MEPS 588:147-161 (2018)  -  DOI: https://doi.org/10.3354/meps12430

ABSTRACT: The ecological importance of Pacific herring (Clupea pallasii) in the Northeast Pacific was re-evaluated by accounting for its high average energy content. An existing mass-balanced Ecopath food web model focusing on northern British Columbia waters was converted into a set of energy-balanced models using published energy content values for all functional groups. Ecosystem size spectrum slopes, proportions of herring in predator diets, and proportions of several large ecological categories in total ecosystem biomass and energy pools were compared across all models. Trophic effects of depleted whale population recovery were reassessed using Ecosim runs in the mass- and energy-balanced models. Balancing the high-energy model required a noticeable but non-significant increase in size spectrum slope relative to the original mass-balanced model. This may reflect energy content overestimates for large organisms, but more likely points to underestimated energy content, and possibly biomass, of planktonic groups. Forage fish and other pelagic organisms also accounted for higher proportions of the total ecosystem pool in the energy-balanced models. The reassessed trophic effects of whale population recovery were noticeably stronger for some active endothermic predators (small odontocetes and piscivorous seabirds) than suggested by published mass-balanced model results. However, most energy-balanced model outputs agreed qualitatively with those of the mass-balanced parent model. These findings suggest a potential for improved analysis of ecosystem structure and function, and forage fish trophodynamics, when prey group energy content is accounted for in ecosystem models.

KEY WORDS: Ecosystem modelling · Energy content · Northeast Pacific · Pacific herring · Clupea pallasii · Forage fish · Trophodynamics