Towards fishery-independent biomass estimation for Hawaiian Islands deepwater snappers

Abstract

The Hawaiian deep-slope (75–400 m) Deep7 bottomfish fishery consists of seven (i.e., six snappers and one grouper) species. This study developed a sampling survey and modeling methodology for estimating biomass for this complex in the Main Hawaiian Islands. The island-wide fishery-independent sampling survey using two gears (commercial fishers with hook-and-line, 3D stereo camera) was conducted to generate estimates of relative abundance- and biomass-at-length for the complex. A length-based modeling approach was applied to the opakapaka fishery and survey size-structured abundance data, life history demography, and total fishery catches to estimate a feasible range of effective sampling area for the standard survey gear (i.e., cameras). These sampling area estimates were then used to expand survey estimates of relative biomass to population total biomass. The longer-term focus of this effort is to improve stock assessments of the Deep7 complex. The survey and modeling methods developed in this study provide the underpinnings of an integrated information and modeling system for assessment that enables multiple levels of comparison and validation with respect to data sources (fishery-dependent and fishery-independent) and modeling approaches (biomass-dynamic and cohort-structured).