On the Dispersal of Leatherback Turtle
Hatchlings from Meso -American Nesting
Beaches
George L. Shillinger 1 , Emanuele Di Lorenzo 2 , Hao Luo 2 , Steven J.
Bograd 3 , Elliott. L. Hazen 3 , Helen Bailey 4 , James R. Spotilla 5
1 C e nte r
for Oc ea n S olu t io ns , S t an fo rd Un i ve r sit y, 9 9 P ac if ic S tr eet , S uit e 1 55A ,
Mon te re y, CA 93 94 0
2 G eo rg i a In st it ut e o f T ec hno lo gy , S ch ool of E art h and At mos p h er ic S ci enc es , Atla nta ,
GA 30 33 2
3 NOAA S out h w est F is h er ie s S ci en ce Ce nte r , En v ir on me nt al R es ear ch D i vi s ion , 135 2
Li g ht hou se A ve nu e , P a cif ic G ro v e, CA 93 950
4 C he sa pe a ke Bi olo g ica l L a bor at or y , U n iv e rs i ty o f Mar yla nd C e nte r of En v ir on m ent al
S t ud i es , S olo mo ns Isla nd , MD 20 6 8 8
5 Dr ex el Un i ve rs it y, De pa rt me nt of B iol o gy , P h ilad el p h ia , P A 1 910 4
For submission to Biology Letters
ABSTRACT
return to the nesting beach is refered to as the
“Lost Years” (Carr et al., 1987). Although very
little information is available on these early life
1. INTRODUCTION
history stages, it is well known that hatchlings
Leatherback turtles (Dermochelys coriacea) in
face a gauntlet of predators on the beach and
the eastern Pacific Ocean have d eclined by up to
within shallow coastal waters and race to get
90% over the past t wo decades and are currently
offshore where decreased predation ri sk and
listed as critically endangered (Spot ila et al.,
increased
2000). These declines have been driven by a
survival potential [ ref??].
variety
of
anthropogenic
impacts,
including
development at nesting beaches, poaching of
eggs,
degradation
of
foraging
habitats,
and
fisheries bycatch (Santidrian Tomillo et
al.,
2008). Although conservat ion efforts at
the
largest
eastern Pacific
nesting
beach
(Playa
Grande, Costa Rica) have contributed to turtle
protection
and
recruitment,
mortality
rates
remain high (~22%; S antidrian Tomillo et al.,
2008), due largely to interactions of juvenile
and
adult
leatherbacks
wit h
artisanal
and
commercial fisheries (E ckert and Sarti, 1997;
Lewison et al., 2004; Donoso and Dutton, 2010).
There is an urgent need to develop integrated
management strategies to protect leatherback
turtles across all life stages.
resource
availability
maximize
The region offshore of the Pacific coast of
Mesoamerica
where
most
of
these
nesting
grounds are found is characterized by dynamic
ocean conditions.
coastal
Wintertime
mountain
gaps
winds through
contribute
to
the
development of large -scale anticyclonic edd ies
within the Gulfs of Tehauntepec and Papagayo
(Palacios and Bograd, 2005). These are intense
and stable features that can last for up to six
months and propagate more than 2000 km
offshore
from
the
continental
margin,
transporting nutrient -rich coastal waters and
organisms
into
the
ocean
interior.
There
signature appears as re -circulation regions (e.g.
Costa Rica Dome, Figure 1a) in long -term sea
level means derived from satellite [Niiler et al.,
The highest density of nesting colonies occur on
2003] and the path of the westward moving
beaches withi n the Parque Nacional Marine Las
eddies emerges a s regions of elevated sea level
Baulas
variance (Figure 1c).
