Research Document 2018/064
An Assessment of Witch Flounder (Glyptocephalus cynoglossus) in NAFO Subdivision 3Ps from Catch and Survey Information
By Wheeland, L., Ings, D., Rogers, B., Tulk, F. and Rideout, R.
Abstract
Information available to evaluate stock status of Witch Founder (Glyptocephalus cynoglossus) in NAFO Subdivision 3Ps consisted of commercial landings data (1974-2017) and information from Canadian RV trawl surveys (1983-2017). The TAC for this stock has been 650 t since 1998. Annual landings from the past 3 years have averaged 472 t, an increase over the previous 3 year period where landings averaged 196 t. Length composition from the fishery has remained stable, with a mode near 40 cm. Witch flounder were found to predominately occupy waters from 100-500 m in depth, in relatively warm waters with bottom temperature of 5-7°C. The availability of thermal habitat within this preferred range in Subdivision 3Ps has fluctuated throughout the time series, but has been consistently higher than average since 2010. Patchy distribution of this species in the spring - associated with pre-spawning aggregations - contributes to large inter-annual variation in survey indices. A large tow in each of the 2016 and 2017 spring RV surveys resulted in indices of biomass and abundance at, or near, time series highs. However, each of these survey indices is associated with a high degree of uncertainty. A proxy for BMSY in this stock was calculated as the geometric mean of survey biomass indices from 1983-1993. Consequently – and consistent with the DFO decision making policy – an interim Limit Reference Point was adopted at 40% BMSY. The stock is currently above the LRP, and has been in most years of the time series (1983-2017).
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