Temperate freshwater soundscapes: A cacophony of undescribed biological sounds now threatened by anthropogenic noise

The soundscape composition of temperate freshwater habitats is poorly understood. Our
goal was to document the occurrence of biological and anthropogenic sounds in freshwater
habitats over a large (46,000 km2) area along the geographic corridors of five major
river systems in North America (Connecticut, Kennebec, Merrimack, Presumpscot, and
Saco). The underwater soundscape was sampled in 19 lakes, 17 ponds, 20 rivers and 20
streams, brooks and creeks that were grouped into broad categories (brook/creek, pond/
lake, and river). Over 7,000 sounds were measured from 2,750 minutes of recording in
173 locations over a five-week period in the spring of 2008. Sounds were classified into
major anthropophony (airplane, boat, traffic, train and other noise) and biophony (fish air
movement, also known as air passage, other fish, insect-like, bird, and other biological)
categories. The three most significant findings in this study are: 1) freshwater habitats in
the New England region of North America contain a diverse array of unidentified biological
sounds; 2) fish air movement sounds constitute a previously unrecognized important
component of the freshwater soundscape, occurring at more locations (39%) and in equal
abundance than other fish sounds; and 3) anthropogenic noises dominate the soundscape
accounting for 92% of the soundscape by relative percent time. The high potential
for negative impacts of the anthropophony on freshwater soundscapes is suggested by
the spectral and temporal overlap of the anthropophony with the biophony, the higher
received sound levels of the anthropophony relative to the biophony, and observations of
a significant decline in the occurrence, number, percent time, and diversity of the biophony
among locations with higher ambient received levels. Our poor understanding of the
biophony of freshwater ecosystems, together with an apparent high temporal exposure to
anthropogenic noise across all habitats, suggest a critical need for studies aimed at identification
of biophonic sound sources and assessment of potential threats from anthropogenic
noises.