Research Document - 2010/059
Assessment of the NAFO Division 4T southern Gulf of St. Lawrence herring stocks in 2009
By C.H. LeBlanc, D. Swain, C. MacDougall, and C. Bourque
Abstract
Assessments of the spring and fall spawning herring components from the southern Gulf of St. Lawrence are required on a regular basis and form a part of the information base used to establish the total allowable catch (TAC).
The 2009 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 in 2009 were 1,667 t. The spring spawner TAC was 2,500 t. The opinions of fixed gear harvesters from the telephone survey was that abundance of spring herring in 2009 was higher than 2008. Mean gillnet catch rate in 2009 was higher than 2008, but similar to values since 2004. The index has been declining since 1997 and remains at a low level in the series that starts in 1990. The 2009 acoustic index was higher than 2008 but remains low in the series that starts in 1994. Overall spawning stock biomass has declined since 1995 and remains at a low level. The current estimate of age 4+ spawning stock biomass (SSB) of 28,200 t is above the limit reference point (LRP) of 22,000 t but below the upper stock reference (USR) of 54,000 t. When the SSB declines below the USR, a harvesting strategy compliant with the Precautionary Approach (PA) would reduce the exploitation rate to promote stock growth to above the USR. The estimated exploitation rate in 2009 was 8%, below the reference level exploitation rate of 27%. The realized reduced exploitation rate on this component since 2007 is consistent with the PA. The abundances of recruiting year-classes (at age 4) after the 1991 year-class have been average or below average. A catch option of about 1,100 t in 2010 would provide a 50% probability of at least a 5% increase in biomass in 2011. Projections for the fisheries over the next two years (2010-2011) show that the probability of a 5% increase in biomass from 2010 to 2012 is 62% with annual catches of 2,000 t or less in 2010 and 2011.
The 2009 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 2009 were 46,747 t. 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. Mean gillnet catch rate in 2009 was slightly higher than 2008 but was lower than the previous three years. The exploitation rate in 2009 was 19%, below the reference level exploitation rate of 25%. Estimated recruitment at age 4 was above average from 1999 to 2005, and again in 2008 and 2009. Overall, the stock remains at a high level of abundance relative to the late 1970s and early 1980s. The 2010 beginning-of-year spawning stock biomass is estimated to be about 307,400 t, above the upper stock reference (USR) level of 172,000 t. For 2010, a catch option of 67,700 t corresponds to a 50% chance that exploitation rate would be above the reference removal rate. There is a low probability (< 25%) of a decline in biomass from 2009 for catch options less than 42,000 t. Projections for the fisheries over the next two years (2010-2011) show that the probability of a decline in biomass of more than 10% from 2010 to 2012 is low (≤10%) with annual catches of 50,000 t or less, rising to nearly 100% with catches of 60,000 t or more.
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