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Research Document 2019/026

Assessment of the Winter Flounder (Pseudopleuronectes americanus) stock of the southern Gulf of St. Lawrence (NAFO Div. 4T) to 2016 and advice for the May 2017 to May 2022 fisheries

By Surette, T., and Rolland, N.

Abstract

Winter Flounder (Pseudopleuronectes americanus) ranges from southern Labrador to Chesapeake Bay. In the southern Gulf of St. Lawrence (NAFO Div. 4T; sGSL), Winter Flounder tends to be distributed in shallow, near shore areas where it is fished primarily for bait. A total allowable catch was first instituted in 1996 at 1,000 t. Following the most recent assessment in 2011, the TAC was reduced to 300 t and has been in effect for the period 2012 to 2016. Winter Flounder is currently caught in a relatively small directed fishery concentrated mainly around the Magdalen Islands with landings ranging from 190 to 320 tonnes over the past 10 years. Abundance indices from a research survey show that there has been a decrease in the size distribution of the Winter Flounder stock with percentages of fish >= 25 cm (minimum size limit for the fishery) decreasing from an average of 85% during 1971 to 1975 to 30% during 2011 to 2015. Estimates of spawning stock biomass (SSB) were highest in the period from 1975 to 1994 at an average of 356,100 t (median). Over the recent period, the SSB estimate has declined to 235,700 t in 2003 and 76,270 t in 2016. The proportion of the SSB represented by older fish (5+) has also decreased over time. Based on a population model, the estimates of natural mortality have recently increased for young fish (ages 2 to 4) and continually increased for older fish (aged 5+). The instantaneous fishing mortality rate is estimated to be low to very low for all ages. The stock is considered to have been below the LRP since 2006. In 2016, the estimated SSB was 54% of the LRP. Projections at catch levels of 0 t, 100 t, and 300 t show no perceivable difference in stock trends over the next five years. Fishing mortality is a very small proportion of the total mortality of Winter Flounder in the southern Gulf of St. Lawrence and natural mortality is estimated to be the dominant factor affecting abundance. The contraction in size structure of Winter Flounder, the decline in the estimated size at 50% maturity, and the decline in abundance indices of the previously abundant commercial sized group are consistent with a stock experiencing very high levels of mortality.

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