Scientists have solved a 50-year mystery as to where basking sharks (Cetorhinus maximus) in the Western Atlantic Ocean go during the winter months, publishing the results of their study in the latest issue of the journal Current Biology.
While commonly sighted in surface waters during summer and autumn months, the disappearance of basking sharks during winter has been a great source of debate ever since an article in 1954 suggested that they hibernate on the ocean floor during this time, said lead author Gregory Skomal. Skomal and coauthors have solved this mystery using satellite-based tagging technology.
The scientists tagged 25 sharks with pop-up satellite archival transmitting tags, of which 18 tags transmitted data for periods between 12"423 days.
Studying this data, the authors found that basking sharks migrate long distances during the winter, staying at depths of 200 to 1,000 metres in the tropical waters of the Atlantic Ocean.
This significantly broadens the geographic range of the basking shark, which was previously believed to be restricted to temperate waters.
This migration and the depth at which the sharks swim also explain why the location of basking sharks during the winter months have remained undetected for so long.
The authors conclude Our results have important conservation implications because tropical waters should no longer be considered a barrier to demographic or genetic connectivity among basking shark subpopulations. Global coordination of conservation efforts will therefore likely be necessary to rebuild basking shark populations throughout the species range.
For more information, see the paper: Skomal, GB, SI Zeeman, JH Chisholm, EL Summers, HJ Walsh, KW McMahon and SR Thorrold (2009) Transequatorial migrations by basking sharks in the Western Atlantic Ocean. Current Biology 19, pp. 1019"1022.