Stock assessment of witch flounder (Glyptocephalus cynoglossus) in NAFO divisions 2J3KL

Abstract

Recent warming, earlier phytoplankton spring bloom, and an increase in the proportion of energy-rich copepod species may have positive effects on total ecosystem production. While this ecosystem continues to experience low productivity levels, and total biomass remains well below pre-collapse levels, there are indications that conditions have improved for some species. Witch Flounder in NAFO Div. 2J3KL are assessed primarily based on fall DFO Research Vessel (RV) survey indices. The survey in 2021 was incomplete, therefore stock status in that year cannot be determined. This stock remained in the Critical Zone (89% of the Limit Reference Point) in 2020 with an 82% probability. A moratorium on directed fishing has been in place in Canadian waters since 1995, and in the NAFO regulatory area since 1998. A survey-based proxy indicates fishing mortality has remained low since the mid-2000s. The stock continues to show signs of rebuilding, with indices of biomass, abundance, and distribution increasing since the early-2000s, and the four highest values in the recruitment index series (1995 to 2020) occurring since 2013. Witch Flounder rely on benthic invertebrates as their principal food source and are not primarily driven by trends in forage species such as Capelin and shrimp. This is contributing to a divergence in trends between Witch Flounder and many other finfish in Div. 2J3KL that have shown stalled biomass growth since the mid-2010s. Consistency with the DFO decision-making framework incorporating the Precautionary Approach (PA) requires that removals from all sources must be kept at the lowest possible level until the stock clears the Critical Zone.