ArticlePDF Available

Genetic Network and Breeding Patterns of a Sicklefin Lemon Shark (Negaprion acutidens) Population in the Society Islands, French Polynesia

PLOS
PLOS One
Authors:

Abstract and Figures

Human pressures have put many top predator populations at risk of extinction. Recent years have seen alarming declines in sharks worldwide, while their resilience remains poorly understood. Studying the ecology of small populations of marine predators is a priority to better understand their ability to withstand anthropogenic and environmental stressors. In the present study, we monitored a naturally small island population of 40 adult sicklefin lemon sharks in Moorea, French Polynesia over 5 years. We reconstructed the genetic relationships among individuals and determined the population's mating system. The genetic network illustrates that all individuals, except one, are interconnected at least through one first order genetic relationship. While this species developed a clear inbreeding avoidance strategy involving dispersal and migration, the small population size, low number of breeders, and the fragmented environment characterizing these tropical islands, limits its complete effectiveness.
Content may be subject to copyright.
Genetic Network and Breeding Patterns of a Sicklefin
Lemon Shark (Negaprion acutidens) Population in the
Society Islands, French Polynesia
Johann Mourier
1*
, Nicolas Buray
1
, Jennifer K. Schultz
2
, Eric Clua
3,4
, Serge Planes
1
1 LabEx «CORAIL» - USR 3278 CNRS-EPHE, Centre de Recherche Insulaire et Observatoire de l’Environnement (CRIOBE), Papetoai, Moorea, French
Polynesia, 2 National Marine Fisheries Service, Silver Spring, Maryland, United States of America, 3 Délégation Régionale à la Recherche et Technologie,
Haut-commissariat de la République française, Papeete, Tahiti, Polynésie Française, 4 Ministère de l’Agriculture et de la Pêche, Paris, France
Abstract
Human pressures have put many top predator populations at risk of extinction. Recent years have seen alarming
declines in sharks worldwide, while their resilience remains poorly understood. Studying the ecology of small
populations of marine predators is a priority to better understand their ability to withstand anthropogenic and
environmental stressors. In the present study, we monitored a naturally small island population of 40 adult sicklefin
lemon sharks in Moorea, French Polynesia over 5 years. We reconstructed the genetic relationships among
individuals and determined the population’s mating system. The genetic network illustrates that all individuals, except
one, are interconnected at least through one first order genetic relationship. While this species developed a clear
inbreeding avoidance strategy involving dispersal and migration, the small population size, low number of breeders,
and the fragmented environment characterizing these tropical islands, limits its complete effectiveness.
Citation: Mourier J, Buray N, Schultz JK, Clua E, Planes S (2013) Genetic Network and Breeding Patterns of a Sicklefin Lemon Shark (Negaprion
acutidens) Population in the Society Islands, French Polynesia. PLoS ONE 8(8): e73899. doi:10.1371/journal.pone.0073899
Editor: Gabriele Sorci, CNRS, Université de Bourgogne, France
Received April 10, 2013; Accepted July 23, 2013; Published August 13, 2013
Copyright: © 2013 Mourier et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study benefited from the financial support of the Direction à l’Environnement (DIREN) of French Polynesia and the scientific support of
Coordination Unit of the Coral Reef Initiatives for the Pacific (CRISP Programme), based in New Caledonia. The funders had no role in study design, data
collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: johann.mourier@gmail.com
Introduction
Human population growth has fragmented the range of many
species [1], leading to significant declines in abundance, loss of
genetic diversity and an elevated risk of extinction [2,3]. Such
patterns are mainly reported from terrestrial systems [4], but
marine systems are now showing similar trends [5]. Isolation
and reduction in population size erode evolutionary potential
and raise the risk of extinction through inbreeding depression,
leading to the loss of genetic variation or the accumulation of
deleterious alleles [3,6]. To this end, many species have
developed inbreeding avoidance strategies [7], although some
animal populations naturally show low genetic variability [8,9].
Globally, sharks are threatened by overfishing [10–12]. While
these threats are evident for pelagic species [13] as by-catch of
commercial fisheries, populations of reef-associated species
are also declining [11,14]. Sharks appear to be particularly
vulnerable to over-exploitation because of their K-selected life-
history strategy (i.e., slow growth, late sexual maturity, long life
spans and low fecundity). As a result, overfished populations
may require several decades to recover [10,11,15]. Chronic
overfishing of sharks has diminished population sizes,
fragmented large populations into small, locally-isolated ones
[14], and led to trophic cascades [16]. Despite these rapid
declines, little is known about their ability to persist in smaller,
more fragmented populations and to recover from human-
induced bottlenecks [17]. In addition, there is a lack of
information about the fine-scale population genetic structure
and breeding patterns of most reef shark species (but see
18–21). As top predators, sharks frequently exhibit small
population sizes and are therefore a good model to investigate
the interactions between demographic parameters, genetic
population structure, mating system and levels of inbreeding in
natural small marine populations, especially in isolated insular
systems.
For 5 years, we monitored a small sicklefin lemon shark
(Negaprion acutidens) population around Moorea, French
Polynesia [22]. This species is a large (≤ 340 cm total length)
coastal shark that occurs in the Indo-Pacific region [23]. The
species is now listed as globally vulnerable on the IUCN
Redlist. It is a viviparous shark giving birth every second year
on average, between August and October, to 1-13 well-
PLOS ONE | www.plosone.org
1 August 2013 | Volume 8 | Issue 8 | e73899
developed pups after a 10-11 month gestation period [23]. The
small population of Moorea [22] has not experienced a high
level of exploitation, as sharks are not of commercial interest or
traditionally fished locally, and sharks in French Polynesia have
been formally protected by law since 2006. Low densities may
therefore be a result of natural ecosystem equilibrium in an
isolated, fragmented, insular system and/or due to some recent
natural bottleneck [24]. Meanwhile this species supports part of
the diving industry in French Polynesia with special feeding
dives organised [22,25].
The aim of this study was to describe genetic relatedness
and assign parentage based on microsatellite DNA markers in
order to investigate the genetic makeup and mating output
within a small isolated shark population. Previous parentage
analyses of sharks were mostly based on the reconstruction of
parental genotypes from sampled offspring and, when possible,
included few opportunistic sampled adults in the analysis
[18–20]. The present approach differs since it combines a 5-
years monitoring of the population in Moorea together with a
genetic analysis of relationships among individuals within and
between generations.
Methods
Ethics Statement
All necessary permits were obtained for the described field
study from the French Polynesia Ministry of Research to the
authors. No specific permission was required for underwater
surveys as they were conducted at a commercial diving site
and only involved photo-identification surveys (see below).
Every shark species is protected under French Polynesian
laws, however, DNA samples were taken by non-invasive
methods approved and conducted under the French Polynesia
Ministry of Research permitting authority (Permit #
653/MRM/SPE/DEV), and no lethal sampling was conducted.
Juvenile sharks were captured with gillnets and released in the
water alive under good conditions and adults were remotely
sampled with a modified speargun with a biopsy tip.
Study background and tissue collection
Our study was conducted in French Polynesia, a fragmented
system of small islands and atolls separated by deep ocean
(depth 2 000 m), which is expected to increase the effective
isolation of reef-associated populations [26]. We monitored a
population of sicklefin lemon sharks (Negaprion acutidens)
visiting a recreational diving site during a 5-year period in
Moorea (17° S, 149° W; Figure S1). Diving surveys were
implemented on a daily basis representing 1058 days between
January 2005 and September 2009 [22]. Based on photo-
identification [27], we consistently identified 40 mature sharks
(18 males and 22 females ranging from 2.4 to 3.1 meters total
length), with an average of 26.75 ± 3.33 individuals sighted per
year (24 in 2005, 28 in 2006, 31 in 2007, 29 in 2008 and 24 in
2009). When possible, a fin clip was removed from the dorsal
fin of each new shark using a modified spear gun. As a result,
29 out of 40 individuals (72.5%) were sampled. All 11 non-
sampled sharks were observed only once or very few times
and disappeared before sampling. Additionally, 4 resident
females were sampled in Bora Bora (230 km from Moorea)
where only 12 females (but no males) have been observed.
From this survey, all sharks were classified into behavioural
groups based on the affinity between sharks and their fidelity to
the site [22] and were assigned to three categories:
Resident sharks of Moorea: composed of 7 males (M03,
M04, M05, M07, M10, M18 and M31) and 7 females (F08, F11,
F15, F20, F23, F25 and F29);
Non-resident sharks visiting Moorea occasionally:
composed of 6 males (M09, M12, M19, M34, M36 and M38)
and 9 females (F01, F02, F06, F13, F17, F21, F26, F27 and
F30);
Bora-Bora resident sharks: composed of 4 females only
sighted in Bora Bora (B1, B2, B3 and B4).
