Underwater sound generated by human activities can potentially adversely affect aquatic animals, including invertebrates. In addition to the sound pressure field, the field of particle velocity can also have an effect. Modern biological-acoustic studies show that fish and invertebrates are sensitive not only to pressure, but also to the level of particle velocity, the vector components of the sound field. The classification of fish by their sensitivity to the components of the sound field is given. The currently accepted sound field levels of traumatic effects on fish are given. The results of modeling the vector field of the power flux in a multimode horizontal layered waveguide of the shallow sea are presented. Modeling of the power flow field is carried out “by definition”, as the product of pressure fields and field components of the particle velocity vector. The pressure and particle velocity fields are calculated using the normal mode method. A qualitative connection is established between the physical and acoustic characteristics of the layered bottom and the averaged laws of decay of the components of the fields of the particle velocity and the field of the power flux for a multimode character of sound propagation.