What are we learning? What have we learned?

The Soundscape of the May River estuary – A One year, Baseline Study (from Monczak A, Mueller C, Miller ME, Ji Y, Borgianini SA, Montie EW (2019). Sound patterns of snapping shrimp, fish, and dolphins in an estuarine soundscape of the southeastern USA. Marine Ecology Progress Series 609:49-68).

Acoustic data revealed that sound pressure levels (i.e. broadband, low, and high frequency) varied spatially and temporally, exhibiting distinct rhythmic patterns.
Acoustic detection rates and diversity of biophonic (e.g. snapping shrimp, fish, and bottlenose dolphins Tursiops truncatus) and anthrophonic sounds (e.g. boat noise) were higher near the river mouth and decreased towards the headwaters.
The soundscape exhibited strong temporal patterns of snapping shrimp (genus Alpheus and Synalpheus) snaps, fish calls and choruses (e.g. silver perch Bairdiella chrysoura, black drum Pogonias cromis, oyster toadfish Opsanus tau, spotted seatrout Cynoscion nebulosus, and red drum Sciaenops ocellatus), bottlenose dolphin vocalizations, and vessel noise. Depending upon the species, certain variables (i.e. location, month, day length, lunar phase, day/night, tide, and temperature anomaly) influenced sound production.
Snapping shrimp snap more during spring and summer as compared to winter and fall. Snap rates also follow the tidal cycle; snap rates were higher during low tides as compared to high tides.
Black drum call most frequently during February and March. Silver perch call the most during March and May; the lowest rates in June and July. Oyster toadfish calling is most prevalent between March and May. Spotted seatrout call the most between May and September – all summer long and are finely tuned to the lunar cycle. Red drum call the most between September and October.

A Multiyear Sound Study of the May River - What’s all that racket! Soundscapes, phenology, and biodiversity in estuaries (from Monczak A, McKinney B, Mueller C, Montie EW (2020). What’s all that racket! Soundscapes, phenology, and biodiversity in estuaries. PLoS ONE 15(9): e0236874).

We used a six-year passive acoustic dataset of the May River to understand the annual and inter-annual variability of an estuarine soundscape.
Our findings show a strong relationship between temporal changes in acoustic activities of estuarine organisms and environmental factors. We showed that the transition between winter and spring is a dynamic time-period with an increase in biological sound during the spring, which mirrors the increase in phytoplankton, zooplankton, invertebrates, and fish abundance that drive changes in primary, secondary, and tertiary productivity within estuaries. In years with warmer spring temperatures, this seasonal transition occurred earlier than in years with cooler spring temperatures. This means that temperature plays an important factor in initiating certain behaviors (e.g. spawning), and earlier occurrences of these behaviors reflect an organismal response to climate variability.
We also found a link between sound production in the estuary and biodiversity. Higher species diversity and abundance occurred during seasonal periods when biological sound levels were the highest. Spatially, areas in the May River that were biologically louder also had a higher diversity and abundance of invertebrates and fish.

Fish Courtship Calls Correlate with Juvenile Fish Appearance and Abundance (from Monczak A, McKinney B, Souiedan J, Marian AD, Seder A, May E, Morgenstern J, Roumillat B, Montie EW. (2021). Sciaenid courtship sounds correlate with juvenile appearance and abundance in the May River, South Carolina. In Progress)

Our objectives were to investigate long-term patterns of calling, shifts in the calling season, and determine the relationship between spawning potential (i.e. measured by sound production) and young-of-the-year (YOY) abundance collected through haul seines.
We found that in years with warmer springs, fish began chorusing earlier and had longer calling seasons than in the years with cooler water temperatures. We detected the appearance of YOY in the estuary approximately one month after initiation of the chorusing season.
Silver perch were the most abundant in the spring, spotted seatrout during the summer, and red drum during the fall.
Additionally, we found positive correlations between sound production and YOY abundance. In years with longer chorusing seasons, we detected higher abundance of silver perch, spotted seatrout, and red drum than in the years with shorter chorusing periods.
These patterns provide support that passive acoustics can aid in monitoring reproductive output of an estuary.

Long-term Sound Monitoring of Bottlenose Dolphins in the May River Estuary (from Marian AD, Monczak A, Balmer BC, Hart LB, Soueidan J, Montie EW. (2021) Long-term passive acoustics to assess spatial and temporal vocalization patterns of Atlantic common bottlenose dolphins (Tursiops truncatus) in the May River estuary, South Carolina. Marine Mammal Science 37(3):1060-1084)

We used data from 2013 to 2018 to establish baseline acoustic patterns for bottlenose dolphins in the May River estuary, South Carolina. We deployed acoustic recorders at six stations during 2013–2014 and three stations during 2015–2018, with locations spanning the entire estuary (headwaters to the mouth).
We discovered that acoustic detection of dolphins varied not only spatially, but also yearly, monthly, and tidally. Higher numbers of echolocation bouts, burst pulse sounds, and whistles were detected at the mouth as compared to the headwaters. At the mouth, vocalization detections were greatest in fall and winter for multiple years, and echolocation detection was greatest during falling and low tides.
The high numbers of echolocation at the mouth indicate this may be an important area for foraging. These data provide information about dolphin behavior below the surface and can help to identify other core use areas.

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