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The analysis of net (bottom to surface vertical hauls) and trap samples taken at night shows that net hauls underestimate abundance of all planktonic organisms from nauplii and mollusc larvae to adult calanids. There is no obvious explanation for this. The underestimation probably results from low net filtering efficiency. The mean ratio between trap and net observed densities is 1.46 (1.2 to 1.9) and does not change significantly according to the organisms.