In addition to adults on Moorea and Bora-Bora sites we also
captured 52 newborn and immature sharks from different
cohorts between 2006 and 2009 in Moorea and three
neighbouring islands: Tetiaora (40 km), Tahaa (200 km) and
Rangiroa (330 km) (Figure S1). Annual sampling of juveniles
took place soon after pupping by adult females (between
December and February). Most newborn sharks (or age-0)
could be identified based on the presence of an open (or
recently closed) umbilical scar that closes few months after
birth. The age of sharks without umbilical scars was
determined based on body length, whose distribution is
generally non-overlapping between age-0, age-1 and age-2
(85<age-1<100 cm TL, 100<age-1<115 cm TL and
115<age-1<130 cm TL, respectively, as determined based on
ongoing growth calculations from capture-recapture data). This
was also confirmed with recapture of individuals in two
consecutive years. Sharks that were larger than 130 cm TL
were assigned to an unknown year of birth (‘other’). Tissues
were stored in 95% ethanol.
Underwater observations of reproductive status
During our underwater photo-identification surveys, we
reported the presence of dermal bite wounds and scars on
females’ body as a sign of mating activity [21,28]. Courtship
behaviour with males engaged in close following of females
was also reported with identification of male and female ID
when possible [29]. Finally, the period of parturition was
estimated based on the reappearance of newly slender female
after the pregnant female left the site for several days or weeks
[21,28].
DNA isolation and microsatellite genotyping
Genomic DNA was isolated from each fin-clip using a DNA
Purification Kit (Puregene). We isolated 2 species-specific
polymorphic microsatellite loci from Negaprion acutidens and
selected 14 polymorphic microsatellite loci developed for other
shark species (Table S1). All specimens (n = 85) were
genotyped at all 16 polymorphic microsatellite loci. PCRs were
conducted with forward primers labelled with Beckman Coulter
dyes D2, D3 or D4 (Table S1). Amplified fragments were
separated on a Beckman Coulter CEQ 8000 Genetic Analysis
System, with a 400-bp internal size standard. Genotypes and
allele sizes were scored using Beckman-Coulter CEQ TM 8000
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 2 August 2013 | Volume 8 | Issue 8 | e73899
Genetic Analysis System-associated software. Allelic frequency
and expected heterozygosity under Hardy–Weinberg
equilibrium were calculated for each locus in GENALEX 6 [30].
The presence of null alleles was investigated using
MICROCHECKER [31]. Tests for Hardy-Weinberg and linkage
disequilibrium were conducted in GENEPOP 3.4 [32] and
significant levels were adjusted with sequential Bonferroni
corrections for multiple tests with P < 0.05. Of the 16
microsatellite loci, three did not satisfy Hardy-Weinberg and
linkage disequilibrium assumptions. To test our photo-
identification technique [27], GENALEX 6 [30] was used to
detect potential identical genotypes belonging to resampled
individuals. No identical genotype was found confirming the
accuracy of our photo-identification technique.
Relatedness and genetic network construction
Maximum likelihood estimates of pairwise relatedness
coefficients and genealogical relationships were calculated with
the software ML-RELATE [33] computing 5000 iterations. The
program calculates the maximum likelihood relationship
between individual pairs. It determines which of parent-
offspring (PO), full-sibling (FS), half sibling (HS) and unrelated
(U) categories yields the greatest likelihood.
Instead of trying to reconstruct an exact pedigree that is
challenging from genetic data alone in wild populations, we
built a genetic network using relatedness information [34].
Network analysis is now a common tool used to characterize
animal social associations [35] including sharks [36]. However,
it has rarely been used to illustrate the genetic relationships
between individuals in a population despite its advantage to
incorporate a large amount of data into a simple visual graph
[34]. The genetic network was built from the matrix of genetic
relatedness together with individual characteristics (size, sex
and group membership) using the programs SOCPROG [37]
and NETDRAW 2.123 [38]. Only the R values of first-order
genetic relationships (PO, FS and HS) inferred from ML-
RELATE were retained in this network for an easier
visualization.
Parentage analysis
The program CERVUS [39] was first used to find highly
probable mother–offspring and father–offspring pairs.
Assignment to these potential parents was done under a strict
confidence level of 95%. These mother–offspring and father–
offspring pairs were then identified in the input file of COLONY
2.0.3.0 [40] as known maternity and paternity. COLONY 2.0.3.0
[40] implements a full-likelihood approach to parentage
analysis and was shown to outperform other programs in cases
of less than 20 microsatellite markers [41]. We considered both
parent-offspring relationships and sibship amongst offspring.
Adults were separated by sex, and we assumed a polygamous
mating system for both sexes, therefore allowing the
assignment of half-siblings. We carried out a long-run with
medium likelihood precision and a genotyping error rate of 1%.
The prior probability that the true parent was present in the
sample was set to 0.5 for fathers and 0.25 for mothers based
on the proportion of sampled males and females that were
assigned to offspring by CERVUS. We conducted other runs
varying the input parameters such as the mating system for
each sex. For each analysis, 3 replicate runs were conducted
on the same data set. Each of the replicate runs used different
random number seeds to initiate the simulated annealing
processes. Parental genotype reconstruction was also
performed with COLONY allowing to infer the number of
breeders in the population. Therefore, total number of breeders
was assessed either by reconstructing males and females’
genotypes from young of the year half-sib groups or by directly
assigning parentage to offspring from sampled adults.
Inbreeding estimations
To test for inbreeding, we used a Monte Carlo simulation
implemented in STORM 1.0 [42]. This analysis generates
offspring internal relatedness (IR) values expected from the
gene pool if mating is random with respect to parental
relatedness. We calculated the average observed IR for all
offspring (n = 52) and adults (n = 33) sampled. We generated
simulated IR measures by sampling random males (n = 13)
and females (n = 20) with replacement. Each random mating
pair produces a simulated offspring whose internal relatedness
can be measured. The observed mean IR was then compared
with the distribution of average simulated IR produced from
1000 iterations. Potential bias of allelic diversity into IR
estimates was tested by resampling and recalculating IR
values on loci with 5 or more alleles.
Results
Microsatellite summary statistics
Across all individuals of Negaprion acutidens collected for
this work, polymorphism varied from 2 to 15 alleles per locus.
Observed heterozygosity ranged from 0.365 to 0.871 per locus
and expected heterozygosity from 0.395 to 0.871 (Table S1).
Null alleles were detected at loci LS15 and Cli107, as
suggested by the general excess of homozygotes using
MICRO-CHECKER. Overall, significant heterozygote
deficiencies were found in three loci (LS15, Cli107 and Cpl169;
with all P < 0.05 following Bonferroni standard correction). We
therefore decided to remove both LS15 and Cli107 from
subsequent analyses due to evidence of null alleles. Once
analyzing together the remaining 14 loci, no significant
heterozygote deficiencies were observed in the global
population (P>0.05).
Adult population genetic structure
As expected in a wild population, the mean coefficient of
relatedness was low among adults, both within the overall
population of Moorea (mean R ± SD = 0.086 ± 0.137) and
when we included individuals from Bora Bora (mean R ± SD =
0.076 ± 0.128; Table S2). However, the genetic network
illustrates that all individuals are interconnected at least by one
first order genetic relationship except for female B4 from Bora
Bora that is isolated from the network (Figure 1). First order
genetic relationships (PO, FS and HS) accounted for 21.6% of
all pairwise relationships in Moorea and 17.6% when
individuals from Bora Bora are included (Figure 1). The number
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 3 August 2013 | Volume 8 | Issue 8 | e73899
of connections a focal individual has in the network (genetic
degree) ranged from 0 to 11 among the 32 other members of
the network (mean ± SD = 5.6 ± 2.6; Figure 1C), indicating that
individuals have a high number of close relatives in the
population. Residency groups as well as sex categories were
also all genetically linked (Figure 1B). Within-group average
genetic relatedness was significantly different from between
group (P < 0.001) even when excluding resident sharks of Bora
Bora (P < 0.05; Table S2). There was no difference between
sex (P > 0.05; Table S2).
Visual information on reproductive status
Pre-copulatory and courtship behavior, characterized by a
male showing a close nose to tail behavior while following a
female (Figure 2F; Table S3; Video S1), started in August and
lasted until early November (first observation in August 20
th
and
last observation in November 1
st
), with a stable calendar each
Figure 1. Genetic network of the sicklefin lemon shark population from Moorea and Bora Bora. (A) Map of the study
location. (B) The genetic network of adult lemon sharks. Each individual is indicated by a node labelled by shark ID. Circles and
squares indicate females and males respectively and symbol size is indicative of the body length of the shark. Node colour
corresponds to the three defined residency groups. Dyads sharing a first-order genetic relationship are connected by a line, with line
thickness indicating the strength of the genetic relationship (proportional to R values). A ‘spring embedding’ algorithm with node
repulsion for laying out the nodes’ positions [38] was used to cluster densely connected nodes together with less connected nodes
placed around the edge. (C) Genetic degree (number of first-order genetic relationships an individual has) distribution within the
population.
doi: 10.1371/journal.pone.0073899.g001
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 4 August 2013 | Volume 8 | Issue 8 | e73899
year. Several males can be involved in courtship behavior at
the same time following the same female (Figure 2F; Table
S3). Females with specific mating scars were then observed
from the end of September throughout November (Figure 2C;
Table S4). Pregnancy in females became visually apparent in
February and progressed until being fully apparent in May
(Figure 2). Most females followed a 2 years reproductive cycle
(Figure 2A–D) with the exception of females F01 (Figure 2E)
and F21 that became pregnant on 2 consecutive years (Table
S4). Considering the reappearance at the site of newly slender
females together with first newborn sharks found in their
nursery in October, we determined that parturition occurs
between July and November (Figure 2E-F; Table S4).
