Introduction & Objectives

The Atlantic Behavioral Response Study (Atlantic-BRS) was designed to build on previous Navy-supported research and monitoring efforts to measure the behavioral responses of deep-diving odontocetes to mid-frequency active sonar (MFAS). This project was initiated in 2017 off Cape Hatteras, North Carolina where extensive previous monitoring efforts have documented the occurrence and baseline behavior of several key species using various sampling methods (e.g., surveys, photo ID, animal-borne tags, and passive acoustics). The research team, led by the Duke University Marine Laboratory, has demonstrated the ability to consistently find and tag large numbers of both Cuvier’s beaked whales (Ziphius cavirostris), a species of high Navy interest in terms of potential MFAS effects, and short-finned pilot whales (Globicephala macrorhynchus). The research site is positioned relatively near (<100 nm), but not within, the highest concentration of operational MFAS sources used during training and testing operations in the Atlantic (e.g. SQS-53C-equipped combat vessels) based out of Norfolk, VA. The Atlantic-BRS is generating novel data that has also substantially increased what was quite limited direct information from anywhere on the behavioral responses of key species to Navy tactical sonar. This project is also expanding the temporal and spatial scales over which potential responses are measured from previous BRS efforts by strategically integrating satellite-linked time-depth recording tags (SLTDRs) with short-term, high-resolution acoustic digital archival tags (DTAGs) in experimental conditions where key aspects of exposure context are known.

The primary objective of the Atlantic-BRS is to conduct controlled exposure experiments (CEEs) with tagged beaked and pilot whales exposed to Navy MFAS signals. The highest priority objective is to conduct CEEs using operational 53C sonar from real Navy vessels through direct coordination during ongoing training operations. This has been successfully and reliably accomplished through close coordination between the research team and colleagues from U.S. Fleet Forces Command. Simulated MFAS from an experimental sound source was also used in earlier phases of the project when Navy vessels were unavailable. This project is ongoing, but transitioning in focus. Earlier baseline tagging efforts and the concentrated field effort have yielded the largest sample size of tagged Cuvier’s beaked whale behavior and behavioral responses to known MFAS exposure obtained to date anywhere in the world. These studies have focused on CEEs with repeated, conventional duration (1-2s) MFAS signals. The analyses of the >100 known exposure events from 20 CEEs with both simulated and operational sources are being finalized, and results published in a number of peer-reviewed publications.

Beginning in 2023, subsequent field effort over the next several years is transitioning to CEEs with continuous active sonar (CAS) MFAS signals of similar frequency content but much longer (~20s or longer) duration. These CEEs will be prioritized to occur with operational Navy vessels as well, but a simulated source option will also be available.

Technical Approach

Deliberate measures have been taken to maintain experimental consistency with previous BRS projects in order for results to be considered and integrated across sites. The overall experimental design for the Atlantic-BRS was derived from methods employed in the Navy-funded southern California behavioral response study (SOCAL-BRS), with adaptations related to the novel use of both SLTDRs and DTAGs. This includes a period during which baseline behavioral data are collected prior to the CEE (at least 60 min for DTAG whales and 24 h for SLTDR whales). Pre-exposure baseline behavioral data collection primarily involves data from tag sensors, supplemented by focal follows of tagged animals by observers in small boats, which are maintained during the pre-exposure baseline, exposure, and post exposure periods. This approach has been highly successful and will be largely maintained in terms of field operations in the transition from conventional MFAS to CAS. Given the high degree of success with Cuvier’s beaked whales during earlier phases of conventional MFAS CEEs as well as their very high priority to the Navy, the objective for CAS CEEs will be to exclusively focus on this species, maintaining common approaches. Such consistency will allow comparisons to be drawn among studies and support meta-analyses needed to derive dose-response probabilistic functions for application in requisite Navy environmental compliance assessments.

Given the coordination that will continue to be required with Navy combat vessels equipped with CAS-capable SQS-53C sonar systems for BRS efforts off Hatteras, identical adaptive approaches to advanced planning will continue to facilitate operational agility in the field. These approaches include regular close communication and planning in advance and up to the occurrence of MFAS CEEs. Sonar transmissions during CAS MFAS CEEs will occur using similar protocols as in the earlier phases with conventional MFAS signals, with established parameters matching typical CAS operating signals. For operational Navy CAS sonars, this includes transmission of full power of a consistent nominal waveform and duration type with ships transiting in a direct course at a speed of 8 kt. Transmissions will occur for a maximum overall duration of 60 minutes, unless any strong contra-indicators from the field team dictate a shut-down of the sound source. Starting positions and course for vessels are determined using in situ propagation modeling given the position of a focal animal using the Navy-consistent models and unclassified databases in software developed and provided by the Naval Postgraduate School (NPS). The course of the vessel results in an escalation in received level at focal individuals based on the ship's movement generally (but not directly) toward individual whales. Given the relatively large number of tagged individuals exposed during CEEs (in some cases up to ten individuals per event), there will be a varied exposure history of range and received level among individuals. Target received levels for focal beaked whales will cover an identical range that was consistently and reliably achieved in conventional MFAS CEEs from 120-140 dB RMS. This experimental design will allow for positioning of sonar sources to result in target received levels at focal individuals that are also being monitored directly using other methods (focal follow, photo ID). However, this also results in a diversity of received levels for non-focal individuals at positions and (generally greater) horizontal ranges that are known but not necessarily controlled.

