Blue Shark
(Prionace glauca)
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Given Names
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French
: Requin bleu; Peau-bleue
German : Blauhai
Spanish : Tintorera; Arlequi; Tiburon azul
Italian : Verdesca; Verdun; Musiedde; Virdiscu
Other Scientific Names : N/A |
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Diagnosis
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| An unmistakable,
gracefully-proportioned, slender-bodied shark with a long snout and no interdorsal
ridge. Eyes large; pectoral fins long and rather slim, with curved
apexes; 1st dorsal fin rather small and with a curved apex, situated well
behind the pectoral fins with its midpoint nearer to the pelvic fin origins.
Low keels present on caudal peduncle; anal fin posterior margin is deeply
notched. Papillose gill-rakers present and are unique amongst carcharhinids.
Upper jaw teeth noticeably obliquely curved and triangular with serrated
margins. Colour dorsally vivid cobalt blue, shading to metallic mid-blue
on the flanks and white ventrally. |
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Size
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| To about
380cm but commonly from 50 to 250cm in the region; size at birth 35 to
44 cm. |
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Distribution
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| Océan
Atlantique : Common and cosmopolitan south of Lat. 50N (i.e, from S.W.
England and S. Ireland southwards). Northerly limit to range is Icelandic
and North Norwegian coasts, where these sharks may stray as sporadic outliers
during particularly warm summers.
Mer Méditerranée : Common; entire Mediterranean,
including Adriatic and Sea of Marmara but not Black Sea.
Océan Indien : Common
Océan Pacifique : Common
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Biology
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| Typically
an offshore, pelagic species from the surface down to at least 150m; highly
nomadic, undertaking journeys between and across the great ocean basins,
including inter-equatorial movements. Occupies sea-temperatures of
7 to 16C, sometimes up to 25C and may swim in the deeper, isothermal Southern
Mediterranean waters during the high summer. Blue sharks also make inshore
incursions, particularly at night; juveniles may also inhabit waters less
than 50m deep, such as off Portugal and within Northern Adriatic waters (both
areas are nursery-zonse for this species) during the summer months. This
species also occurs nearshore off Mediterranean islands adjacent to deep
water (e.g., Isola Ponza and Aeolian Islands in the Tyrrhenian Sea).
Blue sharks are graceful, efficient slow cruisers, typically averaging 0.8km/h
groundspeed over their long-distance meandering; often seen near the surface
but capable of deep, gliding dives (using their long pectoral fins for minimum
effort in controlling descent) in search of deep-ranging or vertically-migrating
prey such as squid. They will often congregate in great numbers at
food-sources (for example, floating whale carcasses) but generally are rather
solitary. Commonly observed to follow ships in Mediterranean waters, quite
possibly for great distances (the writer was told of two blue sharks that
diligently followed a ship non-stop from Cyprus to Malta, feeding voraciously
on discarded kitchen garbage, only then to be hooked and killed by the crew!).
Geographical sexual segregation is common in these sharks; the majority
of specimens taken off Great Britain being females whilst off Long Island,
New York, male sharks predominate. Litter sizes are large, up
to 135 pups but highly variable; gestation period 9-12 months; maturing
5-year old females can store sperm in their shell glands and defer
fertilization until in their 6th year; young are born to females of 7 years,
with neonatal specimens common in Mediterranean waters from late May
to July. Limited tagging returns from an ongoing north Adriatic study
co-ordinated by Dr. Irene Bianchi and Big Game Italia (pers. comm.) suggests
movement of neonates from the Po Delta region to both the Eastern and Western-Central
Mediterranean, but no recaptures are yet known from Atlantic waters.
It is possible that these sharks only exit the Mediterranean when nearing
adulthood, but further tag-return data will confirm or nullify this thesis.
Females mature at about 221cm; males between 182 and 281cm TL. |
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Feeding
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| Typical
prey includes scombroids such as mackerel, scad, bonito and bullet tuna;
clupeids includings herring and sardines; jacks, garfish (especially in
the Adriatic) and other pelagic schooling fish; occasionally demersal, benthic
or littoral fish prey (e.g., thick-lipped mullet, conger eels and flatfish);
pelagic flying-fish eggs (apparently a very common food-item in Adriatic
specimens); squid and cuttlefish (also important regional prey);
crustaceans; an occasional scavenger upon mammalian remains (dolphins, whales
and porpoises) and even consumes seabirds (a gull was recently found inside
an Adriatic specimen), although these may be attacked only post-mortem. |
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Similar Species
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| No similar
species. |
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Endangerment
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| Endangered.
Regularily caught in fisherie. |
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Danger to humans
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| Potentially
dangerous. |
This
page has been designed by Fadi Fakhoury
with the help of the Shark
Trust and its chairman Mr Ian Fergusson.
The Shark Trust
36 Kingfisher Court,Hambridge Road,
Newbury, Berkshire,RG14 5SJ, UK.
Tel(+44) 01635 551150
Fax(+44) 01635 550230
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