The spatial scale of surface swarms of Calanus plumchrus Marukawa observed from consecutive plankton net catches in the northwestern North Pacific

To define the spatial scale of swarms of Calanus plumchrus at the surface in pelagic waters of the North Pacific, three series of consecutive plankton net tows were conducted in summer 1981. Three biomass peaks of C. plumchrus were found in one of the three series of tows. The density of stage C.V. of C. plumchrus, the only swarm-forming stage, reached 429–745 individuals·m⁻³ (x 180.2 ind·m⁻³). The distance between local peaks was from 3 to several kilometers and the spatial scale of the surface swarm of C. plumchrus was estimated as 1–2 km. Major Calanus species exhibit similar sizes of surface swarms in the North Pacific region.