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Pattern of movements from a home reef in the Chesterfield Islands (Coral Sea) by the endangered Giant Grouper, Epinephelus lanceolatus

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This study determined the movements of a Giant Grouper, Epinephelus lanceolatus, in which an acoustic tag was surgically implanted and monitored by an array of six VR2W acoustic receiver units from August 2010 to January 2013 in the remote, uninhabited Chesterfield Islands, Coral Sea (800 km West of New Caledonia). Our data revealed a home reef area (residency rate of 44.9%) with an increased activity revealed by movements at dawn and dusk toward and between two adjacent reef passages, probably for foraging. The fish was absent from its resident reef between October and December 2010 and 2012, corresponding to the time known for spawning aggregations of this species in New Caledonia. A skipped spawning seems to have occurred in 2011. We hope these data will be complemented in the future by locating the spawning site or sites and thus provide adequate conservation measures. The Coral Sea links two World Heritage Sites, the Australian Great Barrier Reefs and the New Caledonian coral reefs. It would be fitting to create a Marine Protected Area for the Chesterfield Islands between these two major conservation areas of the sea.
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Aquat. Living Resour. 28, 53–58 (2015)
c
EDP Sciences 2015
DOI: 10.1051/alr/2015006
www.alr-journal.org
Aquatic
Living
Resources
Pattern of movements within a home reef in the Chesterfield
Islands (Coral Sea) by the endangered Giant Grouper,
Epinephelus lanceolatus
Eric C
lua
1,a
, Claude Chauvet
2
, Johann Mourier
1
, Jonathan Mark Werry
3,4,5
and John E. Randall
6
1
LabEx “CORAIL” – USR 3278 CNRS-EPHE, Centre de Recherche Insulaire et Observatoire de l’Environnement (CRIOBE),
BP 1013, 98729 Papetoai, Moorea, French Polynesia
2
University of New Caledonia, BP 12814, 98802 Noumea, New Caledonia
3
Australian Rivers Institute and School of Environment, Grith University, Gold Coast campus, Parklands Drive, Southport,
Queensland 4222, Australia
4
Grith Centre for Coastal Management, Grith University, Gold Coast campus, Parklands Drive, Southport, Queensland 4222, Australia
5
Ocean and Coast Research, Gold Coast, Queensland 4217, Australia
6
Bishop Museum, 1525 Bernice St., Honolulu, HI 96817-2704, USA
Received 20 May 2015; Accepted 27 August 2015
Abstract This study determined the movements of a Giant Grouper, Epinephelus lanceolatus, in which an acoustic
tag was surgically implanted and monitored by an array of six VR2W acoustic receiver units from August 2010 to
January 2013 in the remote, uninhabited Chesterfield Islands, Coral Sea (800 km West of New Caledonia). Our data
revealed a home reef area (residency rate of 44.9%) with an increased activity revealed by movements at dawn and
dusk toward and between two adjacent reef passages, probably for foraging. The fish was absent from its resident
reef between October and December 2010 and 2012, corresponding to the time known for spawning aggregations
of this species in New Caledonia. A skipped spawning seems to have occurred in 2011. We hope these data will be
complemented in the future by locating the spawning site or sites and thus provide adequate conservation measures.
The Coral Sea links two World Heritage Sites, the Australian Great Barrier Reefs and the New Caledonian coral reefs.
It would be fitting to create a Marine Protected Area for the Chesterfield Islands between these two major conservation
areas of the sea.
Keywords: Coral reefs apex predator / serranidae / site fidelity / acoustic telemetry / spawning aggregations
1 Introduction
With a maximum total length (TL) of 2.3 m and weight
of 300 kg, the Indo-Pacific Giant Grouper, Epinephelus lance-
olatus (Bloch 1790) is the largest known reef fish. It is usually
found on coral reefs, especially where there are large caves,
but it is also known from harbours and deep estuaries, as well
as on wrecks and man-made structures, such as those for oil
exploration or wind generators. Although reported to a depth
of 100 m, it is usually found in much shallower water. It preys
mainly on spiny lobsters, small elasmobranchs, a variety of
bony fishes, large crabs, octopuses, and juvenile marine tur-
tles (Witzell 1981; Heemstra and Randall 1993). It is the most
widely distributed grouper in the world, from South Africa
and the Red Sea to the Pitcairn Islands (Randall and Heemstra
1991; Randall 1995).
