The mathematical model of a fishery object contact against a mesh, while escaping through a trawl chafer, is presented. Based on it t the equations are provided to calculate the object elimination probability caused by cath and mortality in fishery operations. The coefficient of trawl ecological safety is offered, which is the ratio of the amount of the objects caught and objects caught and died during fishery. The equations are presented to estimate the gross removal of an object by the fleet group. Mathematical model is illustrated by a numeric example from the krill fishery. Thus, the calculated gross removal estimate exceeded the catch rate, based on commercial data in December 1984 in the South-Shetland area, only in 1,5 - 26 %, depending on the fishing intensity, i.e. it was within the range of stock estimate bias.