Multi-vessel Expedition Compares Bottomfish Survey Methods in Waters off Maui

The NOAA Ship Oscar Elton Sette recently completed the 15-day (April 15-29, 2013) expedition SE-13-02 off the western coast of Maui. The cruise was part of a multi-faceted research project involving the Sette, the R/V Huki Pono from Sea Engineering (chartered by PIFSC research partners in the University of Hawaii Department of Oceanography), and bottomfish fishing vessels Hokuloa, Imua, and Naomi K associated with the Pacific Islands Fishing Group (PFIG). The expedition was the latest in a series of joint operations to compare and calibrate methods of assessing biomass of deepwater bottomfish. The project objectives included:

Most of the project occurred in a series of 6 pairs of survey grids located off West Maui (see accompanying survey map). These locations were chosen based on feedback from the local fishing community, prior calibration cruise surveys, climatological patterns of weather, and proximity to the small-vessel port at Maalaea Harbor. The survey plan called for intensive replication of sampling at each survey grid to enable an assessment of within- and between-gear variability.

Surveys were conducted at 6 locations (A-F) with paired survey grids (1 and 2) at each location.
Surveys were conducted at 6 locations (A-F) with paired survey grids (1 and 2) at each location.

During 11 days of survey operations the Sette completed 30 acoustic transects and 10 AUV transects covering 10 of the 12 survey grids. The number of replicates ranged from 1 to 4 acoustic transects per survey grid (average replication of 3.0 acoustic transects per survey grid), and a single AUV transect for 10 of the 12 survey grids. Survey effort by the Huki Pono accomplished 142 BotCam stations over the 8 contract days with replication ranging from 9 to16 BotCam stations per survey grid (average replication of 11.8 BotCam stations per survey grid) covering all 12 survey grids. Survey effort by the PIFG vessels accomplished 151 fishing stations for the 3 vessels over the 7 contract days with replication ranging from 10 to 15 fishing stations per survey grid (average replication of 12.6 fishing stations per survey grid) covering all 12 survey grids.

The research project met all 4 objectives despite occasional challenges. Mechanical problems with the AUV necessitating 3 emergency shipments of parts to Maui and placement of a suspended acoustic calibration sphere below the Sette hull. SE-13-02 was the first calibration cruise to fully and successfully deploy all 4 survey methods: active acoustics, AUV, BotCam, and fishing. The over-the-side-pole showed great promise for improving acoustic surveys in a wider variety of sea conditions. The navigational camera aboard the ROV observed 2 species of fish (opelu and opakapaka) and crew members of the Sette captured specimens of at least 6 species of fish (opelu, opakapaka, kalekale, ehu, taape, reef shark) while the active acoustics on the Sette. These ground-truthing data will help in species identification of targets observed in the acoustic data. Although all data remain to be analyzed, it was noted preliminarily that large lehi (Aphareus rutilans) were quite abundant in certain survey grids based on both the bottomfishing catch data and AUV optical data. In one instance a large school of mixed lehi and kahala (Seriola spp.) swam in front of the AUV and were recorded on both the stereo cameras and the BlueView sonar imaging unit.

The research project involved close coordination of acoustic and AUV operations on the NOAA Ship Oscar Elton Sette
        (top left and right), BotCam deployments from the chartered Huki Pono (lower left), and bottomfish operations from the PIFG fishing 
        vessels (bottom right).
The research project involved close coordination of acoustic and AUV operations on the NOAA Ship Oscar Elton Sette (top left and right), BotCam deployments from the chartered Huki Pono (lower left), and bottomfish operations from the PIFG fishing vessels (bottom right).

Besides scientists from the Fisheries Research and Monitoring Division, Ecosystems and Oceanography Division, Coral Reef Ecosystem Division and other work groups within PIFSC, the field operations for the project involved a wide assortment of partners with varied and essential expertise: the Northwest Fisheries Science Center (NOAA/NMFS); University of Hawaii at Manoa Department of Oceanography; University of Hawaii at Manoa Hawaii Institute of Marine Biology; Joint Institute for Marine and Atmospheric Research (JIMAR); Pacific Islands Fisheries Group (PIFG); Sea Engineering; Hawaii Department of Land and Natural Resources; and NOAA Teacher-at-Sea Program. Other colleagues from the University of Miami and Woods Hole Oceanographic Institute were involved in the planning and preparation for the project.