Satellite tag-derived data from two Antarctic blue whales (Balaenoptera musculus intermedia) tagged in the east Antarctic sector of the Southern Ocean as part of the IWC-SORP Antarctic Blue Whale Project.

Virginia Andrews-Goff, Mick Davidson, David Donnelly, Melinda Rekdahl, Natalie Schmitt (small boat team).

The IWC-SORP ABWP voyage occurred within the survey region bounded to the south by the 60°S parallel and between 135°E and 170°W. This survey region was identified prior to the voyage, based on an examination of catch, sightings and acoustic data that suggested the area may have a higher density of blue whales than the circumpolar average (Kelly et al. 2013). The survey employed continuous, real-time acoustic tracking to locate groups of Antarctic blue whales that were widely dispersed across this large area of Southern Ocean in order to locate whales for photographic identification and genetic sampling (Miller et al. 2015). The ship track and associated information are presented in Double et al. (2013).

The satellite-tagged Antarctic blue whales ranged widely and outside of the IWC-SORP ABWP survey region. During the tracking period, the whales traversed across an area spanning 110° in longitude and 12° in latitude, largely remaining within east Antarctica, but crossing the antemeridian to extend 4° into west Antarctica. Movement occurred across IWC Management Areas IV (70°E to 130°E; Donovan (1991)) and V (130°E to 170°W; Donovan (1991)), but remained south of the polar front and crossed the Antarctic circumpolar current. Whilst predominantly confined to the Southern Ocean (defined here as south of 60°S and including movements through the Ross Sea, Dumont d’Urville Sea and Davis Sea), movement did cross 3° into the South Pacific Ocean. The tracking period between mid-February and late April covered a time period of stable and then advancing sea ice. Sea ice retreat generally occurs November through to January and sea ice formation begins in March-April (Massom et al. 2013).

The survey design employed during the IWC-SORP ABWP is presented in Double et al. (2013).

The inaugural Antarctic Blue Whale Voyage (2013) was funded by the Australian Government’s International Whale and Marine Mammal Conservation Initiative (IWMMCI).

Whales moved broadly through the east Antarctic sector of the Southern Ocean.

Satellite tag deployment

Type C implantable satellite tags (Andrews et al. 2019) were deployed on two adult Antarctic blue whales with a modified version of the Air Rocket Transmitter System (ARTS), Restech (Heide‐Jørgensen et al. 2001) and a purpose-designed projectile carrier at a pressure of 7.5 – 8.5 bar. The satellite tag employed was comprised of an 80 mm anchor section attached to a stainless steel cylindrical housing containing a location-only Spot 200 transmitter manufactured by Wildlife Computers (Redmond, Washington, USA). These tags were fitted with a stainless-steel collar to reinforce the bolt that connects the anchor to the cylindrical electronics housing; however, this design is now superseded. Retention teeth on a purpose-designed projectile carrier grip a metal ring fitted to the end of the tag allowing the tag to be fired from the ARTS. When the tag makes contact with the whale, the rapid deceleration of the tag and the projectile carrier withdraws the retention teeth releasing the projectile carrier. The metal ring then falls off in time to reduce the drag of the tag. The tag was sterilised with ethylene oxide prior to deployment and implants up to a maximum of 290 mm into the skin, blubber, interfacial layers and outer muscle mass of the whale. Two actively sprung plates and a circle of passively deployed ‘petals’ aid tag retention.

Each tag was deployed from the bow-sprit of a purpose-built 6.3 m aluminium Naiad RHIB and was positioned high and forward on the body, approximately in line with the pectoral fins. When the tag is immersed in salt water, the salt water switch activates and the tag begins to transmit locations via the Argos satellite system. Tags were programmed to transmit to the Argos satellite system at a duty cycle of three hour on/three hour off and a 30 second repetition rate to extend battery life. These transmissions are relayed to processing centres which calculate the transmitter’s location by measuring the Doppler Effect on transmission frequency. Transmitted data were processed using a least squares analysis and each location was assigned an estimated error and one of seven associated location classes (see CLS 2016). Tags cease transmitting when they are either naturally shed, undergo damage, undergo sensor fouling or the battery is exhausted.

