BBC Wildlife - UK 2020-07)

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

annotat

on:

Ian

Co

eman/NPL

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.