Searching out Deep-7 bottomfish
Extensive effort was required to collect a minimum of 30, and maximum of 50, fin-clip tissue samples from bottomfish in the Johnston Atoll area to conduct DNA analyses. Proposing the collection of 30 fin clips is very different from actually obtaining them, especially in an area where very little is known about bottomfish behavior. See previous bottomfish research expedition post: http://bit.ly/1cI479t
Our bottom fishing expert, Eddie Ebisui III and our Chief Scientist Bob Humphreys were tasked with providing the best spots for collecting the samples. The night before fishing, they would look at the weather for the following day to determine the area most conducive for fishing and away from bad weather. By deciding the night before it allowed the time for the ship to transit through the night to the desired location for scouting.
Once over the desired location, a course would be plotted for the ship to take that covers the targeted depth ranges of the Deep-7 bottomfish species we were seeking. The ship will survey for topography, currents and use an EK-60 fish finder to identify areas of interest. The depth ranges were determined from knowledge we had from Hawaiian waters and also by continually adapting our fishing according to our catch data in the Johnston Atoll waters of the Pacific Remote Islands Marine National Monument. Certain species look for bottom structure and also specific current speeds and direction. For example, hapu’upu’u live in a depth range of 100-130 fathoms and since they are ambush feeders, they like rocky structures with caves and crevices to help them to eat. They are solitary and are spread out over larger spatial areas so requires continuous moving to catch them. gindai and yellowtail kalekale are found over the entire depth range while onaga were typically found around 120-140 fathoms and had the narrowest depth band of each of the Deep-7 species. Once locations were identified they were marked and the GPS coordinates were passed onto the small boats
The depth distribution of the bottomfish seemed shifted toward deeper depths at Johnston Atoll compared to the Main Hawaiian Islands. Louise Giuseffi plotted depth ranges for 8 bottomfish species that included the almaco jack (Seriola riviolani), black ulua, ehu gindai, hapu’upu’u, lehi, onaga, and opakapaka and all had similar deep distributions between 115-140 fathoms. The most abundant species that appeared at all depths was the yellowtail kalekale while the two principal species of jacks encountered (Carangoides orthogrammus and Caranx lugubris) were encountered at the shallower depth from 85-110 fathoms. The bottomfish habitat at Johnston Atoll is likely highly influenced by the steep topography of the bottom.
Our efforts resulted in a cumulative number of fin clip samples obtained for the snapper/grouper complex:
We have now achieved our minimum sample sizes (n=30) for 5 species (onaga, opakapaka, hapu’upu’u, gindai, and yellowtail kalekale) and optimum sample size (n=50) for opakapaka, gindai, and yellowtail kalekale.