Abstract
Little is known about the ecological importance of fin whales found year-round in southwestern offshore Irish waters. Understanding their ecology is important to reduce potential harm through any spatio-temporal overlap with commercial shipping and fishing activities. This study explored the potential environmental drivers and impacts of low-frequency shipping noise on fin whale calling at Porcupine Ridge using the presence/absence of call detections as a proxy for observed changes due to possible masking. Acoustic call data was collected at a low sampling rate (2 ksps) from the end of March 2016 to June 2016 (97 days) using a bottom-moored autonomous acoustic recorder with an omni-directional hydrophone. The high zero-inflated and binary nature of the data was addressed using generalised linear models. The results of our habitat modelling predicted call detections to increase significantly during night-time (p ≤ 0.01) with sea surface height and chlorophyll-a concentration (p ≤ 0.01), implying higher prey availability may occur on Porcupine Ridge. It also indicated a significant decrease in call detections with increasing shipping noise (p ≤ 0.01). Unfortunately, the model had a type II error. To provide robust results, a longer study not limited by data on the prey, and oceanographic drivers including spatial and temporal parameters is required. This study provides the foundations on which further ecological data could be added to establish management and mitigation measures to minimize the effects of shipping noise on fin whales.
Highlights
Over the past 50 years, commercial shipping has doubled, increasing low-frequency background noise in contemporary oceans [1]
Low-frequency signals from shipping overlaps with the frequency bandwidths used by baleen whales, potentially causing masking and behavioural disruptions that could negatively influence feeding and breeding behaviour [4,5,6,7]
The automated detection results closely represent the acoustic occurrence of fin whales during periods of vocal activity with 81–100% correctly classified detections
Summary
Over the past 50 years, commercial shipping has doubled, increasing low-frequency background noise in contemporary oceans [1]. Low-frequency signals from shipping overlaps with the frequency bandwidths used by baleen whales, potentially causing masking (reduction in the hearing and communication range for marine mammals [4]) and behavioural disruptions that could negatively influence feeding and breeding behaviour [4,5,6,7]. Masking may cause a reduction in foraging capacity, increase calf mortality, or reduce breeding capabilities (through loss of contact between mothers and calves or between potential mates at greater ranges of distance) [8,9]. As baleen whales use low-frequency (10–100 Hz) signals to communicate over long distances (over hundreds of kilometres), chronic exposure to low-frequency background noise could negatively impact their health and fitness [8,19,20]. Fin whales use 20 Hz frequency calls to attract the females to regions of high prey abundance [21] and 40 Hz call to hunt the prey portraying foraging dives as a group [13,22]
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