Environmental effects on recruitment dynamics and population projections of NAFO Division 4TVn Spring Spawning Atlantic Herring

Abstract

This document represents an application of the Ecosystem Approach to Fisheries Management by linking Herring recruitment dynamics and environmental drivers to better understand the mechanisms and the implications for assessment and management. In a time series of population estimates analysis, Herring spawning stock biomass was mostly driven by recruitment and high spawning stock biomass did not lead to high recruitment values. A regime shift analysis showed that both the sea surface temperature of all regions of the Southern Gulf of St. Lawrence (sGSL) and the spring spawning Herring recruitment abruptly shifted from a cold water/high recruitment regime (1978-1991) to a warmer water/low recruitment regime (1992-2017) in the early 1990s. Stock recruit relationships were successfully fitted to each of the regime periods and the expected recruitment for a given SSB is lower in the recent regime than in the 1978-1991 regime. A model estimating spring spawning Herring recruitment based on zooplankton variables was able to predict recruitment values with a sufficient level of performance that it could be used in the stock assessment process. The effect of using different assumptions about Herring recruitment in populations projections was tested using a simulation study. In this case, showing the two best models output (5 recent years and zooplankton model) would be the most informative to the 4TVn spring spawning Herring assessment.