Research Document - 2016/066
Assessment framework for fall-spawning Atlantic herring (Clupea harengus) in the southern Gulf of St. Lawrence (NAFO Div. 4T): Population models and status in 2014
By Douglas P. Swain
Abstract
The fall spawning component of Atlantic herring (Clupea harengus) in the southern Gulf of St. Lawrence has been assessed using virtual population analysis (VPA). A review of assessment inputs and models was undertaken due to poor model fit and unresolved model uncertainties. This document compares alternate model formulations (using revised data inputs described elsewhere) and presents status in 2014 based on the preferred model. The base model treated fall spawners as a single population and assumed that population dynamics parameters (e.g., natural mortality, M) and observation parameters (e.g., catchability) were stationary over time. A model incorporating process error in fully-recruited catchability to the gillnet fishery (q) provided the best fit to the data and eliminated the strong pattern in residuals. To address management requests, models treating fall spawners as three putative populations, based on three groups of spawning grounds (North, Middle and South), was examined. The greatest improvement in model fit and reduction in residual patterns occurred using a three-population model with process error in q, allowing q to vary independently among populations. This model was chosen as the preferred model for the provision of advice.
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