Marine soundscapes are dominated by fish choruses, when many fish vocalize concurrently, often for mating purposes. Passive acoustic monitoring (PAM) allows us to analyze spatiotemporal patterns of fish chorusing, identifying breeding grounds, species distributions, and mating seasons. By integrating PAM with environmental data (temperature, salinity, etc.), we can assess the environmental drivers of fish chorusing. Through the Sanctuary Soundscape Monitoring project, we collected PAM data across nine sites in Monterey Bay (MBNMS), Chumash Heritage (CHNMS), and Channel Islands National Marine Sanctuaries (CINMS), each recording for ∼2 years for a cumulative 17.9 years. We identified: (1) WHO: five fish choruses, including plainfin midshipman, bocaccio rockfish, white seabass, and two unidentified species; (2) WHERE: spatial variation in chorus types and occurrence; (3) WHEN: predominantly nocturnal, seasonal chorusing aligned with reproductive cycles; and (4) DRIVERS: environmental variables associated with different water masses drive chorusing presence, and fish tended to chorus more during marine heatwaves. Through non-invasively listening to fish, we gain critical insights into their reproductive behavior and environmental drivers, to better inform effective management and conservation, particularly under changing environmental conditions.

Background In ecosystems influenced by strong seasonal variation in insolation, the fitness of diverse taxa depends on seasonal movements to track resources along latitudinal or elevational gradients. Deep pelagic ecosystems, where sunlight is extremely limited, represent Earth's largest habitable space and yet ecosystem phenology and effective animal movement strategies in these systems are little understood. Sperm whales (Physeter macrocephalus) provide a valuable acoustic window into this world: the echolocation clicks they produce while foraging in the deep sea are the loudest known biological sounds on Earth and convey detailed information about their behavior. Methods We analyze seven years of continuous passive acoustic observations from the Central California Current System, using automated methods to identify both presence and demographic information from sperm whale echolocation clicks. By integrating empirical results with individual-level movement simulations, we test hypotheses about the movement strategies underlying sperm whales' long-distance movements in the Northeast Pacific. Results We detect foraging sperm whales of all demographic groups year-round in the Central California Current System, but also identify significant seasonality in frequency of presence. Among several previously hypothesized movement strategies for this population, empirical acoustic observations most closely match simulated results from a population undertaking a "seasonal resource-tracking migration", in which individuals move to track moderate seasonal-latitudinal variation in resource availability. Discussion Our findings provide evidence for seasonal movements in this cryptic top predator of the deep sea. We posit that these seasonal movements are likely driven by tracking of deep-sea resources, based on several lines of evidence: (1) seasonal-latitudinal patterns in foraging sperm whale detection across the Northeast Pacific; (2) lack of demographic variation in seasonality of presence; and (3) the match between simulations of seasonal resource-tracking migration and empirical results. We show that sperm whales likely track oceanographic seasonality in a manner similar to many surface ocean predators, but with dampened seasonal-latitudinal movement patterns. These findings shed light on the drivers of sperm whales' long-distance movements and the shrouded phenology of the deep-sea ecosystems in which they forage.

Mechanical properties of Arctic sea ice can be inferred by observation of the speeds of compressional, shear and flexural waves generated through in-ice conversion of impulsive energy. In prior work, the impulsive signal was generated by a lead ball or sledge hammer dropped onto the top of the sea ice, and the inversion process required meticulous, manual extraction of signal amplitudes. The work presented here makes use of (a) coherent sources with which broadband signals can be generated to replace the manually generated hammer-drop signals and improve accuracy via matched filter, as well as (b) recent observations and modeling of ice sheet compressional resonances from which ice thickness can be more easily inferred. Analysis and modeling of observations from a recent field experiment in the Beaufort Sea are shown that demonstrate the potential capability of remote monitoring of sea ice mechanical properties.