A recent stranding of a basking shark (Cetorhinus maximus) in north-western Bali is the first confirmed record of this large, filter-feeding shark species in Indonesian waters.

The shark was an adult male. It is possible that the Indonesian throughflow – the warm ocean current which moves water from the Pacific to the Indian Ocean – is an important route for basking sharks during their migrations.

Once thought of as a strictly cool-water species, basking sharks move to tropical seas each winter. While commonly sighted in surface waters in northern Europe and America during summer and autumn months, they disappear during winter. An article in 1954 even suggested that they hibernate on the ocean floor during this time.

Basking shark in European waters by Tim Nicholson
Basking shark in European waters (Isle of Man) by Tim Nicholson

More recently satellite tagging showed that basking sharks instead migrate through tropical waters, travelling at depths of 200 to 1,000 meters and unseen by humans.

The basking shark is the second largest shark after the whale shark (Rhincodon typus). It can grow up to 11 metres long and weigh up to 7 tonnes. It feeds by filtering plankton through its gills whilst swimming with its huge mouth open.

Basking shark
Basking shark and snorkellers by Chris Gotschalk

Further Reading
Marine Biodiversity Records / Volume 8 / 2015DOI: http://dx.doi.org/10.1017/S1755267214001365, Published online: 28 January 2015

Transequatorial Migrations by Basking Sharks in the Western Atlantic Ocean. Skomal, Gregory B.; Zeeman, Stephen I.; Chisholm, John H.; Summers, Erin L.; Walsh, Harvey J.; McMahon, Kelton W.; Thorrold, Simon R.
doi:10.1016/j.cub.2009.04.019

Images: Green Fire Productions CC by 2.0, Tim Nicholson, Chris Gotschalk

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