  Published: Wednesday, December 9, 2009 - 19:25 in Biology &
Nature  Related images (click to enlarge)  This is a blue whale
photographed off San Diego. Larry Wagner Jr./ISSI This is a
high-frequency acoustic recording package, or HARP, used to
record marine mammal sounds. Scripps Institution of
Oceanography, UC San Diego This is a blue whale photographed off
San Diego. Larry Wagner Jr./ISSI  The sound level of songs blue
whales sing across the vast expanses of the ocean to attract
potential mates has been steadily creeping downward for the past
few decades, and a scientist at Scripps Institution of
Oceanography at UC San Diego and his colleagues believe the
trend may be good news for the population of the endangered
marine mammal. Mark McDonald of WhaleAcoustics in Bellvue,
Colo., along with John Hildebrand of Scripps Oceanography and
Sarah Mesnick of NOAA Fisheries Southwest Fisheries Science
Center studied blue whale song data from around the world and
discovered a downward curve in the pitch, or frequenc