Underwater Ambient Noise in a Baleen Whale Migratory Habitat Off the Azores

Abstract

Assessment of underwater noise is of particular interest given the increase in noise-generating human activities and the potential negative effects on marine mammals which depend on sound for many vital processes. The Azores archipelago is an important migratory and feeding habitat for blue (Balaenoptera musculus), fin (Balaenoptera physalus) and sei whales (Balaenoptera borealis) en route to summering grounds in northern Atlantic waters. High levels of low frequency noise in this area could displace whales or interfere with foraging behavior, impacting energy intake during a critical stage of their annual cycle. In this study, bottom-mounted Ecological Acoustic Recorders were deployed at three Azorean seamounts (Condor, Açores, and Gigante) to measure temporal variations in background noise levels and ship noise in the 18-1,000 Hz frequency band, used by baleen whales to emit and receive sounds. Monthly average noise levels ranged from 90.3 dB re 1 µPa (Açores seamount) to 103.1 dB re 1 µPa (Condor seamount) and local ship noise was present up to 13% of the recording time in Condor. At this location, average contribution of local boat noise to background noise levels is almost 10 dB higher than wind contribution, which might temporally affect detection ranges for baleen whale calls and difficult communication at long ranges. Given the low time percentatge with noise levels above 120 dB re 1 µPa found here (3.3% at Condor), we woud expect limited behavioral responses to ships from baleen whales. Sound pressure levels measured in the Azores are lower than those reported for the Mediterranean basin and the Strait of Gibraltar. However, the currently unknown effects of baleen whale vocalization masking and the increasing presence of boats at the monitored sites underline the need for continuous monitoring to understand any long-term impacts on whales.

The Azores: A Mid-Atlantic Hotspot for Marine Megafauna Research and Conservation

“…(1) the targeted or accidental capture by longlining and purseseining industrial fishing (e.g., Bolten et al, 1998;Ferreira et al, 2001;Amandè et al, 2011;Filmalter et al, 2013); (2) the degradation of their habitat due to chemical, noise and light pollution (Halpern et al, 2008;Fontaine et al, 2011;Peng et al, 2015;Rodríguez et al, 2017;Romagosa et al, 2017), to introduced predators and diseases (e.g., Fontaine et al, 2011;Hermosilla et al, 2016;Neves et al, 2017) or to traffic (Tournadre, 2014);…”

“…The most evident is the high by-catch of pelagic sharks and sea turtles in the EU pelagic longlining occurring within Azorean waters (Pham et al, 2013;Afonso et al, 2014b) (Table 1). The increasing marine traffic and noise produced by international cargo vessels, inter-island fast ferries and whale-watching vessels are also a potential problem to cetaceans and other marine megafauna (Romagosa et al, 2017). Documented areas of megafauna aggregation, such as the cetacean ground south of Pico and Faial islands and the of large pelagic fishes aggregations on the summits of the Princess Alice, Condor and Formigas banks, still lack effective protection even when already declared as an MPA (Abecassis et al, 2015;Afonso et al, 2018).…”

Food talk: 40-Hz fin whale calls are associated with prey biomass

“…It could also be argued that inter-annual variability in call rates results from differences in call detectability due to variations in background noise from shipping. Although noise levels in the study area did not vary significantly between 2010 and 2012 [ 64 ], effects of shipping noise on call detectability should be investigated in the future.…”

Cetacean Research and Citizen Science in Kenya

“…Anthropogenic underwater noise is a significant pollutant that is increasingly pervasive worldwide (Williams et al, 2015). Noise associated with both small vessels and commercial shipping is increasingly recognized as the major contributor of anthropogenic noise in marine ecosystems on a global scale (Koper and Plön, 2012;Romagosa et al, 2017;Pirotta et al, 2019). Many inshore vessels outfitted with small outboard engines are operated in inshore waters, whereas large ship traffic tends to be highly concentrated within shipping lanes and near ports.…”