Pygmy Blue Whales (Balaenoptera musculus brevicauda) are a subspecies of Blue Whale discovered in the early 1960s and subsequently targeted by Japanese and Soviet whaling fleets. There are currently known to be four separate populations, ranging from the western Indian Ocean to the waters around New Zealand, with some exchange of individuals between these. Each population migrates between a southern feeding ground in the summer and a northern feeding ground in winter, but little is known about their movement paths, population structures or numbers. The subspecies is listed as ‘data deficient’ on the International Union for the Conservation of Nature’s Red List of Threatened Species, indicating that too little is known about them to make an accurate assessment of their conservation status.
In a paper published in the journal PLoS One on 9 April 2014, a team of scientists led by Michael Double of the Australian Marine Mammal Centre discuss the results of an experiment in which Pygmy Blue Whales were radiotagged in Perth Canyon, off the coast of Western Australia, in April 2009 and March 2011, and their subsequent movements tracked by satellite until the tags stopped working. This population is known to migrate between the southwest coast of Australia and the Banda Sea in Indonesia, where they breed between June and September. This population is known to have been targeted by Soviet whaling fleets in the 1960s, but the health of the current population is not known, nor are the potential threats faced by these Whales.
Four of the tags deployed failed to activate properly, with the remainder lasting for between 8 and 308 days, though one of these failed to activate immediately, activating in June 2011, though when it did so the tagged Whale was with the rest of the population, therefore producing coherent data.
Five of the Whales when first tagged moved southwards towards the Naturaliste Plateau, before turning about and joining the northward migration. The Whales travelled an average of 3009 km, at an average rate of 21.9 km per day.
The Whales travelled northward along the Australian coast, past the Ningaloo Reef to the North West Cape in March and April, then northward through the Savu and Timor Seas in May and June, eventually reaching the Molucca and Banda Seas. The Whales occupied shallower waters while close to Australia, averaging 1369.5 m, then progressively deeper waters while crossing the Savu and Timor Seas, reaching the deepest waters of their range in the Banda and Molucca Seas, where the waters average 3788.5 m.
Filtered satellite tag derived locations of pygmy blue whales (n = 11) by month. Individuals were tagged in March (2011: n = 7) and April (2009: n = 3; 2011: n = 1) in the Perth Canyon. The northern terminus of migration occurred in Indonesia. A single whale was tracked intermittently until February 2012 at which time it was located in the subtropical frontal zone. Double et al. (2014).
The Whales face a number of anthropogenic threats along this route. The western coast of Australia is an area of expanding natural gas exploration, with the associated increase in noise from shipping and seismic exploration. In the waters of Indonesia they run the risk of encountering gillnets used in fishing, and increased noise pollution from reef dynamiting, again used in the fishing industry.
Other species of Whale have been known to abandon parts of their ranges in order to avoid noise pollution, and while most large marine Vertebrates can alter their movement patterns substantially in order to avoid threats and take advantage of novel food sources, the loss of a critical part of the Whales range, particularly the feeding grounds, could potentially have a strongly detrimental effect on the long-term survival of the population.
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