Sharks visit personal hygienists
16 March 2011, by Marion O'Sullivan
Sharks are very fussy about their personal hygiene and health, so they pay regular visits to marine 'cleaning stations' to rid themselves of parasites or have injuries dealt with, a new study reveals.
Pelagic thresher shark.
For the first time, thresher sharks have been observed venturing into shallower waters around tropical reefs or seamounts near the Philippines, to be groomed by small fish known as cleaner wrasse. It's well-documented behaviour for some fish species, but this is the first time it has been studied in a large predator.
When the sharks arrive at the reef they slow down to less than a metre per second and begin swimming in a circular pattern above a particular area, where they 'pose' to become more attractive to the cleaner wrasse.
'On the reef there are fixed stations, or focal points, where cleaner wrasse can be found,' Simon Oliver from Bangor University explains. 'These fish are very selective about which clients they service so we think that the sharks recognise the focal points where their particular cleaners operate. '
'The cleaning stations are a bit like a surgery,' says Oliver. 'The sharks come in with cuts and scrapes where they might have scabs and these are treated by the cleaner wrasse, which remove dead tissue from the wound area and any parasites from the skin. These stations are quite critical to the health of reef communities.'
'What makes it interesting for us is that no-one has studied the interaction between the cleaners and these big predators before,' adds Oliver. 'These large sharks often travel very long distances to visit with specific cleaners, in a similar way that people might visit their family doctor.'
The sharks keep circling for up to 45 minutes, depending on how many injuries or parasites need to be dealt with.
The researchers have observed the sharks for five years and now have a solid dataset that can be used to inform offshore industry, science and conservation policy.
The main drawback of entering these shallower waters for the sharks is that they are more likely to encounter people. They may be caught by fishermen, killed by dynamite fishing along the reefs, or their fins and skin damaged by hooks.
The reefs suffer damage too, both from the dynamite and from tourist divers who sit on the flat areas to watch the sharks, which are not normally a danger to people. Unlike other shark species, thresher sharks hunt with their long tails, rather than their mouths.
'On a typical day you might see around 60 people on the reef, waiting for the animals to come in, so there's little understanding of this critical habitat,' says Oliver.
On the other hand, the income generated by the tourist diving industry generates a lot of revenue for the local area and helps to conserve the region.
Citation: Oliver SP, Hussey NE, Turner JR, Beckett AJ (2011) Oceanic Sharks Clean at Coastal Seamount. PLoS ONE 6(3): e14755. doi:10.1371/journal.pone.0014755.
Simon Oliver is a PhD student at Bangor University's School of Ocean Sciences, and founded the Thresher Shark Research and Conservation Project.
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