Research Document - 2016/064
Abundance indices of Atlantic herring (Clupea harengus) from the southern Gulf of St. Lawrence based on the September multispecies bottom trawl survey
By Tobie J. Surette
Abstract
Fishery-independent abundance indices for the fall spawner component of Atlantic herring (Clupea harengus), one for all large fish (≥ 20 cm) and the other disaggregated by age for fall spawning fish only, are derived from the September multi-species bottom trawl survey in NAFO Div. 4T. Using a Bayesian approach, over-dispersion in the data is handled via a negative binomial error with log-linear mean and additive hierarchical priors over year, survey stratum, time of day, fish age and interaction terms. While indices remained highly variable, cohort tracking was apparent in the age- disaggregated index and inter-cohort correlations were moderate for ages 4 to 7 years. While uncertainty remains as to other types of systematic annual changes, there was little evidence of change in day-night catchability patterns of Atlantic herring over time.
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