Synchronous seasonal change in fin whale song in the North Pacific.

Fin whale (Balaenoptera physalus) song consists of down-swept pulses arranged into stereotypic sequences that can be characterized according to the interval between successive pulses. As in blue (B. musculus) and humpback whales (Megaptera novaeangliae), these song sequences may be geographically distinct and may correlate with population boundaries in some regions. We measured inter-pulse intervals of fin whale songs within year-round acoustic datasets collected between 2000 and 2006 in three regions of the eastern North Pacific: Southern California, the Bering Sea, and Hawaii. A distinctive song type that was recorded in all three regions is characterized by singlet and doublet inter-pulse intervals that increase seasonally, then annually reset to the same shorter intervals at the beginning of each season. This song type was recorded in the Bering Sea and off Southern California from September through May and off Hawaii from December through April, with the song interval generally synchronized across all monitoring locations. The broad geographic and seasonal occurrence of this particular fin whale song type may represent a single population broadly distributed throughout the eastern Pacific with no clear seasonal migratory pattern. Previous studies attempting to infer population structure of fin whales in the North Pacific using synchronous individual song samples have been unsuccessful, likely because they did not account for the seasonal lengthening in song intervals observed here

A tracer study of the Arctic Ocean's liquid freshwater export variability

We present an analysis of the variability of the liquid Arctic freshwater (FW) export, using a simulation from the Community Climate System Model Version 3 (CCSM3) that includes passive tracers for FW from different sources. It is shown that the FW exported through the western Canadian Arctic Archipelago (CAA) comes mainly from the Pacific and from North American runoff. The variability of the FW export from both of these sources is generally in phase, due to the strong influence of variations of the velocity anomaly on the CAA FW export variability. The velocity anomaly in the CAA is in turn mainly governed by variations in the large-scale atmospheric circulation (i.e., the Arctic Oscillation). In Fram Strait, the FW export is mainly composed of Eurasian runoff and FW of Pacific origin. The variability of the Fram Strait FW export is governed both by changes in the velocity and in the FW concentration, and the variability of the FW concentration from the two largest sources is not in phase. The Eurasian runoff export through Fram Strait depends strongly on the release of FW from the Eurasian shelf, which occurs during years with an anticyclonic circulation anomaly (negative Vorticity index) and takes 3 years to reach Fram Strait after leaving the shelf. In contrast, the variability of the Pacific FW export through Fram Strait is mainly controlled by changes in the Pacific FW storage in the Beaufort Gyre, with an increased export during years with a cyclonic circulation anomaly (positive Vorticity index)

Spectrograms of fin whale singlet and doublet song.

<p>The IPI (s) is shown below the pulses for each sequence. Panel A shows a song sequence with a single IPI recorded off Southern California in October 2002 and Panel B shows a song sequence with doublet IPIs from Hawaii in December 2002. Note that the timing of singlet IPIs is more variable than doublet IPIs. Spectrogram characteristics: 1-s FFT, 80% overlap. Occassionally the short IPI of the doublet pair is repeated between doublet sequences, most commonly off Southern California (not shown).</p

Acoustic data used for measurement of fin whale song and months with song present.

<p>Available data from each site are shown as bars by recording year. Years begin July 1 and end June 30 to encompass the continuous nature of fin whale singing throughout the winter season. Months with fin whale song heard during the days monitored at each site are indicated with an asterisk.</p

Median and 25% and 75% quartiles of fin whale interpulse intervals (IPI) by region.

<p>Panel A shows fin whale IPIs from the Bering Sea, panel B from Southern California, and panel C from Hawaii. Both the short and long IPIs within a doublet pair are shown for each month unless only one interval was measured within a given month and site. Across all three panels each singing year is designated by a different symbol and color: 2000-01 —blue circles, 2001-02 — yellow squares, 2002-03 — green diamonds, and 2005-06 — red triangles. Open symbols represent months when singlet IPIs were also detected and measured. Location and recording details in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115678#pone-0115678-t001" target="_blank">Table 1</a>.</p

Example examination of fin whale doublet song IPIs.

<p>All fin whale song IPIs recorded at Hawaii on February 19, 2001. Long (black) and short (gray) IPIs are shown as marked by the anlayst. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115678#pone-0115678-g002" target="_blank">Fig. 2</a> for timing and frequency differences between short and long IPIs in spectrogram form.</p

Relative occurrence of IPIs in December.

<p>Higher variability in song IPIs in December at some sites (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115678#pone-0115678-t002" target="_blank">Table 2</a>) is partially explained by the occurrence of two separate song types with IPIs offset by several seconds. Panel A shows IPIs for December 2001 in the Bering Sea, panel B for December 2001 off Southern California. This presentation of all IPIs measured on a single day illustrates that the song measured for the Bering Sea in December 2001 is composed of two different songs, one with relatively shorter short and long IPIs (labeled ‘short IPI 1’ and ‘long IPI 1’) and another with relatively longer IPIs (labeled ‘short IPI 2’ and ‘long IPI 2’). Whether these variations represent variability within a single singing whale or the presence of two or more whales singing different song on the same day cannot be assessed with the data we have available.</p