This study applied a modified deterrence model to evaluate the effectiveness of legitimacy and ethical factors compared to deterrence measures for compliance with mesh size regulation in the Jebel Aulia Reservoir of Sudan. The ordered probit and zero-truncated negative binomial models were employed to examine influences of determining factors on the choice between typologies of violators and non-violators, and then on frequency of violations (extent) respectively. Reported violation rates were high (87.5%), combined with weak enforcement and effective evasion used by almost all (97%) violators, leading to a low probability of detection, as only 28% of violators were caught. This is consistent with widely observed phenomena in developing countries, calling for increased efficacy of detection, monitoring and enforcement of regulations and higher penalties to fight non-compliance. The study also confirmed the high importance of legitimacy and ethical factors, suggesting that the involvement of stakeholders in the process of designing, monitoring and enforcing regulations is crucial as a process factor that may be more important than mere deterrence measures. This advocates for participatory co-management systems that are most likely to be more effective than top-down mechanisms in promoting compliance. The study also suggests that investments in the education of fishermen, the provision of alternative income and employment opportunities outside of fishing, access to credit to finance the acquisition of legal nets, and the effective regulation of importation of illegal nets will be necessary for enhancing compliance with mesh size regulation in Sudan.