Seasonal migrations of North Atlantic minke whales: novel insights from large-scale passive acoustic monitoring networks

Abstract

Background: Little is known about migration patterns and seasonal distribution away from coastal summer feeding habitats of many pelagic baleen whales. Recently, large-scale passive acoustic monitoring networks have become available to explore migration patterns and identify critical habitats of these species. North Atlantic minke whales (Balaenoptera acutorostrata) perform seasonal migrations between high latitude summer feeding and low latitude winter breeding grounds. While the distribution and abundance of the species has been studied across their summer range, data on migration and winter habitat are virtually missing. 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. Results: Acoustic detections show that minke whales leave their winter grounds south of 30°N from March through early April. On their southward migration in autumn, minke whales leave waters north of 40°N from mid-October through early November. 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. Abundant detections were found off the southeastern US and the Caribbean during winter. Minke whale pulse trains showed evidence of geographic variation, with longer pulse trains recorded south of 40°N. Very few pulse trains were recorded during summer in any of the datasets. Conclusion: This study highlights the feasibility of using acoustic monitoring networks to explore migration patterns of pelagic marine mammals. Results confirm the presence of minke whales off the southeastern US and the Caribbean during winter months. 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. Alternatively, if pulse trains are produced in a reproductive context by males, these data may indicate their absence from the selected recording sites. Evidence of geographic variation in pulse train duration suggests different behavioural functions or use of these calls at different latitudes.

High latitude winter sightings of common minke whale calves (Balaenoptera acutorostrata) in the Northeast Atlantic

“…Based on the timing of sightings and the sizes of the animals encountered, we believe the sightings reported here to be of unweaned minke whale calves. The location of the sightings, in relatively deep waters in the open ocean, is similar to sightings and/or acoustic detections recorded elsewhere (Risch et al, 2014;Folkow & Blix, 1991;Nieukirk et al, 2004), possibly indicating offshore movement, and even calving and nursing, in winter and spring months. Vikingsson and Heide-Jørgensen (2015) recorded the first evidence of autumn migration routes and destination of common minke whales in the North Atlantic, however, the paradigm that all individuals within a mysticete species group (i.e.…”

“…In addition, summer sightings of minke whales have also been recorded in the English Channel, Celtic Sea and as far south as the Bay of Biscay (Hammond et al, 2013;Hammond et al, 2002;Laran et al, 2017). While migratory patterns of this species are generally poorly understood, they are believed to undertake large-scale seasonal migrations between summer feeding grounds at higher latitudes, and breeding grounds at lower latitudes in winter months (Risch et al, 2014;Vikingsson & Heide-Jørgensen, 2015). Although there is no genetic evidence for geographic structure between the putative stocks in the North Atlantic (Anderwald et al, 2011;Quintela et al, 2014), minke whales are thought to distribute across at least two breeding grounds, however the location of these breeding grounds remains poorly known (Anderwald et al, 2011).…”

“…Acoustic data collected in the Northwest and central Atlantic contributes to our understanding of minke whale offshore and winter distributions, especially in remote areas where visual survey effort is difficult to obtain (Risch et al, 2014;Nieukirk et al, 2004;Risch et al, 2013). However, as little is known about sex-specific or calf-specific minke whales vocalisations, identification of their breeding grounds using these data is difficult.…”

NEPAN: A U.S. Northeast Passive Acoustic Sensing Network for Monitoring, Reducing Threats and the Conservation of Marine Animals

“…In contrast to the GOM, the coastal climate of the bight is temperate as a result of direct contact from the Gulf Stream. The NYB appears to be a pivotal point used by northward migrating marine mammals before they turn and head east and north across or around Georges Bank (Risch et al, 2014;Schlesinger & Bonacci, 2014) or west into Massachusetts Bay. Which species passes through the NYB area and how long they remain is not well known.…”

“…Many marine species are highly vocal and much of their social, reproductive, and foraging behavior is acoustically mediated. Studies of the vocalizations that these animals emit-although completely reliant on the animals actually vocalizing-can provide information on their occurrence, distribution, relative abundance, and habitat use (e.g., Moore et al, 2006;Van Parijs et al, 2009;Širović & Hildebrand, 2011;Van Opzeeland et al, 2013a;Risch et al, 2014). In the past decade, passive acoustic approaches for studying marine animal populations have seen a rapid expansion in both the tools available and the geographic scope in which studies have been conducted.…”