Surveys Target Collection of Juvenile Bottomfish to Improve Stock Assessments

One of the top research priorities at the Pacific Islands Fisheries Science Center is to provide the science needed to support sustainable commercial and recreational fisheries for Hawaii bottomfish. The bottomfish resource is a multi-species complex consisting mainly of six species of snappers and a grouper (together referred to as the "Deep-7" species). To improve the accuracy and reliability of stock assessments, the Center has focused on biological studies to fill gaps in knowledge of age, growth, and other aspects of bottomfish life history.

Handline gear was used to catch bottomfish from small boats during the NOAA research cruise.

In late 2008, PIFSC staff in the Fishery Biology and Stock Assessment Division (FBSAD) and Fisheries Monitoring and Socioeconomics Division (FMSD), and a scientist from the Hawaii Division of Aquatic Resources conducted a 15-day research cruise on the NOAA Ship Oscar Elton Sette in calm, nearshore waters off the Kohala and Kona coast of the Island of Hawaii. The main mission of the cruise was to locate and capture juvenile (<30 cm fork-length) specimens of commercially important snapper and grouper species (Deep-7 species) for studies of age and growth. Specimens were collected using both handline gear and fish traps. Handline operations were conducted primarily from small boats deployed from the Sette during daylight hours; each boat was equipped with two battery-powered electric reels. A total of 161 juvenile bottomfish were collected including 52 gindai Pristipomoides zonatus, 42 kalekale Pristipomoides sieboldii, 30 ehu Etelis carbunculus, and 30 opakapaka Pristipomoides filamentosus. However, no juveniles were obtained for two species of particular interest, hapu'upu'u Epinephelus quernus and onaga Etelis coruscans. In addition to specimens of juvenile fish collected for studies in the laboratory, 81 adult bottomfish captured during handline operations were tagged and released.

Large (6'x 4'x 3') and small (2'x 1'x 1') baited fish traps were deployed at depths of 40-112 fathoms to collect additional juvenile bottomfish specimens. Trap operations yielded primarily taape, Lutjanus kasmira but no snapper/grouper species of interest.

The habitat sampled was primarily off Kawaihae, which had large areas of muddy or silty bottom not attractive to fish. Fish were generally caught over hard substrates. The predominance of soft substrate, and timing of the sampling (not the time of year for juvenile settlement) likely explain why juvenile hapu'upu'u and onaga were not caught.

During the cruise, scientists on the Sette also collected environmental data on the fishing grounds. This included salinity and temperature profiles of the water column from Conductivity-Temperature-Depth (CTD) casts and current strength and direction through the water column based on Acoustic Doppler Current Profiler (ADCP) transects. This information was collected to evaluate whether oceanography can help to characterize the juvenile habitat of commercially important bottomfish species.

Based on the results of this first cruise, handline operations using small boats deployed from the Sette are considered an effective way to sample juveniles and optimize use of available research time. Fish traps were not successful in capturing target bottomfish species; further field trials are needed to evaluate their effectiveness.

The Sette expedition enabled scientists to capture specimens of juvenile and adult gindai and other bottomfish for biological studies in support of improved stock assessment.

For more information contact: Ryan Nichols