Galapagos Matters Autumn Winter 2020 - Galapagos Conservation Trust

Darwin's Arch is where most of the whale sharks are tagged © Jonathan Green
The track from Hope's tag
© 2020 Google
Just north of Darwin (1), (see map above)
some 2000 metres beneath the surface, lies
the Galapagos Rift, an East-West tectonic
divide in the ocean floor between the Cocos
Plate to the north and the Nazca Plate to
the south. At this landmark, Hope turned
to the west like other whale sharks before
her, apparently tracking the Rift out into the
open Pacific.
Hope continued her westerly travels until
the last days of December, by which time
she’d carried her tag over 3000 km from
Darwin’s Arch. She looped back on herself
(5) and headed southeast down to the East
Pacific Rise, the fissure between the Pacific
Plate to the west and the Nazca Plate to the
east (6). Then, at the beginning of March
this year, she dived and swam due east,
resurfacing after some 500 km as if heading
back towards Galapagos (7). But instead
of making a single-loop migration as we
imagined, she made a dramatic U-turn
and swam west once more and in mid-May
she re-crossed her own track from several
months earlier (8).
Hope’s last transmission came at the end
of May (9). We do not know why we lost
touch at this point in her travels. It’s possible
that she dived down to 1800m or more, a
depth at which the extreme pressure would
have crushed the satellite tag. Alternatively,
and worryingly, she may have encountered
one of the many industrial
fishing fleets that make
this area one of the most
intensely fished regions of
the Pacific. After a month
of no news, the team
decided to check her last
transmission. The data
suggest that the tag was
fully out of the water and
that it was travelling much
faster than the maximum
speed of a whale shark.
We cannot say for certain
what happened to her and cannot be sure
that she was captured. However, in previous
years, two smaller female sharks we were
tracking both stopped transmitting in this
same patch of water.
Whatever has happened, Hope has made
history. She had covered, as the crow flies,
the greatest distance that any of our tagged
Galapagos whale sharks has travelled. She
will, of course, have moved even further
than this, as the satellite tag – which only
transmits at the surface – can tell us nothing
about the twists and turns she may have
taken when out of range in the cold depths.
Hope’s migration brings us closer to
understanding the many factors – submarine
geological features, water temperature, food
availability and the drive to reproduce – that
underlie the decisions these gentle giants
make as they navigate the ocean. This is key
to their conservation, as it is only with these
insights that we will know when and why
whale sharks are particularly vulnerable and
how we can protect them throughout their
incredible long-distance lives.
This project is part of our Endangered
Sharks of Galapagos Programme and
benefits from the support of the Prince
Albert II of Monaco Foundation
(www.fpa2.org).
Despite being the largest fish in the ocean, little
is known about whale sharks © Jonathan Green
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