Featured Species: Basking Shark (Cetorhinus maximus)

This week’s featured species is one of the three filter species of sharks: the Basking Shark (Cetorhinus maximus). The sole member of the family Cetorhinidae, the basking shark is the second largest shark species; second only to another filter species, the whale shark (Rhincodon typus) (Skomal, 2016). These incredible animals are often seen from late spring through fall on both sides of the Northern Atlantic Ocean, swimming near the surface with their mouths wide.

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Mottershead, K. (Photographer). (n.d.). Basking Shark [Digital Image]. Retrieved from http://www.uwphotographyguide.com/

The basking shark swims with its mouth wide feeding on planktonic animals (Parker, 2008). Unlike the whale shark, which displays a wide range of feeding behaviors, the basking shark is a ram-jet feeder, which means that they rely on their forward movement to force water into their mouths and over their gills in order to feed. Within their gills, they have highly developed gill rakers, which are actually modified placoid scales (or skin denticles), that can actually be seen from behind the basking shark’s head! The rakers are 2 to 3 inches long and are densely packed along the gill arches, about 10 to 12 per inch (Parker, 2008)! Basking sharks use their rakers to trap calanoid copepods. They have been observed giving themselves the occasional shake while feeding; it is thought that they are shaking loose these copepods from their rakers. The planktonic animals then travel from the rakers directly to the esophagus (Parker, 2008).

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Basking shark gill rakers [Digital Image] (2015). Retrieved from https://bigblueblogging.files.wordpress.com/

Basking sharks also display a range of behaviors that we have yet to be able to interrupt (Skomal, 2016). One of the most baffling behaviors is when several sharks swim in a circle, each following the other head to tail. This behavior is referred to as “cartwheeling” (Wilson, 2004). It has been postulated that this behavior may be involved with mating, however many observations of this behavior have taken place with only female sharks participants (Skomal, 2016). For now, this behavior remains one of the many mysteries of the basking shark!

Aerial view of cartwheeling Basking Sharks (Cetorhinus Maximus). Gulf of Maine, USA    (rr)
Valle, C. (Photographer). (n.d.). Aerial view of cartwheeling Basking Sharks (Cetorhinus Maximus). Gulf of Maine, USA [Digital Image]. Retrieved from https://www.robertharding.com/

Cartwheeling isn’t the only unusual behavior the basking shark has been known to perform. They have even been known to breach, raising their amazing body size completely out of the water (Sims, Southall, Quayle,  & Fox, 2000)!

Nat Geo WILD. (2015 September 21). Breaching Basking Sharks | World’s Weirdest [Video Clip]. Retrieved from https://www.youtube.com/

Shark Stats

Authority: Gunnerus, 1765

Family: Cetorhinidae; 1 species

Length: 5 – 6 ft (1.5 – 1.8 m) at birth; maximum of 32 ft  (9.8 m)

Weight: Average 2,200 lbs (998 kg); occasionally more than 11,000 lbs (4,990 kg)- more than 1/4 may be liver

Habitat: Continental and island shelves and slopes, coastal and oceanic waters

Depth: Generally less than 300 ft (92 m); during winter months moves into deeper waters up to 3,000 ft (1,006 m)

Reproduction: Ovoviviparous

Gestation: Unclear, thought to be 12 to 16 months

Litter Range: 6 pups (very few cases recorded)

Home Range: Worldwide in tropical to cool temperate waters seasonally

Diet: Exclusively planktonic animals: Calanoid copepods

IUCN Status: Official status is Vulnerable, however the basking shark is Endangered in Northeastern Atlantic and North Pacific Oceans

(Skomal, 2016; Parker, 2008; Fowler, 2005)

Executive Director at the Pelagic Shark Research Foundation, Sean R. van Sommeran, offered his thoughts on the plight of the basking shark upon reading this blog post and allowed me to share his words.

