Research Document - 2009/049

Assessment of the NAFO Division 4T southern Gulf of St. Lawrence herring stocks in 2008

By C.H. LeBlanc, C. MacDougall, C. Bourque, R. Morin and D. Swain

Abstract

Assessments of the spring and fall spawning herring from the southern Gulf of St. Lawrence are required on an annual basis and form a part of the information base used to establish the total allowable catch (TAC). The 2008 assessment of 4T herring spring spawner component was based on a sequential population analysis calibrated on both the age-disaggregated gillnet catch rate (CPUE) and acoustic survey indices. Reported 2008 landings of the spring spawner component were 2,755 t against the spring spawner TAC of 2,500 t. Mean gillnet catch rate in 2008 was higher than 2007, but similar to the values from 2004 to 2006. The 2008 acoustic index was one of the lowest in the series that starts in 1994. The cumulative index of the opinions of harvesters on the abundance of spring herring in 2008 was the lowest in the time series that starts in 1987. The abundances of year-classes after 1991 have been average or below average. Age 4+ spawning biomass is estimated at 20,300 t for the beginning of 2009. The estimated exploitation rate was below the reference level in 2008. The current estimate of age 4+ biomass (20,300 t) is below the limit reference point (LRP, 22,000 t). At this level of biomass, the precautionary approach requires that removals from the stock should be kept to the lowest level possible. The 2008 assessment of 4T herring fall spawner component was based on a sequential population analysis calibrated on an age-disaggregated gillnet catch rate (CPUE) index. Reported landings of the fall spawner component in both the spring and the fall fisheries in 2008 were 41,471 t. The fall spawner TAC was 68,800 t. Mean gillnet catch rate in 2008 was lower than the previous three years. The cumulative index from the opinions of harvesters on the abundance of fall herring has been decreasing since 2006, although the index is higher than it was prior to 2000. Estimated recruitment at age 4 was above average from 1999 to 2005, and again in 2008. The 2009 beginning-of-year spawning stock biomass is estimated to be about 285,500 t, above the upper stock reference (USR) level of 172,000 t. The exploitation rate in 2008 was below the F_0.1 reference level. For 2009, a catch option of 65,500 t corresponds to a 50% chance that F would be above the F_0.1 removal rate.

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