Hypotheses that planktonic predators are responsible for the spring-summer decrease in copepod abundance and that the dominant predator, Pleurobrachia pileus , is associated with high concentrations of copepods were investigated at a station near the Dutch coast. Neither hypothesis was supported. Predators and copepods were sampled together with a 156 L ‘water box’ from late April through early July, including the season of P.pileus abundance. Using predators and copepods from the same box samples, hence from the same water parcel, feeding rates on copepod nauplii and copepodites + adults were measured onboard ship. Less than 6% of the copepods, the sensitivity of the method, were removed per day. In additional shipboard feeding experiments net-caught P.pileus were added to ambient copepod densities. By combining water volume cleared of copepods with ambient P.pileus density in the sea, the predicted impact was 0–1.6% of copepods eaten per day from late April to early July. The hypothesis that P.pileus associates with copepod concentrations was tested by comparing abundances of both groups from the same box samples. The correlations were not significant for any sample series. The ways measurement methods have restricted progress in understanding the predatory impact of Pleurobrachia sp. are also considered.