Biological Expedition Collects Data to Determine Genetic Relatedness of Botttomfish in Hawaii and Johnston Atoll

August 17, 2013
Specimens of Johnston Atoll bottomfish caught out of small boats launched from the NOAA R/V Sette will provide fin-clip 
                 tissue samples for later genetic analyses to help determine relationships between bottomfish populations at Johnston and Hawaii.
Specimens of Johnston Atoll bottomfish caught out of small boats launched from the NOAA R/V Sette will provide fin-clip tissue samples for later genetic analyses to help determine relationships between bottomfish populations at Johnston and Hawaii.

Scientists aboard the NOAA R/V Oscar Elton Sette departed Honolulu on a 19-day research mission to collect biological samples of bottomfish around Johnston Atoll, a remote U.S. military possession located about 700 nm southwest of Honolulu. The expedition ends September 5 when the ship returns to her home port in Pearl Harbor. The primary focus of the research project is to collect fin-clip tissue samples from all species of the commercially important "Deep-7" bottomfish complex at Johnston. These species include the Hawaiian grouper "hapuʻupuʻu" and the six species of deep-water snappers ("opakapaka", "ehu", "onaga", "lehi", "gindai", and "kalekale"). After completion of the cruise, collaborating scientists at the Hawaii Institute of Marine Biology will conduct DNA analyses of the fin-clip tissues. Samples collected during the project will provide a first opportunity to determine the possible extent that Johnston Atoll and the Hawaiian Archipelago populations of Deep-7 bottomfishes are genetically linked.

Scientists have speculated that populations of both hapuʻupuʻu and opakapaka at Johnston Atoll and Hawaiian Archipelago may be genetically linked through the transport of pelagic larvae and juveniles stages. The pelagic larval stage living in offshore open waters away from land is part of the normal early life cycle of these species. While the Sette is at Johnston Atoll, and later during the ship's transit back to Honolulu in distant offshore waters, the research party will deploy midwater trawls at night to capture sample specimens of the pelagic stage bottomfish. The collection of young pelagic individuals and tissues from adult Deep-7 bottomfish (caught using bottomfish handline gear) will provide the necessary material for an investigation of the extent to which populations between Johnston Atoll and the Hawaiian Archipelago are interconnected.

Midwater Cobb trawl prior to deployment from the NOAA R/V Sette.  The back "cod-end" of the net is shown lying on the deck; 
                 the rest of the net is wrapped around the net reel.  The net will be towed at night to capture specimens of pelagic stage 
                 bottomfish.  After the tow is completed and the net retrieved, the black canvas bag (lying on deck) will be opened to remove the 
                 catch.
Midwater Cobb trawl prior to deployment from the NOAA R/V Sette. The back "cod-end" of the net is shown lying on the deck; the rest of the net is wrapped around the net reel. The net will be towed at night to capture specimens of pelagic stage bottomfish. After the tow is completed and the net retrieved, the black canvas bag (lying on deck) will be opened to remove the catch.

Chief Scientist Robert Humphreys will lead a diverse research team that includes scientists from the NOAA Fisheries Pacific Islands Fisheries Science Center in Honolulu, the Monterey Bay Aquarium, and Hawaii Pacific University. The researchers will be joined by an experienced Hawaii bottomfish fisherman. The scientific team will use handline gear deployed out of small boats to catch specimens of bottomfish within the 100-400 meter depth contours around Johnston Atoll. They will collect fin-clip samples from 50 fish per species at Johnston Atoll to obtain a large enough tissue sample for later DNA analyses. Sampled bottomfish will be released after samples of fin tissue are removed except for the very largest individuals. These fish will be retained for otolith extraction and later age determination.

Sampling of pelagic stage bottomfish around Johnston Atoll will be conducted at night about ~25 nm offshore using a Cobb midwater trawl net towed at depths of 170-175, 100-125 and 20-25 meters. Cobb trawls will also be conducted at night during the transit from Johnston Atoll back to Honolulu to evaluate the extent of the offshore distribution of pelagic stage individuals between these two island areas.

Researchers will use an Acoustic Doppler Current Profiler (ADCP) to collect oceanographic data such as current speed and direction at various depths in the water column. They will also lower a CTD instrument through the water column to measure conductivity, temperature and other properties of the water to see how they vary from the sea surface down to deeper waters. Water-sampling bottles attached to the CTD will collect water at pre-determined depths that will be filtered and processed onboard the ship to determine water chemistry and chlorophyll content. These ocean measurements will help scientists characterize the physical environment that pelagic stage bottomfish may be associated with and may lead to a better understanding of their environmental habitat.

The results of this project will provide important information regarding the degree of isolation that Deep-7 bottomfish populations in Hawaii experience in relation to their closest geographic neighbor.

Bathymmetry surrounding Johnston Atoll. Area in red represents potential handline bottomfishing grounds to be sampled during the 
        expedition.
Bathymmetry surrounding Johnston Atoll. Area in red represents potential handline bottomfishing grounds to be sampled during the expedition.