Trophic Modeling of Shortfin Mako (Isurus Oxyrinchus) and Bluefish (Pomatomus Saltatrix) Interactions in the Western North Atlantic Ocean

An ecosystem model of the western North Atlantic Ocean was constructed that emphasized predator-prey dynamics of shortfin mako, Isurus oxyrinchus Rafinesque, 1810, and bluefish, Pomatomus saltatrix (Linnaeus, 1766). Modeling served to synthesize knowledge about food consumption rates and feeding habits into a framework that could be used to characterize uncertainty in the dynamics of key trophic linkages. The model was used to investigate whether directed fishing for each member of this predator-prey linkage could result in indirect effects on (1) shortfin mako biomass and yield as a result of changes in shared bluefish resources or (2) bluefish biomass and yield as a result of changes in shortfin mako biomass. A preliminary exploration of fishing policies suggested competition between shortfin mako and bluefish fisheries for shared bluefish resources, as increased catches of bluefish had deleterious effects on shortfin mako biomass and yield. Conversely, bluefish biomass and yield were relatively invariant to catch-driven changes in shortfin mako biomass. Sensitivity analysis indicated consistency in model outcomes across a variety of model configurations, but outcomes were sensitive to the magnitude of bluefish consumption by shortfin mako. Model outcomes formed the basis for discussing additional knowledge gaps and alternative modeling assumptions and for guiding research aimed at broadening our understanding of trophic interrelationships involving shortfin mako and bluefish.