Patterns of underwater human-generated noise events and durations of noise-free intervals (NFIs) are soundscape metrics that can potentially affect animal communication and behavior. Due to the arduous task of manual analysis, these metrics have not been described in Glacier Bay National Park and Preserve (GBNP). To surmount this challenge, we created a machine-learning (ML) model trained on 18 hr of labeled audio samples from a hydrophone operating in GBNP since 2000. The validated convolutional neural net transfer-learning model (GBNP-CNN) was used to classify several categories of sound sources in nearly 9,000 hours of data from the same hydrophone, enabling our study of vessel noise between 2017 and 2020. We focused on the occurrence and duration of NFI and the hourly proportion (HP) of vessel noise. As expected, shorter NFI and higher HP were found during daytime hours. The GBNP-CNN F1 score was 75%, largely due to the model’s confusion of vessel noise with harbor seal roars. Therefore, NFI lengths should be considered minimum estimates, but the errors do not qualitatively affect diurnal or seasonal patterns. In 2018, mean daytime NFI during peak tourism months (June–August) was less than half the duration compared to May and September (1.3 min vs. 2.9 min). In 2020, when large-vessel tourism was substantially reduced but small-craft activity continued, we found that HP decreased in June–August. In conjunction with other soundscape metrics, monitoring NFI trends using ML models such as GBNP-CNN will provide crucial information for management and conservation of acoustic habitats and sensitive species in GBNP.

This study investigated the emission of subaquatic noise from recreational tourism motorboats, schooners and a sea-bottom mounted water pump. Analyses demonstrated alterations in several whistle (IF: t = 2.42, P = 0.015; FF: t = −2.22, P = 0.025) and calls patterns (MIF: t = −3.13, P = 0.001; MAF: t = −3.49, P = 0.0005; FD: t = −2.21, P = 0.027; D: t = 2.89, P = 0.004), caused primarily by motorboats. Duration of clicks was also modified (D: t = −3.85, P = 0.0001), mainly by the water pump. The frequency range of all noises (0.43–35.8 kHz) overlaps that used by dolphins (1–48 kHz), causing sound emissions changes, with a considerable increase in number of whistles and a reduction in clicks trains. These changes may be a strategy developed by these dolphins to overcome the noise band. Mitigation measures, such as boating regulations and environmental education for the local community, boaters and tourists are needed to conserve the species. The Guiana dolphin population is apparently already suffering, evidenced by diminished residence time and reduced number of individuals entering the inlet during the presence of pleasure craft.

The power of modern research vessels using diesel engines means significant levels of noise may be radiated underwater. At low frequencies a surveying vessel must not cause fish avoidance behaviour when it is using trawl or acoustic assessment methods. All the main mechanisms that form the essential propulsion system are described and discussed in terms of underwater radiated noise. Diesel engines, generators and propulsion motors contribute significantly to the low frequency spectrum and an illustration is given of underwater noise when an unsuitable propulsion system is used. Avoidance behaviour by a herring school is shown due to a noisy vessel, by contrast there is an example of no reaction of herring to a noise-reduced vessel. Propellers are major sources of both low and high frequency noise. The latter should not reduce echo sounder detection range, nor contaminate echo integrator recordings. Underwater noise levels from four vessels with different machinery and propulsion characteristics are seen in relation to ambient noise levels at 18 kHz. Fish detection is examined in relation to sea background noise and vessel self-noise. Calculated detection ranges for fish target strength classes from –30 to –60 dB at 38 kHz are shown for six vessels travelling at 11 knots, based on self-noise measurements. Echo sounder noise levels from several vessels at 120 and 200 kHz are tabulated. Beyond 100 kHz the effect of vessel-radiated noise is usually insignificant; levels up to that frequency are proposed in the International Council for the Exploration of the Sea (ICES) Cooperative Research Report No. 209 of 1995.

The underwater sound of R/V "Johan Hjort" as a function of aspect angle has been mapped by cruising along parallel transects at various distances from the recording unit. At frequencies over 125 Hz there was a minimum in front of the vessel, and lobes of higher intensity on both sides. About 20% of the herring schools recorded during a survey in the North Sea seemed to react to the survey vessel. The distance at which the schools reacted varied from about 25 m and up to about 1000 m in front of the vessel. Within a sector of 20° on each side of the path of the vessel, the fraction of schools reacting increased to about 50%. Most of the schools that reacted seem to be herded in front of the vessel. This reaction pattern may indicate either that the schools reacted to the higher sound intensity to the side of the vessel or that the pattern occurred because of a "pursuit effect". Despite the apparent herding, more than 40% of the schools in front of the vessel were not recorded by the echo sounder. It is therefore argued that horizontal avoidance close to the vessel may have caused an underestimation of the biomass of herring of about 20%.