Research Document - 2006/035

Assessment of the NAFO Division 4T southern Gulf of St. Lawrence herring stocks in 2005

By LeBlanc, C.H., G.A. Poirier, C. MacDougall, and I. Forest

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 TAC.

A population analysis was conducted on the 2005 4T herring spring spawner component using sequential population analysis. The analysis included the gillnet catch rates abundance index and the acoustic survey index, using intrinsic weighting. Reported 2005 landings of the spring spawner component were 5,139t against a TAC of 11,000t. Mean inshore catch rate in 2005 was similar to that in 2004, and remains near the lowest in the series that starts in 1990. The 2005 acoustic survey abundance of the age 4+ spring spawner component was slightly higher than in 2004, but combined abundance for ages 2 to 8 was lower. The 2005 acoustic index remains near the lowest in the series that began in 1994. Most year-classes produced after 1991 are estimated to be below average. The 1997, 1999 and 2001 year-classes appear to be slightly above average. The 1998 year-class is below average as is the 2000 year-class (age 5 in 2005) which is estimated as the lowest observed since the 1978 year-class. Age 4 to 10 spawning biomass has declined since 1995 and is estimated to be 50,700t at the beginning of 2006. The fully recruited (ages 6 to 8) exploitation rate was below the F_0.1 target in 2005. The F_0.1 catch for the spring spawner component in 2006 is 12,600t. A catch of 7,500t corresponds to a 5% increase in biomass. For a 10% increase in biomass, a catch of slightly less than 5,000t would be required.

The 2005 assessment of 4T herring fall spawner component was based on a sequential population analysis using an abundance index based on gillnet catch rates. Reported 2005 landings of the fall spawner component were 59,924t against the fall spawner TAC of 70,000t. There was no fishery in the 4Vn (Area 17) overwintering area by the purse seine fleet. Mean inshore catch rates in 2005 were higher than 2004 and remain high compared to the mid-1990s. The 1995, 1996, 1998 and 2000 year-classes are estimated to be above average. The 2006 beginning-of-year age 4+ spawning biomass is estimated to be about 283,700t and remains amongst the highest levels since 1978. The fully recruited (age 5+) exploitation rate in 2005 is below the F_0.1 target. The catch at F_0.1 for 2006 is 68,800t. A catch of 52,000t would result in an estimated 10% decline in biomass for 2007.

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