Stable isotope ratios of bone collagen are commonly used to investigate foraging and movement of ... more Stable isotope ratios of bone collagen are commonly used to investigate foraging and movement of human and animal populations. This technique is especially valuable for archaeological and paleoecological applications, as bones are among the few tissues that are commonly preserved in archaeological and assemblages. Selection of skeletal elements for stable isotope analysis is typically driven by sample sizes and convenience, with the assumption that each bone is equally likely to be representative of the entire skeleton. This study investigated the degree of variability in stable carbon and nitrogen isotope ratios (δ13C and δ15N) within the skeletons of individual marine mammals to determine whether any systematic differences in δ13C and δ15N exist among skeletal elements. We measured δ13C and δ15N in paired crania and mandibles from 11 Pacific walruses (Odobenus rosmarus divergens), as well as representative elements from the skeletons of three marine mammals: an adult ringed seal (Pusa hispida, n = 10), a juvenile seal of the genus Phoca (Phoca sp., n = 9), and an adult sea otter (Enhydra lutris, n = 8). Differences among the walrus cranium/mandible pairs were not significant, mostly falling within analytical error. Variability across the skeletons of the seals and sea otter was greater, exceeding 1.0‰ in some cases. Hierarchical cluster analysis indicated systematic differences within all three skeletons, with the distal appendicular bones (metatarsal, phalanx, calcaneus) separating from the rest of the skeleton in the two seals, and the scapula and vertebra distinct from all other bones in the sea otter. Removing these bones from analysis greatly reduced overall variability in all three animals. Further study is required to determine whether the patterns observed in this study are consistent across individuals and taxa as sample sizes increase.
Abstract: Outbreaks of Acanthaster planci, the Crown-of-Thorns starfish, have been known to cause... more Abstract: Outbreaks of Acanthaster planci, the Crown-of-Thorns starfish, have been known to cause considerable amounts of damage to coral reef systems. Surveys of A. planci populations in Moorea, French Polynesia in 2004 indicated the island was experiencing the ...
Large, migratory predators are often cited as sentinel species for ecosystem processes and climat... more Large, migratory predators are often cited as sentinel species for ecosystem processes and climate-related changes, but their utility as indicators is dependent upon an understanding of their response to environmental variability. Documentation of the links between climate variability, ecosystem change and predator dynamics is absent for most top predators. Identifying species that may be useful indicators and elucidating these mechanistic links provides insight into current ecological dynamics and may inform predictions of future ecosystem responses to climatic change. We examine humpback whale response to environmental variability through stable isotope analysis of diet over a dynamic 20-year period (1993-2012) in the California Current System (CCS). Humpback whale diets captured two major shifts in oceanographic and ecological conditions in the CCS. Isotopic signatures reflect a diet dominated by krill during periods characterized by positive phases of the North Pacific Gyre Osci...
Understanding reproductive rates of wild animal populations is crucially important for management... more Understanding reproductive rates of wild animal populations is crucially important for management and conservation. Assessing pregnancy status of free-ranging cetaceans has historically been difficult; however, recent advances in analytical techniques have allowed the diagnosis of pregnancy from small samples of blubber tissue. The primary objectives of this study were as follows: (i) to test the efficacy of blubber progesterone assays as a tool for diagnosing pregnancy in humpback whales (Megaptera novaeangliae); (ii) to estimate the pregnancy rate of humpback whales in Monterey Bay, California; and (iii) to inves- tigate the relationship between stable isotopes and reproductive status of these whales. Progesterone concentrations of female whales fell into two distinct groups, allowing for diagnostic separation of pregnant and non-pregnant individuals. Pregnancy rate varied between years of the study (48.4%% in 2011 and 18.5% in 2012), but fell within the range of other estimates of reproductive success for this population. Stable carbon and nitrogen isotope ratios were examined to investigate the impacts of pregnancy on these values. Neither δ15N nor δ13C varied in a consistent way among animals of different sex or reproductive status. The relationship between δ15N and δ13C was strongly positive for male and non-pregnant female humpbacks; however, no relationship existed for pregnant whales. This difference may be indicative of the effects of pregnancy on δ15N, resulting from tissue synthesis and reduced excretion of nitrogenous waste, as well as on δ13C through increased mobilization of lipid stores to meet the energetic demands of pregnancy. Ultimately, our results support the use of blubber progesterone assays for diagnosing pregnancy in humpback whales and indicate that, when paired with other approaches (e.g., stable isotope analysis), pregnancy status can be an informative tool for addressing questions about animal physiology, ecology and population biology. This information will provide for more effective management and conservation efforts in a rapidly changing world.
