Dataset Information

What happened to gray whales during the Pleistocene? The ecological impact of sea-level change on benthic feeding areas in the North Pacific Ocean.

ABSTRACT: Gray whales (Eschrichtius robustus) undertake long migrations, from Baja California to Alaska, to feed on seasonally productive benthos of the Bering and Chukchi seas. The invertebrates that form their primary prey are restricted to shallow water environments, but global sea-level changes during the Pleistocene eliminated or reduced this critical habitat multiple times. Because the fossil record of gray whales is coincident with the onset of Northern Hemisphere glaciation, gray whales survived these massive changes to their feeding habitat, but it is unclear how.We reconstructed gray whale carrying capacity fluctuations during the past 120,000 years by quantifying gray whale feeding habitat availability using bathymetric data for the North Pacific Ocean, constrained by their maximum diving depth. We calculated carrying capacity based on modern estimates of metabolic demand, prey availability, and feeding duration; we also constrained our estimates to reflect current population size and account for glaciated and non-glaciated areas in the North Pacific. Our results show that key feeding areas eliminated by sea-level lowstands were not replaced by commensurate areas. Our reconstructions show that such reductions affected carrying capacity, and harmonic means of these fluctuations do not differ dramatically from genetic estimates of carrying capacity.Assuming current carrying capacity estimates, Pleistocene glacial maxima may have created multiple, weak genetic bottlenecks, although the current temporal resolution of genetic datasets does not test for such signals. Our results do not, however, falsify molecular estimates of pre-whaling population size because those abundances would have been sufficient to survive the loss of major benthic feeding areas (i.e., the majority of the Bering Shelf) during glacial maxima. We propose that gray whales survived the disappearance of their primary feeding ground by employing generalist filter-feeding modes, similar to the resident gray whales found between northern Washington State and Vancouver Island.

SUBMITTER: Pyenson ND

PROVIDER: S-EPMC3130736 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Publications

What happened to gray whales during the Pleistocene? The ecological impact of sea-level change on benthic feeding areas in the North Pacific Ocean.

Pyenson Nicholas D ND Lindberg David R DR

PloS one 20110706 7

<h4>Background</h4>Gray whales (Eschrichtius robustus) undertake long migrations, from Baja California to Alaska, to feed on seasonally productive benthos of the Bering and Chukchi seas. The invertebrates that form their primary prey are restricted to shallow water environments, but global sea-level changes during the Pleistocene eliminated or reduced this critical habitat multiple times. Because the fossil record of gray whales is coincident with the onset of Northern Hemisphere glaciation, gra ...[more]

PMID: 21754984

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Project description:The Western North-Pacific (WNP) gray whale feeding grounds are off the northeastern coast of Sakhalin Island, Russia and is comprised of a nearshore and offshore component that can be distinguished by both depth and location. Spatial movements of gray whales within their foraging grounds were examined based on 13 years of opportunistic vessel and shore-based photo-identification surveys. Site fidelity was assessed by examining annual return and resighting rates. Lagged Identification Rates (LIR) analyses were conducted to estimate the residency and transitional movement patterns within the two components of their feeding grounds. In total 243 individuals were identified from 2002-2014, among these were 94 calves. The annual return rate over the period 2002-2014 was 72%, excluding 35 calves only seen one year. Approximately 20% of the individuals identified from 2002-2010 were seen every year after their initial sighting (including eight individuals that returned for 13 consecutive years). The majority (239) of the WNP whales were observed in the nearshore area while only half (122) were found in the deeper offshore area. Within a foraging season, there was a significantly higher probability of gray whales moving from the nearshore to the offshore area. No mother-calf pairs, calves or yearlings were observed in the offshore area, which was increasingly used by mature animals. The annual return rates, and population growth rates that are primarily a result of calf production with little evidence of immigration, suggest that this population is demographically self-contained and that both the nearshore and offshore Sakhalin feeding grounds are critically important areas for their summer annual foraging activities. The nearshore habitat is also important for mother-calf pairs, younger individuals, and recently weaned calves. Nearshore feeding could also be energetically less costly compared to foraging in the deeper offshore habitat and provide more protection from predators, such as killer whales.

Project description:The goal of the present study was to complement existing data of testosterone and progesterone in blue whale (Balaenoptera musculus) blubber from the eastern North Pacific Ocean to evaluate effects of seasonality and location on these hormones and to better assess reproductive status of individuals. Physiological parameters regarding reproduction are fundamental for describing population dynamics, and hormones can be a valid tool to estimate those for wildlife populations. In this study, blubber tissue was validated for testosterone and progesterone assays. Hormone concentrations were measured in 69 (35 males and 34 females) blubber samples from live (n = 66) and stranded (n = 3) animals collected between 2002 and 2016 from a known winter reproductive ground in the Gulf of California (GoC) and summer feeding areas along the United States West Coast (USWC), specifically off the states of California and Oregon. Results were combined with sighting histories as a tool to determine reproductive status of individual whales. Testosterone concentrations in adult male blue whales were significantly higher (p < 0.05) in blubber biopsies sampled off the USWC between the months of June and November compared to those sampled in the GoC between February and April. Elevated testosterone concentrations likely indicate physiological preparation for reproductive activity while the animals were present off the USWC. Progesterone concentrations were significantly elevated in pregnant females, confirming progesterone as an indicator of pregnancy in blue whales. Probabilities of being pregnant were estimated for adult females with unknown sighting histories based on progesterone concentrations. Testosterone in females was detected and measured only in pregnant whales suggesting its biosynthesis or metabolism is altered during gestation. These results provide updated and new information on the reproductive cycle of blue whales in the eastern North Pacific, posing new milestones to better estimate the timing of the mating season for this endangered population.

Dataset Information

What happened to gray whales during the Pleistocene? The ecological impact of sea-level change on benthic feeding areas in the North Pacific Ocean.

Publications

What happened to gray whales during the Pleistocene? The ecological impact of sea-level change on benthic feeding areas in the North Pacific Ocean.

Similar Datasets

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