October 29, 2014
Science Advisory Report 2014/040
Assessment of Atlantic herring in the southern Gulf of St. Lawrence (NAFO Div. 4T) to 2013
Spring Spawner Component
Reported landings of the spring spawner component in both the spring and the fall fisheries were 599 t in 2012 and 1,703 t in 2013. The spring spawner TAC was 2,000 t.
The opinions of fixed gear harvesters from the telephone survey were that abundance of spring herring in 2012 and 2013 was similar to 2011.
The mean gillnet catch rate in 2012 was the second lowest in the time series but the 2013 gillnet catch rate was higher than in 2012. The index has been declining since 1997 and remains at a low level in the series that starts in 1990.
The 2012 and 2013 acoustic indices were slightly higher than in 2011 but the indices remain low in the series that starts in 1994.
The stock is considered to be just above the limit reference point. Estimated abundance has increased in recent years from the low level estimated in 2006.
Estimated exploitation rates in 2012 and 2013 are the lowest of the time series at 3% and 12%, respectively.
The abundances of recent recruiting year-classes (at age 4) are below average.
A catch option of about 2,000 t in 2014 would result in about an 80% 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 2014 to January 2016 ranged from almost 100% with no catch to 93% with catches of 2,000 t each year.
Fall Spawner Component
Reported landings of the fall spawner component in both the spring and the fall fisheries were 32,576 t in 2012 and 34,368 t in 2013. The fall spawner TAC was 43,500 t.
The opinion of fixed gear harvesters from the telephone survey is that the abundance of fall herring has been decreasing since 2006.
The mean gillnet catch rate has generally decreased since 2006 but the 2013 mean gillnet catch rate was higher than the two previous years.
The acoustic index for ages 2 and 3 has been declining since 2006, except in 2012, and remains at a low level in the series that starts in 1994.
Two assessment models that varied in the assumptions about catchabilities in the fixed gear for ages 4 and 5 were evaluated. There are reliability issues with the two models for assessing stock status and providing catch advice, therefore the results from both models are presented.
The exploitation rate in 2013 was estimated to have been 31% under model 1 (no change in catchabilities of ages 4 and 5 since 2004) and 21% under model 2 (trend in catchabilities of ages 4 and 5 since 2004). The F0.1 reference level for fall spawners is 25%.
Estimated recruitment at age 4 shows generally similar patterns for both models: recruitment was below average in 2007 and 2012 and above average in 2008 and 2009. Recruitment was estimated to be above average in 2013 under model 2 but not for model 1.
The 2014 beginning-of-year spawning stock biomass with model 1 is estimated to be about 98,000 t and in the cautious zone for this stock. The 2014 beginning-of-year spawning stock biomass under model 2 is estimated to be 182,800 t and above the upper stock reference (BUSR) level of 172,000 t.
Risk analysis results of catch options differ between the models. For model 1, there is a 100% probability that the spawning stock biomass will be below BUSR (172,000 t) even with no fishing in 2014. A catch option of 22,100 t in 2014 corresponds to a 50% chance that the exploitation rate would be above the reference removal rate. For model 2, a catch option of 38,017 t in 2014 corresponds to a 50% chance that exploitation rate would be above the reference removal rate and a probability of 85% that spawning stock biomass would be below BUSR.
Advice cannot be provided for more than one year (2014) for the fall spawner component because of important and unresolved model uncertainties. A review of the assessment approach is recommended including data inputs and alternate model formulations that could incorporate changes in natural mortality, changes in catchability, and proportionality of indices.
This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, regional peer review meeting of March 11-12, 2014 on the Assessment of stock status of Atlantic herring (Clupea harengus) from the southern Gulf of St. Lawrence (NAFO Div. 4T). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
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