Analyses focus on how tagged whales respond to MFAS exposure, in terms of: (a) potential avoidance behavior; (b) potential changes in behavioral state; and (c) potential changes in social behavior. Analyses are transitioning and applying methods developed in other BRS studies and the earlier MOCHA and DOUBLE MOCHA projects. Short- and longer-term consequences of disturbance are being evaluated separately using established analytical methods for short- and medium-term tags. However, the multi-scale nature of this study offers a unique opportunity to explore how these methods may complement one another and how high-resolution, short-term response data may inform methods used for longer-term monitoring.

Progress & Results

Six field seasons (2017-2022), from summer through early fall, of this multi-year project have been completed to date, focused on baseline behavior and behavioral responses to simulated and operational conventional MFAS stimuli. A total of 88 tags of both types have been deployed on Cuvier’s beaked whales and 46 tags have been deployed on pilot whales. A total of 22 conventional MFAS CEEs have been conducted, eight of which involved operational US Navy vessels with 53-C MFAS sources (USS MACFAUL, USS NITZE, USS RAMAGE, USS COLE, USS LABOON, USS DELBERT BLACK, and USS FARRAGUT (twice), 10 involved simulated MFAS sources, and four of which were no-sonar control CEEs. These 22 CEEs have resulted in a total of 101 unique tagged animal exposure events for Cuvier’s beaked whales and 62 unique events for pilot whales.

The analysis of this large data set is complex, extensive, and ongoing. Existing analytical approaches are being applied to these data, with novel integration on different time/space scales. In addition, a new paradigm of spatial analysis has been developed to address errors associated with position estimates from the satellite tags and consequent implications for modeling received noise during CEEs. We are currently analyzing potential responses using several methods to investigate subtler potential responses, to the extent possible given the resolution of available data. Additional data involving operational sources are required to complete the planned analyses of spatial and temporal factors (such as range-received level interactions).

Eleven peer-reviewed papers from this project have already been published on key methodological and technical developments and aspects of baseline behavior and behavioral response, with another ten in review or advanced stages of development. In addition, many aspects of this project have been presented at public forums and scientific meetings worldwide including many that were featured at the 2022 Effects of Noise on Marine Mammals meeting hosted by the Duke University Marine Laboratory and chaired by the lead investigators of the Atlantic-BRS.

Publications

Diving Behavior of Cuvier’s Beaked Whales (Ziphius cavirostris) off Cape Hatteras, North Carolina

Mind the gap - Optimising satellite tag settings for time series analysis of foraging dives in Cuvier’s beaked whales

Accounting for Positional Uncertainty When Modeling Received Levels for Tagged Cetaceans Exposed to Sonar

Adult male Cuvier's beaked whales (Ziphius cavirostris) engage in prolonged bouts of synchronous diving

Aerobic dive limits in Cuvier's beaked whales

Residency and movement patterns of Cuvier’s beaked whales (Ziphius cavirostris) off Cape Hatteras, North Carolina, USA

Continuous-time discrete-state modeling for deep whale dives

Monte Carlo testing to identify behavioral responses to exposure using satellite tag data

Time-discretization approximation enriches continuous-time discrete-space models for animal movement

Varying-Coefficient Stochastic Differential Equations with Applications in Ecology

Kernel density estimation of conditional distributions to detect responses in satellite tag data

Continuous-time modelling of behavioural responses in animal movement

Trade-offs in telemetry tag programming for deep-diving cetaceans: data longevity, resolution, and continuity

Blog posts

-Atlantic BRS - 2022 CEE with the USS Farragut

-Atlantic BRS - First CEE of 2021

-Atlantic Behavioral Response Study Kicks off 2021 Field Season

-First CEE of 2020

-Multi-scale CEE Success!

-Atlantic BRS 2018 – Second Phase

-Wrapping Up The First Phase of the 2018 Atlantic BRS

-Atlantic BRS 2018 Field Work Update

-Atlantic BRS 2018 Field Work Second Update

-Field Work Underway for Atlantic BRS 2018

-May 2017 Satellite tagging field work summary