Therefore, gestation is estimated to last 10 to 11 months.
Parentage analysis
Parentage analysis assigned 35 of the 52 genotyped
juveniles to at least one parent or a parent pair among the 33
sampled adults (Figure 3). In all case, the three runs gave
consistent results and mating system parameters did not
Figure 2. Inference of reproductive cycle from underwater surveys. (A–D) A two-year reproductive cycle as displayed by
female F11 which was pregnant in 2007 (A), then entered in a resting period (B) and mated in 2008 as shown by dermal bite
wounds on its flanks (C), and was pregnant again in 2009 (D). (E–F) Female F01 is pregnant in 2008 (E) and is followed by males
M10 and M31 in a courtship behavior just after parturition in 2008 (F).
doi: 10.1371/journal.pone.0073899.g002
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 5 August 2013 | Volume 8 | Issue 8 | e73899
consistently change parentage assignment results. Of the 35
juveniles, 17 (49%) were assigned only to a female, 13 (37%)
only to a male and 5 (14%) to a parent pair. The two mating
pairs of sampled sharks were F11-M09 (Resident/Non-
resident) and F30-M09 (Non-resident/Non-resident). The 52
juveniles were assigned to 29 distinct litters across the years
(Figure 3). From the adult sharks sampled (13 males and 20
females), only 4 females and 8 males were assigned to a
juvenile. However, the genotype of 29 physically unsampled
sharks (12 males and 17 females) was reconstructed by
COLONY and assigned to a juvenile. No juvenile was assigned
to a female from Bora Bora. Therefore, a total of 41 adult
sharks including 20 males (8 sampled and 12 genetically
reconstructed fathers) and 21 females (4 sampled and 17
genetically reconstructed mothers) contributed to the
reproduction for our sampled juveniles (Table 1).
Female reproductive behaviour
Of the 21 females either sampled or genetically
reconstructed (Table 1), 15 gave birth in Moorea and 4 in
Tetiaroa (Figure 3). Six females returned to the same nursery
on multiple years to give birth, of which 4 returned on a two-
years cycle (F11, F30, #1 and #2; Figure 3) and 2 returned in
consecutive years (#3 and #13; Figure 3). Two litters were
made of juveniles sampled in different nurseries (Figure 3).
Seven (78%) of the 9 litters cumulating more than one young
were the result of polyandrous females with females mating
with 2 to 3 males (Figure 3). Most parturition events confirmed
the dermal bite wounds observed underwater (Figure 2) in the
year prior to parturition (Table S4).
Male reproductive behaviour
In our sample, 10 (50%) of the 20 fathers sired more than
one litter (Figure 3). Five males mated with multiple (2,3)
females in a single year (M09 in 2006; M04 and M09 in 2007;
*6 in 2008; *2 and *3 in 2009). Nine males sired a litter in
multiple years. Male M04 was assigned to offspring of two
different litters of female F30 (Figure 3). Male M05 sired 2
different litters in 2 different years (2008 and 2009) although
this shark has not been sighted in Moorea since early 2006.
Genetic diversity and inbreeding
The mean IR value of offspring was not significantly higher
than expected under random mating (Monte Carlo
randomization (x1000): mean IR ± 95% CI = 0.037 ± 0.056 and
mean simulated IR ± 95% CI = 0.009 ± 0.001, P = 0.142). IR
values calculated from loci with over 5 alleles were not different
from those calculated from all loci (mean IR ± 95% CI = 0.023 ±
0.047; P > 0.05) suggesting that our estimation of IR values
were not inflated by the presence of low allelic diversity at
some loci. Observed maximum IR value was 0.504, 13% (7/52)
of all offspring had IR values higher than 0.25 (the value
expected for offspring of half-sibling mating), and 36% (19/52)
had o-IR larger than 0.125 (Figure S2).
There was a significant inverse relationship between body
size (ca. age) and IR (y = -0.0005x+0.0780; R
2
= 0.0629; P =
0.011). This was confirmed by a significant difference in R
values between maturity status (F
2,82
= 3.248, P = 0.043);
offspring IR values being higher than IR of mature sharks (
P =
0.034; Figure 3A; Figure S2). Finally, offspring IR values did
not vary significantly across years (F
3,46
= 0.853, P = 0.472;
Figure 3B).
Discussion
This study provides a unique case of long term (5 years)
monitoring and genetic survey used to construct the genetic
network and to infer the mating output of an island adult shark
population. This population is also unique since, unlike many
places in the world, it has been preserved from any human
exploitation, implying that low densities observed are normal
for this population. Our results demonstrate that this small
population displays patterns of connectivity throughout the
archipelago and dispersal which are used as a strategy to
avoid mating with closely related partners.
Population genetic structure and dispersal
Although the mean relatedness was low among adults of the
population, all sharks (but 1) were interconnected through
close to moderate genetic relationships. First order genetic
relationships accounted for 17.6% of all pairwise relationships,
reaching 21.6% when excluding individuals from Bora Bora.
The genetic network (Figure 1) illustrates that sharks from
different residency groups and islands are related, that is likely
a consequence of dispersal [37]. Our results also indicate that
sharks are migrating to breed outside their resident population
(Figure 2). While some individuals of its Atlantic sister species,
Negaprion brevirostris, appear to remain at their natal island,
others disperse before reaching maturity [43] to colonize other
islands. A similar situation is found in Negaprion acutidens, as
among four resident female sharks of Bora Bora, three (B1, B2
and B3) appeared genetically linked to sharks sighted in
Moorea (resident M03 and M05; non-resident M12 and M34;
Figure 1B). Also, direct migration evidence is available with
some individuals from Moorea being sighted in Tahiti both
within and outside the mating season (i.e. females F15, F20,
F23, F25 and F30; Figure 1A). Moreover, during each breeding
period (September–November), most resident males
disappeared from days to weeks [22] while non-resident males,
such as male M12, show up in in Moorea, presumably to mate
(Figure 1B). While adult sharks appear to migrate throughout
the archipelago, movement or dispersal in juvenile and
immature sharks may be limited as only two age-0 juveniles
were caught away from their littermates within the same island
(female J4A about 8 km away in Moorea and Tet9 about 1.5
Table 1.
Number of breeders determined by direct
parentage assignment and genotype reconstruction
conducted in program COLONY.
Mothers Fathers Total
Physically sampled 4 8 12
Genetically reconstructed 17 12 29
Total (Ne) 21 20 41
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 6 August 2013 | Volume 8 | Issue 8 | e73899
Figure 3. Female reproduction inferred from parentage assignment. Litters are shown by years for each female with the
assigned father(s) and juvenile(s). Sampled individual adult sharks are indicated in bold. Mothers and fathers inferred through
genotype reconstruction by the program COLONY are identified by #ID and *ID, respectively. Colour of juveniles refers to their
sampling nursery site (Figure S1). Note that juvenile Tet5 was sampled in 2008 in Tetiaroa but was assigned to the birth year 2007
due to its size (110 cm) corresponding to an age-1 juvenile, while subadult Sub1 was sampled in 2008 at the size of 125 cm and
subsequently assigned to year of birth 2006. Finally, Tet1 was assigned to an unknown year as we were not able to determine its
year of birth.
doi: 10.1371/journal.pone.0073899.g003
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 7 August 2013 | Volume 8 | Issue 8 | e73899
km away in Tetiaroa). However, female Tet1 (180 cm TL)
caught in Tetiaroa is an offspring of female 1 that gave birth in
Varari (Moorea) in 2007 and in 2009; therefore, this immature
shark can either correspond to a dispersal event from its birth
location or a change in nursery location of its mother (female 1)
for parturition. The paucity of studies on Negaprion acutidens
does not provide further information on the year of first
dispersal (or emigration from nursery) of juveniles, but a recent
study showed that among immature sharks (i.e., 141 < TL <
202 cm) the first sharks to leave the study area was about 150
cm TL [44]. Individual sharks have been shown to emigrate
from their nursery during their third year in the sister species
Negaprion brevirostris [43] and in their first year in
Carcharhinus melanopterus [45]. However, some species delay
their dispersal until reaching maturity [46]. Therefore, while
sicklefin lemon sharks may start emigration from nurseries
during their first year, dispersal rate in the population may
increase throughout the shark’s growth [43]. Overall, sicklefin
lemon sharks in the Society Islands appear to be structured as
a mixed population of individuals moving throughout the
archipelago (Figure 1; Figure 3).
Reproductive behaviour
From parentage analysis, we were able to investigate the
mating system and recruitment patterns of lemon sharks in the
archipelago. Like other reef sharks depending on nurseries for
recruitment [18,20,21], most females showed philopatry to
particular nurseries (Figure 3) although this was not the case
for all of them (Figure 3). Negaprion acutidens shares nursery
locations with Carcharhinus melanopterus in Moorea and
Tetiaroa [21,47]. As females mostly followed a biennial
reproductive pattern, some did not exhibit a two-year cycle
(Figure 2; Figure 3; Table S4). Therefore, females may follow
an average two-year reproductive cycle in this species, but like
female F01, may sometimes be mated to harassing males just
after parturition (Figure 2E-F; Table S3). Of the 20 genetically
sampled females, only 4 used one of our sampled nurseries.
