No abstract

No abstract

No abstract

Passive Acoustic Monitoring studies have been benefited from open source software initiatives such as PAMGuard and ISHMAEL, but their widespread use is often limited by availability of low cost hardware. This work presents the design of a towed hydrophone array that can be built with off the shelf components. The system comprises a Raspberry Pi computer to log GPS, three-axis accelerometer, magnetometer, gyroscope, and audio from the hydrophone array (20 Hz-44 kHz). Data can be analyzed in PAMGuard, either in real time, through a short range (10 m) RF link, or retrieved later from the data logger. The array has been tested in La Paz bay Mexico, where semi-resident populations of long-beaked common dolphin (Delphinus capensis) and bottlenose dolphin (Tursiops truncatus) have been reported. Results and performance of the array in four modalities are presented; as a drift array, as a secondary array deployed from a small vessel, as an array towed by a Kayak, and as an array towed by an Autonomous Surface Vehicle. This array provides a useful tool for fieldwork, and since it is built form off the shelf components on a low budget, it could also be used for educational purposes, such as in PAMGuard Courses.

Although the broadband high level sounds of snapping shrimps dominate the soundscape of a coral reef, the spatial, spectral, and temporal variations due to biotic and abiotic factors are indicators of the health of these vulnerable environments; for instance, reefs become louder during new moons of the wet season, when many larval organisms settle, or tends to go quiet as animals abandon them when conditions become less favorable. Moreover, the soundscape is able to provide information on the reef benthic composition and has been identified as a possible driver of reef population dynamics. To study this particular environment, a Remote Operated Vehicle (openROV) is being used to visually identify the biota associated with a shallow coral reef near a major port in La Paz, Mexico. An acoustic linear array has been incorporated, providing directional sound recording capabilities to capture better space variability of the coral soundscape. By combining visual and acoustical clues in an acoustic cam, it is also feasible to associate fish species and acoustic signals. A preliminary assessment of the design for monitoring a shallow coral reef is presented, along with a comparison with traditional diving surveys.