“Basking sharks are the most endangered species of shark in the entire Central Eastern Pacific; oddly enough, the basking shark is only listed as a ‘species of concern’ by US Fisheries officials and pay-rolled academics. Although clearly endangered there is a reticence via fisheries centric and invested agencies to deny that level of protection and recognition as the most endangered species of large shark in the entire Eastern pacific. The basking shark is very likely the most endangered large shark in the entire Pacific. The basking shark population is estimated to be fewer than 10% of their historic abundances off of Baja, US and Canadian Pacific Coast. The basking sharks were deliberately wiped out via overfishing and culling in US and Canadian pacific regions, Canada has deemed basking sharks as a full fledged endangered and fully protected and listed species; the US has denied it part in the extermination of basking sharks and currently still refuses to list basking sharks as an endangered and fully protected species, the endangered species listings would be in keeping with the basic fact of the matter being that basking sharks are the most endangered species of large shark in the entire Eastern Pacific, despite NOAA/NMFS relegating the basking shark to a ‘species of concern’.

“Note: the basking shark is NOT listed as an endangered species, or listed as a so called ‘species of special concern’, such a designation does not even exist, the actual listing via NOAA is a most basic ‘species of concern’.

“The concern appears to be that the story of the basking shark, its endangered species status and history of being eradicated and neglected may reach the public’s awareness and issue familiarity.

“Full Protected Status for Eastern Pacific Basking Sharks (all basking sharks) in US waters !!!!

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“…Its amazing how little discussion there is about the basking shark (Eastern Pacific in specific) conservation, the backstory and history and current status.

“The basking shark should be the poster species and banner species headlining conservation of sharks campaigning and public outreach etc. There is almost no discussion whatsoever regarding conservation and because the back story is so embarrassing to US Fisheries centric interests the topic is avoided at almost all costs.

“Typically the discussions orbit around how strange basking sharks are, sometimes about how ‘rare’ they are, but hardly ever is there any discussion, let alone disclosure regarding the basking sharks current situation (Pacific ocean and Easter Pacific in particular), i truly believe its due to conflict of interest (with fisheries) and because it would be a huge embarrassment to the NOAA/NMFS admins, bosses and interests.

“Canada has confessed and listed basking sharks as endangered and fully protected, whereas US interests and leadership at NOAA (think bluefin tuna and salmonids) resents efforts to highlight the history and context of basking shark endangered status and do their best to generalize about basking sharks and avoid the conservation aspects and endangered species status.

“They once were routinely counted in Monterey Bay in the many hundreds and even thousands, nowadays a gathering of 2-4 specimens is exceptional, rare and ‘strange’, but they officials in US don’t want to talk about endangered species listings and are literally pretending it’s A Okay, and that the species of concern listing is sufficient.

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To view our full conversation please visit  https://www.facebook.com/groups/sharkconservation/

I hope you enjoyed reading all about the basking shark in this week’s Featured Species. If you missed last week’s species, please be sure to check out the Leopard Shark (Triakis semifasicata). As always, your feedback and comments are welcomed! Let me know what species you’d like to learn more about!

The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!

Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.

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Featured Image Source

Skomal, G. (Photographer). (2011 June 28). Basking shark (Cetorhinus maximus) [Digital Image]. Retrieved from https://en.wikipedia.org/

Literature Cited

Fowler, S.L. (2005). Cetorhinus maximus. The IUCN Red List of Threatened Species 2005: e.T4292A10763893. http://dx.doi.org/10.2305/IUCN.UK.2005.RLTS.T4292A10763893.en

Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.

Sims, D. W., Southall, E. J., Quayle, V. A., & Fox, A. M. (2000). Annual social behaviour of basking sharks associated with coastal front areas. Proceedings of the Royal Society of London B: Biological Sciences267(1455), 1897-1904.

Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.

Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.

Wilson, S. G. (2004). Basking sharks (Cetorhinus maximus) schooling in the southern Gulf of Maine. Fisheries Oceanography13(4), 283-286.

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