Blue sharks in open water, © Peter Verhoog / Dutch Shark Society
Finding a meal in the vast emptiness of the open ocean is not easy. It is assumed that blue sharks (Prionace glauca) rely on hearing and scent tracking to detect large concentrations of potential prey. These sharks feed predominantly at night, and when closing in on a prey, they rely on their large eyes to detect the faint bioluminescence their prey produces. It could be, that electroreception plays a significant role in detecting prey at night.
Sonic telemetry studies have revealed that blue sharks can use a variert of hunting strategies with characteristic short-term movement patterns.
Research has shown that in California, from March to early June, blue sharks move inshore at night and offshore during the day. After midnight the sharks move into shallow waters to feed on small fish like anchovies. At dawn, the sharks return to open waters. In June to October, the sharks remain offshore to feed mainly on pelagic squids. From December through February the blues to move inshore at night again to feed on spawning squid. In these migrations, the sharks follow their prey. It was also observed, that sharks change depth during the night when searching for teir prey.
The blue shark is listed as Near Threatened in the IUCN Red List, but it is estimated that 10 to 20 million of these species are killed each year as a result of fishing. Recent research by Sebastián A. Lopez, Nicole L. Abarca1 and Roberto Meléndez of the Laboratorio de Biología Marina in Chile showed that the tissues of blue sharks in the Pacific contain high metal concentrations, that constitute a risk for human health, mainly from the high contributions of lead (read the full report here: http://www.dutchsharksociety.org/wp/wp-content/uploads/2013/04/Metal-concentrations_BLue-Sharks_TCS-2013_Vol_61_126-137_Lopez_et_al-1.pdf)
Read more:
Biological info about blue sharks on our species page:
http://www.dutchsharksociety.org/blue-shark/
IUCN Red List assessment:
http://www.iucnredlist.org/details/39381/0
Picture of tagging blue sharks can be found at the site of the Pelagic Shark Research Foundation – Monterrey Bay / Marine Canyon pelagic shark tagging project:
http://www.pelagic.org/research/BLU_methods.html
Tagging blue sharks, picture Sean van Sommeren, PSRF