Supporting information is only available in electronic form at
www.alr-journal.org.
a
Corresponding author: eric.clua@gmail.com
Information on the biology of Epinephelus la nceolatus is
incomplete compared to that of its sister species, the Atlantic
E. itajara (Randall 1967; Bullock et al. 1992;Sadovyand
Eklund 1999). Both species are particularly vulnerable to fish-
ing when they form large spawning aggregations (Coleman
et al. 1996;SadovyandDomeier2005; Saenz-Arroyo et al.
2005). E. lanceolatus does not become sexually mature un-
til it reaches 129 cm TL. It is highly valued in Asian fish
markets (Randall and Heemstra 1991; Lee and Sadovy 1998;
McGilvray and Chan 2003), resulting in special eort to catch
it at islands of the western Pacific. Based on knowledge of
fishermen and divers, local extinctions and extreme scarcity
have been reported for Western Pacific localities (Lavides et al.
2009; Zgliczynski et al. 2013). The species is classified by the
IUCN as “vulnerable”, the second highest risk of extinction
(Shuk Man and Chuen 2006).
Fishing pressure on this species has recently decreased in
some areas as a result of protective legislation. It is illegal to
spear this species in South Africa, where it is known as Brindle
Article published by EDP Sciences
54 E. Clua et al.: Aquat. Living Resour. 28, 53–58 (2015)
Fig. 1. A: The Chesterfield reefs in the Coral Sea situated midway between the east coast of Australia (AUS) and New Caledonia (NC). B:
Close up on the study site that includes Long Island (North-West of the Chesterfield reefs), which is delineated by two passages. The plain
white circle indicates the VR2W receiver called “Home” as it was standing in the vicinity of the Giant Grouper cave. The triangle indicates
the VR2W called “LP” standing for “Large Pass”, corresponding to the large passage North of Long Island. The diamond indicates the VR2W
called “SP” standing for “Small Pass”, corresponding to the Islets passage. These three receivers recorded detections from the tagged Giant
Grouper and these same symbols were also used to describe spatial and temporal distributions of detections in Figure 2A. The three other
receivers on the Eastern side of the Chesterfields reef lagoon are represented by empty circles; they did not record any detection from the giant
grouper. C: Picture of the 1.95 m TL Epinephelus lanceolatus that was caught and released in good health near receiver Home.
Bass (van der Elst 1981), and in Australia, where it is called
Queensland Grouper; such protection should be adopted else-
where. The rearing of the species for human consumption has
been successful (McGilvray and Chan 2003).
The capture of a large adult of Epinephelus lanceolatus
during a program of acoustic tagging of adult tiger sharks in
the Chesterfield Islands provided the opportunity to tag as well
as document its movements.
2 Materials and methods
The Chesterfield Islands are a series of 11 islets, of which
the largest is Long Island (length of 3.4 km). Numerous reefs
and channels, typically 30–40 m deep, lie on a north-south
oceanic ridge in the Coral Sea, isolated from Australia to the
west and New Caledonia to the east by app. 800 km in ei-
ther direction (Fig. 1A). The islands are surrounded by deep
drop-os to over 1000 m. The islets were named for the whal-
ing ship Chesterfield that explored the Coral Sea in the 1790s.
They were used for commercial whaling in the early 1860s,
and guano was extracted in the 1870s. They have been un-
inhabited for over 40 years. Large-scale illegal fishing still
takes place for sharks and reef fishes of high value, such as the
Giant Grouper (Clua et al. 2011). Kulbicki et al. (1994) pub-
lished a checklist of the fishes of the Chesterfield Islands. They
reported 866 species, representing 34 families, noting closer
anity to the fish fauna of New Caledonia than to the Great
Barrier Reef.
