In this work, we present a predator-prey type model where the two predator species engage in mutualistic predation. Constant effort harvesting is also incorporated. 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  .
We first present a predator-prey model for two species and then extend the model to three species where the two predator species engage in mutualistic predation. Constant effort harvesting and the impact of by-catch issue are also incorporated. Necessary sufficient conditions for the existence and stability of positive equilibrium points are examined. 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 an equilibrium quicker than it would with integer time derivatives . Finally, some possible physical explanations are given for the obtained results. It is shown that the stability requires the memory concept in the model .
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