BBC Wildlife - UK 2020-07)

(Antfer) #1

Archive image: Roger Viollet/Getty; snorkelling & tag: Alex Mustard/2020VISION/NPL;


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fromtinyshrimp-likecreaturestojellyfish


  • alsoappearingreatquantitiestofeaston
    thisphytoplanktonbloom.Andthatinturn
    lurestheplanktivores– filter-feedingsharks,
    baleenwhales,turtlesandbonyfish(and
    theirpredators).
    Thismagicalsequenceofeventshappens
    innutrient-richwaters,andwearelucky
    thatScotlandhassomeoftherichest
    watersintheworld,thankstotheocean
    currents.Wefindaggregationsofbasking
    sharksin‘hotspots’aroundthewest
    coast,wherecurrentsdrawdense,cooler,
    nutrient-richwatertowardsthesurfacein
    a processknownasupwelling,andsupport
    planktonblooms.Someofthesehotspots
    areconcentratedaroundtheHebrides,
    particularlyCollandTiree,andformthe
    sitesforourexpeditions.
    Scientificstudieshaveprovidedfascinating
    insightsintothelifeofthebaskingshark.
    A teamofscientistsfromacrosstheworld

    • ledbytheUniversityofAberdeen– used
      genetictagstostudysharkmovements
      inUKwaters,andfoundevidencethat
      individualsreturntothesamesiteyearafter
      year– someevenatapproximatelythesame
      date.Furthermore,sharksrevisitingthe
      samesitesweremorerelatedthanexpected,
      suggestingbaskingsharkmigrations
      area littlelikeextendedfamilyhaving
      a reunionattheirfavouriterestaurant.
      Baskingsharksarehighlymigratory,with
      satellitetaggingandtelemetrydatashowing
      evidenceoftrans-Atlanticandeventrans-
      equatorialmovements,ofuptothousands
      ofkilometres.
      Sharkshavetravelledfromasfaras
      Newfoundland,theBayofBiscayandthe
      Azoresand,duringwinter,plungetodepths
      ofover1,000m.Whattheydoduringthis
      time,however,remainsa mystery.Giventhe
      offshorelocationsandinaccessibledepths
      towhichtheydescend,scientistscan,at




July 2020

Once tagged, the
shark’s movements
can be tracked.

CLASPERS
Sex can be identified by the
presence of claspers. Male
sharks have two claspers,
just beneath the anal fins.
It is believed they are used
in mating but this has never
been scientifically recorded.

LIVER
This is the largest organ in the
body and can be up to a third of
the shark’s bodyweight. Sharks
lack a swimbladder, so the large
liver serves this function. It
contains squalene oil, thought
to be used as an energy source
during long migrations, or times
of low plankton abundance.

SKIN
Like other sharks, the skin
consists of rows of hard,
interlaced scales, called
‘dermal denticles’. Very similar
to teeth, they are covered in
enamel and are very tough.
This design allows the shark to
be extremely hydrodynamic.

DORSALFIN
At up to1m,thisisa prettyimpressive
feature,butcanmakebaskingsharksan
attractiveprospectfortheshark-finning
industry.Oneofthelargestspecimens
was saidtohavefetched$50,000.

TEETH
Though they are filter feeders, basking sharks
do have tiny teeth. Unlike the impressive
gnashers of its great white cousin, basking
shark teeth are only 5-6mm long, placed in
rows on the upper and lower jaw.
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