Comparative analysis of cod and herring production dynamics across 13 northern hemisphere marine ecosystems

Abstract

We conducted a comparative ecosystem analysis to understand environmental and biological drivers of production dynamics of 2 common species groups, cod (Gadus morhua and G. macrocephalus) and herring (Clupea harengus and C. pallasii), across 13 large marine ecosystems. For all 4 species, we fit a hierarchy of nested surplus production models with terms for trophodynamic and biophysical covariates; models were then compared using an information-theoretic framework. Across ecosystems, models including terms for biophysical covariates exhibited stronger fits to the data and were often included in the top set of selected models. However, the numerical effects of covariates differed among systems and species. For example, surplus production in several ecosystems was significantly affected by sea surface temperature, but to differing degrees (i.e. direction and magnitude of effect). Similarly, surplus production of cod was positively associated with herring biomass in 4 of the ecosystems examined, whereas negative trophodynamic interactions alluded to complex cultivation-depensation food-web dynamics in 5 other systems. Importantly, no single covariate emerged as the most important predictor of surplus production nor were biological reference points from models with covariates always more conservative than those without covariates. This suggests that inclusion of tropho dynamic and biophysical covariates in simple production models has the potential to increase model fit, but the relative benefit will be stronger for systems and species where trophodynamic and biophysical processes are tightly coupled to species productivity. © Inter-Research and Fisheries and Oceans Canada 2012.