Research Document - 2008/061

Assessment of the NAFO Division 4T southern Gulf of St. Lawrence herring stocks in 2007

By C.H. LeBlanc, C. MacDougall and C. Bourque

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 2007 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 indices, and the telephone survey abundance opinion as an aggregated biomass index. Reported 2007 landings of the spring spawner component were 3,789 t against the spring spawner TAC of 5,000 t. Mean inshore gillnet catch rate in 2007 remains one of the lowest in the series that starts in 1990. The 2007 acoustic survey index of abundance was the lowest in the series that starts in 1994. The 2007 index from the opinions of harvesters contacted in the telephone survey on the abundance of spring herring was the lowest in the time series that starts in 1987. The abundances of year-classes after 1991 were average or below average. Age 4-10 spawning biomass is estimated at 20,500 t for the beginning of 2008. The estimated exploitation rate in 2006 and 2007 was below the F_0.1 reference level. The current estimate of age 4-10 biomass (20,500 t) is below the lower stock reference. At this level of biomass, the precautionary approach requires that removals from the stock should be kept to the lowest level possible.

The 2007 assessment of 4T herring fall spawner component was based on a sequential population analysis calibrated on both the age-disaggregated gillnet catch rate (CPUE) index and the telephone survey abundance opinion as an aggregated biomass index. Reported 2007 landings of the fall spawner component in both the spring and the fall fisheries were 47,621 t against the fall spawner TAC of 68,800 t. Mean inshore gillnet catch rates in 2007 were lower than 2006 but remain among the highest in the time series that starts in 1978. The 2007 telephone survey index from the opinions of harvesters on the abundance of fall herring has been increasing since 1987. The 1998 and 2000 year-classes are above average. The 2008 beginning-of-year spawning stock biomass is estimated to be about 302,000 t, well above the upper stock reference biomass level of 172,000 t. The exploitation rate in 2007 was below the F_0.1 reference level. For 2008, a catch option of 69,000 t corresponds to a 50% chance that F would be above the F_0.1 removal rate.

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