3 questions on1
HOW DO TURTLES MAKE
THEIR WAY HOME?
They have a magnetic memory! Baby
turtles paddling away from their hatching
place are unlikely to return for many years:
loggerheads, for example, can take over 30
years to reach maturity. In the meantime,
they wander the oceans in search of
food. The Earth’s magnetic field changes
relatively slowly and evidence shows that
byimprintingtheuniquegeomagnetic
signatureoftheirnatalbeach,
turtlescannavigateback
toit withremarkable
accuracy.2
HOW DO THEY PROTECT
THEIR NESTS?
Most turtles will dig chambers in the sand,
into which eggs are laid. To cope with a host
of predators and parasites, female turtles
lay several large clutches in separate nests,
but even so, their eggs and hatchlings are
incredibly vulnerable. New research led
by the University of Glasgow, focusing on
hawksbill and leatherback turtles, shows
that they have another trick up their
flippers. Before leaving a beach, the females
create extra pseudo-nests by scattering
sand widely. These decoy sites distract
would-be attackers and make it more
di cult to locate real nests.3
HOW DO HATCHLINGS
FINALLY EMERGE?
Using a small, pointed bumpontheirnose,
baby turtles start to piptheireggsafter
50–80 days, dependingontemperature.
Once hatched, they tunnelupwards.They
may be buried 1m deep,sodiggingout
can take over a week, withfrequentrests.
High temperatures as theyapproachthe
surface cause them to slow,makingit
more likely they will emergeatnightwhen
the risk from heat and predatorsis lower.
Usually several hatchlingsworktogether
as a team, so that each onereservessome
energy for the final dashtotheocean.
Laurie JacksonNesting turtles
How deep
can seals go?
MARINE BIOLOGY
T
he gold medal goes to a bull
southern elephant seal, recorded
at an incredible 2,388m. While this
is extreme, the species frequently
dives to depths of 400–800m, staying
under for 20–30 minutes. Motivated
by food, elephant seals plumb the
depths for squid and rays, often at
nutrient-rich boundary zones where
different oceanic waterbodies meet.
Since it takes time to get down,
hunt and resurface, these seals have
astounding breath-holding abilities –
up to two hours is known. They can
carry three times more oxygen in their
blood than humans, also storing it in
their tissues. So the precious oxygen
lasts even longer, the seals lower their
heart rate to slow the pace at which it
is used, and are able to tolerate very
low levels of blood oxygen at the end
of dives. Ellen HusainSouthern elephant seals
are the largest of all seal
species and will dive to
great depths in the
brutally cold Antarctic
waters they call home.BBC Wildlife 83Q&A