Research Cruise Focused on Juvenile Bottomfish Biology and Habitat

November 21, 2008
Juvenile opakapaka Pristipomoides filamentosus used for age and growth studies.
Juvenile opakapaka Pristipomoides filamentosus used for age and growth studies.

Scientists aboard the NOAA Ship Oscar Elton Sette are engaged in a 15 day research cruise to study bottomfish stocks in coastal waters off the Kohala and Kona coastlines of the Island of Hawaii ("Big Island"). Their primary focus will be to collect and study young specimens of snappers (such as opakapaka and ehu) and Hawaiian grouper (hapu'upu'u) important to Hawaii commercial and recreational fishers and to conduct surveys of the associated bottomfish habitat. Researchers will gather data on the biology of bottomfish in the early to juvenile stages of their life history, information vital to accurate assessments of the stocks. Particular attention will be given to collecting specimens for studies of age and growth.

Age and growth information is used to determine how many age groups make up the fish population and what proportions of each age group are mature or immature fish. Scientists can tell the age of a snapper by identifying and counting growth marks formed on the ear bones (otoliths) of the fish. Very young specimens are needed to learn at what age the first marks are deposited. Although young snappers are hard to obtain, fishermen cooperating with the NOAA Pacific Islands Fisheries Science Center (PIFSC) have found them along this area of the Big Island. Better knowledge of life history traits such as age, growth rates, and size and age at maturity will help current efforts to assess these important deep-water bottomfish species and ensure their conservation and management in the main Hawaiian Islands.

Scientist aboard the Sette taking length measurements and collecting DNA samples from a young adult 
    opakapaka.
Scientist aboard the Sette taking length measurements and collecting DNA samples from a young adult opakapaka.

During this cruise, Chief Scientist Ryan Nichols will lead a diverse group of scientists from the PIFSC, the Joint Institute for Marine and Atmospheric Research, and the State of Hawaii Department of Land and Natural Resources. The scientific team will conduct handline fishing operations using small boats launched from the Sette and deploy fish traps to catch specimens of juvenile bottomfish. They will record the size and gender of each fish caught, and tag and release incidentally captured species of jacks and adult bottomfish. In conjunction with fish tagging, any incidentally trapped crabs, fish, eels and sharks will also be measured and released.

In addition to collecting bottomfish specimens, the team will gather a variety of environmental data and use a multibeam sonar to map the seafloor and identify key characteristics of juvenile bottomfish habitat. A shallow water conductivity-temperature-depth (CTD) instrument will be deployed at several sites along the coastline to asses the variability of salinity and temperature in the juvenile bottomfish habitat.

By analyzing data gathered aboard the Sette, NOAA fisheries biologists will gain a better understanding of key parameters that characterize juvenile bottomfish habitat. This understanding may be applicable to other islands within the Hawaiian archipelago and help identify essential juvenile habitat for each bottomfish species.