Spatial and temporal trends in fin whale vocalizations recorded in the NE Pacific Ocean between 2003-2013
(A) IPI for the singlet song, (B) frequency for the singlet song, (C) IPI for the doublet song, and (D) frequency for the doublet song. Results are colored by station (Axial, blue; KENE, purple; KEMF, orange), and note type is indicated by shape (Note type A, triangles; note type B, squares). Dashed lines show least-squares straight line fits to the data which are labelled with the slope when it is significantly different from zero. In (A) gray circles show the inter-note interval (i.e., sum of the IPI for the two doublet notes). X-axis year labels correspond to the start of the year and results for a calling season (November-March) are plotted at the start of January in that season (i.e., the point at 2010 corresponds to the 2009–2010 calling season).