2019 Assessment of the Shallow-Water Flatfish Stock Complex in the Gulf of Alaska

In 2017, the scheduled frequency for some stock assessments was changed in response to the National Stock Assessment Prioritization effort. The new schedule has moved shallow water flatfish to a 4-year assessment cycle, with partial assessments for ‘off’ years. For this year we present a partial assessment consisting of an executive summary including recent fishery catch and survey results, and recommend harvest levels for the next two years. Please refer to the 2017 full stock Assessment of the Shallow-Water Flatfish Stock Complex in the Gulf of Alaska (Turnock et al. 2017) (PDF, 52 pages) for more information.

The shallow-water flatfish (SWF) stock complex in the Gulf of Alaska (GOA) includes Alaska plaice (Pleuronectes quadrituberculatus), butter sole (Pleuronectes isolepis), English sole (Parophrys vetulus), sand sole (Psettichthys melanostictus), starry flounder (Platichthys stellatus), yellowfin sole (Pleuronectes asper), northern rock sole (Lepidopsetta ploystra), and southern rock sole (Lepidopsetta bilineata). Northern rock sole and southern rock sole are tier 3 species and assessed separately from the other shallow-water flatfish. The OFL and ABC for the SWF complex are derived as the sum of the tier 3 rock sole assessment values and the tier 5 other shallow water flatfish assessment values.

The random effects model (Spencer, et al. 2013) was fit to the Gulf of Alaska bottom trawl survey biomass data for 1984–2019 to estimate current biomass for each of the tier 5 species within the SWF complex. The 2001 survey data were excluded because the eastern area was not surveyed. The random effects model was also fit to total SWF survey biomass summed over the tier 5 species. The biomass estimates from the species-specific random effects models were adjusted so that the sum over species was equal to the result from the random effects model fit to total tier 5 species survey biomass. The adjusted biomass estimates were used to develop species-specific OFLs and ABCs and added to the management advice from the 2019 projection model for northern rock sole and southern rock sole (Bryan 2019) to provide a SWF complex OFL and ABC.

The apportionment by area was estimated by fitting the random effects model to the survey biomass summed for all species (including tier 3 rock sole) by area and estimating the percent biomass in 2019 by area.