Science Advisory Report 2012/018
Biomass limit reference point consistent with the precautionary approach for American plaice (Hippoglossoides platessoides) from the southern Gulf of St. Lawrence (NAFO Div. 4T)
- An age-structured population model to estimate spawning stock biomass and recruitment was updated to 2011. Model estimates of the spawning stock biomass (SSB) show a general decline from the late 1970s to the early 2000s. SSB was at its lowest level in 2009 at less than 31,000 tonnes; the latest estimate (2012) was 41,676 tonnes.
- Age-4 recruits were most abundant in the late 1970s, up to 13 times their average abundance over the last five years. Recruitment has fluctuated at a low level since the early 1980s.
- The dynamics of the 4T plaice stock are dominated by a pattern of high natural mortality on adults, combined with chronic poor recruitment.
- Model estimates of SSB and their corresponding recruits at age-4 formed the basis for analyses of the stock-recruit relationship.
- Based on Beverton-Holt and Ricker stock and recruitment models, the median SSB that produced 50% of maximum recruitment (Blim) is estimated at 68,000 and 60,000 tonnes, respectively.
- The Blim value for 4T American plaice is defined as the average of the estimates from the Beverton-Holt and Ricker models, 64,000 tonnes. The SSB for the 4T plaice stock has been met or exceeded Blim once since 1996.
- Fishing mortality (F) was negligible on 4 to 9-year-old plaice throughout the time series, but for older plaice, estimated F varied between about 0.1 and 0.2 from the mid 1970s to the early 1990s, falling to below 0.01 in recent years.
- Data and analyses were insufficient neither to define the removal rate limit reference point (Flim) nor to propose candidates for the upper stock reference point (BUSR).
This Science Advisory Report is from the February 21, 2012 meeting on the Reference points for American plaice (Hippoglossoides platessoides) from NAFO Division 4T. Additional publications from this process will be posted as they become available on the Fisheries and Oceans Canada Science Advisory Schedule at www.dfo-mpo.gc.ca/csas-sccs/index-eng.htm.
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