51’W),
(PNMB),
Cost a
although
Rica
(10°
smaller
20’N,
colonies
85°
exist
throughout the region from Panama to central
Mexico (Reina et al., 2002). Leatherback turtles
at PNMB nest multiple times within a single
season
(generally
December -April)
at
approximately 8-10 day intervals (Steyermark et
al., 1996; Shillinger et al., 2010). Most tagging,
genetic,
and
mark -recapture
stud ies
have
focused on the internesting and post nesting
movements of nest ing adult females (S hil linger
et al., 2008, 2010, 2011). However, little is
known
about
the
early
life
history
of
In
this
study,
we
perform
passive
tracer
experiments within an eddy -resolving model of
the eastern tropical Pacific Ocean to investigate
leatherback
hatchling
dispersal
from
Meso -
American nesting beach es. In particular, we test
the
hypothesis
successful
that
nesting
the
colony,
largest
at
and
Playa
most
Grande,
Costa Rica, is the optimal location in the eastern
Pacific for nesting due to the efficient eddy
transport (Figure 1c) of hatchlings to offshore
waters where mortality risks are lower.
leatherbacks such t hat the period from hatching
to approximately ten years later when females
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L E ATHERB ACK D ISPERSAL M ANUSCRIPT DRAFT -8/04/2011
In order to gain more confidence on the model
2. METHODS
ability to capture realistic circulation features in
The modeling framework uses a global eddy resolving ocean mod el to provide t he boundary
conditions for a nest ed regional ocean model
that is used to compute the d ispersion statistics.
the central tropical Pacific ROMS nested domain
we performed comparative analysis with satellite
derived ocean currents [Niiler et al., 2003] and
ocean
sea
surface
height
(SSH)
anomalies
(http://www.aviso.oceanobs.com /).
These
physical-biological ocean
analyses reveal that ROMS is able to capture the
model is from t he Japanese Eart h Simulator
mean circulation as inferred from the SSH mean
(OFES) [see
(Figure 1b) with significant spatial correlation
The global coupled
detail descript ion in Masumoto et
al., 2004; Sasai et al., 2006]. With a 1/10°
(R>0.9).
horizontal resolut ion and 54 vertical levels, this
deviation in the SSH anomaly fields associated
OFES model is driven by the daily mean forc ing
with the eddy variability to confirm that the
of NCEP/NCAR reanalysis from 1950 to 2010
numerical model exhibits high variance along
[Kalnay et al., 1996]. In a comparison of the
the path of the strong eddies (Figure 1c and 1d).
OFES simulated fields with observations Sasai et
The spatial correlation of the eddy standard
al. [2007] show that the model is able to
deviation (R>0.7) maps is not has high as for the
reproduce with a high degree of accuracy the
mean
physical and biological dyna mics in t he central
significant and retains the important features
eastern tropical Pacific bet ween the equator and
evident in the satellite. These results combined
20N, which is the region where we explore the
with previous more in depth analyses of the
effects of ocean currents on t he transport of
OFES model (Sasai et al., 2007] provides us
hatchlings.
confidence that the modeling framework possess
The
regional
ocean
(ROMS )[Shchepet kin
and
mode ling
McWilliams,
system
2005;
We
als o
circulation
compared
but
is
the
still
standard
statistically
sufficient realism to conduct the passive tracer
dispersion experiment.
Haidvogel et al., 2008] is nest ed within the
T he ad ve cti on an d m i xi n g d is p ers io n s tat ist ics
OFES model to comput e the dispersion statistics
are d ia g nos ed by i n je cti ng a pas s iv e tra ce r in
of passive tracers released from selected turtle
sel ect ed co asta l r eg io ns o f t he mod el at t he
nesting beaches. The ROMS computational grid
locat io ns o f t he t urtl e n est i ng g rou nds . T he
is nested in the OFES model in the tropical
dyna m ics
eastern Pacific region [5S -20N; 110W-70W] with
im p le m ent ed
the exact same horizontal resolution as the
adv ect io n -d i ffu si on e q uati on w it h a de cay t e rm
OFES model and 30 vertical terrain -following
follo w in g t he a p pr oac h of C om b es et al . , 2 0 09:
of
t he
in
pas s iv e
t he
RO MS
tr ace rs
mod el
as
are
an
layers. The boundary and init ial conditions for
the ROMS model are provid ed directly from the
OFES simulation. This type of nested ocean
modeling approach has been used in previous
studies to successfully capture both the mean
w he re P i s t he p ass i ve tra ce r co nce nt rat i on ,
and long -term variability of t he regional scale
AH = 5 m 2/s i s t he ho ri zon tal d i ffu si v ity , AV
Pacific circulations
th e
[Chhak and Di Lorenzo,
ve rt ical
di ff us iv i ty
et
al,
1 99 4] ,
by
Q
a
a
K PP
2007; Di Lorenzo et al., 2008; 2009; Combes et
sch e me
al., 2007; 2009].