Acoustic telemetry was used for studying the movements
of large sharks in the Chesterfield Islands. An acoustic array
of six Vemco VR2W receivers were moored on concrete-filled
tyres at depths of 5–25 m in August 2010 and maintained un-
til January 2013 to track the movements of tagged Tiger Shark
(Fig. 1B, see Werry et al. 2014). One receiver was moored on a
patch reef in the lagoon opposite Long Island at a depth of ap-
prox. 5 m. For the purpose of this study, it was named “Home”.
Another receiver was moored at the edge of the large passage
north to Long Island, down the reef slope at 25 m depth and
1300 m from the receiver Home; this receiver was named LP
for “Large Pass”. A third receiver was moored 8250 m south
of the receiver Home at a depth of 22 m, at the entrance of
a smaller passage; it was named SP for “Small Pass”. The
three other receivers were moored on the Eastern side of the
lagoon and did not get any specific name during this study (see
Fig. 1B). On August 16, 2010, while fishing for large sharks
with a barbless hook and heavy line, a Giant Grouper 1.95 m
TL was caught in close vicinity of receiver “Home” (Fig. 1B).
The fish was restrained in a special harness in the sea that pro-
vided ecient protection and oxygenation of the animal, and
avoided the use of anesthetic during tagging. A small incision
was made on the central part of the abdomen, a transmitter
(Vemco V16, 69 kHz, length 54 mm, weight in the water 8.1 g,
battery life > 7 years, delay pulse 90 s) was inserted into the
peritoneal cavity, and the incision was closed with stitches.
The fish swam away vigorously on release (Fig. 1C).
Range tests were conducted to assess the distance from
which the receivers were able to detect the tagged fish. These
showed that detections significantly dropped after 400 m.
In November 2011, the acoustic data were downloaded,
batteries were replaced, and the receivers redeployed. The gear
was completely retrieved in January 2013. Following the data
download, we cleaned the raw data by deleting the rare false
detections. The valid detections were then sorted by site, date,
and time. For each receiver, we determined the number of de-
tections and a residency index, defined as the number of days
the fish was detected at a given receiver, divided by the total
number of days at liberty since tagging.
We used a generalized linear modelling framework (GLM)
to examine the eects of time of year (Month), time of day
(Hour) and site (Receiver) factors on the presence of the
grouper. The cyclicity of the “Month” and “Hour” factors were
modelled by including the variables as the cyclical function of
their sine and cosine components. The analysis used a bino-
mial error structure with a logit link function. We coded the
binomial dependent variable with 1 when the fish was detected
E. Clua et al.: Aquat. Living Resour. 28, 53–58 (2015) 55
Fig. 2. A: Scatterplot of diel detection patterns of the Giant Grouper recorded at Chesterfield reefs between August 2010 and January 2013.
Horizontal curves show daily sunrise and sunset. Shapes of the symbols on the scatterplot correspond to the receiver locations indicated in the
map in Figure 1B. B: Predicted probability of presence of the grouper at the three receivers for each calendar month and time of day inferred
from the most parsimonious GLM model.
and 0 when not detected for each hour of each day, and at each
receiver. Therefore, the fish had a total of 72 records for each
calendar day. Akaike’s Information Criterion (AIC) was used
to compare relative model support, where lower AIC values
indicate greater support for the model.
We used network analysis to investigate the spatial dy-
namics of the grouper. We implemented an Empirical derived
Markov chain (EDMC) analysis, which takes into account the
frequency of movements between receivers but also the res-
idency times and absence from the array (see Garcia et al.
2015; Stehfest et al. 2015). A Markov chain is a random pro-
cess and consists of transitions from one state to another (in
our case from receiver to receiver). The raw series of acoustic
detections was organized into an hourly detection time series.
For every hourly time step, if the fish was detected by a re-
ceiver, then the receiver ID was assigned to the state; if the fish
was not detected, it was assigned an absent state. A movement
count matrix was then computed containing movements be-
tween each receiver, as well as the movements from each state
to itself (residency periods when the fish stayed at the same
receiver) and movements to the absent state (transition periods
outside of detection range). The transition probability matrix
was constructed by dividing each number of transitions made
from one state to another or itself by the number of transitions
made from the state. We also calculated the eigenvector cen-
trality of each receiver which is a measure not only of the cen-
trality of a receiver, but also of the centrality of the receivers
it is connected to (see Stehfest et al. 2015).Thesameanalysis
was reiterated using day of year instead of hour in order to test
for dierences in movement and residency timing.
