Abstract
In Australian waters during the austral summer, pygmy blue whales (Balaenoptera musculus brevicauda) occur predictably in two distinct feeding areas off western and southern Australia. As with other blue whale subspecies, outside the austral summer their distribution and movements are poorly understood. In order to describe the migratory movements of these whales, we present the satellite telemetry derived movements of eleven individuals tagged off western Australia over two years. Whales were tracked from between 8 and 308 days covering an average distance of 3,009±892 km (mean ± se; range: 832 km–14,101 km) at a rate of 21.94±0.74 km per day (0.09 km–455.80 km/day). Whales were tagged during March and April and ultimately migrated northwards post tag deployment with the exception of a single animal which remained in the vicinity of the Perth Canyon/Naturaliste Plateau for its eight day tracking period. The tagged whales travelled relatively near to the Australian coastline (100.0±1.7 km) until reaching a prominent peninsula in the north-west of the state of Western Australia (North West Cape) after which they travelled offshore (238.0±13.9 km). Whales reached the northern terminus of their migration and potential breeding grounds in Indonesian waters by June. One satellite tag relayed intermittent information to describe aspects of the southern migration from Indonesia with the animal departing around September to arrive in the subtropical frontal zone, south of western Australia in December. Throughout their migratory range, these whales are exposed to impacts associated with industry, fishing and vessel traffic. These movements therefore provide a valuable tool to industry when assessing potential interactions with pygmy blue whales and should be considered by conservation managers and regulators when mitigating impacts of development. This is particularly relevant for this species as it continues to recover from past exploitation.
Highlights
Two blue whale subspecies are recognised in the Southern Hemisphere – the Antarctic or true blue whale (B. m. intermedia) and the pygmy blue whale (B. m. brevicauda) [1]
In order to describe the movement and migratory behaviours of pygmy blue whales and to investigate whether pygmy blue whales feeding in Australian waters do migrate into Indonesian waters, we present here the first published satellite telemetry data for pygmy blue whales
Satellite tags were deployed on three blue whales in 2009 and 12 blue whales in 2011 within the Perth Canyon, approximately 32.0uS, 115.0uE, off western Australia
Summary
Two blue whale subspecies are recognised in the Southern Hemisphere – the Antarctic or true blue whale (B. m. intermedia) and the pygmy blue whale (B. m. brevicauda) [1]. The vast majority of blue whale catches in the Southern Hemisphere and northern Indian Ocean were carried out prior to the identification of the pygmy blue whale subspecies and as such, the impact of commercial whaling on this subspecies is not well known [3]. Both Japan (1959/60–1963/64) and the USSR (1962/63–1972/73) ran expeditions capitalising on their recognition [4] and it is thought that almost all historical blue whale catches north of 52uS and between 35uE and 180uE were pygmy blue whales [3,5]. The current conservation status of this subspecies is highly uncertain with the IUCN Red List of Threatened Species listing it as data deficient [6]
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