Research Document - 2012/111
Assessment of the NAFO Division 4T southern Gulf of St. Lawrence herring stocks in 2011
By C.H. LeBlanc, A. Mallet, C. MacDougall, C. Bourque, and D. Swain
Abstract
Assessments of the spring and fall spawning herring components from the southern Gulf of St. Lawrence are prepared every two years and form a part of the information base used to establish the annual total allowable catch (TAC).
The 2011 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 landings of the spring spawner component in both the spring and the fall fisheries were 1,267 t in 2010 and 1,425 t in 2011. The spring spawner TAC was 2,000 t. The opinions of fixed gear harvesters from the telephone survey was that abundance of spring herring in 2010 and 2011 was higher than 2009. Mean gillnet catch rate in 2010 was the lowest in the time series; the 2011 gillnet catch rate was the second lowest. The index has been declining since 1997 and remains at a low level in the series that starts in 1990. The 2010 acoustic index was slightly higher than 2009, but declined again in 2011. The 2011 index remains low in the series that starts in 1994. The stock is considered to be within the critical zone but just below the limit reference point. Estimated abundance has increased in recent years from the low level estimated in 2006. Estimated fishing mortality rates in 2010 and 2011 are the lowest of the time series at less than 0.1. The abundances of recent recruiting year-classes (at age 4) are below average. A catch option of about 1,000 t in 2012 would provide a 90% probability of at least a 5% increase in biomass. Projections for the fisheries over the next two years show that the probability of an increase in biomass from January 2012 to January 2014 ranged from 79% with no catch to 21% with catches of 3,000 t each year.
The 2011 assessment of 4T herring fall spawner component was based on a sequential population analysis calibrated on an age-disaggregated gillnet catch rate (CPUE) index and an acoustic index for ages 2 and 3. Reported landings of the fall spawner component in both the spring and the fall fisheries were 47,004 t in 2010 and 38,408 t in 2011. The fall spawner TAC was 65,000 t. The opinion of fixed gear harvesters from the telephone survey is that the abundance of fall herring has been decreasing since 2006, with a slight increase in 2009 and decrease again into 2010 and 2011. Mean gillnet catch rate has generally decreased since 2006. The acoustic index has been declining since 2006 and remains at a low level in the series that starts in 1994. The exploitation rate in 2011 was 21%, below the F0.1 reference level of 25%. Estimated recruitment at age 4 was above average in 2008 and 2009, but below average in 2010 and 2011. Overall, the stock remains at a moderate level of abundance. The 2012 beginning-of-year spawning stock biomass is estimated to be about 183,800 t, above the upper stock reference (BUSR) level of 172,000 t. For 2012, a catch option of 42,842 t corresponds to a 50% chance that exploitation rate would be above the reference removal rate. There is a 90% probability of a 5% decline in biomass from 2011 for a catch option of 42,842 t. Projections for the fisheries over the next two years (2012-2013) show that the probability that SSB would be below BUSR in 2014 varied from 16% with catches of 20,000 t to 69% with 50,000 t of catch each year based on recent recruitment rates, and from 14% with catches of 20,000 t to 58% with 50,000 t of catch each year when based on recruitment rates over the past 20 years.
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