Research Document 2019/066
Assessment of Witch Flounder (Glyptocephalus cynoglossus) NAFO Divisions 2J3KL
By L. Wheeland, B. Rogers, R. Rideout, D. Maddock Parsons
Abstract
Information available to evaluate stock status of Witch Founder (Glyptocephalus cynoglossus) in NAFO Divisions 2J3KL consisted of commercial landings data (1960-2017) and information from Canadian fall RV trawl surveys (1977-2017). This stock has been under moratorium in Canadian waters since 1995, and in the NAFO regulatory area since 1998. Following a contraction of the stock to shelf slope areas through the 1990s, the distribution of the stock has expanded in recent years, returning to deep channels occupied in the mid-1980s. A general increase has been observed in indices of both abundance and biomass since the early 2000s, however variability in RV survey coverage has resulted in increased uncertainty in indices, particularly given recent coverage issues in the deep water of Div. 3L. A series of positive pre-recruit anomalies indicate improved recruitment in this stock since 2013, with a time series high in 2016. Bivariate habitat associations indicate that distribution of this stock is largely driven by temperature, with Witch Flounder consistently seeking out waters warmer (i.e. within 3.2 to 3.6°C, across Divs. 2J, 3K and 3L) than the median available (-0.3 to 2.7°C). A Limit Reference Point was set for this stock at 40% BMSY, with a proxy for BMSY calculated as the mean of survey biomass indices from 1983-1984.
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