Research Document - 2014/092

Effect of environmental variability on the Atlantic Mackerel (Scomber scombrus L.) stock dynamics in the Gulf of St. Lawrence

By Stéphane Plourde, François Grégoire, Caroline Lehoux, Peter S. Galbraith, and Martin Castonguay

Abstract

The objective of this study was to assess the effect of environmental variability on the dynamics of the Atlantic mackerel (Scomber scombrus L.) stock in the Gulf of St. Lawrence (GSL). We first describe the dominant modes of physical and biological (zooplankton) environmental variability using Principal Components Analyses (PCA) of 40 variables and identify potential environmental regimes during the 1990-2012 period. Two principal modes of variability were identified, a long-term mode (15-20 years) associated with a warming of the GSL and a second mode at higher frequency (5-10 years) describing alternating cold and warm periods. The results also identified a strong link between variations in physical environmental conditions and the abundance, composition and seasonality of zooplankton species known to be important for Atlantic mackerel larvae, juveniles and adults. Moreover, sudden changes in physical environmental conditions and zooplankton dynamics in 1996-1997, 2004 and from 2009 to 2012 were revealed by the analyses. Second, a set of Generalized Additive Models (GAM) was developed to explore the role that these variations in bottom-up processes could play in the control of Atlantic mackerel condition (Fulton’s K) and recruitment success (Rs). Optimal GAM including variations in abundance, species composition and phenology of key copepod species such as Calanus finmarchicus, Pseudocalanus spp. and Temora longicornis improved models performance by 40-50% relative to those considering only physical environmental conditions, illustrating the key role of zooplankton dynamics in controlling variations in K and Rs and supporting the match-mismatch hypothesis. Finally, our study showed that large variations in Rs could be caused by varying environmental conditions independently of spawning stock biomass, and they should be considered in the development and application of an ecosystem-based approach to Atlantic mackerel stock management.

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