3 Results
The Giant Grouper was monitored for a total of 857 days
within the study area. It was detected on 135 days (15.75%) at
receiver LP, 196 days (22.87%) at receiver Home and 161 days
(18.78%) at receiver SP, for a total of 385 days (44.92%)
on at least one receiver, 101 days (11.78%) on a minimum
of 2 receivers and 6 days (0.70%) on the three receivers
(Fig. 2A; Table 1). The best GLM model determined by the
lowest AIC was one that incorporated the factors Month, Hour
and Receiver and an interaction between Hour and Receiver
(Model 9; Tables S.1 and S.2). For all receivers, the lowest
probability of presence was in October and November and the
greatest probability of presence outside these two months was
in the morning between 6:00 and 8:00 AM (Fig. 2B). Based on
real detections, the fish was totally absent from the area dur-
ing October and November 2010 and 2012, but still present
during the same months in 2011 (Fig. 2A). Although the fish
was more present at receiver Home compared to the others, the
patterns of probabilities were consistent across all receivers
(Fig. 2B) as the fish was detected by all receivers similarly
throughout the monitoring period (Fig. 2A).
Transition probabilities between states revealed low resi-
dency at the daily scale (Fig. 3A) and relatively high residency
at the hourly scale (Fig. 3B) with the highest probability of
hourly residency being at receiver Home. Movements between
receivers occurred mostly at a daily scale (Fig. 3A) rather than
at an hourly scale (Fig. 3B). Most movements occurred be-
tween receivers Home and LP but some direct movements in
both directions did also occur between the receivers LP and SP,
56 E. Clua et al.: Aquat. Living Resour. 28, 53–58 (2015)
Tab le 1. Receiver statistics. The residency index and number of detections are given by receiver as well as for all receivers combined. Residency
index is defined as the number of days the fish was detected divided by the number of monitoring days. The eigenvector centrality values of the
matrices of movement between receivers are given for the daily and hourly time scales.
Receiver Residency Number of Eigenvector centrality Eigenvector centrality
index detections (Day) (Hour)
SP 0.157 678 0.099 0.008
Home 0.228 3587 0.145 0.020
LP 0.187 1098 0.118 0.010
All 0.449 5363
Fig. 3. Movement and residency of the grouper over two temporal scales: using A- daily and B- hourly time series of detections. For each case,
a map showing the movements is presented in which arrow size is proportional to the transition probabilities between receivers and filled circles
are proportional to the probability of residency. Number of day the fish was detected at each receiver is indicated in parentheses. Empty circles
represent the three other receivers located on the east side which did not record any detections.
probably along the outer slope of the barrier reef (Fig. 3A). The
receiver Home was the most central as suggested by the high-
est eigenvector centrality (Table 1). Probabilities of being in
an absent state or coming from/going to an absent state were
higher at the hourly scale (Fig. 3). The fish was never recorded
by the three other receivers on the opposite side of the lagoon
(Fig. 3).
4 Discussion
Movements occurred between the three receivers in
the lagoon and channels surrounding Long Island, but the
distribution of detections suggests that the usual shelter of this
grouper would be around receiver Home, as confirmed by the
sighting during a diving session of a Giant Grouper of a similar
size in a reef cave of the area in August 2010 (J.C. Toison, Pers.
Comm.). The fish used the adjacent passages (in particular the
closest Long Island passage) mainly at dawn (between 5:00
and 12:00 AM), probably for foraging purposes. The lower
detection rate recorded outside the morning period (Fig. 2B)
may be due to the fish residing in a cave, which would re-
duce its detection by the receivers. High probabilities of being
out-of-receiver range are common in reef fish (Garcia et al.
