Dolphin communication during widespread systematic noise reduction-a natural experiment amid COVID-19 lockdowns

Abstract

Underwater noise from human activities is recognized as a world-wide problem, with important repercussions on the acoustic communication of aquatic mammals. During the COVID-19 pandemic, the government of Panama went into a nationwide lockdown to limit the spread of the virus. This lockdown resulted in the closing of tourism infrastructure and limited mobility in both land and coastal areas. We used this “natural experiment” as an opportunity to study the impact of tour-boat activities on dolphin communication by using passive acoustic monitoring data collected before and during the lockdown at Dolphin Bay, Bocas del Toro, Panama. During the lockdown, tour-boat activity was absent, but boats transporting people and supplies were allowed to circulate. The shift in type of boat activity within the lockdown resulted in lower ambient noise levels and more frequent detections of dolphin sounds. We also detected a more diverse whistle repertoire during the lockdown than in the pre-lockdown period, even when accounting for variation in sample coverage. A Random Forest Analysis classified whistles between the two periods with high accuracy (92.4% accuracy, κ = 0.85) based primarily on whistle modulation and duration. During the lockdown, whistles were longer in duration and less modulated than pre-lockdown. Our study shows that a shift in boat traffic activity can generate significant changes in dolphin habitat, and in their communicative signals, an important consideration given ongoing unregulated ecotourism in the region.

Temporal and spatial biosonar activity of the recently established uppermost Yangtze finless porpoise population downstream of the Gezhouba Dam: Correlation with hydropower cascade development, shipping, hydrological regime, and light intensity

“…It is necessary to regulate and control boat traffic. Significant changes in dolphin habitat, such as in the western portion of Panama's Dolphin Bay, might result from a shift in boat traffic activities (Gagne et al., 2022 ). The echolocation signals of Yangtze finless porpoise are distinguished by their narrow‐band characteristics (with a 3 dB bandwidth of approximately 22 kHz) and high frequencies (with a peak frequency around 129 kHz).…”

Whistle repertoire and structure reflect ecotype distinction of pantropical spotted dolphins in the Eastern Tropical Pacific

“…Table S3 ). Overall, dolphins show a great degree of plasticity in their whistle frequency range, which allows them to quickly respond to changes in their acoustic environments 5 , 49 , 50 .…”

“…Our study suggests that offshore dolphins have a greater use of frequency modulated contours than coastal dolphins, and we are interested in determining if other offshore pantropical spotted dolphin populations show similar levels of modulation. Frequency modulation patterns in dolphins can serve for species identification 16 , 64 , carry information about individual identity 65 , express emotional state during social interactions 5 , 66 , and vary with different acoustic environments 8 , 49 . Therefore, the observed differences in the proportion of modulated whistles in the repertoire of coastal and offshore dolphins could indicate population-specific differences in group size, social dynamics, and habitat specialization.…”

Comparing the underwater soundscape of the Hawaiian Islands Humpback Whale National Marine Sanctuary and potential influences of the COVID-19 pandemic

“…In Hawaiʻi, the potential delay in the rebound period, as exhibited in the Hawaiʻi island vessel data, was likely due to the extended shut-down periods and strict travel restrictions imposed by the State of Hawaiʻi that lasted until summer 2021. Globally, the effects of COVID-19 are thought to have increased the communication range for some marine mammals (Pine et al, 2021), which led to an increase in humpback whale calling (Laute et al, 2022) and an increase in the detection of delphinid whistles (Gagne et al, 2022). Laute et al (2022) found that the decrease in whale watch vessels in Iceland during the pandemic correlated with an increase in the humpback whale calling rate on the foraging ground.…”