Stable isotope ratios of bone collagen are commonly used to investigate foraging and movement of ... more Stable isotope ratios of bone collagen are commonly used to investigate foraging and movement of human and animal populations. This technique is especially valuable for archaeological and paleoecological applications, as bones are among the few tissues that are commonly preserved in archaeological and assemblages. Selection of skeletal elements for stable isotope analysis is typically driven by sample sizes and convenience, with the assumption that each bone is equally likely to be representative of the entire skeleton. This study investigated the degree of variability in stable carbon and nitrogen isotope ratios (δ13C and δ15N) within the skeletons of individual marine mammals to determine whether any systematic differences in δ13C and δ15N exist among skeletal elements. We measured δ13C and δ15N in paired crania and mandibles from 11 Pacific walruses (Odobenus rosmarus divergens), as well as representative elements from the skeletons of three marine mammals: an adult ringed seal (Pusa hispida, n = 10), a juvenile seal of the genus Phoca (Phoca sp., n = 9), and an adult sea otter (Enhydra lutris, n = 8). Differences among the walrus cranium/mandible pairs were not significant, mostly falling within analytical error. Variability across the skeletons of the seals and sea otter was greater, exceeding 1.0‰ in some cases. Hierarchical cluster analysis indicated systematic differences within all three skeletons, with the distal appendicular bones (metatarsal, phalanx, calcaneus) separating from the rest of the skeleton in the two seals, and the scapula and vertebra distinct from all other bones in the sea otter. Removing these bones from analysis greatly reduced overall variability in all three animals. Further study is required to determine whether the patterns observed in this study are consistent across individuals and taxa as sample sizes increase.
Abstract: Outbreaks of Acanthaster planci, the Crown-of-Thorns starfish, have been known to cause... more Abstract: Outbreaks of Acanthaster planci, the Crown-of-Thorns starfish, have been known to cause considerable amounts of damage to coral reef systems. Surveys of A. planci populations in Moorea, French Polynesia in 2004 indicated the island was experiencing the ...
Large, migratory predators are often cited as sentinel species for ecosystem processes and climat... more Large, migratory predators are often cited as sentinel species for ecosystem processes and climate-related changes, but their utility as indicators is dependent upon an understanding of their response to environmental variability. Documentation of the links between climate variability, ecosystem change and predator dynamics is absent for most top predators. Identifying species that may be useful indicators and elucidating these mechanistic links provides insight into current ecological dynamics and may inform predictions of future ecosystem responses to climatic change. We examine humpback whale response to environmental variability through stable isotope analysis of diet over a dynamic 20-year period (1993-2012) in the California Current System (CCS). Humpback whale diets captured two major shifts in oceanographic and ecological conditions in the CCS. Isotopic signatures reflect a diet dominated by krill during periods characterized by positive phases of the North Pacific Gyre Osci...
Understanding reproductive rates of wild animal populations is crucially important for management... more Understanding reproductive rates of wild animal populations is crucially important for management and conservation. Assessing pregnancy status of free-ranging cetaceans has historically been difficult; however, recent advances in analytical techniques have allowed the diagnosis of pregnancy from small samples of blubber tissue. The primary objectives of this study were as follows: (i) to test the efficacy of blubber progesterone assays as a tool for diagnosing pregnancy in humpback whales (Megaptera novaeangliae); (ii) to estimate the pregnancy rate of humpback whales in Monterey Bay, California; and (iii) to inves- tigate the relationship between stable isotopes and reproductive status of these whales. Progesterone concentrations of female whales fell into two distinct groups, allowing for diagnostic separation of pregnant and non-pregnant individuals. Pregnancy rate varied between years of the study (48.4%% in 2011 and 18.5% in 2012), but fell within the range of other estimates of reproductive success for this population. Stable carbon and nitrogen isotope ratios were examined to investigate the impacts of pregnancy on these values. Neither δ15N nor δ13C varied in a consistent way among animals of different sex or reproductive status. The relationship between δ15N and δ13C was strongly positive for male and non-pregnant female humpbacks; however, no relationship existed for pregnant whales. This difference may be indicative of the effects of pregnancy on δ15N, resulting from tissue synthesis and reduced excretion of nitrogenous waste, as well as on δ13C through increased mobilization of lipid stores to meet the energetic demands of pregnancy. Ultimately, our results support the use of blubber progesterone assays for diagnosing pregnancy in humpback whales and indicate that, when paired with other approaches (e.g., stable isotope analysis), pregnancy status can be an informative tool for addressing questions about animal physiology, ecology and population biology. This information will provide for more effective management and conservation efforts in a rapidly changing world.
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