Behavioural polymorphism in one of the world's largest populations ...
Behavioural polymorphism in one of the world's largest populations ...
Behavioural polymorphism in one of the world's largest populations ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
202<br />
Mar Ecol Prog Ser 418: 201–212, 2010<br />
Meylan 1995, Limpus & Limpus 2001). However, <strong>the</strong><br />
adoption <strong>of</strong> satellite telemetry <strong>in</strong> recent decades has<br />
revealed a wealth <strong>of</strong> hi<strong>the</strong>rto unobta<strong>in</strong>able <strong>in</strong>sights<br />
(Godley et al. 2008). Researchers are now able to<br />
accurately and remotely track <strong>in</strong>dividual turtles over<br />
many hundreds <strong>of</strong> kilometres for many months and <strong>in</strong><br />
some cases multiple years (Broderick et al. 2007).<br />
Although sample sizes are <strong>of</strong>ten constra<strong>in</strong>ed, f<strong>in</strong>d<strong>in</strong>gs<br />
are almost <strong>in</strong>stant and spatial <strong>in</strong>formation <strong>of</strong>ten surpasses<br />
that result<strong>in</strong>g from flipper tagg<strong>in</strong>g <strong>of</strong> hundreds<br />
or thousands <strong>of</strong> turtles over a number <strong>of</strong> years (e.g.<br />
Godley et al. 2003a, Troeng et al. 2005, and compare<br />
Margaritoulis et al. 2003 with Zb<strong>in</strong>den et al. 2008).<br />
Movement data have facilitated <strong>the</strong> question<strong>in</strong>g <strong>of</strong><br />
exist<strong>in</strong>g management methods (Zb<strong>in</strong>den et al. 2007,<br />
Witt et al. 2008, Sch<strong>of</strong>ield et al. 2009) and suggestion <strong>of</strong><br />
new <strong>one</strong>s (Shaver & Rubio 2008, Shill<strong>in</strong>ger et al. 2008).<br />
Of <strong>the</strong> sea turtles, <strong>the</strong> loggerhead turtle Caretta<br />
caretta is <strong>the</strong> species for which <strong>the</strong> spatial ecology has<br />
been best elaborated. For example, neonate turtles<br />
from <strong>the</strong> NW Atlantic rookeries spend <strong>the</strong>ir first years<br />
<strong>in</strong> <strong>the</strong> open oceanic realm (Wi<strong>the</strong>r<strong>in</strong>gton 2002), mov<strong>in</strong>g<br />
with<strong>in</strong> <strong>the</strong> North Atlantic Gyre (Bolten et al. 1998,<br />
Bolten 2003) before return<strong>in</strong>g to <strong>the</strong> neritic coastal<br />
z<strong>one</strong> to complete <strong>the</strong>ir maturation (Bolten 2003,<br />
Schroeder et al. 2003). Once adult, <strong>the</strong> turtles undertake<br />
regular migrations between nest<strong>in</strong>g grounds and<br />
forag<strong>in</strong>g areas, which may or may not<br />
<strong>in</strong>volve oceanic periods (Plotk<strong>in</strong> & Spotila<br />
2002, Hawkes et al. 2007). Evidence is<br />
accumulat<strong>in</strong>g that this life-history pattern<br />
is not so rigidly adhered to, <strong>in</strong> that<br />
ontogenetic shifts between oceanic and<br />
neritic developmental habitats may be<br />
reversible (Kamezaki & Matsui 1997,<br />
Bolten 2003, McClellan & Read 2007,<br />
McClellan et al. 2010) and that variation<br />
exists <strong>in</strong> behaviour dur<strong>in</strong>g both <strong>in</strong>ternest<strong>in</strong>g<br />
and <strong>in</strong>tranest<strong>in</strong>g periods (Blumenthal<br />
et al. 2006, Hawkes et al. 2006, see also<br />
Sem<strong>in</strong><strong>of</strong>f et al. 2008 and Hatase et al.<br />
2006 for green turtles Chelonia mydas).<br />
The loggerhead population at Masirah<br />
Island, <strong>of</strong>f <strong>the</strong> coast <strong>of</strong> <strong>the</strong> Sultanate <strong>of</strong><br />