Therefore, the other females either did not reproduce during
the study period or gave birth at different, unsampled nursery
locations (Table S4). Based on our parentage analysis and
genotype reconstruction, a total of 41 adult breeders (20 males
and 21 females; Table 1) were found in our system. Although
this may be an underestimate due to unsampled nursery
locations in our study area, the number of breeders is relatively
low. Most litters (78%) had multiple sires showing the
prevalence of polyandrous female mating as it is commonly
found in reef sharks [19,20]. This proportion may be
underestimated as the monogamous females had small,
potentially incompletely sampled litters. Male reproductive
success was highly skewed with few males siring litters on
multiple occasions within and across years (Figure 3),
potentially due to dominance hierarchy among them or
migratory strategies during the mating season [22].
Genetic diversity
The mean offspring internal relatedness (mean IR = 0.03)
was not significantly higher than expected under random
mating. However, maximum offspring IR values (IRmax = 0.50)
were higher than those found in offspring of its sister species
Negaprion brevirostris in the Bahamas (IRmax = 0.05 [48]). IR
values were lower to that of full-siblings (mean IR = 0.14) in
Squalus acanthias litters [49], although the estimates were
limited to 7 microsatellite markers. Even the critically
endangered Pristis pectinata did not reveal inbreeding (mean
IR = -0.02 [50]), perhaps due to the absence of migration
barriers of a continuous coastal environment. The same level
of inbreeding was found in Carcharhinus melanopterus,
another shark species of the Society Islands [21]. Negaprion
acutidens clearly developed some inbreeding avoidance
strategy by conducting specific behaviour including dispersal
and migrations across the archipelago. Polyandry is often
expected to effectively increase the cumulative genetic
variation in a single litter and therefore decrease inbreeding. At
the population level, this effect is likely to be mitigated by an
increased variance in male reproductive success [51].
Additionally, studies on Negaprion brevirostris [19,48]
suggested that high multiple paternity in lemon sharks is more
likely a result of convenience polyandry than of indirect genetic
benefits such as inbreeding avoidance. Therefore, it remains
unlikely that polyandry alone play a major role in inbreeding
avoidance mechanisms.
Considering these behaviours and the mating system
displayed by sicklefin lemon sharks to avoid inbreeding, the
observed degree of inbreeding is unusual for mobile free-living
marine species. Chapman et al. [50] argue that male-biased
dispersal from their natal area as well as no evidence that
certain males dominate paternity may reduce the likelihood of
inbreeding in K-selected elasmobranchs. These life history
characteristics and reproductive behaviour are less evident for
Negaprion acutidens in French Polynesia as: (1) a few males
appear to dominate paternity (Figure 3) (2), some males are
resident to an island and do not roam like other species do
[22], and (3) although evidence for dispersal was found,
individuals within the entire Archipelago remain closely related
(Figure 1). Another reason that may limit the effectiveness of
inbreeding avoidance may be the fragmented habitat in this
region which tends to isolate populations [26] and may reduce
the opportunity to find unrelated mates.
In addition, significantly higher IR values in juveniles than in
adults (Figure 4; Figure S2) demonstrate a temporal change in
inbreeding levels. Such a change, that suggests variation in
fitness through time can result either from individuals with
higher IR values progressively migrating away from their natal
site or some differential mortality with individuals with higher IR
values showing lower survival rate than juveniles with higher
genetic diversity. Longer monitoring and redundancy of such
pattern in inbreeding values will be necessary to determine
which hypothesis should be favored.
Conclusion
Individuals from this local population of sickefin lemon sharks
in the Society archipelago share many first-order genetic
relationships providing evidence that population size in this
species is fairly limited in the context of islands at least in
French Polynesia, but likely in isolated islands system of the
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 8 August 2013 | Volume 8 | Issue 8 | e73899
Pacific. This low genetic variability has encouraged sicklefin
lemon sharks to develop different strategies to avoid mating
between close relatives with evidence of migrations across
islands and atolls. The highly isolated and fragmented
environment of French Polynesia [26] may limit encounter rate
of unrelated mates despite dispersal and migrations across the
Society Islands. These results encourage for long-term
monitoring to survey the population response to increasing
anthropogenic factors [22] despite the economic importance of
these sharks in the local tourism industry [24].
Figure 4. Patterns of distribution in internal relatedness
values (IR). (A) IR values across the maturity stage of
individuals (categories: juvenile < 100 cm, immature = 100-199
cm and mature > 200 cm). (B) IR values of newborn sharks
(cohorts) across years. Box plots show the median (line within
the boxes), mean (white diamond) and interquartile ranges IQR
(boxes). Raw data points are indicated by black circles.
doi: 10.1371/journal.pone.0073899.g004
Supporting Information
Figure S1. Sampled nursery locations. (A) Map of French
Polynesia with sampled islands. (B) Sampled nursery locations
in Tetiaroa. (C) Nursery locations in Moorea. Circles are
coloured according to the nursery location used in the study
and black circles refers to adult sampling sites.
(TIF)
Figure S2. Distribution of internal relatedness values (IR)
of adult (black bars) and juvenile (grey bars) lemon sharks.
(TIF)
Table S1. Description of the 16 microsatellite loci used to
genotype sicklefin lemon sharks. Dyes: fluorescent
Beckman Coulter dyes labels; Ta: annealing temperature (°C);
N: number of individual scored; H
0
: observed heterozygosity;
H
E
: expected heterozygosity; k: number of alleles; Fis:
inbreeding coefficient; H–W: exact test for departure from
Hardy-Weinberg.
(DOCX)
Table S2. Distribution of average relatedness values
across categories (sex and socio-residency groups). Mean
relatedness is displayed together with SD in parenthesis.
(DOCX)
Table S3. Underwater observations of male courtship
behaviour in sicklefin lemon sharks in Moorea. For each
year, the females that each male was observed to follow is
indicated.
(DOCX)
Table S4. Underwater visual estimations of reproduction
timing in sicklefin lemon sharks in Moorea. DBW: Dermal
Bite Wound (dates of observations are indicated); P: Parturition
indicated in grey (estimated to have occurred during the time
the female was absent from the observation area; dates of
disappearance for pregnant females are indicated when
available).
(DOCX)
Video S1. Courtship behavior with female F01 is closely
followed by male M10 in 23 October 2008. Female F01 was
in near to term gestation in August 2008 (Figure 2E) and
presumably gave birth between August and October 2008
(Table S4). This female returned to our study site on 8 October
2008, was seen followed by male M10 in a courtship and then
joined by male M31 (Figure 2F). Note that both male M10 and
female F01 are focused in their courtship behavior and do not
pay attention to the diver.
(MP4)
Acknowledgements
We would like to thank the private diving company Top Dive in
Moorea for logistic support and René Galzin, Centre de
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 9 August 2013 | Volume 8 | Issue 8 | e73899
Recherche Insulaire et Observatoire de l’Environnement
(CRIOBE), Pablo Saenz-Agudelo, Thomas Vignaud and
Elisabeth Rochel, Centre de Biologie et d’Ecologie Tropicale et
Méditerranéenne (CBETM) for scientific and technical support.
Author Contributions
Conceived and designed the experiments: JM NB EC SP.
Performed the experiments: JM NB JKS EC SP. Analyzed the
data: JM SP. Contributed reagents/materials/analysis tools: JM
SP. Wrote the manuscript: JM NB JKS EC SP.
References
1. Ceballos G, Ehrlich PR (2002) Mammal population losses and the
extinction crisis. Science 296: 904–907. doi:10.1126/science.1069349.
PubMed: 11988573.
2. Frankham R (2005) Genetics and extinction. Biol Conserv 126: 131–
140. doi:10.1016/j.biocon.2005.05.002.
3. Willi Y, van Buskirk J, Hoffmann AA (2006) Limits to the adaptive
potential of small populations. Annu Rev Ecol Evol Syst 37: 433–478.
doi:10.1146/annurev.ecolsys.37.091305.110145.
4. Berger J (1999) Anthropogenic extinction of top carnivores and
interspecific animal behaviour: implications of the rapid decoupling of a
web involving wolves, bears, moose and ravens. Proc R Soc Lond B
266: 2261-2267. doi:10.1098/rspb.1999.0917.
5. Hutchings JA, Reynolds JD (2004) Marine fish population collapses:
consequences for recovery and extinction risk. BioScience 54: 297–
309. doi:10.1641/0006-3568(2004)054[0297:MFPCCF]2.0.CO;2.
6.
Keller L, Waller DM (2002) Inbreeding effects in wild populations.
Trends Ecol Evol 17: 230–241. doi:10.1016/S0169-5347(02)02489-8.
7. Pusey A, Wolf M (1996) Inbreeding avoidance in animals. Trends Ecol
Evol 11: 201-206. doi:10.1016/0169-5347(96)10028-8. PubMed:
21237809.
8.
