Effect of environmental factors and density-dependence on somatic growth of Eastern Georges Bank haddock (Melanogrammus aeglefinus)

Abstract

Haddock (Melanogrammus aeglefinus) is an important commercial fish species in the Northwest Atlantic, with the Eastern Georges Bank population a transboundary resources utilized by both Canada and the United States. With the dramatic increase recruitment of this population in the last decade, in particular concentrations of fish on the eastern portion of the Bank, there has been a precipitous decrease in somatic growth, raising concerns for managers and stakeholders. In this study, the effect of environmental factors and density-dependence on somatic growth of eastern Georges Bank haddock was studied using a 2-step Generalized Additive Model (GAM) regression approach. The biotic and abiotic factors examined in the regression analysis included haddock density, sampling location, local sea surface and bottom temperature, salinity and short time series of phytoplankton bloom statistics. The relative importance of each covariate in the best selected model was investigated using the nested GAMs. We found that density-dependence explained most of the variation in haddock growth, where the impact of temperature varied by season. Though of less model importance, annual winter salinity and phytoplankton bloom magnitude (lagged by one year) also contributed the growth model fits. These relationships have the immediate application of contextualizing the observed change in haddock growth, but may also inform various aspects of the stock assessment process.