2015) which may be due to the distance between receivers or
E. Clua et al.: Aquat. Living Resour. 28, 53–58 (2015) 57
to the sheltering behaviour of the studied species. Analysis of
the movement sequences also showed that the grouper went
from one passage to another by swimming either inside the la-
goon or along the outer slope. The second hypothesis seems
more plausible as the way inside the lagoon preventing any
detection by the receiver Home would oblige the grouper to
swim and remain on a nearly bare sandy bottom area, which is
probably less attractive than the outer slope of the barrier reef
that hosts more potential prey. The dierences between move-
ment matrices at hourly and daily scales (Fig. 3) indicate that
movements between receivers took more than one hour. The
absence of any detections on the three other receivers located
inside the Chesterfield lagoon indicated a strong attachment to
the passages and outer slope, with a strong residency pattern
(44.9% of days) in an area of about 12 km of diameter delin-
eated on the North and South sides by the two reef passages.
Based on the definition provided by Colin et al. (2003),
spawning aggregations of E. lanceo latus were observed along
the west coast of New Caledonia in October and November (C.
Chauvet, Pers. Comm.). The absence of the tagged E. lance-
olatus in the Chesterfields during this period and could be
explained by migration for spawning. Our observations of
E. lanceolatu s in the Chesterfields are also consistent with
a 2-month period which is dedicated to mating by its sister
species, E. itajara, in the Caribbean Sea (Mann et al. 2009).
The detection of the tagged grouper in the network of
receivers during the mating period in 2011 could be ex-
plained by its failure to build up the caloric reserve needed
for the long migration in the open sea to the spawning site.
“Skipped spawning” has been documented for several fish
species (Rideout and Tomkiewicz 2011).
A slight increase in activity, mainly at dusk, was noted for
the months May to August prior to the migration before the
end of September (see Fig. 2B), indicating an increase in for-
aging needed for the production of gametes and the upcoming
intense activity of spawning (Rideout and Tomkiewicz 2011).
Regarding the observed site fidelity of the tagged E. lance-
olatus, Elkund and Schull (2001) showed that among the 50
tagged Goliath Grouper (E. itajara) that were resighted in
the framework of their study, 64% had been tagged inshore
(outside the spawning season) and resighted on the same site
within two weeks to two months post-tagging. They could then
show evidence of site fidelity, already mentioned by Sadovy
and Elkund (1999). One fish tagged at a popular diving site
was resighted on the same wreck repeatedly for eight months.
Our findings on E. lanceolatus are consistent with such site
fidelity, except for the spawning season.
5 Conclusion
Our data suggest that Epinephelus lanceolatus moves be-
yond its Chesterfield Islands home area only for spawning. As
a large apex predator, the population of E. lanceolatus at any
site within its broad distribution is very low, even without fish-
ing. Because of its enormous size, it is the goal of fishermen,
whether by hook and line or spear, to land one of these huge
fish. Its high value in the live reef fish trade (McGilvray and
Chan 2003), makes it very susceptible to targeted fishing, es-
pecially if spawning sites are discovered. This results in the
removal of a higher percentage of the males of the population
and increases the danger of extinction. The low population of
the species, its high value, and its vulnerability should be taken
into account for conservation and management strategies. Arti-
sanal fishing does occur in the Chesterfield Islands. It primarily
targets invertebrates (such as sea cucumbers and lobsters) but
it also includes reef fishes (Clua et al. 2011).Thedataprovided
by our study will help to define the Essential Fish Habitat (see
Conover et al. 2000) of this endangered species and will aid
in creating a Marine Protected Area (MPA) for the Chester-
field Islands. The optimal MPA would be one that includes the
entire critical habitat for the species, including one or more
spawning sites. Further acoustic tagging, especially if based
on satellite tracking methodologies, is needed to identify and
protect the spawning sites.
Acknowledgements. We acknowledge the nancial support of the
Agence Française de Développement through the funding of
the CRISP programme and the technical support of the Secretariat
of the Pacific Community in Noumea. We thank Thomas Vignaud for
the photo of the tagged E. lanceolatus. We also thank the IRD team
in Nouméa, in particular Armelle Renaud, for the technical support
for retrieving the VR2 receivers from the study area in January 2013.
This work was conducted under permit No. 6024-4916/DENV/SMer
(New Caledonia) and ethics ENV/17/09/AEC (Grith University).
The contribution of two anonymous reviewers and the associate edi-
tor were highly appreciated for the improvement of this paper.
