2018 Assessment of the Shallow-Water Flatfish Stock Complex in the Gulf of Alaska
January 30, 2019
The shallow-water flatfish 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 sole, yellowfin sole (Pleuronectes asper), northern rock sole (Lepidopsetta ploystra), and southern rock sole (Lepidopsetta bilineata). Northern and southern rock sole are tier 3 species and assessed separately from the other shallow-water flatfish. The shallow-water flatfish stock complex has been moved to a 4-year assessment cycle. Last year, 2017, was the first year of the new schedule and a full assessment was completed. This year a partial assessment was done.
The 2017 assessment of the shallow-water flatfish complex excluding northern and southern rock sole used a random effects model to estimate current biomass (for details see Spencer, et al. 2013). Last year the random effects model was fit to survey biomass for 1984 to 2017, leaving out 2001 where the Eastern area was not surveyed. The survey biomass for each year was summed over species (not including rock sole). The apportionment by area was estimated by fitting the random effects model to the survey biomass summed for all species (including rock sole) by area and then estimating the percent biomass in the ending year by area. The percent biomass by species (excluding rock sole) was estimated using the random effects model fit to survey biomass by species and dividing by the total from the fit by species. The random effects model was not run in 2018 because it was an off year for the GOA trawl survey. The estimates from the 2017 assessment were used this year to estimate the OFL and ABC for 2019 and 2020.