US Navy

divider

Marine Species Monitoring

Atlantic Behavioral Response Study

Introduction & Objectives

In June 2016, researchers from Duke University, Southall Environmental Associates (SEA), and the University of St. Andrews met with representatives from Navy monitoring and research programs to discuss potential marine mammal behavioral response studies (BRS) in several key regions of the Atlantic coast. Potential research sites off Virginia, Florida, and North Carolina were considered and the relative logistical challenges and advantages of each location were evaluated, together with Navy interests regarding mid-frequency active sonar (MFAS) usage and the potential for coordination with sonar training operations.

There was clear agreement among researchers and Navy personnel that the area off Cape Hatteras, North Carolina represents the best opportunity for an initial Atlantic-BRS (ABRS) effort using Navy MFAS. This was due to a variety of practical and logistical factors including the proven ability to consistently find and tag both Cuvier’s beaked whales (Ziphius cavirostris) and short-finned pilot whales (Globicephala macrorhynchus), as well as the proximity and availability of actual sonar sources (e.g. SQS-53C-equipped combat vessels) to participate. This project will generate BRS data in a new geographic area and increase the currently limited sample size of the behavioral response of key species to Navy tactical sonar. In addition, the effort will expand the temporal and spatial scales of previous BRS efforts by combining satellite-linked time-depth recording tags (SLTDRs) and short-term, high-resolution acoustic digital archival tags (DTAGs) in the same controlled exposure experiments (CEEs).

The experimental objective for the first ABRS is to conduct a total of six CEE sessions per year over an initially anticipated two-year study period. We will conduct two field seasons each year (in spring and fall, based on extensive previous field work in these areas), with three CEE sessions conducted during each field season. To maximize the data collected during each CEE, many individual cetaceans will be monitored before, during, and after MFAS exposures using the two complementary types of tags. Ideally, each CEE will involve a focal individual of each species equipped with DTAGs. Thus, our goal is to deploy 12 DTAGs (six on pilot whales and six on beaked whales) during the CEEs each year. This will be complemented by a larger number of individuals (approximately 15 for each field season), primarily of the two target species, monitored using SLTDRs deployed in the weeks prior to CEE sessions. We will attempt to deploy DTAGs on groups of pilot and beaked whales that include animals previously equipped with SLTDRs and, in the case of pilot whales, to place DTAGs on individuals already tagged with an SLTDR.

Technical Approach

There is considerable value in maintaining consistency with previous BRS projects. Such consistency will allow comparisons to be drawn among studies and support the meta-analyses needed to derive dose-response probabilistic functions. Given that the coordination required with Navy combat vessels equipped with SQS- 53C sonar systems for BRS efforts off Hatteras, the overall experimental design will be based on the methods employed in SOCAL-BRS. This includes a period during which baseline behavioral data are collected prior to the CEE. These baseline data will be collected during a minimum of 60 minutes for animals with DTAGs, as in SOCAL-BRS. A minimum 24-hour baseline data period will be used for animals equipped with satellite tags, although most baseline data periods will be longer for this tag type. Pre-exposure baseline behavioral data collection will primarily involve data from tag sensors, supplemented by focal follows of tagged animals by observers in small boats. The methods employed during focal follows will be consistent with those employed in SOCAL-BRS and will be identical during the pre-exposure baseline, exposure, and post exposure periods.

Sonar transmissions during CEEs will occur in the same manner as in SOCAL-BRS. This includes transmission of full power (235 dB (RMS) re 1 µPa) signals of a constant nominal 53-C waveform type (single ping sequence using two sequential CP/CW waveforms 0.5 sec duration each with 0.1s separation for total ping series 1.1 sec duration) transmitted with a 25s duty cycle, using surface duct sector search mode, 3°downward vertical steering, and with ships transiting in a direct course at a speed of 8 kt. Transmissions will occur for a maximum 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 will be 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 will result in an escalation in received level at focal individuals based on their movement generally (but not directly) toward individuals. Given the relatively large number of tagged individuals expected to be exposed during CEEs, individuals will have a varied exposure history of range and received level. Target received levels for the focal animals will range from 120-160 dB RMS and will likely differ between the target species (lower starting levels in beaked whales than pilot whales), at least in initial trials. This experimental design will allow for positioning of sonar sources to result in target received levels at focal individuals, but will also result in a diversity of received levels for other individuals at positions and ranges that will not be controlled, but known from positions derived from satellite tags.

The analyses will focus on how beaked and pilot 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 will transition and apply successful methods developed in other BRS studies and the MOCHA project. Short- and longer-term consequences of disturbance will be evaluated separately using established analytical methods for short- and medium-term tags. However, this study will offer 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

Satellite tagging field work for the first field session of 2017 was conducted from May 8-18 and resulted in deployment of 14 SLTDRs (5 Cuvier’s beaked whales and 9 short-finned pilot whales) in preparation for a CEE during the week of 22 May, and all preparations are in place for attaching DTAGs to both species for the same CEE. 

May 2017 Satellite tagging field work summary