SOUNDSCAPE ANALYSIS OF THE WEST FLORIDA SHELF (GULF OF MEXICO)

 

Overview

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My 2016-2017 research, as a part of the E.C. Dolphin Project, focused on conducting a soundscape analysis of the Gulf of Mexico. Soundscape ecology is a growing field that can help us understand how different types of noise are affecting marine species (Pijanowski et al 2011).

 

WHY IS IT IMPORTANT? 

Soundscape ecology can tell us information about how climate, land transformations, biodiversity patterns, timing of life history events and human activities create the dynamic soundscape. In Tampa Bay and the West Florida Shelf,  there is a dynamic ecosystem consisting of marine species and human related activities, such as vessel traffic. Soundscape ecology will allow us to understand the effects of sound on these ecosystem.


DSG recorder deployed in the Gulf of Mexico

Figure 1. Map of study area showing acoustic recorder stations

Research questions

  1. Did diel differences in sound pressure level exist at individual stations (summer and winter)?
  2. Did seasonal differences in sound pressure level exist between stations?
  3. Did seasonal differences in sound pressure level exist within each of the stations?
 

Methods

Field

  • DSG autonomous acoustic recorders (Figure 1) were deployed at three locations (Figure 2)
  • Boca Ciega Bay (“Boca 2”, ~3m depth, sand bottom)
  • Inshore Gulf of Mexico (“AC5”, ~10m depth, near a limestone reef)
  • Offshore Gulf of Mexico (“Florida Fisherman’s Ledge [FFL], ~30m depth, near a limestone reef
  • Recorders were on a 10 sec / 10 min duty cycle, 50 kHz sample rate, system sensitivity -150 dB re 1 uPa

Analysis

  • Acoustic recordings were analyzed from July 7th and 11th, December 1st,  3rd, and 20th
  • RMS amplitude in 2 kHz bins was calculated for each file (0-24 kHz) and binned into daily, seasonal and 6-hour mean values in Matlab
  • The potential sources of frequency-specific sounds were determined by inspecting spectrograms in Raven Pro

 


Results

Question 1

Figure 1.  Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in summer (n=2 days, SD 1.38-9.37, F=0.187, df=3, P=0.904).

Figure 1. Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in summer (n=2 days, SD 1.38-9.37, F=0.187, df=3, P=0.904).

Figure 3.  Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in summer (n=2 days, SD 0.655-4.79, F=0.503, df=3, P=0.682).

Figure 3. Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in summer (n=2 days, SD 0.655-4.79, F=0.503, df=3, P=0.682).

Figure 5.  Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour cycles in summer (n=2 days, SD 0.670-6.21, F=0.113, df=3, P=0.952).

Figure 5. Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour cycles in summer (n=2 days, SD 0.670-6.21, F=0.113, df=3, P=0.952).

Figure 2.  Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in winter (n=3 days, SD 1.84-6.29, F=0.447, df=3, P =0.721).  

Figure 2. Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in winter (n=3 days, SD 1.84-6.29, F=0.447, df=3, P =0.721).  

Figure 4.  Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in winter (n=3 days, SD 1.39-9.39, F=0.035, df=3, P=0.991).

Figure 4. Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in winter (n=3 days, SD 1.39-9.39, F=0.035, df=3, P=0.991).

Figure 6.  Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in winter (n=3 days, SD 0.862-11.04, F=0.034, df=3, P=0.983).  

Figure 6. Mean RMS amplitude (dB re 1 μPa) as a function of frequency (kHz) between 6-hour periods in winter (n=3 days, SD 0.862-11.04, F=0.034, df=3, P=0.983).  

 

Question 2 & 3

Figure 7.  Mean RMS amplitude (dB re 1 μPa) as a function of average frequency (kHz) between each site (n=3) during both season, summer (n=2) and winter (n=3), with a minimum standard deviation of ± 1.19 and a maximum of ± 9.68.

Figure 7. Mean RMS amplitude (dB re 1 μPa) as a function of average frequency (kHz) between each site (n=3) during both season, summer (n=2) and winter (n=3), with a minimum standard deviation of ± 1.19 and a maximum of ± 9.68.

Table 1.  Results from the t-test was performed to compare average amplitude (kHz) between summer and winter at each site (question 2). Results from the ANOVA used to compare the difference in average amplitude (kHz)  between sites for each season (question 3).

Table 1. Results from the t-test was performed to compare average amplitude (kHz) between summer and winter at each site (question 2). Results from the ANOVA used to compare the difference in average amplitude (kHz)  between sites for each season (question 3).


Discussion

  • Most noise was caused by (a) fish chorusing (200-1000 Hz), (b) snapping shrimp (200-25000 Hz) and (c) boat engines (1-5000 Hz and higher)

Question 1: no significant differences were found in diel sound pressure levels at any station in summer or winter

  • Suggests little diel periodicity in major noise sources
  • Diel periodicity documented in fish chorusing (Locascio and Mann 2008), snapping shrimp (Bohnenstiehl et al 2016) and boating activity (Sidman et al 2004) – therefore lack of significance potentially an artifact of analysis

Question 2: Significant difference found between summer and winter sound pressure levels at shallow reef site (AC5) but not at other stations

  • Higher sound pressure levels in summer likely represent increased recreational boating (Sidman et al 2004) and snapping shrimp activity (Bohnenstiehl et al 2016)

Question 3: Significant difference found between sound pressure level at the three sites in both summer and winter

  • Sound pressure level decreases with increasing depth
  • These differences appear to be due to snapping shrimp and recreational boating levels, both of which are more common in shallower water (Everest et al 1948, Sidman et al 2004)

Acknowledgements 

  • Funding provided by the Florida Fish and Wildlife Artificial Reef Program, Eckerd College Natural Sciences Summer Research Program
  • Field assistance from Pinellas Co. Dept. of Environment and Infrastructure, members of USF Fish Ecology Lab, and many others

 

References

  • Bohnenstiehl et al (2016) The curious acoustic behavior of estuarine snapping shrimp. PLoS ONE 11(1): e0143691
  • Everest et al (1948) Acoustical characteristics of noise produced by snapping shrimp. J. Acoustical Soc. Am. 20: 137-142.
  • Locascio & Mann (2008) Diel periodicity of fish sound production in Charlotte Harbor, Florida. Trans. Am. Fish. Soc. 137: 606-615.
  • Pijanowski et al (2011) What is soundscape ecology? An introduction and overview of an emerging new science. Landscape Ecology 26: 1213-1232.
  • Sidman et al (2004) A recreational boating characterization for Tampa and Sarasota Bays. FL Sea Grant Report TP-130

Authors

Anjali Boyd(1)*, Shelby McKean(1), David Mann(2), Christopher Stallings(3), Shannon Gowans(1) and Peter Simard(1)

1: Eckerd College, St. Petersburg FL,

2: Loggerhead Instruments, Sarasota, FL,

3: University of South Florida College of Marine Science, St. Petersburg FL

*Primary/presenting author

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