PS 37-19 - Insects, not fish biophonies, significantly contribute to daily bioacoustics variations in tropical streams

Abstract: Freshwater bioacoustics is a relatively new area of research with great utility in environmental and ecological studies. This line of research generates essential data for conservation and monitoring initiatives for streams and river biodiversity. This study quantitatively assesses which sound-emitting biota significantly contribute to the daily bioacoustics variations in the tropical streams of Puerto Rico. To comply with this objective, we selected four tropical streams in the Puerto Rico watersheds of Río Grande de Manatí, Río La Plata, and the Río Grande de Loíza, specifically the rural streams Río Emajagua (EMA), Río Toro Negro (TNG), and the urban streams Río Grande de Loíza (GLZ) and Río Bucarabones (BUC). Two hydrophones were placed at each stream for 24 continuous hours per week for three consecutive weeks. The first minute of each hour was selected to form a subsample of 24m per day of frequencies between 0 to 22kHz. The subsamples were then analyzed for their Acoustic Complexity Index (ACI) in two distinct frequency ranges that account for both fish and insect biophonies and its Normalized Difference Soundscape Index (NDSI) to quantify possible anthropophonies, using the soundecology R package.



Through the acoustic analyses, the most significant difference in sound diversity was found at the TNG, where an average higher ACI was recorded, especially during mornings (08:00 to 09:00 AM) and early afternoons (12:00 to 3:00 PM), showing a higher and more constant quantity of biotic sounds during the study period. On the contrary, BUC was the less active stream regarding ACI, although the hours of significant activity were the same. The results of the Generalized Linear Mixed Models indicate that the daily variation in the stream biophony is primarily driven by insect sounds with minor to no contributions by anthropogenic sounds (represented by the NDSI index) and fish biophonies. These results are helpful for future underwater bioacoustics monitoring studies since they show at which time during a 24 h period there is a richer acoustic activity and which sound-emitting biota contribute the most to the stream biophony.