Analysis of the environmental noise in Laguna de Términos, Campeche, México

Abstract

Sound energy, generated by both natural and man-made sources, spreads particularly efficiently in the marine environment as underwater noise in the ocean. In Laguna de Términos, Campeche, in the southern Gulf of Mexico, the environmental noise is mainly due to the presence of snapping shrimp and other marine life. Anthropogenic noise is not frequent, and it is mainly due to small fishing vessels. The general objective of this study was to measure the underwater environmental noise in Laguna de Términos, Campeche, México from 2004 to 2008 (five years) in seven sampling periods. The recordings were made at 20 stations at a sampling rate of 48 kHz with 16 bits resolution, from which 1-minute segments were created in WAV format for each station. The environmental noise in the lagoon was calculated as a noise-to-highest-value ratio (NHR) and averaged to obtain four values for each of the seven sampling periods that represent four different geographical areas of Laguna de Términos (western and eastern mouths, center, and river mouth). NHR changed from one sampling to another. Only in October 2005 there was a large decrease in NHR near the river mouth due to the pass through Laguna de Términos of two very strong hurricanes (Stan and Wilma) one week before sampling was performed. At the western and eastern mouths (Bocas del Carmen and Puerto Real) NHR seems to follow a similar pattern over time, which may be related to the boat traffic at Ciudad del Carmen and Isla Aguada, respectively, and are the areas where the environmental noise decreased significantly in March 2007. We are investigating the reasons for these changes and their relationship with the presence of bottlenose dolphins (Tursiops truncatus) in the lagoon.