Research Document - 2014/012

Witch Flounder (Glyptocephalus cynoglossus) in NAFO Subdivision 3Ps: Catch and Survey Information Updated for 2005-2013

By D. Maddock Parsons and R.M. Rideout

Abstract

Landings of Witch Flounder (Glyptocephalus gynoglossus) in the Northwest Atlantic Fisheries Organization’s (NAFO) Subdivision 3Ps have been variable since 1974, ranging from 200 to 4200 tons (t). During 1986-93 catches were relatively stable and averaged around 1000 t annually. Landings declined subsequently and for the past 10 years, landings averaged 375 t, well below the 650 t Total Allowable Catch (TAC). The main directed fishery is prosecuted by offshore otter trawlers complemented by a near-shore Danish seine fishery. In some years, by-catch of American Plaice in the Witch Flounder directed otter trawl fishery reached 100 % of the witch catch, and in the last five years has ranged from 10 % to 75 %. By-catch of American Plaice was not high in the Danish seine component of this fishery (averaging only 5 % in the past 10 years). Although Fisheries and Oceans Canada (DFO) Research Vessel (RV) survey indices have been highly variable since 1983, survey biomass and abundance indices have remained near the 1983-2013 average over the past 10 years. During recent years (2008-13), the survey biomass index is, on average, about 85 % of the 1984-2013 average. Size structure observed in this stock in both the commercial fishery and the RV surveys are comparable to those reported in past assessments. Geographic distribution has remained consistent since 1983, except during the early to mid-1990s when fish disappeared from the 83‑193 m depth zone coincident with extremely cold sea bottom water temperatures. There has been no aging of Witch Flounder for assessment purposes since 1994 and tracking cohorts through size distributions from the survey series is difficult for this slow growing flatfish. The abundance of 16‑30 cm Witch Flounder in the RV survey has been variable over 1997-2013, but showed above average values for 2002-04 and 2009-11. Although it is unclear how the abundance of this size group relates to abundance of spawning fish or fishable size witch in subsequent years, there has been no trend in this pre-recruit index.

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