Temporal Variation in Humpback Whale (Megaptera novaeangliae) Demographics Along the Western Antarctic Peninsula Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w3763c373

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  • Humpback whale populations in Antarctica are recovering after intensecommercial whaling in the 20th century. Along the Western Antarctic Peninsula (WAP)this recovery is occurring in an environment that is experiencing the fastest warming ofany region on the planet. To begin to understand the dynamics of this recovery undersuch dramatic climate change, we are studying the demography of these whales. To date,we have collected 583 biopsy samples from 239 individual males and 268 individualfemales during the austral feeding season from 2010, 2013-2016. The overall sex ratio ofour sample population is 0.89 M:F, supporting early observations that sexes mixrandomly on the feeding grounds. Additionally, we did document a significant seasonalincrease in the proportion of females along the WAP into the fall. We believe that thisshift represents a tendency for pregnant female humpback whales to depart last from thefeeding grounds. Furthermore, we examined progesterone levels of females to assign apregnancy status; providing to our knowledge, the first non-lethal estimation ofpregnancy rates in Antarctic whales. A series of female humpback whales of knownpregnancy status (n=29) from the Northwestern Atlantic, verified from field observations,were used as control samples to develop a logistic regression model, modelling theprobability of pregnancy relative to blubber progesterone concentrations. A pregnancystate was then assigned to females biopsied along the WAP by modelling theirprobability of being pregnant across the control model. Based on our assignment offemales as pregnant not-pregnant, mean progesterone levels for pregnant assignedhumpback whales from the WAP was 250 ng progesterone g blubber (n = 155). Themean value for not-pregnant assigned females was 2.10 ng progesterone g blubber (n =89). Pregnancy rates varied significantly across all years, from 36% in 2010 to 86% in2014.We detected a significant increase in the proportion of pregnant females (58% to72%) from summer to autumn across all years. Some female whales in this populationappear to experience a post-partum ovulation followed by conception (annualpregnancy); on average, more than half (52%) of female whales accompanied by calveswere pregnant. These are some of the first quantitative observations of the demographyof recovering humpback whale populations in the Antarctic and provides a criticalreference point as the Antarctic climate continues to change and populations recover fromwhaling.
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