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Cafe Society

In recent years, shark scientists have been becoming increasingly curious about a mysterious site, far offshore in the Pacific Ocean that they have nicknamed the White Shark Cafe... Every June and July, great white sharks (Carcharodon carcharias) undertake an enormous migration, away from the prey-rich coastal regions, thousands of kilometers off the coast, to spend several months aggregated at this obscure location in the middle of nowhere. So why do they do this? What is out there? And what could posisbly be worth all that effort?


The magnificent great white shark (Image Source: www.blogs.mathworks.com)

The White Shark Cafe is a roughly circular area of 785,000 km2, with a diameter of approximately 1000 km. Great whites migrate to the White Shark Cafe every year; departing from their coastal areas between January and February, and swimming at least 119 km per day, across open ocean, until they reach this specific site in the middle of the Pacific Ocean. They can stay there for anywhere between 3 and 15 months, before heading back home (Weng et al, 2007, Jorgensen et al, 2009, Jorgensen et al, 2012b, Domeier & Nasby-Lucas, 2013).


Location of the White Shark Cafe based on satellite tag data [shown as coloured tracks] (Jorgensen et al, 2012a)

Because white sharks migrate to the White Shark Cafe from both Guadalupe Island (off the coast of Mexico) and from the Farallon Islands (off the California coast), the site has also been called the Shared Offshore Foraging Area or SOFA. The Farallons white sharks commence their travels to the Cafe earlier than those from Mexico and these individuals also stay in the Cafe longer than those from Guadalupe. Yet, both groups always arrive back in their respective coastal homes around the same time and no sharks go back to the wrong place; a Guadalupe shark always goes back to Mexico and a Farallon shark back to the USA (this is known as “philopatry” or "site fidelity") (Weng et al, 2007, Jorgensen et al, 2009, Jorgensen et al, 2012b, Domeier & Nasby-Lucas, 2013).


Tags show individual white sharks return to the exact same location after visiting the SOFA (Jorgensen et al, 2009)

As they often swim near to the surface on their travels to the White Shark Cafe, it is thought great whites might use the position of the sun and stars for navigation. But, as white shark parents do not care for their young at all - they are literally born and left to fend for themselves - no one knows how they learn when and how to migrate to the Cafe or how they find their way back home with such incredible accuracy. How do they do it!?... It's a wonderful mystery! (Weng et al, 2007, Domeier & Nasby-Lucas, 2008).


Generally speaking, animals undergo large-scale migrations for one of two reasons: foraging or reproduction. So scientists think that the area is likely used for feeding or finding a mate… like a cafe or bar, hence the name (see, scientists can have a sense of humour!) (Weng et al, 2007, Domeier & Nasby-Lucas, 2008, Jorgensen et al, 2012a, Domeier & Nasby-Lucas, 2013).


Mating injuries seen on shark in the White Shark Cafe (Jorgensen et al, 2012b)

In the past, it was thought that the White Shark Cafe might be used by white sharks for mating and/or giving birth to their young (known as “parturition”). Females in the Cafe were repeatedly seen with distinctive rakes and bites in their skin, which often occur during rather rough shark mating sessions. Whatsmore, sharks which have been traced through tagging have shown patterns of repeated, rapid oscillatory diving when in the Cafe, which scientists thought might be a "courtship behaviour", used for attracting a mate (Jorgensen et al, 2012a & Weng et al, 2007).


However, white sharks are dispersed over a very wide area in the White Shark Cafe, rarely coming close to each other. There is also "sexual segregation" whilst there are there. The boys hang out in a smaller the core region whilst the girls swim over a wider range (over an area as large as 3,383,105 km2) around the edge. Also, mature and immature sharks both go to the White Shark Cafe. Taken together, this all suggests that maybe mating does not take place in the White Shark Cafe (Domeier & Nasby-Lucas, 2008, Jorgensen et al, 2012a, Domeier & Nasby-Lucas, 2013).


