Page 2 - DNAfromhistorical

234 Endang Species Res 27: 233–241, 2015
INTRODUCTION
Life-history characteristics of elasmobranchs (long
life span, slow maturation, long gestation periods,
and low fecundity) make them highly vulnerable to
fishing pressure (Baum et al. 2003). Recent estimates
suggest that 25% of described sharks and rays are
threatened with extinction (according to IUCN Red
List criteria; Dulvy et al. 2014). This makes the devel- Mediterranean all had the same Pacific clade mito-
opment of responsible sustainable stock exploitation
and conservation strategies difficult (Dulvy & Forrest
2009), especially as only 8% of threatened shark and
ray species are currently protected (McClenachan et
al. 2012). Such difficulties may be exacerbated in
species known to exhibit some form of natal philopa-
try. Here widespread protection in conjunction with
local conservation efforts is required to preserve the
management unit (MU; Avise 1995), as defined by
connectivity sufficiently low that each population
should be monitored and managed separately. In
these instances, and where top predators or keystone
species are established from small founding propa-
gules, there is particular urgency to identify the tip-
ping point where anthropogenic pressures begin to
impact genetic diversity, and so the resilience of a
stock. Supporting this view, Spielman et al. (2004)
suggest there is significant erosion of genetic diver-
sity in advance of apparent demographic declines,
and a recent meta-analysis demonstrated a signifi-
cant effect of fishing pressure on genetic diversity
(Pinsky & Palumbi 2014). Hence, development of sus-
tainable management strategies may benefit from
incorporating longitudinal assessments of regional
fishing pressure and declines in genetic diversity
derived from a comparison of historical and contem-
porary material.
The great white shark Carcharodon carcharias
(Linnaeus, 1758) is an apex predator, capable of
long-distance migrations (Bonfil et al. 2005), display-
ing complex segregation by size and sex (Domier &
Nasby-Lucas 2013, Jewell et al. 2013, Kock et al.
2013), and natal philopatry (Pardini et al. 2001, Jor-
gensen et al. 2010). It is classified as ‘Vulnerable’ in (Vennemann et al. 2001) and no pulp cavity (filled
the IUCN Red List, and in 2004 was placed on CITES
Appendix II. Many populations have undergone dra-
matic declines (Baum et al. 2003), and first estimates
of white shark abundance in Californian waters
seemed to suggest substantially smaller numbers
than other large marine predators (Chapple et al.
2011), prompting urgent calls for protection. How-
ever, a recent study refuted this, indicating a greater
estimated population size in the eastern Pacific
(Burgess et al. 2014), while historic abundance trends
in the western North Atlantic suggest recovering
populations (Curtis et al. 2014). Nonetheless, genetic
analysis of Australian white shark populations sug-
gests estimates of contemporary effective population
sizes approach levels at which adaptive potential
may be lost (Blower et al. 2012). A similar concern
was expressed following the observation that several
contemporary white sharks sampled from across the
chondrial haplotype (Gubili et al. 2011). In Turkish
waters white sharks are considered extinct in the Sea
of Marmara, although contemporary records of neo-
nates in the northern Aegean Sea suggest nearby
breeding grounds (Kabasakal 2014). These conflict-
ing views and observations illustrate that the impact
of anthropogenic effects on connectivity, and conse-
quently genetic diversity and effective population
size, are probably complex and currently poorly
known for this species throughout most of its range.
Population genetic analysis has been useful for
shark management and conservation efforts (Dud-
geon et al. 2012). However, the veracity of population
and demographic parameters estimated from analysis
of DNA sequences depends to a large degree on sam-
pling a reasonable number of individuals. For exam-
ple, between-population migration estimates from
molecular data improve with large sample sizes (∼50
individuals) (Paetkau et al. 2004). Unfortunately, be-
cause white sharks are rare, large, and difficult to
sample in an unpredictable marine environment, tis-
sue for DNA analysis is difficult to obtain, hindering
application of molecular genetics to address some
conservation questions. Yet, in common with other
apex predators, the many trophy artifacts, as well as
jaws and teeth of white sharks, held in public and pri-
vate collections may permit retrospective population
genetic analysis, provided these dried specimens still
contain intact DNA fragments of sufficient size to be
reliably and routinely recovered and characterized.
Here we explore the potential of contemporary
white shark teeth, containing only osteodentine
with living connective tissue and odontoblasts), as a
source of DNA. While Ahonen & Stow (2008) suc-
cessfully extracted DNA from the pulp cavity of teeth
and jaws of several shark species from the Car-
charhinidae family, DNA recovery from dentine
presents some technical challenges, but has been
successful from mammal teeth (Pääbo 1989, Höss &
Pääbo 1993, Pfeiffer et al. 1998). Additionally, we
extended our investigations to skin and cartilage
recovered from trophy specimens collected from the
Mediterranean and Pacific Ocean.