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
- ledbytheUniversityofAberdeen– used
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.