and the use of the smaller M/V Kākū enabled us to work closer to shore.
We would like to extend our thanks to the numerous partners who assisted with the survey or provided existing seafloor imagery, as well as the survey team and boat captains. This two-part mapping mission resulted in two excellent datasets that will produce maps of coral reefs and other seafloor features. These maps will help resource managers plan and monitor results of mitigation activities they undertake to improve the health of coral reef ecosystems.