Award: OCE-2035354

By preventing access, the COVID -19 quarantine created a human exclusion experiment termed the anthropause and an opportunity to assess how natural communities function in the absence of people. We wanted to find out if the indirect effects of a human pandemic could spill over to influence Galapagos marine ecosystems. Scuba diving there was abruptly terminated in March 2020 due to the quarantine. Reasoning that wary fish would be emboldened by a reduction of tourist diver disruption (boat noise, diver presence) and responding by increasing their feeding activity, interactions with other species and consequently their level of sound production, we investigated reef fish ecology and their acoustic soundscape at 3 high and 3 low diver visitation sites in the Galapagos during (September November 2020, January 2021) and after the quarantine (July-August 2021, January 2022, July-August 2022). Our methodology consisted of a 2 pronged effort by deploying hydrophones (https://www.oceaninstruments.co.nz/soundtrap-300/) and video cameras on stands at 10-15 m depth to record the sound produced by fish while simultaneously video recording their behaviors (Figure 1). Hydrophones were deployed for 2 8 days per site during each period, recording 98 times per second (Hertz, Hz). The long duration video cameras were specially fabricated (https://marineimagingtech.com/cameras-housings/housings/) for 6-10 hours recording per deployment. In total, we analyzed 1875 hours, (1.3 terabytes) of sound data. PI Jon Witman and post-docs Robert Lamb and Franz Smith supervised all of the various types of data analyses, but the detailed analysis of the soundscape was done by Glennie LeBaron for her Senior Honors thesis at Brown University. The videos also provided a trove of novel information about reef fish behaviors from the anthropause to the resumption of diving tourism. More specifically, we were able to record spatial and temporal variation in fish abundance, diversity, herbivory, cleaning and flight behaviors as well as behavioral indirect responses of fish to megafaunal predators (4 shark species, 1 sea lion). We termed these fast passes by megafaunal predators sending prey fish scattering, strafes. 605 strafes and other behaviors in 1500 videos (220 hours) were carefully analyzed by Rebecca Ward-Dioro for her Senior Honors thesis at Brown. We also evaluated changes in fish behavior and abundance directly while scuba diving. Some of the key results of this research are enumerated and summarized below. 1. There were large, predictable differences in the sound produced by organisms from day to night at all 6 sites regardless of their designation as high or low diver visitation sites. This increase in sound pressure levels began around 6 PM and ended around 6 AM (Figure 2), indicating that the acoustic record is primarily biologic. This interpretation is strengthened by the fact that dive tourism is prohibited at night. It also indicates that a minimum of 24 hrs is needed to characterize the shallow Galapagos soundscape. 2. Fish vocalizations were found at all 6 sites occurring under the 1500 Hz frequency band. These vocalizations occur for 2 -5 seconds and were found more often at night. Sea lion barks operated in a wider band between 100 to 2000 Hz. Unlike fish vocalizations, snapping shrimp appeared as a constant presence in all acoustic records with varying levels of strength. 3. A multifactor statistical model evaluating a hierarchy of factors influencing the magnitude of biotic sound production indicated that diel variation had the largest effect, followed by site effects, then period (the anthropause) and season. 4. Peak abundance of two species of sharks occurred a year after the anthropause (January 2022), not during it. 5. Of the megafaunal predators potentially causing changes in prey behavior during and after the anthropause, sea lions had significantly faster swimming speed during a strafe than sharks. Divers were the slowest, but this was based on a small sample of natural encounters of tourist divers swimming by the video cameras. 6. Fish fled from sea lions and white tip sharks faster than any other species, including divers. 7. Strafes by two thirds of the shark and sea lion species decreased fish species richness and delayed the return to herbivory by reef fish. In summary, with one exception of fish cleaning behavior (still being analyzed), we did not find significant change in biological sound production or species interactions among reef fish that was correlated with the timing of the anthropause. Rather, spatial and diel patterns were prominent in the Galapagos marine soundscape. We discovered many ecologically important behavioral indirect effects among reef fish and megafaunal predators but they were mostly species specific. Our continued data analyses may indicate that the Galapagos marine region may be a relatively intact soundscape that is not highly impacted by anthropogenic activity. Therefore, even though a doubling of anthropogenic activity level was detected, it may still be below the threshold necessary to cause long-term change to reef fish behaviors and communities. Last Modified: 03/05/2024 Submitted by: JonDWitman