A method for tracking blue whales (Balaenoptera musculus) with a widely spaced network of ocean bottom seismometers

Passive acoustic monitoring is an important tool for studying marine mammals. Ocean bottom seismometer networks provide data sets of opportunity for studying blue whales (Balaenoptera musculus) which vocalize extensively at seismic frequencies. We describe methods to localize calls and obtain tracks using the B call of northeast Pacific blue whale recorded by a large network of widely spaced ocean bottom seismometers off the coast of the Pacific Northwest. The first harmonic of the B call at ~15 Hz is detected using spectrogram cross-correlation. The seasonality of calls, inferred from a dataset of calls identified by an analyst, is used to estimate the probability that detections are true positives as a function of the strength of the detection. Because the spacing of seismometers reaches 70 km, faint detections with a significant probability of being false positives must be considered in multi-station localizations. Calls are located by maximizing a likelihood function which considers each strong detection in turn as the earliest arrival time and seeks to fit the times of detections that follow within a feasible time and distance window. An alternative procedure seeks solutions based on the detections that maximize their sum after weighting by detection strength and proximity. Both approaches lead to many spurious solutions that can mix detections from different B calls and include false detections including misidentified A calls. Tracks that are reliable can be obtained iteratively by assigning detections to localizations that are grouped in space and time, and requiring groups of at least 20 locations. Smooth paths are fit to tracks by including constraints that minimize changes in speed and direction while fitting the locations to their uncertainties or applying the double difference relocation method. The reliability of localizations for future experiments might be improved by increasing sampling rates and detecting harmonics of the B call.

Opportunistic sightings of blue whales off Sydney, Australia

ABSTRACT Two subspecies of blue whale occur in Australian waters, (1) the pygmy blue whale (Balaenoptera musculus brevicauda) and (2) the Antarctic blue whale (Balaenoptera musculus intermedia). Understanding blue whale presence in Australian waters is critical to ensuring Australia’s protection of these marine mammals as both subspecies were heavily exploited during historical whaling. This short note documents pygmy blue whale sightings in New South Wales waters over the last 18 years. Observations were opportunistically made via citizen science and verified by scientists. Sightings in this note contribute to our limited knowledge of pygmy blue whale distribution along the east coast of Australia and may help understand the migratory movements of New Zealand pygmy blue whales off Australia and in the Tasman Sea. Overall, information presented in this note contributes to Australia’s national and international conservation efforts to protecting blue whales as a migratory and threatened species.

Blue whale (Balaenoptera musculus musculus) genome: population structure and history in the North Atlantic

Knowledge of genetic diversity and structure is essential for developing conservation strategies for endangered species. The advances in museum genomics can assist in better understanding the effects of over-hunting on the genome by comparing historical to present-day samples. Blue whales were hunted to the point of near extinction in the mid-twentieth century. Herein, we use whole genome sequencing to elucidate the poorly understood population structure of North Atlantic (NA) blue whales (Balaenoptera musculus musculus). We generated a de novo genome assembly of 2.49 Mbp for a NA blue whale (N50 of 1.46 Mb) to analyze 19 whole genomic sequences and 28 complete mitochondrial genomes. We included present-day and historical samples (earliest from 1900) from the Atlantic and Antarctica to understand the impact of whaling on the genetic diversity. We found low population structuring, but high genetic diversity, suggesting a single, panmictic population in the NA. We identified gene flow from fin whale to blue whales, accounting for ~3.5% of the genome. Introgression between blue and fin whales was observed in all the present-day samples but were lacking in some whales sampled early in the 20th century, which suggests increasing disruption in mate choice concomitant with decline in blue whale population. We also assembled and analyzed the transcriptome and revealed positive selection of oncogenes, which may be involved in reduced cancer rates in this largest of mammals ever known. Our sequencing and population structuring studies provide a genomic framework to guide ongoing conservation strategies for this iconic species.

First confirmed sightings of Blue Whales Balaenoptera musculus Linnaeus, 1758 (Mammalia: Cetartiodactyla: Balaenopteridae) in the Philippines since the 19th century

For over two centuries there were no records of Blue Whales Balaenoptera musculus in the Philippines. Whalers recorded Blue Whales in the Philippines in the 19th century, and the next confirmed sighting in the country was of a mother and calf in 2004. Since then 33 subsequent Blue Whale sightings of potentially one individual were recorded between 2004 and 2019, all within the central region of the Philippines around the Bohol Sea. This individual, recognized through photo-identification, was sighted on at least 13 occasions during eight different years: 2010, 2011, 2012, 2015, 2016, 2017, 2018, and 2019. The geographic location and timing of the sightings (January to July) suggest that Blue Whales in the Philippines may extend the outer range edge of the Indo-Australian population that migrate between western Australia, Indonesia, and East Timor. Blue Whale sightings in the Bohol Sea coincide with times of high ocean productivity, although further investigation is needed to determine if they are actually feeding in this region. Acoustic studies and photo-identification matching with other Blue Whale catalogues will clarify the stock identity of Blue Whales in the Philippines and their relation to the rest of the Blue Whale population, with implications for the conservation of this endangered species across multiple jurisdictions.

Body size data collected non-invasively from drone images indicate a morphologically distinct Chilean blue whale (Balaenoptera musculus) taxon

The blue whale Balaenoptera musculus (Linnaeus, 1758) was the target of intense commercial whaling in the 20th century, and current populations remain drastically below pre-whaling abundances. Reducing uncertainty in subspecific taxonomy would enable targeted conservation strategies for the recovery of unique intraspecific diversity. Currently, there are 2 named blue whale subspecies in the temperate to polar Southern Hemisphere: the Antarctic blue whale B. m. intermedia and the pygmy blue whale B. m. brevicauda. These subspecies have distinct morphologies, genetics, and acoustics. In 2019, the Society for Marine Mammalogy’s Committee on Taxonomy agreed that evidence supports a third (and presently unnamed) subspecies of Southern Hemisphere blue whale subspecies, the Chilean blue whale. Whaling data indicate that the Chilean blue whale is intermediate in body length between pygmy and Antarctic blue whales. We collected body size data from blue whales in the Gulfo Corcovado, Chile, during the austral summers of 2015 and 2017 using aerial photogrammetry from a remotely controlled drone to test the hypothesis that the Chilean blue whale is morphologically distinct from other Southern Hemisphere blue whale subspecies. We found the Chilean whale to be morphologically intermediate in both overall body length and relative tail length, thereby joining other diverse data in supporting the Chilean blue whale as a unique subspecific taxon. Additional photogrammetry studies of Antarctic, pygmy, and Chilean blue whales will help examine unique morphological variation within this species of conservation concern. To our knowledge, this is the first non-invasive small drone study to test a hypothesis for systematic biology.