Acoustic assessment of trophic dominance in a marine ecosystem

High‐frequency acoustic surveys over the past 15 years show that the trophic structure in Prince William Sound (PWS), Alaska, functions as a wasp‐waist ecosystem. Three dominant biomasses in PWS are: (1) Pacific herring (2) walleye pollock and (3) the large‐bodied copepods (Neocalanus spps.) that dominate the spring zooplankton assemblage. The acoustic surveys and associated ecosystem observations suggest that the relative dominance of herring and pollock affects the composition of the apex predators. The near‐shore and near‐surface distribution of herring provides access by surface‐oriented marine mammal and seabird predators, such as sea lions, seals, murres and cormorants, to a crucial winter‐period food source. In contrast, the deep, off‐shore distribution of the pollock favors large benthic predators, such as demersal sharks, halibut, and flounder. The acoustic surveys also demonstrated that the abundance of large‐bodied copepods in PWS is critical to ecosystem productivity, including survival of juv...