78 Sharks: The Animal Answer Guide
how fast the host swims. A remora thus gets a free ride, covering distances
that alone it would never be able to traverse, placing it in the right area
when its host tears up prey. The remora then feeds on the scraps, as well as
an occasional small nearby fish.
The costs and benefits of this relationship are a matter of debate. The
shark may suffer a small energetic cost associated with the drag created by
having a small hitchhiker. Some rays appear to find an attached remora an-
noying, which may explain why Mantas and Spotted Eagle rays jump out
of the water. They could be trying to dislodge remoras when they land, but
a definitive study hasn’t been performed to test this idea. We do know that
some sharks such as Caribbean Reef Sharks and Blacktip Sharks chafe (rub)
their bodies against sand ripples to dislodge sharksuckers.
Recent findings also indicate that sharks and marlins may even ben-
efit from an attending remora. Remoras apparently undertake cleaning be-
havior: their stomachs contain copepod parasites from the gills and fins of
their hosts, making the relationship beneficial to both host and “parasite.”
Such a cleaning behavior relationship between an elasmobranch and an-
other fish is not restricted to remoras and their hosts. Manta rays that have
been bitten by sharks in Mozambique visit “cleaning stations” set up by
various reef fishes such as wrasses. The mantas then hover in the water and
let the cleaners pick over their wounds, removing dead tissue, attention
that presumably prevents infection.
Another fish is often found in association with stingrays. This is the
Cobia (Rachycentron canadum), a large bony fish (up to 68 kg, or 150 lb) that
follows rays and some sharks around, presumably to feed on fishes and in-
vertebrates flushed out of the sand or otherwise distracted by the foraging
ray or shark. (Bottlenose dolphins off western Australia also follow large
rays and steal prey such as octopus that the rays flush out of grass beds.)
Fishers looking for Cobia home in on large rays and cast lures near them
to catch the Cobia. Interestingly, Cobia are closely related to sharksuckers,
suggesting that the relationship between sharksucker and shark may have
first involved following behavior, which became more intimate as natural
selection favored individuals that could attach themselves to a shark rather
than having to expend energy staying close.
Sharks have benefited from associating with humans for probably as
long as people have gone to sea. Large sharks such as Tiger and Blue sharks
often followed sailing ships, feeding on scraps thrown overboard (not to
mention an occasional luckless sailor). Sharks also learn that fishing activi-
ties create easy meals. This behavior goes beyond sharks hearing fish fight-
ing on a fishing line, although anyone who has fished at sea, particularly in
tropical waters, has experienced the disappointment of fighting a tuna for
an extended period only to have the line go limp and find that only a head
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