Oman, was first researched <strong>in</strong> <strong>the</strong> 1970s<br />
and was determ<strong>in</strong>ed to be <strong>one</strong> <strong>of</strong> <strong>the</strong><br />
<strong>largest</strong> nest<strong>in</strong>g aggregations <strong>in</strong> <strong>the</strong><br />
world, compris<strong>in</strong>g several tens <strong>of</strong> thousands<br />
<strong>of</strong> <strong>in</strong>dividual turtles nest<strong>in</strong>g annually<br />
(Ross & Barwani 1995). In <strong>the</strong> ensu<strong>in</strong>g<br />
decades, flipper tagg<strong>in</strong>g has been<br />
undertaken to some extent and nest<strong>in</strong>g<br />
beach surveys generated a more recent<br />
update on <strong>the</strong> population at 20 000 to<br />
40 000 turtles nest<strong>in</strong>g annually (Baldw<strong>in</strong><br />
et al. 2003). However, certa<strong>in</strong> key facts relevant for<br />
conservation management—<strong>in</strong>ternest<strong>in</strong>g habitat, reproductive<br />
output and details <strong>of</strong> post nest<strong>in</strong>g migrations —<br />
are lack<strong>in</strong>g.<br />
In <strong>the</strong> present study we sought to ga<strong>in</strong> <strong>in</strong>sights <strong>in</strong>to<br />
<strong>the</strong> spatial ecology <strong>of</strong> this population by equipp<strong>in</strong>g<br />
nest<strong>in</strong>g turtles with satellite transmitters. We deliberately<br />
deployed near <strong>the</strong> beg<strong>in</strong>n<strong>in</strong>g <strong>of</strong> <strong>the</strong> breed<strong>in</strong>g season<br />
to facilitate <strong>in</strong>sights <strong>in</strong>to movements dur<strong>in</strong>g <strong>the</strong>ir<br />
breed<strong>in</strong>g season and post-nest<strong>in</strong>g migration.<br />
MATERIALS AND METHODS<br />
Adult female turtles (turtles A to J; see Table 1) were<br />
located on <strong>the</strong> nest<strong>in</strong>g beaches <strong>of</strong> Masirah Island<br />
(20.62° N 58.91° E, n = 8; 20.49° N 58.94° E, n = 2;<br />
Fig. 1). After completion <strong>of</strong> nest<strong>in</strong>g and egg cover<strong>in</strong>g,<br />
turtles were equipped with Kiwisat 101 platform transmitter<br />
term<strong>in</strong>al (PTT) satellite tags (Sirtrack). All<br />
deployments were undertaken between 11 and 16<br />
May 2006, which was early <strong>in</strong> <strong>the</strong> nest<strong>in</strong>g season,<br />
shown <strong>in</strong> Ross & Barwani (1995) as start<strong>in</strong>g <strong>in</strong> April.<br />
The precise level <strong>of</strong> nest<strong>in</strong>g occurr<strong>in</strong>g prior to tag<br />
deployment was not available for <strong>the</strong> current season.<br />
Previous data (Ross 1979) suggest that approximately<br />
26% <strong>of</strong> <strong>the</strong> study <strong>in</strong>dividuals would have nested<br />
Fig. 1. Study region for Caretta caretta. Q <strong>in</strong>dicates tagged turtle orig<strong>in</strong><br />
(Masirah Island). <strong>in</strong>dicate <strong>the</strong> end locations <strong>of</strong> turtles tracked <strong>in</strong> <strong>the</strong> present<br />
study. <strong>in</strong>dicate f<strong>in</strong>al locations <strong>of</strong> a fur<strong>the</strong>r 10 transmitters placed on<br />
loggerheads at Masirah, August 2006 (B. E. Wi<strong>the</strong>r<strong>in</strong>gton & E. Possardt pers.<br />
comm.). Circles <strong>in</strong>dicate <strong>the</strong> locations <strong>of</strong> long-distance tag recoveries published<br />
prior to <strong>the</strong> present study; no <strong>in</strong>dication <strong>of</strong> numbers given (Baldw<strong>in</strong> et al. 2003)