Dear colleagues, On behalf of our coauthors, we are happy to share two new publications resulting from the 3S Behavioural Response Study. Using different but complementary analyses of the same set of experiments, these studies show that behavioural responses of sperm whales to operational naval sonar are affected by both sonar received level and source-receiver distance. Paper 1: Curé, C, Isojunno, S, Wensveen, PJ, Siemensma, ML, von Benda-Beckmann, AM, Kvadsheim, PH, Burslem, A, Benti, B, Roland, R, Lam, FPA & Miller, PJO (2025). Severity scoring of sperm whale behavioral responses to an operational sonar source reveals importance of received level and source-receiver distance. Aquatic Mammals 51, 8-27 Naval sonar's impact on marine life is a long-standing concern. Our study conducted off Norway aimed to investigate the effect of both the received level (RL) and the source-receiver distance on whales' responses to sonar. We cooperated with a naval frigate and used an experimental sonar (SOCRATES) to conduct controlled sonar exposure experiments at different source levels and at various distances from sperm whales (Physeter macrocephalus) tagged with acoustic-and-movement-recorder devices (Mixed-DTAGs). Behavioral responses were scored using a severity scale from 0 to 9. We showed that the probability and severity of scored responses increased significantly with higher RL (scored as SELmax, the maximum sound exposure level received during an exposure session) and lower distance (scored as DISTmin, the minimum source-receiver distance during an exposure session). Various behavioral responses occurred over a broad range of severities (1 to 7), including changes in vocal and dive behaviors, avoidance responses, cessation of feeding or resting activities, orientation responses, and changes in locomotion. Close proximity (< 1.5 km) of the source vessel without sonar transmission influenced whale behavior, although it was to a significantly lesser extent than with sonar. Dose-response relationships, including onset response RL and source-receiver distance, revealed that whale responsiveness declined more sharply with source-receiver distance than expected based solely on RL. The model predicted 14 km as a statistically significant distance threshold beyond which no responses would be expected independent of RL. At 225 dB re 1 µPa m source level, the model predicted that the estimated effective impacted area dropped from 1,770 km2 when only RL was considered to 27 km2 (factor 65) when both RL and source-receiver distance were considered. These findings underline the importance of taking into account both RL and source-receiver distance in assessing the impact of naval sonar on whale behavior. Open access link: https://doi.org/10.1578/AM.51.5.2025.8 Paper 2: Wensveen, PJ, Isojunno, S, Kvadsheim, PH, Lam, FPA, Curé, C von Benda-Beckmann, AM & Miller, PJO (2025). Distance matters to sperm whales: Behavioural disturbance in response to both sonar received level and source distance. Marine Pollution Bulletin 214, 117742. Understanding the main drivers of behavioural disturbance in deep-diving cetaceans would improve predictions of anthropogenic noise effects on individual animals, habitats and populations. To investigate the potential roles of received level and source distance on behavioural disturbance, we tagged 14 sperm whales in northern Norway with multi-sensor data loggers and conducted dose-escalation experiments. Each experiment included 1 to 4 tagged individuals and involved multiple vessel passes ('exposure sessions', n = 25 total) by a navy frigate or research vessel towing a naval sonar, at different starting distances and maximum source levels. We analysed behaviour state series and proxies for locomotor activity and foraging success with generalized additive mixed models. The probability of occurrence of non-foraging active behaviour was affected by received level, source distance and session order, with decreased foraging effort at higher received levels and shorter distances, and during subsequent sessions (indicating short-term sensitisation). Prey capture attempts decreased with increasing received level when whales kept foraging. Similar to what has been suggested for some populations of blue whales and beaked whales regularly exposed to navy sonar, but unlike northern bottlenose whales in more pristine waters, source distance affected sperm whale behavioural responses on a high-latitude foraging ground. Open access link: https://doi.org/10.1016/j.marpolbul.2025.117742 All the best, Paul