Overview of the southern flounder stock

In January 2019, the N.C. Division of Marine Fisheries completed a stock assessment of the southern flounder stock to estimate population size and harvest rate. The stock assessment compiles available fisheries-independent (state surveys) and fisheries-dependent (commercial and recreational) information collected from throughout the range of the biological unit stock, which includes southern flounder occurring in the waters of North Carolina, South Carolina, Georgia, and the East Coast of Florida.

These available data are entered into a quantitative model that estimates both historical and current population sizes and harvest rates. When considering population size, stock assessments are most often interested in female spawning stock biomass, which includes female fish that are mature or capable of producing offspring. The harvest rate is a measure of how fast fish are being removed from the population by the different fisheries. Removals include those fish that are kept and those that are discarded dead or die after release.

The stock assessment’s current (2017) estimates of female spawning stock biomass and harvest rate were compared to levels that are considered sustainable to determine stock status. These sustainable levels are also known as reference points. If current female spawning stock biomass is less than the reference point, the stock is said to be overfished. If the current harvest rate is greater than the associated reference point, overfishing is said to be occurring.

The level of female spawning stock biomass that represents the minimum level of sustainability for southern flounder was estimated at 8.6 million pounds. The stock assessment estimate of female spawning stock biomass for southern flounder in 2017 was 2.3 million pounds. Because the current (2017) estimate of female spawning stock biomass is below the reference point, the stock is considered overfished.

The assessment model estimated that the harvest rate (fishing mortality), abbreviated as F, can be no greater than 0.53 for a sustainable southern flounder population. The current (2017) estimate of the harvest rate from the stock assessment was 0.91, which is above the harvest rate reference point. Because the current (2017) harvest rate is above the reference point, overfishing is occurring.

In order to rebuild the stock to sustainable levels, reductions in the harvest rate are necessary. The General Statutes of North Carolina state that overfishing should be ended within two years from the date of the adoption of the fishery management plan (NCGS § 113-182.1). The General Statutes also state that sustainable harvest should be achieved within 10 years, unless the species biology, environmental conditions, or lack of sufficient data make implementing these requirements incompatible with professional standards for fisheries management.

Ending overfishing in two years requires a 31% reduction in total catch (landings plus dead discards from all fleets); however, this reduction is not enough to rebuild the female spawning stock biomass to meet the 10-year schedule to end the overfished status. A minimum 52% reduction in total removals is needed to rebuild the female spawning stock biomass to sustainable levels and end the overfished status within 10 years by 2028, assuming harvest reductions begin in 2019.