Research Document - 2012/099

Assessment of the southern Gulf of St. Lawrence (NAFO Division 4T) American plaice (Hippoglossoides platessoides)

By R. Morin and S.G. LeBlanc

Abstract

Landings of NAFO 4T American plaice declined to 126 tonnes in 2009, their lowest level on record for this stock. The annual quota on 4T plaice has been 500 tonnes since 2008. Low quota and poor market demand have contributed to the drop in fishing effort, although there is also evidence that stock abundance is at a low level. Research trawl surveys, conducted yearly in 4T since 1971, indicate that the plaice stock was most abundant in the late 1970s, but declined in the 1980s and is currently at its lowest level. A population model for 4T plaice was reviewed in December 2010 in preparation for an assessment of the recovery potential of American plaice under the Species at Risk Act. This model is based on survey data and commercial catch-at-age (1976-2009) that incorporates estimates of discarding in the mobile gear fishery. Natural mortality was estimated in 5-year periods ending in 2006-2009 and in two age groups over the first 10 years, from 1976 to 1985. The decline in the stock in the late 1970s is mainly accounted for by high natural mortality (0.859) on age 4-9 plaice during the 1976-1985 period, possibly due to unaccounted discarding in the fishery. Natural mortality in the 2006-2009 period was estimated at 0.45 for plaice aged 4-20 years of age. Trends in the abundance of age-4 plaice, estimated from the population model, indicate that recruiting year classes have been persistently weak since the early 1970s. The spawning stock biomass of plaice in 2010 was projected by the model to decline by 0.5% without a commercial fishery.

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