title: Heavy with child? Pregnancy status and stable isotope ratios as determined from biopsies of humpback whales.
abstract: 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 investigate 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.
authors.affiliation: Moss Landing Marine Laboratories, Moss Landing, CA 95039, USA; College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775, USA.
authors.forename: Casey T
authors.initials: CT
authors.lastname: Clark
authors.affiliation: Department of Paleobiology and Vertebrate Zoology , National Museum of Natural History Smithsonian Institution , Washington, DC 20013 , USA.
authors.forename: Alyson H
authors.initials: AH
authors.lastname: Fleming
authors.affiliation: Cascadia Research Collective , Olympia, WA 98501 , USA.
authors.forename: John
authors.initials: J
authors.lastname: Calambokidis
authors.affiliation: Marine Mammal and Turtle Division , Southwest Fisheries Science Center , National Marine Fisheries Service , National Oceanic and Atmospheric Administration, La Jolla, CA 92037 , USA.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Kellar
authors.affiliation: Marine Mammal and Turtle Division , Southwest Fisheries Science Center , National Marine Fisheries Service , National Oceanic and Atmospheric Administration, La Jolla, CA 92037 , USA.
authors.forename: Camryn D
authors.initials: CD
authors.lastname: Allen
authors.affiliation: Marine Mammal and Turtle Division , Southwest Fisheries Science Center , National Marine Fisheries Service , National Oceanic and Atmospheric Administration, La Jolla, CA 92037 , USA.
authors.forename: Krista N
authors.initials: KN
authors.lastname: Catelani
authors.affiliation: Marine Mammal and Turtle Division , Southwest Fisheries Science Center , National Marine Fisheries Service , National Oceanic and Atmospheric Administration, La Jolla, CA 92037 , USA.
authors.forename: Michelle
authors.initials: M
authors.lastname: Robbins
authors.affiliation: Marine Mammal and Turtle Division , Southwest Fisheries Science Center , National Marine Fisheries Service , National Oceanic and Atmospheric Administration, La Jolla, CA 92037 , USA.
authors.forename: Nicole E
authors.initials: NE
authors.lastname: Beaulieu
authors.affiliation: Marine Mammal Institute and Department of Fisheries and Wildlife , Oregon State University , Newport, OR 97365 , USA.
authors.forename: Debbie
authors.initials: D
authors.lastname: Steel
authors.affiliation: Moss Landing Marine Laboratories , Moss Landing, CA 95039 , USA.
authors.forename: James T
authors.initials: JT
authors.lastname: Harvey
keywords: Blubber; hormones; humpback whale; pregnancy; progesterone; stable isotopes