@article {53357,
	title = {Long-Term and Seasonal Changes of Large Whale Call Frequency in the Southern Indian Ocean},
	journal = {Journal of Geophysical Research: Oceans},
	year = {2018},
	month = {Mar-11-2020},
	abstract = {<p>In the past decades, in the context of a changing ocean submitted to an increasing human activity, a progressive decrease in the frequencies (pitch) of blue whale vocalizations has been observed worldwide. Its causes, of natural or anthropogenic nature, are still unclear. Based on 7 years of continuous acoustic recordings at widespread sites in the southern Indian Ocean, we show that this observation stands for five populations of large whales. The frequency of selected units of vocalizations of fin, Antarctic, and pygmy blue whales has steadily decreased at a rate of a few tenths of hertz per year since 2002. In addition to this interannual frequency decrease, blue whale vocalizations display seasonal frequency shifts. We show that these intra-annual shifts correlate with seasonal changes in the ambient noise near their call frequency. This ambient noise level, in turn, shows a strong correlation with the seasonal presence of icebergs, which are one of the main sources of oceanic noise in the Southern Hemisphere. Although cause-and-effect relationships are difficult to ascertain, wide-ranging changes in the acoustic environment seem to have a strong impact on the vocal behavior of large baleen whales. Seasonal frequency shifts may be due to short-term changes in the ambient noise, and the interannual frequency decline to long-term changes in the acoustic properties of the ocean and/or in postwhaling changes in whale abundances.</p>
},
	doi = {10.1029/2018JC014352},
	url = {http://doi.wiley.com/10.1029/2018JC014352},
	author = {Leroy, Emmanuelle C. and Royer, Jean-Yves and Bonnel, Julien and Samaran, Flore}
}
@article {53103,
	title = {On the reliability of acoustic annotations and automatic detections of Antarctic blue whale calls under different acoustic conditions},
	journal = {The Journal of the Acoustical Society of America},
	volume = {144},
	year = {2018},
	month = {Jan-08-2018},
	pages = {740 - 754},
	abstract = {<p>Evaluation of the performance of computer-based algorithms to automatically detect mammalian vocalizations often relies on comparisons between detector outputs and a reference data set, generally obtained by manual annotation of acoustic recordings. To explore the reproducibility of these annotations, inter- and intra-analyst variability in manually annotated Antarctic blue whale (ABW) Z-calls are investigated by two analysts in acoustic data from two ocean basins representing different scenarios in terms of call abundance and background noise. Manual annotations exhibit strong inter- and intra-analyst variability, with less than 50\% agreement between analysts. This variability is mainly caused by the difficulty of reliably and reproducibly distinguishing single calls in an ABW chorus made of overlaying distant calls. Furthermore, the performance of two automated detectors, based on spectrogram correlation or subspace-detection strategy, is evaluated by comparing detector output to a \&ldquo;conservative\&rdquo; manually annotated reference data set, which comprises only analysts\&$\#$39; matching events. This study highlights the need for a standardized approach for human annotations and automatic detections, including a quantitative description of their performance, to improve the comparability of acoustic data, which is particularly relevant in the context of collaborative approaches in collecting and analyzing large passive acoustic data sets.</p>
},
	issn = {0001-4966},
	doi = {10.1121/1.5049803},
	url = {http://asa.scitation.org/doi/10.1121/1.5049803},
	author = {Leroy, Emmanuelle C. and Thomisch, Karolin and Royer, Jean-Yves and Boebel, Olaf and Van Opzeeland, Ilse}
}
