NOAA Research Expedition Learning about Early Life History of "Deep-7" Bottomfish in the Main Hawaiian Islands
From August 12-26, scientists on the NOAA Ship Oscar Elton Sette are engaged in a research cruise in leeward waters off the Hawaiian islands of Niihau, Oahu, and Lanai, and off the Kona coast of the Island of Hawaii ("Big Island"). The primary focus is to collect rarely-encountered pelagic stage juveniles of the commercially-important "Deep-7" bottomfish species. These species include the Hawaiian grouper, hapu'upu'u, and six species of deep-water snappers: opakapaka, ehu, onaga, lehi, gindai, and kalekale. Mature bottomfish reproduce by releasing eggs into nearshore waters. After the eggs are fertilized, they drift offshore from the island and bank areas into pelagic waters (open water, away from land). The pelagic stage is part of the normal early life cycle of these species. Later, the pelagic juveniles return to nearshore waters and settle into bottom habitat where they complete their life cycle. Virtually nothing is known about the early, pelagic stage, including the amount of time the developing bottomfish remain in the pelagic habitat, how far away they drift from the islands, and at what size and age pelagic juveniles return to the islands and switch to a bottom-dwelling existence. Collection of the pelagic stage juveniles will provide the necessary specimens to begin to answer these questions.
During the 15-day cruise, Chief Scientist Robert Humphreys, a fishery biologist from the NOAA Pacific Islands Fisheries Science Center, will lead a diverse research team that includes other scientists from PIFSC, the University of Hawaii Waikiki Aquarium and Department of Oceanography, and the Monterey Bay Aquarium. Twice each night, the scientific team will deploy a Cobb midwater trawl in offshore waters at depths of 100-125 meters and 20-25 meters. In a 2011 cruise, scientists using the same trawl at the same depths captured 45 pelagic juvenile snappers offshore of the Kona coast and Penguin Banks. During the current cruise, more sites will be sampled with the Cobb trawl and tows will be conducted farther offshore to determine just how far these juveniles range from the islands.
In addition to collecting pelagic juvenile bottomfish, the team will gather oceanographic data to help describe the juvenile pelagic habitat. An onboard acoustic instrument will be used to measure the speed and direction of subsurface currents. And a conductivity-temperature-depth (CTD) instrument will be lowered from the ship and retrieved to provide a depth profile of temperature, salinity, and oxygen concentration throughout the water column. Water bottles will be attached to the CTD to collect samples of seawater at designated depths; later, the samples will be filtered and processed to determine the chemistry and chlorophyll content of the water. These ocean measurements will help to characterize the physical environment that juvenile pelagic stage snappers may be associated with.
Genetic analysis of DNA extracted from the specimens will help us identify the species of these hard-to identify pelagic juvenile stages and the extent to which pelagic juveniles recruit to islands and banks different from those where they were born. Ultimately, the results of this research, along with other early life history information, will help scientists better assess how connected various bank and island populations of Deep-7 bottomfish are to one another, within and outside of the main Hawaiian Islands.