Research Document - 2015/025

Assessment of the NAFO Division 4T southern Gulf of St. Lawrence Atlantic herring (Clupea harengus) stocks in 2013

By C.H. LeBlanc, A. Mallet, T. Surette, and D. Swain

Abstract

The document presents the assessments of the spring spawning and fall spawning Atlantic herring components from the southern Gulf of St. Lawrence, NAFO Div. 4T. The 2013 assessment of the spring spawner component was based on a sequential population analysis calibrated on both the age-disaggregated gillnet catch rate (CPUE) and acoustic survey indices. The stock is considered to be just above the limit reference point. 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. The 2013 assessment of the fall spawner component was based on two sequential population analyses calibrated on an age-disaggregated gillnet catch rate (CPUE) index and an acoustic index for ages 2 and 3. The two assessment models varied in the assumptions about catchabilities in the fixed gear for ages 4 and 5, but neither model was considered superior for assessing stock status and providing catch advice, therefore the results from both models are presented. 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. 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.

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