Effects of hauling speed on zooplankton catches

Abstract

Three plankton nets, similar in all respects but size, were hauled vertically through the water column (100 m) at speeds ranging from 0.4 to 2.4 m/sec. Several components of the catch were counted, and the counts compared to test the effect of hauling speed. With increased hauling speed, the number of juvenile and adult euphausiids decreased (beyond 0.6-0.8 m/sec) ; the number of small organisms increased; and the condition of the catch deteriorated (beyond 1.5 m/sec).

It is suggested that the mesh selectivity of a net depends in part upon the number of contacts between organism and mesh in transit from mouth to cod-end. This could explain why fewer small organisms were taken at low hauling speeds than at high hauling speeds.