Research Document - 2005/069

An Assessment of American plaice in NAFO Subdivision 3PS

By Morgan, M.J., W.B. Brodie, P.A. Shelton

Abstract

The stock of American plaice in Subdivision 3Ps has been under moratorium since September 1993. Catches averaged just under 4,000 t during the 1980’s but rapidly declined after 1991. There has been no directed fishery since the moratorium was instituted. Indices of abundance and biomass showed a large decline from the mid 1980’s to 1990. Since 1992 stock size has been very low. There has been a slight increase over the 1992-2005 time period in both biomass and abundance indices but average biomass over the last 3 years is only 20% and abundance 26% of the 1983-87 average. Year class strength has declined since 1998 and the 2002 year class is the third lowest in the time series. Catch increased substantially since 1995, and was over 1,000 t in each year from 2001 to 2003. Catch to survey biomass ratios indicate that exploitation rate has been increasing since the mid 1990’s. Catch to survey biomass ratios have continued to increase although catch declined somewhat in 2003 and 2004. This is the result of a somewhat lower exploitable biomass. The 1998 and 1999 year classes are near average and may result in some increase in the exploitable biomass over the short term. However they are followed by several below average year classes. Although there is variability at low stock size, there is a fairly clear stock recruit relationship. A changepoint regression analysis estimates that an SSB index of about 13.6 gives a recruitment that is 50% of the maximum estimated. The SSB index is currently at 10 (average of 8.6 over last 3 years) and has been below 13.6 since the early 1990’s. The SSB index is therefore at a level that suggests that recruitment will be less than half of its maximum potential. Catches at recent levels are contributing to the lack of recovery.

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