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Pacific Islands. Coral Reefs 32, 637–650.
... Rideout et al. (2005) reported that skipped spawning had been described in more than 30 species. Since then, it has been reported in a variety of new species including sablefish Anoplopoma fimbria (Rodgveller et al., 2016), humpback chub Gila cypha (Pearson et al., 2015(Pearson et al., , 2016, grey mullet Mugil cephalus (Fowler et al., 2016), and giant grouper Epinephelus lanceolatus (Clua et al., 2015). The observable characteristic that allows the identification of skipped spawning varies from system to system. ...
... The observable characteristic that allows the identification of skipped spawning varies from system to system. In populations that migrate to spawning grounds, individuals of adult size or age that stay behind at the feeding grounds are often assumed to skip spawning (e.g, Trotter et al., 2012;Young et al., 2014;Clua et al., 2015;Fowler et al., 2016). In other cases, visual gonad inspection can conclude that ovaries or testes are nondeveloping but have a distinct appearance from having spawned earlier in life (e.g, (Yaragina, 2010). ...
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Although the phenomenon of skipped spawning has been described in numerous fishes, time-series are scarce. We used the presence of post-ovulatory follicles in histological gonad slides from females not developing oocytes for Northeast Arctic (NEA) haddock Melanogrammus aeglefinus from 2009 to 2012 to construct a length-based statistical model giving the probability that a non - developing female was skipping spawning, as opposed to not being sexually mature. This model was then applied on demographic winter survey data from the Barents Sea from 1989 to 2014. This indicated large annual variation in skipping numbers. Comparing these survey estimates to the total annual ICES stock numbers, we found that skipping peaked in the years 1994–1996 and 2009–2014, when the median yearly estimate of skipped spawners was 20–45 % of all females aged ≥ 3 years. In contrast, only ∼ 3 % of females at age ≥ 3 years skipped spawning in 2007. The proportional representation of skipped spawners at the stock level appeared linked to stock energy reserves with more skipping occurring when energy levels were low. Skipping also became more frequent with increasing population age, i.e. when immatures were less abundant, although the very largest/oldest fish tended to spawn. Because the proportion of NEA haddock that skips spawning is variable and can be high, understanding variation in this phenomenon and its drivers may improve population dynamic models.
... FSAs are known to occur along promontories and reef channels (Johannes and Hviding, 2000;Claydon, 2004;Heyman et al., 2005;Nemeth, 2012;Colin, 2012;Kobara et al., 2013), although data on FSAs in proximity to reef passages are rare or hidden (Shcherbina et al., 2008). In addition to supporting FSAs, reef passages are known for hosting iconic, sometimes endangered, species such as giant groupers (Clua et al., 2015) and humphead wrasse (Sadovy et al., 2003), and they are used by migratory species such as cetaceans, mantas and sharks (Breckwoldt et al., in review;Anderson et al., 2011;McCauley et al., 2014;Mangubhai et al., 2019) or green turtles, which travel between distant reproduction areas and foraging areas located in lagoons (Read et al., 2014;Piovano et al., 2019). Distance from reef passage was found to be a clear predictor of whale shark presence at Ningaloo Reef (Anderson et al., 2014), and Takekawa (2000) documented the hunting of dolphins with the 'help' of a reef passage. ...
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Coral reefs host exceptionally diverse and abundant marine life. Connecting coasts and sheltered lagoons to the open ocean, reef passages are important yet poorly studied components of these ecosystems. Abiotic and biotic elements ‘pass’ through these reef passages, supporting critical ecological processes (e.g. fish spawning). Reef passages provide multiple social and ecological benefits for islands and their peoples, but are so far neither characterized nor recognized for their multifaceted significance. This study investigated 113 reef passages across nine Pacific islands (Fiji, New Caledonia, Vanuatu). GIS-based visual interpretations of satellite imagery were used to develop criteria to define three distinct types, mainly based on distance to coastline and presence/absence of an enclosed water body. The discussion identifies ways to refine and augment this preliminary typology as part of a research agenda for reef passages. With these next steps, this typology will be extendable to other regions to better document reef passages and their various roles, supporting biodiversity conservation and sustainable fisheries management.
