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| Killer whales are social animals that navigate all oceans and seas between the Arctic and Antarctica – they can be regarded eusocial since reproduction ceases around 40 years of age and menopausal females help care for offspring: like humans [13, 14]. Group cohesion in killer whales relies on a complex repertoire of vocalisations including clicks, whistles and calls. Sounds are instrumental for prey searching, orientation and communication. Foote [5] focused on calls, which are made up of series of discrete sounds that resemble squeaks, screams, and squawks to the human ear. It has been postulated that individuals learn to vocalise by imitation of peers of the same pod, and that only the base structure has a genetic, hence heritable, component [15]. Regardless, pods develop regional dialects. Those dialects, along with aspects of diet, genetics, morphology and behaviour, differentiate the three main lineages of killer whales (resident, transient and open sea) that might have been genetically isolated for ~ 150 to 700 thousand years and, potentially represent different taxa [16, 17]. The species might abandon the IUCN conservation category of ‘Data Deficient’ as soon its taxonomic uncertainty is resolved.Resident killer whales form matrilineal groups of 2 to 15 individuals (the matriarch and her offspring) – known as pods, in turn subdivided into subpods centred around grandmothers and great-grandmothers. The Southern Resident population is regarded as an acoustic clan comprising 3 pods currently numbering 81 individuals = 26 (J pod) + 19 (K pod) + 36 (L pod) (2013 survey), among whom the matriarch Granny is the oldest at 103 years! This clan feeds mainly on fish, and dwells in the coastal waters between British Columbia (Canada) and Washington State (USA), particularly south of Vancouver Island – nothing is known about where they spend the winter. The clan lost 20 % of its members between 1995 & 2001, and 13 more by 2013, and now faces the decline of its main prey: Chinook salmon (Oncorhynchus tshawytscha) [18]. The two pics show two sub pods of this clan swimming close to a whale-watching boat near Friday Harbour (San Juan Island) and a Chinese ship at Puget Sound (Seatle, USA). Photo credits: Marla Holt, NOAA/NMFS Northwest Fisheries Sciences Center. |
Acoustic pollution has become a transnational issue, particularly in marine ecosystems [1] by virtue of the physical fact that sounds travel in water farther and faster than in air. In our noisy, modern world, many species are now forced to modify their vocal repertoire in response to noise. The pivotal social role that vocalisations play in all cetacean species makes these predators and filter feeders particularly vulnerable to this environmental problem.
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Last night, an ambulance siren woke me, only seconds before the neighbour’s washing machine started spinning, and a good friend of mine rang from overseas. Gradually more and more people are living in societies plugged in to noisy mechanical and electronic devices 24 hours a day, 356 days a year.
Engine-powered vehicles are the main source of anthropogenic noise, and their numbers can grow even at a higher rate than the human population – so spreading not only diseases [2] but also decibels over a global network of travelling routes. In an ecological context, we refer to noise as a kind of sound (= energy wave detected by an auditory system) that is not considered a biologically meaningful cue by wildlife (including us) and might also cause physiological stress. Experts refer to ‘masking’ as those situations in which noise interferes the perception or emission of sounds that matter to the life history of species – a global concern in both terrestrial [3] and aquatic [4] ecosystems.
Andy Foote [5] has assessed the effect of vessel traffic on the vocal behaviour of the three pods forming the Southern Resident population of killer whales (Orcinus orca¸ see video). He recorded calls from these cetaceans from a ship, and through an array of submarine microphones in Haro Straight, between San Juan Island (Washington State, USA) and Vancouver Island (British Columbia, Canada). Between the 1990s and the 2000s, local traffic density had multiplied by a factor of 5 and currently, > 20 whale-watching vessels follow these killer whales daily among an active fleet of > 70 commercial vessels. Foote compared call length through 35 hours of underwater killer whale recordings over three periods (1977-1981, 1989-1992, 2001-2003), each comprising situations in which the pods were exposed to both noisy and quiet environments. Over the study, call length varied between 0.3 and 2.0 seconds; while on average, L-pod calls were the shortest (0.6-0.8 seconds), and J-pod calls the longest (0.9-1.0 seconds). Read the rest of this entry »
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