Navigating the unknown: assessing anthropogenic threats to beaked whales, family Ziphiidae.

This review comprehensively evaluates the impacts of anthropogenic threats on beaked whales (Ziphiidae)-a taxonomic group characterized by cryptic biology, deep dives and remote offshore habitat, which have challenged direct scientific observation. By synthesizing information published in peer-reviewed studies and grey literature, we identified available evidence of impacts across 14 threats for each Ziphiidae species. Threats were assessed based on their pathways of effects on individuals, revealing many gaps in scientific understanding of the risks faced by beaked whales. By applying a comprehensive taxon-level analysis, we found evidence that all beaked whale species are affected by multiple stressors, with climate change, entanglement and plastic pollution being the most common threats documented across beaked whale species. Threats assessed as having a serious impact on individuals included whaling, military sonar, entanglement, depredation, vessel strikes, plastics and oil spills. This review emphasizes the urgent need for targeted research to address a range of uncertainties, including cumulative and population-level impacts. Understanding the evidence and pathways of the effects of stressors on individuals can support future assessments, guide practical mitigation strategies and advance current understanding of anthropogenic impacts on rare and elusive marine species.

Characteristics and spatiotemporal variation of sei whale (Balaenoptera borealis) downsweeps recorded in Atlantic Canada.

The call characteristics and vocal behaviour of sei whales (Balaenoptera borealis) off eastern Canada, including potential spatiotemporal variation, is poorly understood. Such information can improve the performance of automated detector-classifiers, enhancing the accuracy and efficiency of identifying sei whales in large acoustic datasets. Ultimately, these data can be used to understand the occurrence, distribution, and population structure of sei whales in Atlantic Canada. We measured sei whale downsweep characteristics recorded from six locations off Nova Scotia (NS) and Newfoundland and Labrador (NFLD), Canada over a two-year period (2015-2017), and examined variation between call subtypes (singlets, doublets, triplets+), and seasons (Spring, Summer, Fall, Winter). We found that downsweeps had a mean duration of 1.58 s, sweeping from 75.66 to 34.22 Hz, with a peak frequency of 43.89 Hz and an intra-call interval of 2.22 s. Most call characteristics did not vary between location, subtype, or season; however, significantly longer downsweeps occurred off NS, within doublet calls, and in fall months. We also found that NFLD had a higher proportion of doublets (70%) than NS (52%). This variation may be evidence of acoustically diverging sei whale populations, as well as useful for improving detector-classifiers of sei whales in the region.

Changes in the acoustic activity of beaked whales and sperm whales recorded during a naval training exercise off eastern Canada.

Experimental research has shown that beaked whales exhibit strong avoidance reactions to naval active sonars used during antisubmarine warfare training exercises, including cessation of echolocation and foraging activity. Behavioural responses to sonar have also been linked to strandings and mortality. Much of the research on the responses of beaked whales and other cetaceans to naval active sonar has occurred on or near U.S. naval training ranges, and the impacts of sonar in other regions remain poorly understood, particularly as these impacts, including mortality, are likely to go unobserved in offshore areas. In September 2016 the multinational naval exercise 'CUTLASS FURY 2016' (CF16) was conducted off eastern Canada. We used passive acoustic recordings collected in the region to quantify the occurrence and characteristics of sonar signals, measure ambient noise levels, and assess changes in the acoustic activity of beaked and sperm whales. The number of hours per day with echolocation clicks from Cuvier's beaked whales and sperm whales were significantly reduced during CF16, compared to the pre-exercise period in 2016 (sperm whales) and to control data from 2015 (both species). Clicks from an unidentified Mesoplodont beaked whale species, sporadically detected prior to CF16, were absent during the exercise and for 7 days afterward. These results suggest that beaked and sperm whales ceased foraging in the vicinity of CF16 and likely avoided the affected area. Such disturbance may have energetic, health, and fitness consequences.

Effects of duty-cycled passive acoustic recordings on detecting the presence of beaked whales in the northwest Atlantic.

This study investigated the effects of using duty-cycled passive acoustic recordings to monitor the daily presence of beaked whale species at three locations in the northwest Atlantic. Continuous acoustic records were subsampled to simulate duty cycles of 50%, 25%, and 10% and cycle period durations from 10 to 60 min. Short, frequent listening periods were most effective for assessing the daily presence of beaked whales. Furthermore, subsampling at low duty cycles led to consistently greater underestimation of Mesoplodon species than either Cuvier's beaked whales or northern bottlenose whales, leading to a potential bias in estimation of relative species occurrence.