Barlow J.,Southwest Fisheries Science Center |
Calambokidis J.,Cascadia Research Collective |
Falcone E.A.,Southwest Fisheries Science Center |
Falcone E.A.,Cascadia Research Collective |
And 17 more authors.
Marine Mammal Science | Year: 2011
We estimated the abundance of humpback whales in the North Pacific by capture-recapture methods using over 18,000 fluke identification photographs collected in 2004-2006. Our best estimate of abundance was 21,808 (CV = 0.04). We estimated the biases in this value using a simulation model. Births and deaths, which violate the assumption of a closed population, resulted in a bias of +5.2%, exclusion of calves in samples resulted in a bias of -10.5%, failure to achieve random geographic sampling resulted in a bias of -0.4%, and missed matches resulted in a bias of +9.3%. Known sex-biased sampling favoring males in breeding areas did not add significant bias if both sexes are proportionately sampled in the feeding areas. Our best estimate of abundance was 21,063 after accounting for a net bias of +3.5%. This estimate is likely to be lower than the true abundance due to two additional sources of bias: individual heterogeneity in the probability of being sampled (unquantified) and the likely existence of an unknown and unsampled breeding area (-8.7%). Results confirm that the overall humpback whale population in the North Pacific has continued to increase and is now greater than some prior estimates of prewhaling abundance. © 2011 by the Society for Marine Mammalogy Published 2011. This article is a US Government work and is in the public domain in the USA.
Baker C.S.,Oregon State University |
Steel D.,Oregon State University |
Calambokidis J.,Cascadia Research Collective |
Falcone E.,Cascadia Research Collective |
And 15 more authors.
Marine Ecology Progress Series | Year: 2013
ABSTRACT: We quantified the relative influence of maternal fidelity to feeding grounds and natal fidelity to breeding grounds on the population structure of humpback whales Megaptera novae - angliae based on an ocean-wide survey of mitochondrial (mt) DNA diversity in the North Pacific. For 2193 biopsy samples collected from whales in 10 feeding regions and 8 breeding regions during the winter and summer of 2004 to 2006, we first used microsatellite genotyping (average, 9.5 loci) to identify replicate samples. From sequences of the mtDNA control region (500 bp) we identified 28 unique haplotypes from 30 variable sites. Haplotype frequencies differed markedly among feeding regions (overall FST = 0.121, FST = 0.178, p > 0.0001), supporting previous evidence of strong maternal fidelity. Haplotype frequencies also differed markedly among breeding regions (overall FST = 0.093, FST = 0.106, p > 0.0001), providing evidence of strong natal fidelity. Although sex-biased dispersal was not evident, differentiation of microsatellite allele frequencies was weak compared to differentiation of mtDNA haplotypes, suggesting male-biased gene flow. Feeding and breeding regions showed significant differences in haplotype frequencies, even for regions known to be strongly connected by patterns of individual migration. Thus, the influence of migratory fidelity seems to operate somewhat independently on feeding and breeding grounds over an evolutionary time scale. This results in a complex population structure and the potential to define multiple units to conserve in either seasonal habitat.© Inter-Research 2013. www.int-res.com.
Hoekman S.T.,University of Alaska Fairbanks |
Moynahan B.J.,National Park Service |
Lindberg M.S.,University of Alaska Fairbanks |
Sharman L.C.,Glacier Bay National Park |
Johnson W.F.,National Park Service
Marine Ornithology | Year: 2011
We assessed boat-based line transect sampling for monitoring population status and trend of the Kittlitz's Murrelet Brachyramphus brevirostris in Glacier Bay National Park and Preserve, Alaska. We used field experiments to compare efficiency of one versus two observers and to test the assumption that detection near the transect center line was 100%. Because coexisting Kittlitz's Murrelets and Marbled Murrelets B. marmoratus cannot always be distinguished on sight, we developed analytic methods to account for unidentified murrelets in density estimates. Relative to one observer, two observers had 56% higher encounter rates, a >20% higher probability of species identification, and better met the criteria for robust estimation of detection probability. More encounters also increase precision of estimated detection probability and group size. We estimated detection probability near the transect center line to be 0.94 (SE 0.03) and considered methods to relax the assumption of complete detection near the transect center line when estimating density. Relative to methods that exclude unidentified birds (53% of observations), analytic methods incorporating unidentified murrelets increased density estimates for both Kittlitz's and Marbled murrelets by >100% and reduced coefficients of variation by 9% and 15%, respectively. Failure to account for unidentified murrelets and for incomplete detection near the transect center line creates substantial and variable bias and error in density estimates, lessening the ability to assess population status and trend. We recommend the use of two observers, periodic calibration of detection near the transect center line and its incorporation into density estimates, and the use of skilled observers coupled with analytic methods to account for unidentified murrelets.
Chenoweth E.M.,Glacier Bay National Park |
Gabriele C.M.,Glacier Bay National Park |
Hill D.F.,Oregon State University
Marine Ecology Progress Series | Year: 2011
In order to design marine protected areas that are ecologically meaningful, it would be useful to improve our understanding of headland wake foraging systems, which are commonly exploited by baleen whales and other mobile marine predators. We used humpback whale Megaptera novaeangliae sighting data from 1997 to 2008 in combination with tidal prediction software to investigate the effects of current direction (ebb vs. flood) and tidal amplitude on the distribution and abundance of humpback whales around 3 headlands and 5 non-headlands in Glacier Bay and Icy Strait in southeastern Alaska, USA. Headlands were defined as points of land that disrupt tidal flow creating distinct tideward and leeward conditions. We used an advanced tidal circulation model (ADCIRC) to identify these conditions. Current direction and tidal amplitude each significantly affected whale distribution at only one non-headland (χ 2 = 6.1, p < 0.01; χ 2 = 13, p = 0.002, respectively). At all 3 headlands, current direction significantly affected whale distribution (p < 0.0001). Whale abundance was greater in the leeward areas. Tidal amplitude significantly affected distribution at the 3 headlands (χ 2 = 97, p < 0.0001; χ 2 = 75, p < 0.0001; χ 2 = 6.1, p = 0.05) such that whales selected habitat that moderated, rather than maximized, the effect of tidal amplitude, suggesting that headlands also have the potential to be important features in areas with less extreme tidal exchange. © Inter-Research 2011.