Research Cruise Aimed at Better Understanding of Hawaii Bottomfish

August 28, 2011

Scientists aboard the NOAA Ship Oscar Elton Sette are engaged in a 15 day research expedition to study the biology of bottomfish stocks off the Kohala and Kona coasts of the Island of Hawaii ("Big Island"). The primary purpose of the cruise is to collect adult specimens of the "Deep 7" bottomfish species (opakapaka, onaga, ehu, lehi, gindai, kalekale, and hapu'upu'u) for on-going life history studies. Particular objectives of the life history research are to determine the length and age at which these deepwater species become reproductively mature, how fast they grow, and how long they are likely to live. The bottomfish specimens will be collected using handline fishing gear deployed from small boats launched from the Sette. Specimen collection will focus on opakapaka and gindai. Knowledge of growth rate and reproductive life history traits will enable PIFSC scientists to better assess the stock status of these commercially and recreationally important bottomfish. More accurate stock assessments will improve the scientific basis for bottomfish fishery management.

Researchers will collect specimens of gindai and other bottomfish species to learn more about their 
             growth rates, maturation, and longevity.
Researchers will collect specimens of gindai and other bottomfish species to learn more about their growth rates, maturation, and longevity.

During the cruise, running from August 28 to September 11, 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 University of Hawaii Joint Institute for Marine and Atmospheric Research, Monterey Bay Aquarium, and the University of Nations in Kailua-Kona.

In addition to collecting adult bottomfish specimens using handlines, the scientific field party will conduct research to learn more about the little-known early life history of Deep-7 bottomfish in the waters off west Hawaii. Subsurface plankton net tows (using an Isaacs-Kidd trawl) will be conducted during daylight hours to collect larvae of these fishes. Larger larvae and early pelagic juveniles of Deep-7 bottomfish will be collected from subsurface depths using a Cobb midwater trawl during the evening.

An Isaacs-Kidd trawl will be deployed from the NOAA Ship <em>Oscar Elton Sette</em> to collect eggs and 
             larvae of bottomfish and billfish in surface waters of the ocean.
An Isaacs-Kidd trawl will be deployed from the NOAA Ship Oscar Elton Sette to collect eggs and larvae of bottomfish and billfish in surface waters of the ocean.

Although the focus of the cruise is to study bottomfish, surface Isaacs-Kidd net tows will also be conducted to collect specimens of billfishes in their early life stages. These tows will target surface slicks off the Kona coast where eggs and larvae become concentrated. Scientists will be able to learn more about which species of billfish are spawning, when and where their eggs and larvae occur, and whether spawning is associated with certain environmental conditions, such as sea surface temperature and salinity. To measure environmental conditions, the research team will gather data on ocean temperature and salinity using a conductivity-temperature-depth (CTD) instrument and information on the direction and velocity of subsurface currents using an acoustic Doppler current profiler (ADCP).

By analyzing the biological data and oceanographic data gathered during this Sette expedition, NOAA fisheries scientists hope to gain a better understanding of key factors that characterize the habitat of pelagic stage larvae and juvenile bottomfish and affect patterns of billfish spawning. The information gained in the Big Island studies may be applicable to other islands within the Hawaiian archipelago and may provide a foundation for similar studies in other areas of the Pacific.