Compared with MHK energy, widely-used hydropower have also been facing similar environmental concerns. To help investigate the potential of fish injury and mortality from passage through hydropower turbines, PNNL developed the JSATS. Recent JSATS development included several state-of-the-art acoustic transmitters, such as the injectable transmitter and the juvenile eel/lamprey transmitter. The latter is the world's smallest acoustic tag. Both these small transmitters have been successfully demonstrated in field studies and helped gather information on species of early life stages that had previously been unobtainable. The highly efficient transducer and circuit designs as well as the high-density micro-battery technology specifically developed for these transmitters were the innovations that made these technological advancements possible. The JSATS operates at 416.7 kHz, a relatively high acoustic frequency that works well filtering out acoustic noises in freshwater environments. With hardware and software modifications, these technologies can be readily adopted for a lower-frequency transmitter for use in marine environments. Our feasibility assessment and laboratory benchtop testing of the transmitter concept at three different frequencies around 200 kHz have shown significant improvements (detailed results listed in the attached document).