The cyclic and unstable chaotic dynamics in models of two populations of sturgeon fish

This paper considers nonlinear effects in the dynamics of biological models. We describe two dynamic systems, which are elaborated for the simulation of populations (Russian sturgeon and stellate sturgeon) and are based on the formalization of the relationship between the spawning stock and recruitment according to the analysis of observational data. For the numerical study of differential equations with structurally changing right-hand side, we use the method of representing models, based on maps of states with conditional transitions. For the dynamic systems, the presence of the qualitatively different modes of behavior of trajectories is revealed: stable periodic oscillations (model sturgeon), unstable chaotic (model stellate), realized in a limited time interval due to the presence in the phase space of a chaotic subset not being an attractor.