Ultrasonic antifouling devices negatively impact Cuvier's beaked whales near Guadalupe Island, México

Abstract

Widespread use of unregulated acoustic technologies in maritime industries raises concerns about effects on acoustically sensitive marine fauna worldwide. Anthropogenic noise can disrupt behavior and may cause short- to long-term disturbance with possible population-level consequences, particularly for animals with a limited geographic range. Ultrasonic antifouling devices are commercially available, installed globally on a variety of vessel types, and are marketed as an environmentally-friendly method for biofouling control. Here we show that they can be an acoustic disturbance to marine wildlife, as seasonal operation of these hull-mounted systems by tourist vessels in the marine protected area of Guadalupe Island, México resulted in the reduced presence of a potentially resident population of Cuvier's beaked whales (Ziphius cavirostris). Human activities are rapidly altering soundscapes on local and global scales, and these findings highlight the need to identify key noise sources and assess their impacts on marine life to effectively manage oceanic ecosystems.

Fig. 1. Beaked whale sighting distributions.

Maps of Guadalupe Island in the Mexican waters of the Pacific Ocean (inset), illustrating the sighting locations of Cuvier’s beaked whales (black circles) and visual search effort tracklines (white lines) from cetacean surveys conducted during a non-tourism seasons (spring 2017 and 2019) when cage diving boats were absent, b a canceled tourism season (summer/fall 2020) when cage diving boats were absent due to COVID-19 restrictions, and c tourism seasons (summer/fall 2018 and 2019) when cage diving boats operating ultrasonic antifouling (UA) systems were present. The location of the seafloor-mounted acoustic recorder (HARP) within Bahía Norte is denoted by a brown diamond in each plot, and the anchorage area used by tourist vessels for cage diving activities is outlined in orange. Depth contours are indicated by gray lines.

Fig. 2. Ultrasonic antifouling signal.

Long-term spectral average (top), spectrogram (middle), and spectrum (bottom) recorded on the seafloor-mounted acoustic recorder within Bahía Norte of tourist boats equipped with UA systems a transiting over the recorder and b anchored near the coastline ~2 km away. A shipboard echosounder operating at 88 kHz by the transiting boat is also present in a.

Fig. 3. Acoustic detections.

Weekly (black bars) and daily (blue dots) acoustic presence of a motorized vessel noise, b shipboard echosounders, c ultrasonic antifouling (UA) systems, and d Cuvier’s beaked whale echolocation clicks at the recording site in Bahía Norte from November 19, 2018 to October 3, 2020. Weekly plots show the number of hours of acoustic presence each week. Daily plots show acoustic presence in 1-min bins and the gray hourglass shading denotes nighttime. Gray vertical shading at the start and end of all plots denotes absence of recording effort. Yellow shading across all weekly plots in November 2018 and from July to November 2019 indicates the weeks with UA signal occurrence. A brief ~27 h effort gap in October 2019 corresponds to the time period used to refurbish the seafloor-mounted acoustic recorder.

Fig. 4. Differences in hourly beaked whale acoustic detections.

Following a Kruskal–Wallis test, pairwise comparisons were computed to assess whether Cuvier’s beaked whale acoustic presence on an hourly scale differed depending on the presence/absence of the various vessel-based anthropogenic sounds. The circles and lines represent the group mean estimates and comparison intervals, respectively. Groups sharing the same color are not statistically different from one another, although asterisks denote one significant pairwise comparison (*p < 0.05). See Supplementary Table 4 for all p values and sample sizes.

Fig. 5. Noise levels.

a Long-term spectrogram of acoustic data recorded in Bahía Norte from November 19, 2018 to October 3, 2020, as well as sound energy in frequency bands representative of b low-frequency vessel noise (nominal 125 Hz third-octave band) and c high-frequency signals including UA devices and echosounders transmitting at 28 kHz and 50 kHz. The minimum noise floor for the c measurements (~40 dB re: 1 µPa²/Hz) was determined by electronic self-noise produced by the acoustic recording system and was not a reflection of the true minimum ambient noise levels.

Fig. 6. Cruise ships.

Spectrograms of ultrasonic antifouling signals recorded from seven individual cruise ships from five different cruise lines, including the vessels a Koningsdam, b Carnival Miracle, c Oceania Regatta, d Navigator of the Seas, e Royal Princess, f Grand Princess, and g Majestic Princess. The recorder used for the Royal Princess had a 96 kHz sampling rate, and the recorders used for all other vessels had a 576 kHz sampling rate.