Exploring drivers of capelin (Mallotus villosus) and Atlantic cod (Gadus morhua) population dynamics using Empirical Dynamic Modelling (EDM)

Steele, Reid (2023) Exploring drivers of capelin (Mallotus villosus) and Atlantic cod (Gadus morhua) population dynamics using Empirical Dynamic Modelling (EDM). Masters thesis, Memorial University of Newfoundland.

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Abstract

Capelin (Mallotus villosus) populations on the Newfoundland shelf collapsed in the early 1990s, coinciding with an ecosystem regime shift and greatly reduced capelin biomass which both persist to this day. The dual-regime nature of this stock’s history suggests it may experience nonlinear dynamics, which are difficult to predict using linear models. This thesis explores the application of nonlinear Empirical Dynamic Modelling (EDM) forecasting tools to capelin biomass data, seeking to determine if capelin dynamics are nonlinear, if nonlinear predictive models of capelin population dynamics outperform linear models, what climatic and ecological factors drive nonlinear changes in capelin biomass, and if these driving forces can be measured and compared. In my first chapter, I found capelin dynamics were nonlinear, and EDM predictive models returned equal or improved model diagnostics to linear models in most situations. In my second chapter, I identified a strong positive association between capelin and Atlantic cod dynamics, with both species being driven by long term climatic change and likely to benefit from mild warming. This thesis clearly identifies the utilities of EDM as a tool for use in stock assessment in detecting and forecasting nonlinear stock dynamics, and identifying and characterizing factors driving population dynamics.

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