Olson LE, Blumstein DT, Pollinger JP, Wayne RK (2012) No evidence
of inbreeding avoidance despite survival costs in a polygynous rodent.
Mol Ecol 21: 562-571. doi:10.1111/j.1365-294X.2011.05389.x.
PubMed: 22145620.
9.
Frère CH, Krützen M, Kopps AM, Ward P, Mann J, Sherwin WB (2010)
Inbreeding tolerance and fitness costs in wild bottlenose dolphins. Proc
R Soc Lond B 277: 2667-2673. doi:10.1098/rspb.2010.0039. PubMed:
20392729.
10.
Baum JK, Myers RA, Kehler DG, Worm B, Harley SJ, Doherty PA
(2003) Collapse and conservation of shark populations in the Northwest
Atlantic. Science 299: 389-392. doi:10.1126/science.1079777.
PubMed: 12532016.
11. Robbins WD, Hisano M, Connolly SR, Choat HJ (2006) Ongoing
Collapse of Coral Reef Shark Populations. Curr Biol 16: 2314-2319.
doi:10.1016/j.cub.2006.09.044. PubMed: 17141612.
12. Worm B, Davis B, Kettermer L, Ward-Paige CA, Chapman D, Heithaus
MR, Kessel ST, Gruber SH (2013) Global catches, exploitation rates,
and rebuilding options for sharks. Mar Policy 40: 194–204. doi:10.1016/
j.marpol.2012.12.034.
13. Clarke SC, Harley SJ, Hoyle D, Rice JS (2012) Population trends in
Pacific Oceanic sharks and the utility of regulations on shark finning.
Conserv Biol 27: 197-209. PubMed: 23110546.
14. Nadon MO, Baum JK, Williams ID, McPherson JM, Zgliczynski BJ,
Richards BL, Schroeder RE, Brainard RE (2012) Re-creating missing
population baselines for Pacific reef sharks. Conserv Biol 26: 493–503.
doi:10.1111/j.1523-1739.2012.01835.x. PubMed: 22536842.
15. Ward-Paige CA, Keith DM, Worm B, Lotze HK (2012) Recovery
potential and conservation options for elasmobranchs. J Fish Biol 80:
1844-1869. doi:10.1111/j.1095-8649.2012.03246.x. PubMed:
22497409.
16. Myers RA, Baum JK, Shepard TD, Powers SP, Peterson CH (2007)
Cascading effects of the loss of apex predatory sharks from a Coastal
Ocean. Science 315: 1846-1850. doi:10.1126/science.1138657.
PubMed: 17395829.
17. Field IC, Meekan MG, Buckworth RC, Bradshaw CJ (2009)
Susceptibility of sharks, rays and chimaeras to global extinction. Adv
Mar Biol 56: 275-363. doi:10.1016/S0065-2881(09)56004-X. PubMed:
19895977.
18. Feldheim KA, Gruber SH, Ashley MV (2002) The breeding biology of
lemon sharks at a tropical nursery lagoon. Proc R Soc Lond B 269:
1471-2954.
19. Feldheim KA, Gruber SH, Ashley MV (2004) Reconstruction of parental
microsatellite genotypes reveals female polyandry and philopatry in the
lemon shark, Negaprion brevirostris. Evolution 58: 2332-2342. doi:
10.1554/04-023. PubMed: 15562694.
20. DiBattista JD, Feldheim KA, Thibert-Plante X, Gruber SH, Hendry AP
(2008) A genetic assessment of polyandry and breeding site fidelity in
lemon sharks. Mol Ecol 17: 3337-3351. doi:10.1111/j.1365-294X.
2008.03833.x. PubMed: 18564083.
21. Mourier J, Planes S (2013) Direct genetic evidence for reproductive
philopatry and associated fine-scale migrations in female blacktip reef
sharks (Carcharhinus melanopterus) in French Polynesia. Mol Ecol 22:
201-214. doi:10.1111/mec.12103. PubMed: 23130666.
22. Clua E, Buray N, Legendre P, Mourier J, Planes S (2010) Behavioural
response of sicklefin lemon sharks Negaprion acutidens to underwater
feeding for ecotourism purposes. Mar Ecol Prog Ser 414: 257–266. doi:
10.3354/meps08746.
23. Compagno LV, Dando M, Fowler S (2005) Sharks of the world.
Princeton (NJ): Princeton University Press.
24. Schultz JK, Feldheim KA, Gruber SH, Ashley MV, McGovern TM,
Bowen BW (2008) Global phylogeography and seascape genetics of
the lemon sharks (genus Negaprion). Mol Ecol 17: 5336–5348. doi:
10.1111/j.1365-294X.2008.04000.x. PubMed: 19121001.
25. Clua E, Buray N, Legendre P, Mourier J, Planes S (2011) Business
partner or simple catch? The economic value of the sicklefin lemon
shark in French Polynesia. Mar Freshw Res 62: 764-770. doi:10.1071/
MF10163.
26.
Vignaud T, Clua E, Mourier J, Maynard J, Planes S (2013)
Microsatellite Analyses of Blacktip Reef Sharks (Carcharhinus
melanopterus) in a Fragmented Environment Show Structured
Clusters. PLOS ONE 8(4): e61067. doi:10.1371/journal.pone.0061067.
PubMed: 23585872.
27.
Buray N, Mourier J, Planes S, Clua E (2009) Underwater photo-
identification of sicklefin lemon shark, Negaprion acutidens, at Moorea
(French Polynesia). Cybium 33: 21-27.
28.
Porcher IF (2005) On the gestation period of the blackfin reef shark,
Carcharhinus melanopterus, in waters off Moorea, French Polynesia.
Mar Biol 146: 1207–1211. doi:10.1007/s00227-004-1518-0.
29.
Pratt HL Jr, Carrier JC (2001) A review of elasmobranch reproductive
behavior with a case study on the nurse shark, Ginglymostoma
cirratum. Environ Biol. Fish 60: 157-188. doi:10.1023/A:
1007656126281.
30. Peakall ROD, Smouse PE (2006) GENALEX 6: genetic analysis in
Excel. Population genetic software for teaching and research. Mol Ecol
Notes 6: 288-295. doi:10.1111/j.1471-8286.2005.01155.x.
31. van Oosterhout CV, Hutchinson WF, Willis DPM (2004) Microchecker:
software for identifying and correcting genotyping errors in
microsatellite data. Mol Ecol Notes 4: 535–538. doi:10.1111/j.
1471-8286.2004.00684.x.
32. Raymond M, Rousset F (1995) GENEPOP (Version 1.2): Population
genetics software for exact tests and ecumenicism. J Hered 86:
248-249.
33. Kalinowski ST, Wagner AP, Taper ML (2006) ML-Relate: a computer
program for maximum likelihood estimation of relatedness and
relationship. Mol Ecol Resour 6: 576-579.
34. Rollins LA, Browning LE, Holleley CE, Savage JL, Russell AF, Griffith
SC (2012) Building genetic networks using relatedness information: a
novel approach for the estimation of dispersal and characterization of
group structure in social animals. Mol Ecol 21: 1727-1740. doi:
10.1111/j.1365-294X.2012.05492.x. PubMed: 22335253.
35. Krause J, Croft DR, James R (2007) Social network theory in the
behavioural sciences: potential applications. Behav Ecol Sociobiol 62:
15–27. doi:10.1007/s00265-007-0445-8.
36. Mourier J, Vercelloni J, Planes S (2012) Evidence of social
communities in a spatially structured network of a free-ranging shark
species. Anim Behav 83: 389-401. doi:10.1016/j.anbehav.2011.11.008.
37. Whitehead H (2009) SOCPROG programs: analyzing animal social
structures. Behav Ecol Sociobiol 63: 765-778. doi:10.1007/
s00265-008-0697-y.
38. Borgatti SP (2002) Netdraw Network Visualization. Harvard, MA:
Analytic Technologies.
39. Marshall TC, Slate J, Kruuk LEB, Pemberton JM (1998) Statistical
confidence for likelihood-based paternity inference in natural
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 10 August 2013 | Volume 8 | Issue 8 | e73899
populations. Mol Ecol 7: 639–655. doi:10.1046/j.1365-294x.
1998.00374.x. PubMed: 9633105.
40. Jones OR, Wang J (2010) COLONY: a program for parentage and
sibship inference from multilocus genotype data. Mol Ecol Resour 10:
551-555. doi:10.1111/j.1755-0998.2009.02787.x. PubMed: 21565056.
41. Harrison HP, Saenz-Agudelo P, Planes P, Berumen M, Jones G (2013)
Relative accuracy of three common methods of parentage analysis in
natural populations. Mol Ecol 22: 1158-1170. doi:10.1111/mec.12138.
PubMed: 23278953.
42. Frasier TR (2008) STORM: software for testing hypothesis of
relatedness and mating patterns. Mol Ecol Resour 8: 1263-1266. doi:
10.1111/j.1755-0998.2008.02358.x. PubMed: 21586016.
43. Chapman DD, Babcock EA, Gruber SH, DiBattista JD, Franks BR,
Kessel SA, Guttridge T, Pikitch EK, Feldheim KA (2009) Long term
natal site-fidelity by immature lemon sharks (Negaprion brevirostris) at
a subtropical island. Mol Ecol 18: 3500-3507. doi:10.1111/j.1365-294X.