in de p end e nt so urc e t er m a nd τ is t h e d e cay
page 3 of 7
[L ar g e
o bta i ne d
ti me
t i me scal e . T he sou rc e t er m is us ed t o r el e ase
ex p er i me nts fo r a ll t h e y ea rs fr om 20 00 - 20 0 8
t h e pa ss i ve tr ace r at a d es ir ed loc at ion in s pa c e
we ar e a ble to co mp il e a nd c om p ar e d is p er s io n
and t i m e by s et t in g Q =1 . In t h i s st udy w e
stat ist ics for fou r s ele cted nes ti n g s ite s: Pl a ya
p erf or m ed r el eas e ex p er i me nt s for t he ye ars
Gr and e , Play a C arat e , B ara d el la Cru z a nd
20 00 - 20 0 8 w he n t ra ck in g d at a is av ai la bl e .
C haco ce nt e (F i gu re 3 -4 ), w h ic h w e d iscu ss in
T he
th e ne xt s ect io n .
t rac e r
is
co nt i nuou sly
re lea se d
( Q =1 )
d ur in g th e m ont hs o f J an /F e b/ Mar in e a ch
mod el ye ar . T h es e ar e t h e mo nt hs w h en t he
3. RESULTS
hat c hl i n gs l ea ve t h e b eac h . I n t he s u bs e qu ent
mo nt hs bet w ee n A pr il and D ec e m be r w e st op
The evolution of tracer distribution following
t h e t r ac er re le as e ( Q = 0) and e va luat e ho w t he
release
t rac er con ce ntr at ion i s d i s pe rs ed b y t he oc ea n
confirms
cir culat io n . I n ord er not t o accu m ulat e tra cer
coastal currents (Figure 3). Most the nesting
conc ent rat io n fr om p re v ious y ea r re le ase s we
sites that were tested with the release of tracer
use t h e t h e d ecay t e r m wi t h a t i me scal e τ of 8
show offshore dispersion of the tracer in the
mo nt hs .
p ro vi des
long-term mean (Figure 3). However, at Playa
in si g ht o n t he ea rly p ha ses of t h e t urt le’ s l if e
Grande (Figure 3c) and to some degree at Bara
and i nt era cti on wit h t h e e nv i ro nm en t -- it
de la Cruz (Figure 3a) and Playa Chacocente
t ak es bet w e e n 60 d a ys t o 6 mo nt hs for th e
(Figure
t urt l es to d e vel o p t he ir ful l s w i mm i ng a b il ity
concentration up to 1000 km in the offshore
so
be
waters (~95°W). In contrast, tracer released
cons id er ed as pa ss i ve t rac er s ad v ert ed b y th e
further south, at Playa Carate, demonstrates
ocea n cur re nts .
significant
T hi s
t hat
Fi gu re
ty p e
du r in g
2
s ho ws
of
this
an
s i mula t i on
p ha se
t h ey
ex am pl e
of
c an
t wo
tr ace r
rel ea se ex p er i m ent s f or t he P la ya Gr an de and
P laya Car ate n es t i n g s it e s d ur in g y ear 20 00 . It
is ev id e nt t hat in A pr i l, a b out o ne mo nt h a f ter
t h e la st hat ch li n gs l ea ve t he b ea ch s it e, th e
t rac er r ele as ed at P la ya Gra nd e (F i gur e 2a ) i s
ent ra in ed i n t h e ed d y pat h a nd i s ad v ec ted
offs h or e w h il e t h e t ra cer fro m t h e P la ya Car at e
re ma in s
cl os er
to
the
s ho re
a nd
is
pr ed o m i nan tly ad v ect e d alo ng t h e c oast . La r ge scal e edd i es l i ke t hos e o bse r ve d in t h e mo de l
out put for 20 00 w er e ob se rv ed i n a ll y ea rs f or
w hi ch
20 0 8) .
