Mechanical rock grinding in the Mississippi River: anthropogenic noise production and implications for the federally endangered pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905)

Abstract

Summary The use of mechanical rock grinding to remove rock pinnacles and outcroppings, considered to be navigation hazards in the Mississippi River, was evaluated as a less damaging alternative when compared to the more conventional use of drilling and blasting. The project area contains the federally endangered pallid sturgeon (Scaphirhynchus albus) and there was concern that intense sound pressure levels (SPLs) could impact the species. SPLs were measured during production rock grinding (January 2012, just north of Thebes, Illinois) and compared to those values with SPLs known to cause fish mortality, hearing damage, temporary hearing threshold shifts (TTS), and stress. The source SPLs’ maxima for each time block analyzed ranged from 160–172 dB (re 1 μPa @ 1 m) at frequencies ranging from 100–1250 Hz (1/3-octave band). The highest source SPL maximum recorded for the sound recording session was 172 dB (re 1 μPa @ 1 m) at 1250 Hz. These SPL levels at 1 m from the grinder were well below levels responsible for mortality or noise induced hearing damage. The impact zone for stress (increases in cortisol) was calculated to be within a 9 m radius of the grinder, while the impact zone for TTS was calculated to be within 31 m of the grinder. Considering the small impact zones and continuous noise production during grinding, there is a strong possibility that sturgeon would either avoid or move out of the impact zone.