2009.04289.x. PubMed: 19659480.
44. Filmalter JD, Dagorn L, Cowley PD (in press) Spatial behaviour and
site fidelity of the sicklefin lemon shark Negaprion acutidens in a
remote Indian Ocean atoll. Mar Biol. doi:10.1007/s00227-013-2237-1.
45.
Chin A, Heupel M, Simpfendorfer C, Tobin A (2013) Ontogenetic
movements of juvenile blacktip reef sharks: evidence of dispersal and
connectivity between coastal habitats and coral reefs. Aquat Conserv
Mar Freshw Ecosyst. doi:10.1002/aqc.2349.
46. Larson S, Christiansen J, Griffing D, Ashe J, Lowry D, Andrews K
(2010) Relatedness and polyandry of sixgill sharks, Hexanchus griseus,
in an urban estuary. Conserv Genet 12: 1–12.
47. Mourier J, Mills SC, Planes S (2013) Population structure, spatial
distribution and life history traits of blacktip reef sharks Carcharhinus
melanopterus at Moorea, French Polynesia. J Fish Biol 82: 979–993.
doi:10.1111/jfb.12039. PubMed: 23464555.
48. DiBattista JD, Feldheim KA, Gruber SH, Hendry AP (2008) Are indirect
genetic benefits associated with polyandry? Testing predictions in a
natural population of lemon sharks. Mol Ecol 17: 783–795. doi:
10.1111/j.1365-294X.2007.03623.x. PubMed: 18194167.
49. Veríssimo A, Grubbs D, McDowell J, Musick J, Portnoy D (2010)
Frequency of multiple paternity in the spiny dogfish Squalus acanthias
in the Western North Atlantic. J Hered 102: 88-93. PubMed: 20650933.
50. Chapman DD, Simpfendorfer CA, Wiley TR, Poulakis GR, Tringali M,
Carlson JK, Feldheim KA (2011) Genetic diversity despite population
collapse in a critically endangered marine fish: the smalltooth sawfish
(Pristis pectinata). J Hered 102: 643-652. doi:10.1093/jhered/esr098.
PubMed: 21926063.
51.
Daly-Engel TS, Grubbs RD, Bowen BW, Toonen RJ (2007) Frequency
of multiple paternity in an unexploited tropical population of sandbar
shark. Can J Fish Aquat Sci 64: 198–204. doi:10.1139/f07-005.
Relatedness and Reproduction in a Shark Population
PLOS ONE | www.plosone.org 11 August 2013 | Volume 8 | Issue 8 | e73899
... Debaere et al. 2023), whereas the parturition season for N. acutidens occurs biennially from July through November(Porcher 2005;Mourier et al. 2013b). Then, the abundance of neonates decreases around January, as parturition ends and neonates emigrate from the sampling sites or experience mortality(Mourier and Planes 2013;Mourier et al. 2013b). ...
... Debaere et al. 2023), whereas the parturition season for N. acutidens occurs biennially from July through November(Porcher 2005;Mourier et al. 2013b). Then, the abundance of neonates decreases around January, as parturition ends and neonates emigrate from the sampling sites or experience mortality(Mourier and Planes 2013;Mourier et al. 2013b). ...
Article
Full-text available
Context Coastal habitats function as shark nursery areas; however, coastal habitats can experience extreme variation in abiotic conditions and are susceptible to human disturbances. Aims Drivers of abundance were tested within a shark nursery-area system in two populations of reef-associated neonate sharks, namely, blacktip reef sharks (Carcharhinus melanopterus) and sicklefin lemon sharks (Negaprion acutidens). Methods Catch data from a fisheries-independent gill-net survey (n = 90 sets from October 2018 to March 2019) at 10 sites around Moorea, French Polynesia, were used to test for associations between shark abundance and abiotic conditions (temperature, oxygen, pH, salinity, lunar phase and depth). Historical levels of fin-fish fishing effort, trampling (i.e. human movement through habitat), and coastal artificialisation (i.e. walls and embankments) estimated for each site were used to test for anthropogenic effects on shark abundance. Key results There were no effects of any abiotic or anthropogenic factor on abundance of either species. Conclusions Previous work corroborates our findings by demonstrating neonate sharks’ physiological tolerance to extreme abiotic conditions and high survival in response to anthropogenic stressors. Alternatively, populations are already degraded from decades of coastal development. Implications These data can aid in predicting the use of coastal habitats as shark nursery areas.
... Gillnets were set at dusk from ∼17h00 to 20h00 at ten sites (Apaura, Haapiti, Maharepa, Paorea, Papetoai, Pihaena, Tiki, Vaiane, Vaiare, and Valorie; Fig. 1) five days per week (i.e. Monday through Friday) between September and February (from 2016 to 2023), which represent the peak parturition months (Debaere et al. 2023;Mourier et al. 2013a). These sites, evenly spread out around the 60-km coastline of Moorea, were randomly assigned two fixed sampling slots per month at the start of each season (e.g. ...
... Thus, considering the small home ranges of these sharks (Bouyoucos et al. 2020), their continuous swimming patterns, and the negligible tidal variation, the probability of capturing neonates at Moorea can be expected to remain somewhat constant, irrespective of lunar phase. In contrast, adult reef sharks can move throughout the deeper parts of the fore reef and lagoons (Compagno 1984;Gruber et al. 1988;Mourier et al. 2013b) or even disperse to other reefs (Chin et al. 2013a;Mourier et al. 2013a) and, hence, are not confined to the small home ranges observed in neonates (Cortes & Gruber, 1990;Morrissey & Gruber 1993). In this case, lunar phase can potentially influence foraging behaviour and decisions of the adult sharks, where the adults move closer to the fringe reefs where prey may be more abundant (Papastamatiou et al. 2009) in anticipation of lunar-mediated foraging opportunities. ...
Article
Full-text available
Elasmobranch (i.e. sharks, skates, and rays) behaviours have been found to align with moon phases; yet, it is not fully understood how the moon influences elasmobranchs’ foraging habits. In coastal ecosystems, tidal changes are typically seen as the primary influence on the behavioural rhythms of fishes, which are linked to the lunar cycle. Sharks have been documented to synchronise behaviours, such as foraging patterns, with the phases of the moon, but studies have yet to clearly separate and identify the mechanisms by which the lunar phase affects these patterns. The island of Moorea, French Polynesia, serves as a nursery habitat for neonatal blacktip reef and sicklefin lemon sharks within the South Pacific amphidromic system, which experiences minimal tidal ranges (~ 0.2 m). This setting provides a unique opportunity to isolate the lunar cycle’s effects from tidal influences. We compared catch rates of neonates of both shark species and foraging success, through stomach content analysis, of blacktip reef sharks across the lunar cycle. Our findings did not support the hypothesis of lunar-induced entrainment of foraging patterns for these neonatal reef sharks. However, understanding the environmental factors that shape the behavioural patterns and foraging strategies of neonatal reef sharks is becoming increasingly important against the backdrop of human disturbances.
... Some studies have even found that adult lemon sharks exhibit greater residency than juveniles (Pillans et al., 2021). The restricted dispersal patterns, combined with fragmented habitats and a lower number of breeders, may have resulted in potentially isolated and vulnerable small populations of lemon sharks (Schultz et al., 2008;Mourier et al., 2013;Liu et al., 2023). ...
... The gestation of N. acutidens is around 10-11 months, and each female can reproduce 6-12 well-developed pups every 1-2 years in shallow nursery areas (Stevens, 1984;Mourier et al., 2013). From March to May, many heavily pregnant females can be observed cruising around Dongsha Island and moving from subtidal zones to the shallow seagrass flat during high tide periods, sometimes even becoming stranded (Fig. 3). ...
Article
Full-text available
Collecting basic biological information of a species is crucial for developing effective conservation strategies and ensuring its sustainable management. Dongsha Atoll is considered a vital, possibly the primary, nursery ground for the endangered sicklefin lemon shark (Negaprion acutidens) in the South China Sea. In this study, we employed acoustic telemetry to investigate the habitat utilization and preferences of N. acutidens at different life stages in Dongsha Atoll. A total of 44 sharks, including 16 juveniles, 14 small sharks, 11 sub-adults, and three adults, were tagged and tracked for 1-848 days. Results of this preliminary assessment revealed that: (1) juvenile and small sharks commonly utilize the shallow seagrass flats around Dongsha Island, with juveniles spending a significant amount of time in the embedded lagoon; (2) sharks of all sizes utilize the lagoon mouth area, especially small and sub-adult sharks; (3) adult sharks exhibit a broader activity range within the atoll and are unlikely to enter the embedded lagoon. We hypothesize that the embedded shallow lagoon of Dongsha Island serves as a shelter area for newborns and juveniles, while the lagoon mouth may function as an important hunting ground for small and sub-adult sharks. Adult sharks may have the broadest home range around the atoll and close to Dongsha Island during the breeding season. This study underscores the importance of considering habitat shifts and changes in home range size throughout the ontogeny of N. acutidens when planning effective spatial management strategies.
