Science Advisory Report  2016/031

Stock assessment of American plaice (Hippoglossoides platessoides) of the southern Gulf of St. Lawrence (NAFO Div. 4T) to 2015

Summary

• American plaice is currently caught as bycatch in fisheries primarily directed for witch flounder and Greenland halibut. Preliminary landings in 2015 were 40 t.
• There has been a decrease in the size of American plaice with the mean length decreasing from around 25 cm prior to 1995 to 21.3 cm during the 2011 to 2015 time period. The mean length and weight at age of American plaice have also decreased.
• Natural mortality for American plaice ages 4 to 9, decreased from about 53% (annual mortality) in the late 1970s to about 39% since 2005. The estimated natural mortality for plaice aged 10+ increased from 22% in the 1970s to greater than 39% since 1995.
• The median estimate of spawning stock biomass (SSB) was about 350 kt in the late 1970s decreasing rapidly to 100 kt or less by 1984. Estimated SSB was estimated at 55 kt in 2015.
• The stock has been in the critical zone since 1993. In 2015, the median of the SSB estimate was 40% of the limit reference point (LRP) with essentially zero chance of the SSB being above the LRP.
• Fully recruited exploitation rate on age 10+ was estimated to have peaked in 1992 at just over 26% but has been less than 1% in the recent five years. Fishing mortality is a very small proportion of the total mortality (natural plus fishing) of American plaice of the southern Gulf of St. Lawrence.
• Under current productivity conditions, the SSB is expected to remain in the critical zone with essentially zero chance of the SSB being above the LRP during 2016 to 2021 at TAC options of 0 t, 100 t, or 250 t.
• The rebuilding prospects for this stock under current conditions are low because of the high level of natural mortality. Predation by grey seals is thought to be a major component of the high level of natural mortality.

This Science Advisory Report is from the March 1 and 2, 2016 science peer review meeting on the Stock assessment of Amercian Plaice (Hippoglossoides platessoides) of the southern Gulf of St. Lawrence (Northwest Atlantic Fisheries Organization (NAFO) Division 4T). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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