Research Document - 2005/016

Assessment of the NAFO Division 4T southern Gulf of St. Lawrence herring stocks in 2004

By LeBlanc, C.H., G.A. Poirier, C. MacDougall, C. Bourque

Abstract

A population analysis was conducted on the 2004 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 2004 landings of the spring spawner component were 8,414t against a TAC of 13,500t. Mean inshore gillnet catch rates in 2004 were slightly lower than 2003 and remain at a low level compared to the early 1990s. The 2004 acoustic survey abundance of the age 4+ spring spawner component was the lowest in the time series that began in 1994. Most year-classes produced after 1991 are estimated to be below average. The 1997 and 1999 year-classes appear to be slightly above average. The 2000 year-class (age 4 in 2004) was estimated for the first time in this assessment and is below average. Age 4+ spawning biomass has declined since 1995 and is estimated to be 47,600t at the beginning of 2005. The exploitation rate of fully recruited ages 6 to 8 was below the target in 2004. The estimated F_0.1 catch for the spring spawner component in 2005 is 12,900t. A catch of 11,000t corresponds to a 20% chance of exceeding F_0.1. For a 10% increase in biomass, a catch of about 6,000t would be advised.

The 2004 assessment of 4T herring fall spawner component was based on a sequential population analysis using an abundance index based on gillnet catch rates. Reported 2004 landings of the fall spawner component were 43,208t against the fall spawner TAC of 73,000t. There was no fishery in the 4Vn (Area 17) overwintering area by the purse seine fleet. Mean inshore catch rates in 2004 were slightly less than 2003, but remain at a high level in the time series starting in 1978. The 1995, 1996, 1998 and 2000 year-classes are estimated to be above average. Estimates of population biomass and abundance are currently high; however, retrospective patterns indicated a tendency to overestimate the size of the biomass in the current year. The 2005 beginning-of-year age 4+ biomass is estimated to be about 255,000t, the lowest in the last six years, but remains amongst the highest levels since 1978. The age 7+ exploitation rate in 2004 is estimated to be below the target. After adjusting for the tendency to overestimate population numbers, the estimated catch at F0.1 for 2005 is 71,900t. A catch of 64,000t corresponds to a 20% chance of exceeding F_0.1.

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