Scientific Studies Designed to Learn More About Juvenile Bottomfish and Larval Billfish in Hawaiian Waters

April 14, 2009
Scientist releasing a tagged Almaco jack, Seriola rivoliana. Recapture of the fish will provide 
    valuable information about the fish's growth and movements.
Scientist releasing a tagged Almaco jack, Seriola rivoliana. Recapture of the fish will provide valuable information about the fish's growth and movements.

A team of scientists from the NOAA Pacific Islands Fisheries Science Center is conducting a 2-week survey to improve biological understanding of juvenile bottomfish and larval billfish in the main Hawaiian Islands. A good knowledge of each stage of a fish's life cycle is essential for sound, science-based management. However, often little is known about younger life stages of a species because they are not targeted by fisheries, so are less available to scientists.

The NOAA team is trying to reduce that information gap. Working from the NOAA Ship Oscar Elton Sette, they are collecting specimens of juvenile bottomfish, including snappers and Hawaiian grouper, in waters off the islands of Hawaii (Big Island) and Maui for studies of age and growth and to determine the bottom habitat occupied by juvenile bottomfish. Along with the bottomfish studies, the scientists will be collecting eggs and larvae of billfish to learn more about billfish spawning activity and ancillary oceanographic data to determine whether the presence of eggs and larvae is linked to certain environmental conditions.

Specimens of Gindai, <em>Pristipomoides zonatus</em>, show growth and development over different life 
    stages.
Specimens of Gindai, Pristipomoides zonatus, show growth and development over different life stages.
Larvae of Pacific blue marlin (Makaira mazara)(top) and swordfish (Xiphias gladius) collected using 
    an Isaacs-Kidd trawl.  Each larva is about one centimeter long.
Larvae of Pacific blue marlin (Makaira mazara)(top) and swordfish (Xiphias gladius) collected using an Isaacs-Kidd trawl. Each larva is about one centimeter long.

Although information about juvenile bottomfish and larval billfish is hard to obtain, cooperating fishermen have provided valuable specimens of bottomfish from waters off the Kohala coast of the Big Island and previous research cruises have successfully sampled bottomfish in the Kohala region and billfish eggs and larvae along the Big Island's Kona coast. Better knowledge of life history traits such as age and growth and size and age at maturity will help current efforts to assess the bottomfish resource and manage bottomfish fisheries in the main Hawaiian Islands. The information on billfish larvae will improve understanding of billfish reproductive biology and stock structure. Bottomfish and billfish are valuable components of Hawaii's marine ecosystems and support valuable commercial and recreational fisheries.

The expedition's Chief Scientist, Ryan Nichols, will lead a diverse group of researchers including staff of the NOAA Pacific Islands Fisheries Science Center and the University of Hawaii Joint Institute for Marine and Atmospheric Research (JIMAR), a NOAA Hollings Scholarship intern from the University of Miami and a participant in the NOAA Teacher at Sea Program. The scientific team will be conducting handline fishing operations for bottomfish using small boats launched from the Sette. They will deploy an Isaacs-Kidd trawl to sample billfish eggs and larvae in surface slicks and a Cobb trawl to take specimens of small fish and other organisms in subsurface waters. The scientists will record the size and gender of each bottomfish fish caught. Incidentally-captured jacks and adult bottomfish will be measured, tagged and released alive to support ongoing studies of growth and movement. Data on physical characteristics of the surveyed waters will be collected using shallow-water casts of a conductivity-temperature-depth profiler (CTD) at designated locations off the Kohala and Kona coasts. Currents will be measured using an acoustic Doppler current profiler (ADCP) throughout the cruise.

In addition to collecting data to support NOAA science, the cruise is providing valuable experience and training for the Hollings Scholarship intern and Teacher-at-Sea participant. They will gain insight into the techniques used to investigate juvenile bottomfish habitats and first-hand knowledge of bottomfish fishing operations and use of environmental and plankton sampling equipment. They will be able to apply this knowledge in their research and classroom lectures, respectively.

By analyzing data gathered aboard the Sette, NOAA fisheries biologist hope to gain a better understanding of key parameters that characterize both juvenile bottomfish habitat and larval billfish spawning patterns. This understanding may be applicable to other islands within the Hawaiian archipelago and may provide a foundation for similar studies in other areas of the Pacific.