Upon tag deployment, a small amount of skin and blubber was simultaneously collected for genetic analyses. These were collected using a biopsy dart fired from a modified 0.22 Paxarms system (Krutzen et al. 2002). Biopsy samples were stored in 70% ethanol and DNA subsequently extracted using a Tissue DNA purification kit for the Maxwell 16 DNA extraction robot (Promega Corporation). The sexes of the tagged whales were determined using a 5′ exonuclease assay of the polymorphisms in the sex-linked Zinc Finger genes as described by Morin et al. (2005). Photo-identification images were also collected simultaneously with tag deployment. Photographs from the tagged whales were compared to those in the Antarctic Blue Whale Catalogue (Olson et al. 2013).

This research was conducted using non-lethal methods that are designed to learn about whales without harming them. The research was approved by the Australian Antarctic Ethics Committee (under Australian Antarctic Science Project 4102) and complied with all relevant permits including the Australian Government Environment Protection and Biodiversity Conservation Act Cetacean Permit (C12-0006).

Argos data processing

Argos locations were filtered using an algorithm, based on swimming speed, distance between successive locations and turning angles using the using the R (R Core Team 2021) package Argosfilter (Freitas et al. 2008) to remove unlikely position estimates (speed of 10 ms⁻¹, spike angles of 15° and 25°, spike lengths of 2500 m and 5000 m). Removals were verified manually via visual inspection. This resulted in the removal of 15% (PTT 123223) and 22% (PTT 121205) of locations for each whale, respectively (Table 1).

Argos location error

To account for the spatial error associated with Argos locations, we fit a random walk state-space model to estimate locations at a two hour time step (fit_ssm function in the foieGras package; Jonsen et al. (2019)). Individual tracks were split into track segments where data gaps exceeded 24 hours. The state-space-model was implemented per track segment > 10 locations resulting in the removal of two short track segments (n = 5 locations over 12 days at the end of PTT 123223 track segment 1 and n = 6 locations over 1 day for PTT 123223 at the start of track segment 2; see also Temporal coverage for retained track segment details).

Behavioural context

In order to provide context to the observed movement, a move persistence model was fitted to the state-space location estimates of each track (fit_mpm function in foieGras with unpooled random walk variance parameters; Jonsen et al. (2019)). The move persistence model assigns a behavioural classification to each state-space location estimate. The move persistence model estimates the time-varying autocorrelation in speed and directionality along the track generating a move persistence value (gamma) at each location. Move persistence ranges along a continuum between 0 and 1 - move persistence values approaching 1 indicate directed travel (transit) and move persistence values approaching 0 represent slower, tortuous movements (area restricted search - ARS), representative of putative foraging. We used the mean of all gamma values as a cut-off point to categorically assign each location as either transit or ARS. Following Bailey et al. (2009) and Andrews-Goff et al. (2018), we assigned ARS patches, comprising of successive location estimates classified as ARS, ending when three or more consecutive location estimates are classified as transit. These patches represent distinct clusters of area restricted search.

The geographic range of the bulk of the dataset is within the east Antarctic sector of the Southern Ocean, south of the polar front and crossing the Antarctic circumpolar current (Fig. 1).

-68.9 and -57. Latitude; 184.4 and 73.9 Longitude.

This dataset focuses exclusively on the Antarctic blue whale (Balaenoptera musculus intermedia), which is categorised as Critically Endangered in the IUCN Red List (Cooke 2018). It belongs to the family Balaenopteridae within the order Cetartiodactyla.

CC BY: This licence allows reusers to distribute, remix, adapt and build upon the material in any medium or format, so long as attribution is given to the creator. The licence allows for commercial use.

Antarctic blue whale tracking data - satellite tag-derived Argos locations and associated information, state space model with move persistence/behavioural index and the reference data detailing the satellite tag deployments. These datasets are published on Movebank (https://www.movebank.org/cms/webapp?gwt_fragment=page=studies,path=study2391441038), GBIF (https://www.gbif.org/dataset/6942e235-3ac0-418a-a042-f515cc7da235) and the Australian Antarctic Data Centre (https://data.aad.gov.au/metadata/AAS_4102_sat_tag).

https://www.movebank.org/cms/webapp?gwt_fragment=page=studies,path=study2391441038

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