... A more detailed investigation into the closing rate of the umbilical wound for this species, based on time-0 recaptures (i.e., neonates with remnants of the umbilical cord that are subsequently recaptured during the following weeks; similar to Debaere et al., 2023), would likely provide for a more precise estimate and narrower confidence interval. It is likely that the Moorea dataset did not capture the early weeks/ months of sicklefin lemon shark parturition due to its earlier season than blacktip reef sharks (Mourier, Buray, et al., 2013), resulting in the absence of time-0 sicklefin lemon sharks. Also note that, although the underlying muscle tissue remains visible throughout the first 2 months, the umbilical vein opening-remnant of the connection to the yolk-sac placenta (see Figure S1)-closes within the first few days post-parturition (personal observation). ...
Article
Full-text available
Elasmobranch fishes (i.e., sharks, skates, and rays) exhibit remarkable wound‐healing capabilities and consistently maintain a high capacity for tissue regeneration throughout their lives. This high capacity for wound healing may be particularly important for neonatal elasmobranchs that are still developing their immune system. However, little is known about the costs associated with wound healing and the potential influence of environmental variables or life history. In this study, we explore (1) the impact of minor, external injuries on the growth and body condition of neonatal blacktip reef (Carcharhinus melanopterus) and sicklefin lemon (Negaprion acutidens) sharks using a long‐term fisheries‐independent dataset from Moorea, French Polynesia, (2) the influence of ambient temperature on healing rates in neonatal blacktip reef sharks at two experimental temperatures (25°C and 29°C), and (3) variations in umbilical wound‐healing rates between blacktip reef and sicklefin lemon sharks using an additional long‐term dataset from St. Joseph Atoll, Seychelles. We found no impact of minor, external injuries on growth and body condition in neonatal blacktip reef and sicklefin lemon sharks, accelerated umbilical wound healing in neonatal blacktip reef sharks exposed to elevated ambient temperatures, and distinct umbilical wound‐healing rates between neonatal blacktip reef and sicklefin lemon sharks. Enhancing our understanding of sharks' healing capabilities and the influence of environmental factors on this process is crucial for informing handling practices aimed at improving post‐release survival rates of captured sharks under current and future oceanic conditions.
... Theoretically, individuals in small and isolated populations tend to inbreed [80]. Nevertheless, in some sharks (e.g., the sicklefin lemon shark Negaprion acutidens and the basking shark), specific mating behaviors have evolved to avoid inbreeding during the mating season [81,82]. Therefore, we suggest that the silky shark in Aceh may also exhibit special mating behavior or migratory patterns to reduce the chance of mating with close kin. ...
Article
Full-text available
The silky shark, Carcharhinus falciformis, is a cosmopolitan species commonly caught as a bycatch for longline fisheries. However, the genetic stock structure for the Indo-Pacific Ocean is not well-defined yet. Here, we used eight microsatellite loci to examine the genetic stock structure and effective population size of 307 silky sharks across 5 Indo-Pacific sampling locations. A major genetic break was found between Aceh and the remaining locations (FST = 0.0505–0.0828, p = 0.001). The Indian Ocean displayed a slightly lower effective population estimate (Ne) compared to the Pacific Ocean, potentially due to the higher fishing pressure in the Indian Ocean region. The lowest Ne was found in the Aceh population (Ne = 2.3), suggesting it might be a small and endemic population. These findings offer valuable information for the conservation and management of the silky shark. We suggest that the population around Aceh waters constitutes a distinct stock and should be managed independently. Further investigations into migratory and movement patterns are needed to define the boundaries of different stocks, ensuring effective management the silky shark across the Indo-Pacific region.
... Natal philopatry, the return of female individuals for parturition in the areas in which they were born, might emphasize the density disparity among sites, and juvenile female shark survival might lead to the settlement of its future offspring in that same site. Adult female N. acutidens parturition bi-annually around the Island of Moorea (Mourier, Buray, et al., 2013) and might alter the parturition behavior of C. melanopterus females by preventing them to give birth in some coastal areas. Indeed, N. acutidens were found to be part of apex predators on coral reefs along other species such as Galeocerdo cuvier, Sphyrna mokarran, Carcharhinus obscurus, and Carcharhinus albimarginatus because of their larger size and higher trophic niche, possibly allowing them to exert a top-down control on mesopredator reef sharks such as C. melanopterus (Frisch et al., 2016). ...
Article
Full-text available
Reef shark species have undergone sharp declines in recent decades, as they inhabit coastal areas, making them an easy target in fisheries (i.e., sharks are exploited globally for their fins, meat, and liver oil) and exposing them to other threats (e.g., being part of by‐catch, pollution, and climate change). Reef sharks play a critical role in coral reef ecosystems, where they control populations of smaller predators and herbivorous fishes either directly via predation or indirectly via behavior, thus protecting biodiversity and preventing potential overgrazing of corals. The urgent need to conserve reef shark populations necessitates a multifaceted approach to policy at local, federal, and global levels. However, monitoring programmes to evaluate the efficiency of such policies are lacking due to the difficulty in repeatedly sampling free‐ranging, wild shark populations. Over nine consecutive years, we monitored juveniles of the blacktip reef shark (Carcharhinus melanopterus) population around Moorea, French Polynesia, and within the largest shark sanctuary globally, to date. We investigated the roles of spatial (i.e., sampling sites) and temporal variables (i.e., sampling year, season, and month), water temperature, and interspecific competition on shark density across 10 coastal nursery areas. Juvenile C. melanopterus density was found to be stable over 9 years, which may highlight the effectiveness of local and likely federal policies. Two of the 10 nursery areas exhibited higher juvenile shark densities over time, which may have been related to changes in female reproductive behavior or changes in habitat type and resources. Water temperatures did not affect juvenile shark density over time as extreme temperatures proven lethal (i.e., 33°C) in juvenile C. melanopterus might have been tempered by daily variation. The proven efficiency of time‐series datasets for reef sharks to identify critical habitats (having the highest juvenile shark densities over time) should be extended to other populations to significantly contribute to the conservation of reef shark species.
... However, data on days-old neonates are scarce, and direct observations of parturition in the wild are rare. The period of parturition has therefore often been estimated based on reappearances of newly slender female sharks, for which recent observations indicated pregnancy (Porcher, 2005;Mourier et al., 2013a). However, this method requires intensive monitoring of the adult population via many hours of underwater surveying, and female reappearance may take several weeks. ...
Article
Full-text available
Sharks can incur a range of external injuries throughout their lives that originate from various sources, but some of the most notable wounds in viviparous shark neonates are at the umbilicus. Umbilical wounds typically heal within 1 to 2 months post-parturition, depending on the species, and are therefore often used as an indicator of neonatal life stage or as a relative measure of age [e.g. grouping by umbilical wound classes (UWCs), according to the size of their umbilicus]. To improve comparisons of early-life characteristics between studies, species and across populations, studies using UWCs should integrate quantitative changes. To overcome this issue, we set out to quantify changes in umbilicus size of neonatal blacktip reef sharks (Carcharhinus melanopterus) around the island of Moorea, French Polynesia, based on temporal regression relationships of umbilicus size. Here, we provide a detailed description for the construction of similar quantitative umbilical wound classifications, and we subsequently validate the accuracy of our classification and discuss two examples to illustrate its efficacy, depletion rate of maternally provided energy reserves and estimation of parturition period. A significant decrease in body condition in neonatal sharks as early as twelve days post-parturition suggests a rapid depletion of in utero-allocated energy reserves stored in the liver. Back calculations of timing of birth based on the umbilicus size of neonates determine a parturition season from September to January, with most parturitions occurring during October and November. As such, this study contributes valuable data to inform the conservation and management of young-of-the-year blacktip reef sharks, and we therefore encourage the construction and use of similar regression relationships for other viviparous shark species.
Article
Indo-Pacific coral reefs host diverse assemblages of elasmobranchs from small-bodied mesopredators to apex predators that may vary in the amount of time they spend on reefs. Reef sharks and rays as a group are threatened by human activities and are facing widespread population declines, primarily due to fishing. These human factors may affect not only elasmobranch abundance, but also their assemblage composition. Thus, a better understanding of the factors associated with differences in species-specific abundances and assemblage structure across multiple spatial scales in relatively undisturbed systems could enhance the conservation of shark and ray populations on reefs generally. Here, we used baited remote underwater video stations to examine species richness and assemblage composition of elasmobranchs across forereefs in French Polynesia, the world’s largest shark sanctuary. Boosted regression tree models revealed that island group, latitude, and island geomorphology had the greatest effect on elasmobranch species richness. Assemblages at most islands were dominated by blacktip reef sharks Carcharhinus melanop terus and grey reef sharks C. amblyrhynchos , while rays were generally rare, although there was significant spatial variation in elasmobranch assemblage composition. This variation was not associated with human factors, and appears to reflect species interactions and species-specific responses to environmental variation. Further studies on species interactions (facilitation, competition, and predation) among elasmobranchs will provide a better functional understanding of drivers of elasmobranch species composition on individual coral reefs.
