“Specialist” lifeforms that live under Arctic sea ice are at risk as the ice retreats, new research shows.

Three years after bulk carrier MV Wakashio ran aground on a coral reef off Mauritius, spilling 1000 tonnes of a new type of marine fuel oil, Curtin University-led research has confirmed the oil is still present in an environmentally sensitive mangrove forest close to important Ramsar conservation sites.

By mapping global ship traffic and whale habitats, researchers found that 92% of whale habitats overlap with shipping routes, illuminating hotspots for whale-ship collision risk, according to a new study. Although only 7% of high-risk areas currently contain management strategies to reduce ship strikes, the findings show that expanding efforts to just 2.6% of the ocean’s surface could significantly reduce these fatal collisions, aiding whale conservation amid booming global shipping. “Mitigating the negative environmental impacts of marine shipping is essential for the coming decades,” write the authors. “Ship-strike risk is a ubiquitous yet solvable conservation challenge for large whales, and our results can provide a foundation for expanded management measures to protect these ocean giants.” The global shipping industry poses significant threats to marine ecosystems. Among these, collisions with ships – ship strikes – have become a concerning source of whale mortality worldwide. Although many large whale species struggle to recover from centuries of commercial whaling, these animals play vital ecological roles and hold cultural and economic significance. Ship collisions contribute to unsustainable mortality rates for several populations, including critically endangered species. Given the global nature of both maritime shipping and whale migrations, addressing ship strikes requires a comprehensive understanding of risk patterns on an international scale. However, while regional studies on whale-ship collision risks have grown in number, the global spatial distribution of this threat remains largely uncharted. Here, Anna Nisi and colleagues combined extensive data on whale locations – ~435,000 observations for 4 globally ranging species from hundreds of datasets – with automated identification system (AIS) positional data for nearly 176,000 large vessels to identify ship-strike hotspots for blue, fin, humpback and sperm whales. Nisi et al. found that global shipping overlaps with 92% of whale habitats, yet fewer than 7% of identified high-risk areas are managed to mitigate ship-whale collisions. Notably, however, the authors show that expanding ship-strike mitigation efforts, such as implementing vessel speed reduction zones, over just 2.6% of the ocean could significantly reduce fatal collisions in all high-risk areas.

For the first time, scientists have directly measured the hearing range of minke whales, discovering that the species can detect high-frequency sounds as high as 90 kilohertz (kHz), according to a new study, demonstrating hearing sensitivity far greater than previously believed. The findings suggest that baleen whales – the planet’s largest mammals – may be even more impacted by anthropogenic ocean noise than currently recognized but have been excluded from regulatory consideration due to underestimated hearing ranges. Concerns about the impacts of anthropogenic noise on marine mammals have been a focus for decades, largely because of several notable research initiatives and high-profile whale stranding events linked to naval sonar noise activity. As a result, substantial progress has been made in developing criteria and thresholds for evaluating impacts on marine mammals exposed to anthropogenic noise. Although researchers have suggested using behavioral changes, hearing damage (primarily noise-induced hearing loss), and other physical effects as ways to measure the impact of noise on marine mammals, setting clear thresholds is challenging because different species of marine mammals respond to noise in widely varying and poorly understood ways. Audiograms – graphs illustrating an animal's hearing sensitivity – are essential for identifying the sound frequencies that affect marine mammals. However, while audiograms are available for at least one representative species in most major marine mammal groups, none exist for baleen whales, as their large size makes traditional hearing tests impractical. Current estimates of baleen whale hearing rely on indirect methods like vocalization analysis, anatomical modeling, and behavioral studies.

To better understand how ocean noise impacts baleen whales, Dorian Houser and colleagues developed a novel catch-and-release method to temporally hold adolescent minke whales (Balaenoptera acutorostrata) for auditory evoked potential (AEP) tests, which estimate hearing sensitivity by measuring electrical signals produced in the brain in response to sound. Leveraging a natural channel between two islands in Norway, and a system of net barriers, Houser et al. contained two adolescent minke whales making their norward migration. AEPs were recorded noninvasively via gold-plated electrodes temporarily attached to the whales’ skin, and acoustic stimuli were delivered through a nearby underwater sound transducer. While it has been assumed that baleen whales are exclusively low-frequency hearing specialists, the authors discovered that minke whales can detect frequencies as high as 45 to 90 kHz – a range much higher than previously believed based upon their ear anatomy and the frequencies at which they vocalize.

Podcast: A segment of Science's weekly podcast with Dorian Houser, related to this research, will be available on the Science.org podcast landing page [www.science.org/podcasts] after the embargo lifts. Reporters are free to make use of the segments for broadcast purposes and/or quote from them – with appropriate attribution (i.e., cite "Science podcast"). Please note that the file itself should not be posted to any other Web site.