These limitations are intensified during migration, when their locations and movements are generally less predictable. ĭue to the high mobility of individuals, short surface times and the dependence on daylight and favorable weather conditions, it is generally difficult to visually survey for marine mammals. Nonetheless, at least parts of most populations of baleen whales seasonally migrate between summer feeding and winter breeding grounds. For example, several long-term passive acoustic monitoring (PAM) studies show the extended year-round presence of baleen whales on higher-latitude feeding grounds. However, there is also increasing evidence that partial (a fraction of the population stays on the feeding grounds) or differential (differences in migratory behaviour between different age classes or sexes) migration might be more the norm than the exception in baleen whales. The driving forces for these long-range migrations to often unproductive breeding grounds are still debated and a number of explanations have been suggested, including increased calf survival and avoidance of killer whale ( Orcinus orca) predation. Most baleen whale species perform to-and-fro migrations between productive high latitude summer feeding and low latitude winter breeding grounds and have been shown to cover very large distances, including the longest documented migration distance by any mammal. Typically, migration develops as an adaptation to take advantage of seasonal peaks in resource abundance, escape inter- and intra-specific competition, or avoid predators and parasites. Evidence of geographic variation in pulse train duration suggests different behavioural functions or use of these calls at different latitudes.Īnimal migration is a common phenomenon and has evolved at multiple times and in a variety of species. Alternatively, if pulse trains are produced in a reproductive context by males, these data may indicate their absence from the selected recording sites. The absence of pulse train detections during summer suggests either that minke whales switch their vocal behaviour at this time of year, are absent from available recording sites or that variation in signal structure influenced automated detection.
Results confirm the presence of minke whales off the southeastern US and the Caribbean during winter months. This study highlights the feasibility of using acoustic monitoring networks to explore migration patterns of pelagic marine mammals. Very few pulse trains were recorded during summer in any of the datasets. Minke whale pulse trains showed evidence of geographic variation, with longer pulse trains recorded south of 40° N. Abundant detections were found off the southeastern US and the Caribbean during winter. In the western North Atlantic spring migrants appear to track the warmer waters of the Gulf Stream along the continental shelf, while whales travel farther offshore in autumn.
On their southward migration in autumn, minke whales leave waters north of 40° N from mid-October through early November. ResultsĪcoustic detections show that minke whales leave their winter grounds south of 30° N from March through early April. Acoustic recordings, from 16 different sites from across the North Atlantic, were analyzed to examine the seasonal and geographic variation in minke whale pulse train occurrence, infer information about migration routes and timing, and to identify possible winter habitats. While the distribution and abundance of the species has been studied across their summer range, data on migration and winter habitat are virtually missing. North Atlantic minke whales ( Balaenoptera acutorostrata) perform seasonal migrations between high latitude summer feeding and low latitude winter breeding grounds. Recently, large-scale passive acoustic monitoring networks have become available to explore migration patterns and identify critical habitats of these species. Little is known about migration patterns and seasonal distribution away from coastal summer feeding habitats of many pelagic baleen whales.
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