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Climate change is warming the Arctic faster than the rest of the planet. Shifts in whale migration timing have been linked to climate change in temperate and sub-Arctic regions, and evidence suggests Bering–Chukchi–Beaufort (BCB) bowhead whales (Balaena mysticetus) might be overwintering in the Canadian Beaufort Sea.

We used an 11-year timeseries (spanning 2009–2021) of BCB bowhead whale presence in the southern Chukchi Sea (inferred from passive acoustic monitoring) to explore relationships between migration timing and sea ice in the Chukchi and Bering Seas.

Fall southward migration into the Bering Strait was delayed in years with less mean October Chukchi Sea ice area and earlier in years with greater sea ice area (p = 0.04, r² = 0.40). Greater mean October–December Bering Sea ice area resulted in longer absences between whales migrating south in the fall and north in the spring (p < 0.01, r² = 0.85). A stepwise shift after 2012–2013 shows some whales are remaining in southern Chukchi Sea rather than moving through the Bering Strait and into the northwestern Bering Sea for the winter. Spring northward migration into the southern Chukchi Sea was earlier in years with less mean January–March Chukchi Sea ice area and delayed in years with greater sea ice area (p < 0.01, r² = 0.82).

As sea ice continues to decline, northward spring-time migration could shift earlier or more bowhead whales may overwinter at summer feeding grounds. Changes to bowhead whale migration could increase the overlap with ships and impact Indigenous communities that rely on bowhead whales for nutritional and cultural subsistence.

 

Changes in gray whale ( Eschrichtius robustus ) phenology and distribution are related to observed and hypothesized prey availability, bottom water temperature, salinity, sea ice persistence, integrated water column and sediment chlorophyll a , and patterns of wind-driven biophysical forcing in the northern Bering and eastern Chukchi seas. This portion of the Pacific Arctic includes four Distributed Biological Observatory (DBO) sampling regions. In the Bering Strait area, passive acoustic data showed marked declines in gray whale calling activity coincident with unprecedented wintertime sea ice loss there in 2017–2019, although some whales were seen there during DBO cruises in those years. In the northern Bering Sea, sightings during DBO cruises show changes in gray whale distribution coincident with a shrinking field of infaunal amphipods, with a significant decrease in prey abundance (r = -0.314, p<0.05) observed in the DBO 2 region over the 2010–2019 period. In the eastern Chukchi Sea, sightings during broad scale aerial surveys show that gray whale distribution is associated with localized areas of high infaunal crustacean abundance. Although infaunal crustacean prey abundance was unchanged in DBO regions 3, 4 and 5, a mid-decade shift in gray whale distribution corresponded to both: (i) a localized increase in infaunal prey abundance in DBO regions 4 and 5, and (ii) a correlation of whale relative abundance with wind patterns that can influence epi-benthic and pelagic prey availability. Specifically, in the northeastern Chukchi Sea, increased sighting rates (whales/km) associated with an ~110 km (60 nm) offshore shift in distribution was positively correlated with large scale and local wind patterns conducive to increased availability of krill. In the southern Chukchi Sea, gray whale distribution clustered in all years near an amphipod-krill ‘hotspot’ associated with a 50-60m deep trough. We discuss potential impacts of observed and inferred prey shifts on gray whale nutrition in the context of an ongoing unusual gray whale mortality event. To conclude, we use the conceptual Arctic Marine Pulses (AMP) model to frame hypotheses that may guide future research on whales in the Pacific Arctic marine ecosystem. 

The source levels, SL, of Antarctic blue and fin whale calls were estimated using acoustic recordings collected from directional sonobuoys deployed during an Antarctic voyage in 2019. Antarctic blue whale call types included stereotyped song and downswept frequency-modulated calls, often, respectively, referred to as Z-calls (comprising song units-A, B, and C) and D-calls. Fin whale calls included 20 Hz pulses and 40 Hz downswept calls. Source levels were obtained by measuring received levels (RL) and modelling transmission losses (TL) for each detection. Estimates of SL were sensitive to the parameters used in TL models, particularly the seafloor geoacoustic properties and depth of the calling whale. For our best estimate of TL and whale-depth, mean SL in dB re 1 μPa ± 1 standard deviation ranged between 188–191 ± 6–8 dB for blue whale call types and 189–192 ± 6 dB for fin whale call types. These estimates of SL are the first from the Southern Hemisphere for D-calls and 40 Hz downsweeps, and the largest sample size to-date for Antarctic blue whale song. Knowledge of source levels is essential for estimating the detection range and communication space of these calls and will enable more accurate comparisons of detections of these sounds from sonobuoy surveys and across international long-term monitoring networks. 

The Distributed Biological Observatory (DBO) was established to detect environmental changes in the Pacific Arctic by regular monitoring of biophysical responses in each of 8 DBO regions. Here we examine the occurrence of bowhead and beluga whale vocalizations in the western Beaufort Sea acquired by acoustic instruments deployed from September 2008-July 2014 and September 2016-October 2018 to examine inter-annual variability of these Arctic endemic species in DBO Region 6. Acoustic data were collected on an oceanographic mooring deployed in the Beaufort shelfbreak jet at ~71.4°N, 152.0°W. Spectrograms of acoustic data files were visually examined for the presence or absence of known signals of bowhead and beluga whales. Weekly averages of whale occurrence were compared with outputs of zooplankton, temperature and sea ice from the BIOMAS model to determine if any of these variables influenced whale occurrence. In addition, the dates of acoustic whale passage in the spring and fall were compared to annual sea ice melt-out and freeze-up dates to examine changes in phenology. Neither bowhead nor beluga whale migration times changed significantly in spring, but bowhead whales migrated significantly later in fall from 2008–2018. There were no clear relationships between bowhead whales and the environmental variables, suggesting that the DBO 6 region is a migratory corridor, but not a feeding hotspot, for this species. Surprisingly, beluga whale acoustic presence was related to zooplankton biomass near the mooring, but this is unlikely to be a direct relationship: there are likely interactions of environmental drivers that result in higher occurrence of both modeled zooplankton and belugas in the DBO 6 region. The environmental triggers that drive the migratory phenology of the two Arctic endemic cetacean species likely extend from Bering Sea transport of heat, nutrients and plankton through the Chukchi and into the Beaufort Sea. 

There is limited information about the biology and seasonal distribution of bearded seals (Erignathus barbatus) in Greenland. The species is highly ice-associated and depends on sea ice for hauling out and giving birth, making it vulnerable to climate change. We investigated the seasonality and distribution of bearded seal vocalizations at seven different locations across southern Baffin Bay and Davis Strait, West Greenland. Aural M2 and HARUphone recorders were deployed on the sea bottom during 2006–2007 and 2011–2013. Recordings were analyzed for presence/absence of bearded seal calls relative to location (including distance to shore and depth), mean sea ice concentration and diel patterns. Calling occurred between November and late June with most intense calling during the mating season at all sites. There was a clear effect of depth and distance to shore on the number of detections, and the Greenland shelf (< 300 m) appeared to be the preferred habitat for bearded seals during the mating season. These results suggest that bearded seals may retreat with the receding sea ice to Canada during summer or possibly spend the summer along the West Greenland coast. It is also possible that, due to seasonal changes in bearded seal vocal behavior, animals may have been present in our study area in summer, but silent. The number of detections was affected by the timing of sea ice formation but not sea ice concentration. Diel patterns were consistent with patterns found in other parts of the Arctic, with a peak during early morning (0400 local) and a minimum during late afternoon (1600 local). While vocalization studies have been conducted on bearded seals in Norwegian, Canadian, northwest Greenland, and Alaskan territories, this study fills the gap between these areas.