Estimating the mortality rate of humpback whale calves in the central North Pacific

• Main Authors: Christine M. Gabriele, Janice M. Straley, Sally A. Mizroch, C. Scott Baker, Alison S. Craig, Louis M. Herman, Debbie Glockner-ferrari, Mark J. Ferrari, Salvatore Cerchio, Olga Von Ziegesar, Jim Darling, Dan Mcsweeney, Terrance J. Quinn Ii, Jeff K. Jacobsen
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2001
• Subjects: Pacific; Humpback Whale; Megaptera novaeangliae; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.516.8440; http://www.dolphin-institute.org/our_research/pdf/Gabriele_2001CalfMortality.pdf

Abstract: Sighting histories of individually identified female humpback whales (Megaptera novaeangliae) in their win-ter and summer ranges were used to investigate mortality of North Pacific humpback whale calves. We compiled re-cords collected between 1979 and 1995 by eight independent research groups, which yielded 29 cases where 25 different mothers sighted in Hawai ¢ i were identified later the same year in Alaska. In 7 of 29 cases, a calf sighted with its mother in Hawai ¢ i was missing from its mother’s Alaska sighting(s). After investigating many factors, we deter-mined that the largest potential bias would occur in late-autumn observations, when calf absences might indicate wean-ing or temporary mother–calf separation rather than calf mortality. Our minimal and most robust estimate excluded all mortalities and survivals based on sightings of the mother after October 31; 3 of 20 cases or 0.150 (95 % confidence intervals (CI) = 0.032, 0.378). The maximal calf mortality rate, derived from all the available data, was 7 of 29 cases or 0.241 (95 % CI = 0.103, 0.434). An intermediate estimate that excluded all cases based on single Alaska sightings and omitted late-season sightings (2 of 11 cases or 0.182; 95 % CI = 0.023, 0.518) is perhaps closest to the actual first-year mortality rate for humpback whale calves, although it is compromised by its small sample size. Our results dem-onstrate both the value and the limitations of using longitudinal data to determine the life-history parameters that are essential for documenting the recovery of endangered populations. 600 Résumé: L’observation suivie de Baleines à bosse (Megaptera novaeangliae) femelles identifiées individuellement dans leurs aires d’hiver et d’été a permis d’étudier la mortalité des petits dans la population du Pacifique Nord. Nous avons compilé des données obtenues de 1979 à 1995 par huit groupes indépendants de chercheurs et l’opération a révélé 29 cas où 25 mères différentes aperçues dans les eaux hawaïennes ont été observées de nouveau en ...