The Biological and Anthropogenic Soundscape of an Urbanized Port – the Charleston Harbor Estuary, South Carolina, USA

Abstract

Soundscape ecology provides a long-term, noninvasive approach to track animal behavior, habitat quality, and community structure over temporal and spatial scales. Using soniferous species as an indicator, biological soundscapes provide information about species and ecosystem health as well as their response and resiliency to potential stressors such as noise pollution. Charleston Harbor, South Carolina, USA provides important estuarine habitat for an abundance of marine life and is one of the busiest and fastest growing container ports in the southeast USA. Six passive acoustic recorders were deployed in the Charleston Harbor from December 2017 to June 2019 to determine biological patterns and human-associated influences on the soundscape. Anthropogenic noise was detected frequently across the estuary, especially along the shipping channel. Despite this anthropogenic noise, biological sound patterns were identified including snapping shrimp snaps (Alpheus spp. and Synalpheus spp.), fish calling and chorusing (Sciaenidae and Batrachoididae families), and bottlenose dolphin vocalizations. Biological response to anthropogenic activity varied among trophic levels, with decreased detection of fish calling when anthropogenic noise occurred and increased dolphin vocalizations in the presence of anthropogenic noise. Statistically, fine-scale, temporal patterns in biological sound were not clearly identified by sound pressure levels (SPLs), until files with anthropogenic noise presence were removed. These findings indicate that SPL patterns may be limited in their interpretation of biological activity for noisy regions and that the overall acoustic signature that we find in more pristine estuaries is lost in Charleston Harbor.

Enhancing Interpretation of Cetacean Acoustic Monitoring: Investigating Factors that Influence Vocalization Patterns of Atlantic Bottlenose Dolphins in an Urbanized Estuary, Charleston Harbor, South Carolina, USA

“…Spatial and temporal variation in vocalization detection rates has been documented in multiple odontocetes in relation to distribution, habitat use, and behavior (Lin et al, 2015;Simard et al, 2015;Marian et al, 2021;Díaz López, 2022). In the current study, acoustic detections were highest at the three sites of the Cooper-Wando confluence region-the Wando River, Drum Island, and SC Aquarium stations-suggesting this area is preferential habitat for bottlenose dolphins, similar to the core use areas described by Bouchillon et al (2019) and Transue et al (2023). In the Bouchillon et al (2019) study, visual surveys also indicated high numbers of dolphins sighted at the Wando River station, which could explain the higher number of vocalizations detected in this area.…”

“…In Charleston Harbor, long-term patterns in acoustic repertoire showed multi-year peaks in vocalizations during fall and winter as first reported by Transue et al (2023). Visual surveys indicated a higher abundance of bottlenose dolphins in the fall and winter as compared to the spring and summer, which matched the vocalization patterns.…”

“…This finding has been supported in similar studies across the southeast United States in North Carolina (Gannon & Waples, 2006) and in Florida (Berens McCabe et al, 2010). Soniferous fish calling intensity in Charleston Harbor increased during the spring and summer evenings and displayed species-specific chorusing periods resemblant of those described in the May River and Chechessee Creek, SC, estuaries (Monczak et al, 2019;Mueller et al, 2020;Transue et al, 2023). In the May River, chorusing seasons (occurrence and duration) were highly correlated to young-of-the-year abundance, supporting the assumption that chorusing initiates fish spawning (Monczak et al, 2022).…”

“…In addition, the high occurrence of echolocation suggests that this location may be an important foraging area for dolphins. Chorusing of soniferous fish species, which are known prey items of bottlenose dolphins (Pate & McFee, 2012), were also higher at the Wando River and Drum Island stations (Transue et al, 2023).. In other similar salt marsh ecosystems, higher dolphin densities also occur at the confluence of multiple rivers (e.g., SC's Cape Romain National Wildlife Refuge; Sloan, 2006).…”

“…In a previous study, a brief report of the vocalization types of bottlenose dolphins as well as their spatial and temporal patterns was provided in a publication on the biological and anthropogenic soundscape of Charleston Harbor (Transue et al, 2023). However, it was outside the scope of that study to thoroughly investigate dolphin acoustic behavior and variables that may affect vocalization patterns.…”