Tags show females [colours] occupy a larger area [big yellow circle] than males [small white circle] in the SOFA (Domeier & Nasby-Lucas, 2013

Similarly, very young sharks (known as "neonates") have never been seen in the White Shark Cafe, so it seems unlikely that females use the offshore area for giving birth (Domeier & Nasby-Lucas, 2008, Domeier & Nasby-Lucas, 2013).


So scientists now wonder if the White Shark Cafe might be used for foraging instead. At first this seems unlikely because the area is actually relatively unproductive, with few food resources. However, the rapid oscillatory diving patterns (which were thought to be for courting a mate) might actually be hunting dives. These dives can reach whopping depths of 980 metres! This tells scientists these dives might be to find food, like squid, swordfish and even other shark species that live in deep waters (Weng et al, 2007, Jorgensen et al, 2012a, Domeier & Nasby-Lucas, 2013).


White sharks make rapid oscillatory dives in the White Shark Cafe (Jorgensen et al, 2012a)

As males and females have different metabolic requirements (females require larger amounts of energy to grow to a larger size than the males), this might also explain the sexual segregation in the White Shark Cafe. Maybe the different sexes are choosing subtley different habitats based on differences in prey availability out there (Domeier & Nasby-Lucas, 2013).


As white sharks returning to Guadalupe Island and the Farallons are not noticeably thin, it seems unlikely that they are starving when they are out in the Cafe. Whatsmore, electronic tagging has shown that white sharks do not deviate off course or pause to take a road-side snack stop whilst migrating to and from the area. This suggests they are not hungry because they had plenty to eat out there. So it does seem very likely that the White Shark Cafe is indeed used for foraging (Weng et al, 2007, Domeier & Nasby-Lucas, 2013).


We have only just begun to understand how and why white sharks visit the White Shark Cafe and we still have many questions about it… Several research groups are working on learning more as you are reading this. But it is the mystery that I personally love! As scientists we ask questions and search for answers, but the truth is that we may never know everything about these wonderful animals and this obscure environment… and there is something inspiring and romantic about that... Maybe some of the mysteries of the deep will stay just that… fascinating mysteries!




References

Domeier ML & Nasby-Lucas N (2008). Migration patterns of white sharks Carcharodon carcharias tagged at Guadalupe Island, Mexico, and identification of an eastern Pacific shared offshore foraging area. Marine Ecology Progress Series, 370, 221-237.


Domeier ML & Nasby-Lucas N (2013). Two-year migration of adult female white sharks (Carcharodon carcharias) reveals widely separated nursery areas and conservation concerns. Animal Biotelemetry, 1. DOI: 10.1186/2050-3385-1-2.


Jorgensen SJ, Reeb CA, Chapple TK, Anderson S, Perle C, Van Sommeran4 SR, Fritz-Cope C, Brown AC, Klimley AP & Block BA (2009). Philopatry and migration of Pacific

white sharks. Proceedings of the Royal Society B, 1682:277, 679-688. Access online.


Jorgensen SJ, Arnoldi NS, Estess EE, Chapple TK, Rückert M, Anderson SD & Block BA (2012a). Eating or meeting? Cluster analysis reveals intricacies of white shark (Carcharodon carcharias) migration and offshore behaviour. PLoS One, 7: e47819. Access online.


Jorgensen SJ, Chapple TK, Anderson S, Hoyos M, Reeb C & Block BA (2012b). Connectivity among white shark coastal aggregation areas in the northeastern Pacific. In : Domeier, M. (Ed.). Global Perspectives on the Biology and Life History of the Great White Shark, Taylor & Francis, New York, p. 159-167.


Weng KC, Boustany AM, Pyle P, Anderson SD, Brown A & Block BA (2007). Migration and habitat of white sharks (Carcharodon carcharias) in the eastern Pacific ocean. Marine Biology, 152:4, 877-894.


By Sophie A. Maycock for SharkSpeak.

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