Changes in gray whale phenology and distribution related to prey variability and ocean biophysics in the northern Bering and eastern Chukchi seas

Abstract

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.

Modeling the Recent Changes of Phytoplankton Blooms Dynamics in the Arctic Ocean

“…An increase in oligotrophic conditions will have severe consequences for the AO planktonic ecosystem (Comeau et al., 2011; W. K. W. Li et al., 2009) and for upper trophic levels that depend on the export flux of organic matter to the seafloor (Kedra et al., 2015). These changes could impact planktonic species composition and the abundance of benthic fauna (Grebmeier, 2012), with important implications for future fisheries (Fossheim et al., 2015; Lam et al., 2016) and upper trophic levels of the AO marine ecosystems (Moore et al., 2022). The results obtained in our study by the use of the ECCO2‐Darwin model are also in agreement with previous studies (Henson et al., 2018; Yamaguchi et al., 2022) based on the use of Earth System models including ocean ecology and biogeochemistry.…”

Biologically important areas II for cetaceans in U.S. and adjacent waters - Arctic region

“…Gray whales remain in the U.S. Arctic throughout summer and early autumn before making a return migration south. The predominant behavior of gray whales in Arctic waters is feeding (Clarke et al, 2016;Brower et al, 2017;Moore et al, 2022). Benthic feeding is easily identified via the presence of mud plumes visible at the surface that are produced when whales surface after feeding on benthic or epibenthic species (Nerini, 1984).…”

“…The ASAMM project documented gray whale feeding in the eastern Chukchi Sea from summer through autumn with moderate variability in feeding location within these seasons (Clarke et al, 2020). The two main areas for gray whale feeding were in the northeastern Chukchi Sea within about 120 km of shore from Icy Cape to Point Barrow, Alaska, (Moore et al, 2022) and in the southern Chukchi Sea southwest of Point Hope, Alaska. These areas were delineated as BIAs previously (Clarke et al, 2015b), although the southern area was truncated west of the U.S. EEZ.…”

“…Note that there are data available for gray whale feeding nearshore along the Chukotka peninsula coast (e.g., Heide-Jørgensen et al, 2012;Blohkin et al, 2013;Blokhin et al, 2017;Zdor, 2021) but those data differ spatiotemporally from this child BIA and were used to support a completely unique F-BIA (https://oceannoise.noaa.gov/biologicallyimportant-areas). Spatiotemporal variability was designated ephemeral because, while both areas are used for feeding every year, feeding locations within these areas may change annually due to changes in prey abundance (Moore et al, 2022). The delineation of the June-October gray whale parent F-BIA included the two child BIAs identified in the process described above and >90% of all ASAMM gray whale sightings south of Cape Lisburne, Alaska, from June-October.…”

Polar biocenosis cumulative response to environmental stressors reveals who benefits from marine ice loss

“…Despite some signs of adaptation, it is generally agreed that the ice-obligate species cannot survive absent sea ice. The abrupt loss of sea ice is creating a dichotomy between ice-dependent mammals and seabirds that are losing habitat (Iverson et al 2014, Trathan et al 2020, and some cetaceans that appear to be thriving during periods of rapid sea ice loss with extended open-water seasons enabling the establishment of macrozooplankton and fish populations (Moore et al 2022).…”