Stock Assessment Update for the Main Hawaiian Islands Deep 7 Bottomfish Complex in 2021, With Catch Projections Through 2025

The Hawaii Deep 7 bottomfish complex is a U.S. fishery management unit made up of seven deep-water species of snappers along with a single grouper species that inhabit waters of the Hawaiian Archipelago. All bottomfish fishing currently takes place in the main Hawaiian Islands (MHI) zone due to the closure of the Northwestern Hawaiian Islands under Presidential Proclamation 8031. Stock assessments conducted since 2011 assess the Deep 7 bottomfish complex within the MHI zone.

A stock assessment update of the main Hawaiian Islands Deep 7 bottomfish complex was conducted in 2021. The assessment followed methods from the 2018 benchmark stock assessment and used a Bayesian surplus production model fit to bottomfish catch and effort data from commercial catch reports for fishing years 1949–2018 and a fishery-independent survey conducted in fishing years 2017–2020. Similar to the 2018 benchmark assessment, a single-species assessment model for opakapaka (Pristipomoides filamentosus) was also updated with corresponding data. The surplus production model for the Deep 7 complex was used to evaluate the risk of overfishing as a function of alternative annual reported catches from fishing years 2021 through 2025. The projections included uncertainty in the posterior distribution of estimated bottomfish biomass in 2018 and population dynamics parameters estimated from the assessment model.

The Deep 7 bottomfish stock complex in the main Hawaiian Islands was categorized as not overfished (where overfished was defined as B/BMSY < 0.844) and not experiencing overfishing (where overfishing was defined as H/HMSY > 1) in 2018. The overfishing limit (OFL), defined as the future amount of reported catch that would yield a P*=50% probability of overfishing ranged from 556–618 thousand pounds depending on the future year. The smallest Deep 7 future catch that would lead to a roughly P*=40% chance of overfishing was 486 thousand pounds.

The Bayesian surplus production model developed for opakapaka produced similar overall results to the model for the Deep 7 complex. Results were approximately proportional to the corresponding value in the Deep 7 bottomfish model with biomass over all years scaled by 55%, which was intermediate between the ratio of opakapaka to Deep 7 biomass from the fishery-independent survey (46%), and the overall proportion of total of Deep 7 bottomfish catch composed of opakapaka (68%).

Syslo J, Brodziak J, Carvalho F. 2021. Stock Assessment Update for the Main Hawaiian Islands Deep 7 Bottomfish Complex in 2021, with Catch Projections Through 2025. U.S. Dept. of Commerce, NOAA Technical Memorandum NOAA-TM-NMFS-PIFSC-118, 213 p. https://doi.org/10.25923/mym1-w042.