Before revision:  Linear stability analysis of the resulting models is performed and it is shown that harvesting is sustainable . We next introduce a fractionalised time derivative to the model and investigate its effect. It is revealed that the so-called memory concept of the fractional derivative damps out oscillations in the population numbers so that the system as a whole settles on a equilibrium quicker than it would with integer time derivatives  .
After revision:  Linear stability analysis of the resulting models is performed and it is shown that harvesting is sustainable , and the memory concept of the fractional derivative damps out oscillations in the population numbers so that the system as a whole settles on a equilibrium quicker than it would with integer time derivatives .