“…As a result, modelling population dynamics with size structure has been an active and fruitful theme in mathematical biology (to name a few, see [2,4,6,7,11,12,13,15,17,18,19,20,22,23,24,26,31]). Unfortunately, only a few papers deal with the control problem [2,11,12,13,15,18,19,23,31]. Moreover, all focus on optimal harvesting except Araneda et al [2] on optimal harvesting time and He et al [11] on optimal birth control.…”