The Bohai Sea, in Northeastern China, which has been severely overexploited since the 1950s, is not only an exemplary case of the ‘fishing down’ phenomenon (where large, high-trophic level fish are replaced by smaller fish and invertebrates as the overall biomass is reduced), but also can be used to illustrate one of the masking effects for fishing down. Thus, the decadal decline in the mean trophic level of the biomass in the Bohai Sea is more pronounced than the decline of the mean trophic level of the catch extracted from that sea. This effect is similar to what occurred in the Celtic Sea, where previous authors called this difference ‘skipper effect’ (because skippers try to maintain catches of larger fish), and in the Gulf of Thailand. The skipper effect appears to be a powerful masking factor for the fishing down phenomenon, i.e., biomass tend to be more affected than suggested by time series of the mean trophic of catches.