Article
Populations of sharks, including those inhabiting coral reefs, have experienced dramatic global declines. Setting appropriate targets for restoring reef shark populations requires estimates of expected relative abundances in the absence of intense fishing. It is therefore important to identify factors that drive the carrying capacity of sharks in relatively intact reef systems and to determine whether expected shark abundance varies according to easy to assess variables. These variables could then be used by managers for setting restoration targets, or prioritizing resource allocation, for particular areas in the absence of detailed data. French Polynesia, the world’s largest shark sanctuary, provides a model system for addressing this question. We used baited remote underwater video surveys to assess relative abundance of sharks on 35 reefs across the broad geographic range of French Polynesia. Boosted regression tree models revealed that relative abundance of sharks varied significantly with island geomorphology. Overall, relative shark abundances at high islands were nearly 3 times lower than on atolls, and among atoll geomorphology types, open atolls had abundances nearly 20% higher than closed atolls. Island group, temperature, and net primary productivity had more limited effects. Human pressure (measured as market gravity) was not a significant factor. Although species-specific patterns varied, our findings suggest that environmental factors, particularly island geomorphology, should be taken into account when setting shark abundance recovery targets. Using this easy to assess factor can facilitate the allocation of conservation effort and improve assessments of species recovery efforts for islands in the Indo-Pacific region.
Article
Full-text available
Article
Full-text available
Understanding the movement behaviour of any species is important for developing species-specific management and conservation measures. In recent years, the sicklefin lemon shark Negaprion acutidens has shown rapid range reductions and has even disappeared altogether in certain areas. In this study, the area use patterns and site fidelity of the N. acutidens were assessed at the St. Joseph Atoll in the Seychelles. Passive acoustic telemetry methods were employed to monitor the movements of 19 tagged individuals for 1 year. Area use within the lagoon of the atoll was found to be highly restricted, with individuals typically utilising a small portion of the available area throughout the year. A high-use zone was apparent in the south-east of the atoll’s lagoon, which was shared by many of the monitored individuals. Fidelity to the study site was found to be extremely high, with the 79 % of tagged N. acutidens still present in the atoll at the end of the study. Individuals displayed both diel and tidal movements between the lagoon and surrounding habitats. The restricted area use and high site fidelity observed in this study highlight both the vulnerability of this species to rapid over exploitation and importance of remote habitats such as the St. Joseph Atoll in their future conservation. The results obtained here can be used to inform management decisions regarding the development and utilisation of similar atoll environments throughout the species’ range.
Article
Full-text available
Most arguments invoked so far by the scientific community in favour of shark conservation rely on the ecological importance of sharks, and have little impact on management policies. During a 57-month study, we were able to individually recognise 39 sicklefin lemon sharks that support a shark-feeding ecotourism activity in Moorea Island, French Polynesia. We calculated the direct global revenue generated by the provisioning site, based on the expenses of local and international divers. The total yearly revenue was around USD5.4 million and the 13 sharks most often observed at the site had an average contribution each of around USD316 699. Any one of these sharks represents a potential contribution of USD2.64 million during its life span. We argue that publicising economic values per individual will be more effective than general declarations about their ecological importance for convincing policy makers and fishers that a live shark is more valuable than a dead shark for the local economy. Studies monitoring the potential negative ecological effects of long-term feeding of sharks should, however, be conducted to ensure these are also considered. Besides declarations about the non-consumptive direct-use value of sharks, as promoted by ecotourism, the calculation of their other economic values should also benefit shark conservation.
Article
Full-text available
Large, solitary, marine predators such as sharks have been observed to aggregate at specific areas. Such aggregations are almost certainly driven by foraging and behavioural strategies making space for diverse spatial organizations. Reef-associated shark species often show strong patterns of site fidelity that could be viewed as a prerequisite for sociality. However, there is limited empirical evidence that such aggregations are driven by intrinsic social factors. Association data for blacktip reef sharks, Carcharhinus melanopterus, were obtained from photoidentification surveys conducted in Moorea coral reefs (French Polynesia). We adapted a social network approach to demonstrate evidence of four main communities and two subcommunities within the population. We confronted the resulting structure with candidate explanatory variables. Sharks formed spatial groups characterized by nonrandom and long-term associations, despite opportunities for social relationships to develop between communities. Sex and length of sharks tended to influence assortment at the population and community levels. Individual space use also explained community structure, although spatial assortment was globally weaker than random expectations, suggesting that observed associations were not an artefact of the sampling design or spatial distribution of individuals. We conclude that the observed grouping patterns not only resulted from passive aggregations for specific resources, but rather the communities developed from an active choice of individuals as a sign of sociability. Individual preferences and adaptation to local conditions, as well as demographic, ecological and anthropogenic factors, may explain the social variability between communities. This suggests that a stable grouping strategy may confer substantial benefits in this marine predator.
Article
Full-text available
The feeding of marine predators is a popular means by which tourists and tour operators can facilitate close observation and interaction with wildlife. Shark-feeding has become the most developed provisioning activity around the world, despite its controversial nature. Amongst other detrimental effects, the long-term aggregation of sharks can modify the natural behaviour of the animals, potentially increase their aggression toward humans, and favour inbreeding. During 949 diving surveys conducted over 44 mo, we investigated the ecology and residence patterns of 36 photo-identified adult sicklefin lemon sharks Negaprion acutidens. The group contained 20 females and 16 males. From this long-term survey, we identified 5 different behavioural groups that we described as ‘new sharks’ (7), ‘missing sharks’ (4), ‘resident sharks’ (13), ‘unpredictable sharks’ (5) and ‘ghost sharks’ (7). In spite of movements in and out of the area by some males and females, which were probably related to mating, the general trend was that residency significantly increased during the study, particularly in males, showing a risk of inbreeding due to the reduction of shark mobility. Intra- and interspecific aggression was also witnessed, leading to an increased risk of potentially severe bites to humans. Our findings suggest the need for a revision of the legal framework of the provisioning activity in French Polynesia, which could include a yearly closure period to decrease shark behavioural modifications due to long-term shark-feeding activities.
Article
Because sharks possess an unusual suite of reproductive characteristics, including internal fertilization, sperm storage, relatively low fecundity, and reproductive modes that range front oviparity to viviparity, they can provide important insight into the evolution of mating systems and sexual selection. Yet, to date, few studies have characterized behavioral and genetic mating systems in natural populations of sharks or other elasmobranchs. In this study, highly polymorphic microsatellite loci were used to examine breeding biology of a large coastal shark, the lemon shark, Negaprion brevirostris, at a tropical lagoon nursery. Over six years, 910 lemon sharks were sampled and genotyped. Young were assigned into sibling groups that were then used to reconstruct genotypes of unsampled adults. We assigned 707 of 735 young sharks to one of 45 female genotypes (96.2%), and 485 (66.0%) were assigned to a male genotype. Adult female sharks consistently returned to Bimini on a biennial cycle to give birth. Over 86% of litters had multiple sires. Such high levels of polyandry raise the possibility that polyandry evolved in viviparous sharks to reduce genetic incompatibilities between mother and embryos. We did not find a relationship between relatedness of mates and the number of offspring produced, indicating that inbreeding avoidance was probably not driving pre- or postcopulatory male choice. Adult male sharks rarely sired more than one litter at Bimini and may mate over a broader geographic area.
Article
Connectivity between coastal habitats and mid‐shelf and offshore coral reefs is a topical issue in the conservation and management of fishes and coastal ecosystems. Coastal habitats provide a range of ecosystem functions for sharks and rays and the use of coastal ecosystems by these species affects conservation and management outcomes. There is a growing need to better understand movement and habitat use patterns given recorded declines of many shark and ray species around the world. This study presents evidence of connectivity of blacktip reef sharks between coastal and offshore habitats, with juveniles dispersing from natal grounds at the onset of maturity and moving to new locations including offshore coral reefs. These dispersal patterns differ from previous accounts of reef shark movements and provide new evidence of connectivity among coastal habitats and offshore coral reefs. These large‐scale movements may help to maintain genetic diversity of populations, and could increase the resilience of blacktip reef shark populations to localized pressures. These movement and connectivity patterns also illustrate the potential importance of coastal habitats to reef shark conservation. Copyright © 2013 John Wiley & Sons, Ltd.
Article
Elasmobranch reproductive behavior has been inferred from freshly caught specimens, laboratory examinations of reproductive structures and function, or determined from direct observations of captive or free swimming wild animals. Several general behaviors have been described including seasonal sexual segregation, courtship and copulation. Courtship behavior was inferred for many species from the presence of scars and tooth cuts on the female's body, and noted in more detail from underwater observations. Copulation has been directly observed in captive settings for several species of elasmobranchs in large aquaria, and in the wild for three species of urolophids and for Triaenodon obesus and Ginglymostoma cirratum. A detailed ‘case history’ of nurse shark reproductive behavior is presented that may be used as a template for future work on shark reproductive behavior of other species. Our studies, using diver identifiable tags and in situ behavioral observations, provide unprecedented information on social structure and mating behavior in this species. Since 1993, 115 G. cirratum, 45 adults and 70 juveniles have been tagged in the Dry Tortugas, Florida. Observations show that adult males visit the study site every year with three males dominant. Individual adult females visit the study area to mate in alternate years. Polygyny and polyandry are common. Future research on reproductive behavior of elasmobranchs should address questions on male access to females, sexual selection and dominance hierarchies.