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Homeward Bound

You might imagine that in the vast expanses of the deep blue, that sharks wander here there and everywhere. In fact, sharks are very specific about where they live, and their habitats are so specific that many species even return to the same spots again and again, year after year. So which species of sharks are capable of homing? Where do they go? And why do they do it?


Leopard sharks return to La Jolla, California in their hundreds every year (Image Credit: National Marine Sanctuaries / WikimediaCommons)

There and Back Again

The phenomenon of leaving and then returning to the same specific location over several years is known as "philopatry" and sharks are some of the most prodigious of all animals to do this. It is not universakl, but philopatry is practiced by sharks in every single extant taxonomic order and scientists think that the majority of sharks do it (Heuter et al, 2005).

Blacktip sharks are philopatric (Image Credit: Dray van Beeck / Shutterstock)

Even after moving hundreds of miles away for months or even years, sharks are capable of coming back to the exact same spot later on with pin-point accuracy. For example, blacknose sharks (Carcharhinus acronotus) return to the same bays every year and scientists have found that they are often resighted within a matter of miles from where they were found the year before (Heuter et al, 2005).


Blacktip sharks (Carcharhinus limbatus) have been found returning to the exact location where scientists fitted them with tracking tags the year before, despite the tagging data showing they had travelled some 300 miles offshore in the mean time (Chapman et al, 2015).


Blacknose sharks are philopatric to specific bays, where they return year after year (Image Credit: D Ross Robertson / WikimediaCommons)

Let's Eat!

Sharks are philopatric to specific locations because those habitats are critical either for feeding or breeding (or both). Those blacknose sharks we talked about earlier hone in on those spots specifically because it's where they all get together to feed and mate (Heuter et al, 2005; Chapman et al, 2015).


Many sharks come back to the same place in order to target seasonally abundant prey. For instance, whale sharks (Rhincodon typus) come back to the same spots to feed on seasonal zooplankton blooms. Tiger sharks (Galeocerdo cuvier) hit the same albatross islets and great whites (Carcharodon carcharias) come back to the same seal rookeries annually because they can target naive or vulnerable young animals during the breeding seasons (Chapman et al, 2015).


Caribbean reef sharks (Carcharhinus perezi) return to the same reefs in The Bahamas annually. During the summer they return back to feed with such accuracy that they are often resighted within 2 km of where scientists fitted their tags the year before (Brooks et al, 2013).

They can only be found off the southern coast of Australia, but Port Jackson sharks are still philopatric within their relatively contracted range (Image Credit: Jimmy Walsh / Shutterstock)

Let's Get Together

Evidence that sharks return to the same site to mate is relatively few and far between, but this might simply be because it is rare to witness sharks mating. We do know that nurse sharks (Ginglymostoma cirratum) practice "mating site fidelity"; with inidviduals coming back to the same lagoon in Florida to mate each summer Chapman et al, 2015).


It is however, it is quite common for "gravid" (aka pregnant) sharks to return back to the same site to give birth repeatedly. Female blacktip reef sharks (Carcharhinus melanopterus) will travel 50 km away from their home range in Moorea Island to go to the same "parturition site" to give birth to their pups over and over again (Chapman et al, 2015).


Female Lemon Sharks (Negaprion brevirostris) practice "natal philopatry", where they return back to the site of their own birth to give birth to their pups. They have even been reported coming back to the same parturition site every year to give birth for almost two decades. They are so specific about this that females will actively choose to return to either the north or south island in Bimini, despite them both being suitable parturition sites located only 10km apart (Feldheim et al, 2014).


Female blacktip reef sharks return to the same parturition site repeatedly, even if other suitable habitats are nearby (Image Credit: Igor Kruglikov / Shutterstock)

There and Back Again

Scientists think that philopatry is so common in sharks because it is beneficial to them; either ensuring successful feeding or breeding, or both. Returning back to the same foraging sites every year is a good tactic because it allows sharks to exploit seasonally abundant prey (Heuter, 1998; Chapman et al, 2015).


Despite mixing with sharks from many other areas normally, female scalloped hammerheads will return to the site of their own birth to give birth to their pups (Image Credit: Seawatch.org / WikimediaCommons)

Going back to the same parturition site, where a female has successfully given birth before, ensures she can be safe during this vulnerable time. Similarly, reusing the same nursery habitats again and again ensures that her young have the best chance of survival she can give them. This is especially important for sharks, as they do not stick around to give their pups any care as they grow to adulthood. To learn more check out Cuban Root.


Scientists think that female sharks return to the site of their own birth site for the same reason - if they did ok there, then it must be a good place. In fact, some female sharks will even return to their natal site over several years when they are not even old enough to breed. It seems they practice the journey so they don't forget where to go when they are ready to have pups of their own (Chapman et al, 2015).


There is some evidence that sharks can form mental maps to find their way. Experts suspect they may use be able to use the stars or underwater landmarks, like canyons and seamounts to navigate. There is even evidence that some species can use geomagnetism to orient themselves. To learn more check out Animal Magnetism. But noone knows how they manage to find their way so perfectly, without a parent or family member to teach them. It may be some mysterious innate behaviour that is somehow, inexplicably built into their very DNA. Incredible!


Female lemon sharks return to the nursery habitat they were born in to give birth to their own pups (Image Credit: Sophie Hart / Shutterstock)


References

Brooks EJ, Sims DW, Danylchuk AJ & Sloman KA (2013). Seasonal abundance, philopatry and demographic structure of Caribbean reef shark (Carcharhinus perezi) assemblages in the north-east Exuma Sound, The Bahamas. Marine Biology, 160. Access online.


Chapman DD, Feldheim KA, Papastamatiou YP & Hueter RE (2015). There and back again: a review of residency and return migrations in sharks, with implications for population structure and management. Annual review of marine science, 7. Access online.


Feldheim KA, Gruber SH, DiBattista JD, Babcock EA, Kessel ST, Hendry AP, Pikitch EK, Ashley MV & Chapman DD (2014). Two decades of genetic profiling yields first evidence of natal philopatry and long‐term fidelity to parturition sites in sharks. Molecular Ecology, 23:1). Access online.


Jorgensen SJ, Reeb CA, Chapple TK, Anderson S, Perle C, Van Sommeran SR, Fritz-Cope C, ACBrown, Klimley AP & Block, B. A. (2010). Philopatry and migration of Pacific white sharks. Proceedings of the Royal Society B: Biological Sciences, 277:1682. Access online.


Hueter RE (1998). Philopatry, natal homing and localised stock depletion in sharks. Shark News, 12. Access online.


Hueter RE, Heupel MR, Heist EJ & Keeney DB. (2005). Evidence of philopatry in sharks and implications for the management of shark fisheries. Journal of northwest atlantic fishery Science, 35:1. Access online.


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