Expedition in Maui Triangle Evaluates Methods for Next-Generation Assessment of Hawaii Bottomfish Stock

In April of 2014, researchers from the NOAA Pacific Islands Fisheries Science Center (PIFSC) carried out a multi-faceted scientific expedition in waters in the main Hawaiian Islands as part of the Center's mission to develop an advanced, fishery-independent survey for Hawaiʻi Deep 7 bottomfish. The study area was the "Maui Triangle", the waters between Maui, Molokai, Lanai and Kahoʻolawe (Maui Nui). A research team of PIFSC scientists on the NOAA Ship Oscar Elton Sette was joined in the study by colleagues from the NOAA Northwest Fisheries Science Center, University of Hawaii at Manoa (UHM), Joint Institute for Marine and Atmospheric Research at the University of Hawaii at Manoa (JIMAR), and the Pacific Islands Fisheries Group (PIFG). NOAA Corps LT Faith Knighton served as Chief Scientist for the 15-day expedition (designated as SE1402), with PIFSC scientist Dr. Benjamin Richards serving as Science Advisor.

The expedition's objective was to accomplish a near-simultaneous survey of deepwater bottomfish using 3 fishery-independent methods, or gears: an autonomous underwater vehicle (AUV) stereo-video camera system, deployed from the Sette; baited underwater stereo-video camera systems (or BotCam), deployed by a UHM team aboard the collaborating research vessel Huki Pono; and research hook-and-line fishing from several cooperating PIFG bottomfish fishing vessels.

During past expeditions, sampling areas for the survey were selected to maximize bottomfish encounter rates and to build a comprehensive dataset for method-to-method comparison and gear calibration. The April 2014 research effort departed from that experimental design, and instead adopted a stratified-random sampling approach to best characterize bottomfish abundance across the survey domain. Each gear was allocated to selected 500 m x 500 m survey grids within designated habitat strata, with the grids chosen at random in proportion the prevalence of each habitat type in the overall survey domain and taking into account the variation in the data from each habitat stratum as sampled during prior research missions. Survey grids were selected shortly before project mobilization to best allow for prevailing weather conditions, proximity to ports, and patterns of fish abundance, and to mitigate impacts of the fishing operations on activities of local fishermen and management regions.

For the research fishing, a standard sampling unit was defined as 30 minutes of active fishing effort within a grid cell by one bottomfish vessel using each of two bait types on separate lines each containing four #22 hooks.

For the BotCam, a standard survey was defined as three BotCam deployments of 15-minute duration. Prior BotCam surveys have varied from 15 minutes to 45 minutes duration. For 75-85% of samples in which a bottomfish was observed, the time to first arrival of a bottomfish at the BotCam station occurred within 15 minutes. Habitat-specific abundance patterns did not differ between 15 and 45-minute deployments. Reducing the deployment time for BotCam increases sampling effort and reduces the likelihood that fish observed by the BotCam are attracted from outside the defined sample area.

For the AUV, two 2-hour surveys provided an efficient ratio of sample number, survey time and refitting time. Within each grid cell, the AUV conducts three parallel 200 meter transects separated by 25 meters.

The results of the surveys are being used by the PIFSC Stock Assessment Program to evaluate the potential for development of an operational, fishery-independent, non-extractive, non-lethal survey methodology to estimate size-structured abundance of the Hawaii Deep 7 Bottomfish assemblage. The data collected during SE1402 will enable PIFSC to determine gear-specific optimum sampling rates and the sample size necessary to adequately quantify the Deep-7 bottomfish stock across its range. If the research is successful, the fishery-independent methodology can supplement the fishery-dependent methods presently used for stock assessment.

A map of the SE1402 survey area showing the primary sampling units (500-m x 500-m grid cells) within waters of the Maui-Nui region. 
        Each of the candidate fishery-independent gears (BotCam, AUV, Research Fishing) was randomly allocated to each sampling unit.
A map of the SE1402 survey area showing the primary sampling units (500-m x 500-m grid cells) within waters of the Maui-Nui region. Each of the candidate fishery-independent gears (BotCam, AUV, Research Fishing) was randomly allocated to each sampling unit.