Abstract: Devices and methods are disclosed for monitoring at fishing vessels to detect blast fishing activity. A blast sensor is mountable to a vessel such that it produces a signal in response to pressure waves in water. A controller receives the signal and is operable to analyze the signal to detect blast events based on signal characteristics. A position measurement device measures a position of the vessel. A transmitter is provided to wirelessly transmit status information including a unique identifier of the monitoring unit and indicative of the position of the monitoring unit and to send a wireless alarm signal in response to a detected blast event.