Variability and Drivers of the Feeding Guild Structure of Small Pelagic Fishes in the Western North Pacific Ocean During 1980–2022

ABSTRACT Pacific stocks of Japanese anchovy ( Engraulis japonicus ), chub mackerel ( Scomber japonicus ), Japanese sardine ( Sardinops melanostictus ), and Pacific saury ( Cololabis saira ) are dominant small pelagic fishes sharing common food (zooplankton) in the western North Pacific, thus forming a feeding guild. Here, we present temporal changes in the guild structure based on their biomass and recruitment trajectories with nonmetric multidimensional scaling (NMDS) and cluster analyses. NMDS outputs were compared with harvest rates (HR) and environmental indices. These results on biomass indicated that (1) the sardine‐dominated era (1980s) was characterized by a positive Pacific Decadal Oscillation Index and Siberian High Index, southward Oyashio, and low sardine HR, (2) anchovy‐dominated era (1900s–2000s) was characterized by the opposite environment and high sardine HR, and (3) mackerel‐dominated and saury‐depleted era (2010s–) was characterized by low mackerel HR and high HR of saury and anchovy. Results for recruitment were similar to those for biomass but not identical. Published knowledge on interspecies interactions among the feeding guild suggests that the effects of sardine and mackerel are prevailing; specifically predation by sardine on zooplankton may decrease the carrying capacity of the feeding guild. The four guild species shared a common feeding habitat along a temperature gradient with slight differences in their optimum temperatures. The previously suggested interspecies competition hypothesis for space between sardine and mackerel was not supported by the present results. Environment, fishing, and interspecies interactions (excluding spatial competition) are considered key factors in the variability of the guild structure, and marine heatwaves may increase uncertainties in assessing the future environmental effects.