The ambient acoustic environments at two locations in Laguna San Ignacio, Baja, Mexico

Abstract

Each winter gray whales (Eschrichtius robustus) breed and calve in Laguna San Ignacio, with the lagoon's northern section more heavily used by mothers rearing calves. The southern section of the lagoon is open to milling and ecotourism traffic, while the northern section is restricted to vessel transits only. Ambient acoustic data from autonomous underwater recorders have been collected between 2008 and 2013 at Punta Piedra (southern section) and Camp Kuyima (northern section). Multiple sources of acoustic sound exist in the lagoon, including tidal flows, fish chorusing, gray whale vocalizations, snapping shrimp, daily land/sea breezes, and panga activity. Here the cumulative distributions of rms sound pressure levels from all deployments during daytime and nighttime are presented for several frequency bands that represent contributions from the varying source mechanisms. Since concurrent data from both restricted (northern) and unrestricted (southern) sections exist, comparing sound level distributions between sites can provide insight into the relative contributions of various mechanisms to the overall ambient noise environment. These data have established a baseline for monitoring trends and changes in acoustic environments of the lagoon in anticipation of future tourist development. [Work sponsored by LSIESP and Ocean Foundation.]