Timing of migratory baleen whales at the Azores in relation to the North Atlantic spring bloom

Abstract

Each year, a phytoplankton spring bloom starts just north of the North Atlantic Subtropical Gyre, and then expands northwards across the entire North Atlantic. Here, we investigate whether the timing of the spring migration of baleen whales is related to the timing of the phytoplankton spring bloom, using 4 yr of dedicated whale observations at the Azores in combination with satellite data on ocean chlorophyll concentration. Peak abundances of blue whale Balaenoptera musculus, fin whale B. physalus, humpback whale Megaptera novaeangliae and sei whale B. borealis were recorded in April-May. The timing of their presence tracked the onset of the spring bloom with mean time lags of 13, 15, 15 and 16 wk, respectively, and was more strongly related to the onset of the spring bloom than to the actual time of year. Baleen whales were actively feeding on northern krill Meganyctiphanes norvegica in the area, and some photo-identified individuals stayed in Azorean waters for at least 17 d. Baleen whales were not observed in this area in autumn, during their southward migration, consistent with low chlorophyll concentrations during summer and autumn. Our results support the hypothesis that baleen whales track the secondary production generated by the North Atlantic spring bloom, utilizing mid-latitude areas such as the Azores as foraging areas en route towards their summer feeding grounds.KEY WORDS: Baleen whales · Balaenopteridae · Phytoplankton spring bloom · Whale migration · Feeding area · Satellite remote sensing · North Atlantic Ocean · Azores Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 440: [267][268][269][270][271][272][273][274][275][276][277][278][279] 2011 tune their migration to the timing of the North Atlantic spring bloom. Baleen whales need dense aggregations of krill or fish to enable efficient foraging (Whitehead & Carscadden 1985, Friedlaender et al. 2006, Goldbogen et al. 2011, and temporal synchrony with the presence of suitable prey is evident in these species. Most baleen whale species undertake extensive north-south migrations associated with feeding at mid-to high latitudes in summer and breeding in (sub)tropical regions during winter (Kellogg 1929, Norris 1967; but see Simon et al. 2010 for a counterexample). Seasonal presence of baleen whales at the summer feeding grounds coincides with increased food availability in these waters. Nevertheless, migratory patterns over the North Atlantic are still largely unknown for most species of baleen whales.The North Atlantic spring bloom could temporarily produce sufficient prey densities to induce foraging of baleen whales during their spring migration towards the high-latitude feeding grounds. This might particularly apply to areas where the phytoplankton spring bloom combines with physical factors to con- centrate prey. Physical conditions conducive to concentrating prey may include coastal zones, upwelling areas, fronts and seamounts. For example, offshore regions of high marine productivit...

Spatial and temporal distribution of cetaceans in the mid-Atlantic waters around the Azores

“…Here we show that B. physalus, B. borealis and B. musculus are frequently sighted every year, especially in spring and summer. Landbased observations indicate that these species also occur in the region in late autumn and winter, as has been recently shown for B. physalus using passive acoustic data (Silva et al 2011;Nieukirk et al 2012), and contradicting previous reports (Visser et al 2011). Baleen whales are thought to undertake annual migrations between low latitude wintering grounds and high latitude summer feeding areas.…”

Foraging areas, migratory movements and winter destinations of blue whales from the western North Atlantic

“…Reilly & Thayer 1990, Mate et al 1999, Visser et al 2011, Silva et al 2013, Owen et al 2015. A closer look at seasonal movements within and across baleen whale populations has revealed that dynamic migration strategies do not conform with a feast and famine yearly cycle (Geijer et al 2016).…”

“…Feeding opportunities during the return journey to feeding grounds are undoubtedly valuable, particularly if energy reserves are running low as a result of breeding and/or nursing (e.g. Best et al 1995, Visser et al 2011, Silva et al 2013. Whales may also use major current systems to reduce energy expenditure during long migrations.…”

A week in the life of a pygmy blue whale: migratory dive depth overlaps with large vessel drafts

“…Diameter is calculated from girth by assuming a circular shape. The wave drag depth-rounded threshold is calculated to represent the level of accuracy of the pressure sensor in the biotelemetry device used in this study the increase in evidence of whales feeding while migrating [30][31][32][33], and suggestions that some species such as blue whales (Balaenoptera musculus) may feed yearround [27,34], understanding whether ARS behavior is likely to indicate where lunge feeding occurs is necessary. The ability to describe migratory behavior in detail has been largely constrained due to limitations in tag attachment methods and the transmission bandwidth of the available telemetry systems.…”