e xp e ri m ent s
T h is
is
we re
pe rfo r med
co ns ist ent
w it h
( 20 00 sat ell ite
ob se rv at ion s (Pa lac io s and Bo g rad , 2 00 5) . T he
offs h or e edd y tra ns p ort fr om P l aya Gra n de ,
and coa stal r ete nt io n fr om P la ya Ca rat e , w ill
b e s h ow n t o b e p er si st ent c ha ract er ist ic s o f t he
re g ion .
By
p e rfo rm i ng
t h es e
t rac er
re le ase
from
the
3b)
surrounding
dispersion
each
impact
there
retention
the
of
the
of eddy
is
in
beach.
statistics
nesting
transport
significant
the
The
between
beaches
coastal
tracer
waters
difference
the
and
in
selected
nesting sites is more apparent if we look at the
tracer mean distribution in the month of June,
about 3 month after the hatchling leave the
beach and begin developing swimming ability
(Figure 4). We find that in the first few month
following the release the evolution of passive
tracer distribution, and presumabl y hatchling
turtles, is markedly different. Playa Grande, and
to some extent Playa Chacocente, exhibits the
highest tracer density in the offshore water
(Figure 4c).
Results from these dispersion statistics (Figure
4) corroborate the hypothesis that hatch lings
from
Playa
Grande
are
more
likely
to
be
entrained and transported offshore by the large scale eddies during the early month followin g
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L E ATHERB ACK D ISPERSAL M ANUSCRIPT DRAFT -8/04/2011
the nesting. This efficient removal
mechanism
vulnerable and were the most at risk from
from the coastal waters where predation is
fisheries bycatch (Heppell et al., 2000; Lewison
higher should reduce the m ortality risks of the
et al., 2004). Because leatherbacks spend 10
hatchlings.
years or more at sea before returning to the
Although
these
beaches
are
separated by only 120(?) km,
nesting
beach,
these
years
are
potentially
critical for population viability. Models such as
those
4. DISCUSSION & CONCLUSIONS
employed
important
here
offshore
can
transport
identify
corridors
other
that
Passive tracer experiments embedded within a
could be buffered from human impacts to ensure
ROMS model of the eastern tropical Pacific
leatherback survival. Validation of these models
demonstrate significant offshore eddy transport
will
in late winter from P laya Grande, Costa Rica.
leatherback turtles across multiple years and life
This is in contrast with other beaches to the
stages.
south
and
north
where
t here
is
significant
coastal retention. These model results support
the idea that hatchling leatherbacks ent ering the
ocean in late winter at Playa Grande can be
rapidly
and
efficient ly
transported
offshore
within Papagayo eddies. Because turtles face
increased predation risk near the beach, quick
offshore
transport
is
likely
to
increase
the
probability of survival. Moreover, these eddies
provide a relatively productive refuge within
which young turtles can develop during their
first few months.
We
hypothesize
that
Playa
Grande
was
evolutionarily selected as an optimal nesting site
due to enhanced hatchling survival probability
from offshore eddy transport . A corrolary to this
hypothesis is that red uced early life mortality
leads to increased ret urn of adult females, who
show high site fidelity to nesting beaches. Thus,
the relatively large leatherback population at
Playa Grande compared to other eastern Pacific
beaches may be the result of enhanced survival
during early life stages.
Understanding the fate of leat herback turtle
hatchlings is critical t o prot ect the population.
Research on the life history of loggerhead turtles
identified that juven ile life stages were the most
page 5 of 7
require
new
technologies
to
track
Niiler et al. Dynamically balanced absolute sea
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links
The
Modelling
L E ATHERB ACK D ISPERSAL M ANUSCRIPT DRAFT -8/04/2011
Shillinger et al., 2011
Spotila et al., 2000
Steyermark et al., 1996
page 7 of 7