... However, these locations are home to abundant sea bird populations that produce large quantities of guano, which is rich in both organic nitrate and phosphate. In fact, Chesterfield, Bellona and Entrecasteaux were exploited for guano extraction (Clua, Chauvet, Mourier, Werry, & Randall, 2015) in the 1870s. The phosphate origin may be mineral or organic (including anthropogenic). ...
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Aim: To determine the ecoregions (spatial marine areas with similar environmental and physical conditions associated with relatively homogeneous fish assemblages) for shallow reef fish assemblages based on predictive models of beta diversity (b-diversity) that account for both large-scale environmental factors and local habitat characteristics. We assessed the influence of a spatial scale to rank the importance of these factors. Location: New Caledonian (south-west Pacific Ocean, 17–24° S, 158–172° W) Exclusive Economic Zone, Coral Sea Marine Park. Taxon: Fish. Methods: Fish and habitat data that were collected at 13 sites around New Caledonia using unbaited rotating underwater video (285 sampling stations) were analysed. Gradient forest modelling was used to predict the fish b-diversity along the gradients of environmental factors. Ecoregions were obtained by applying clustering methods to gradient forest predictions. Results: The gradient forest models of b-diversity retained 59 species (total: 206 fish species) with R² > 0, including 19 fish species with R² from 0.03% to 69%. For these 19 species, the models explained up to 26% of the variance. At a large scale, b-diversity was significantly explained by nutrient concentrations, sea surface salinity and temperature. Among the eight ecoregions that were delineated based on the b-diversity predictions, three regions corresponded to remote sites under oceanic influence where human pressures are low and the surface nutrient concentrations are high. On the local scale, the benthic habitat explained b-diversity better than the physical and chemical parameters, particularly in the areas subject to anthropogenic pressures. Main conclusions: On the local scale, the respective importance of environmental factors (physical and chemical parameters versus benthic habitat) differed according to ecosystem health. Our findings suggest that nutrient enrichment due to avifauna may have a positive effect on fish b-diversity when an ecosystem is healthy. The ecoregions reflect fish species composition in relation to a large set of environmental parameters.
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A better understanding of the key ecological processes of marine organisms is fundamental to improving design and effective implementation of marine protected areas (MPAs) and marine biodiversity. The movement behavior of coral reef fish is a complex mechanism that is highly linked to species life-history traits, predation risk and food resources. We used passive acoustic telemetry to study monthly, daily and hourly movement patterns and space use in two species, Schoolmaster snapper (Lutjanus apodus) and Stoplight parrotfish (Sparisoma viride). We investigated the spatial overlap between the two species and compared intra-specific spatial overlap between day and night. Presence-absence models showed different diel presence and habitat use patterns between the two species. We constructed a spatial network of the movement patterns, which showed that for both species when fish were detected by the array of receivers most movements were made around the coral reef habitat while occasionally moving to silt habitats. Our results show that most individuals made predictable daily crepuscular migrations between different locations and habitat types, although individual behavioral changes were observed for some individuals across time. Our study also highlights the necessity to consider multiple species during MPA implementation and to take into account the specific biological and ecological traits of each species. The low number of fish detected within the receiver array, as well as the intraspecific variability observed in this study, highlight the need to compare results across species and individuals to be used for MPA management. Copyright © 2015 Elsevier Ltd. All rights reserved.
Technical Report
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This 264 pp. report details the findings of a multidisciplinary scientific mission that took place in the Chesterfields islands in August 2010. 12 scientists have been assessing the coral reefs diversity, fish and invertebrates ressources, sharks, marine mammals and birds populations. The main findings are: - CORALS : the species diversity in scleractinian corals is higher than anticipated, given the isolation of the area and the limited variety of biotopes; - CORAL HABITAT : the health status is globally good with some punctual and natural stresses; - BENTHIC INVERTEBRATES : the diversity of species with a commercial value is low; a single holothurian was in high densities, with a medium economic value; one giant clam was also in good densities; the global level of resources is still good despite signs of intensive exploitation above 12 m of depth; - FISH : no viable nor sustainable management of commercial fishing seems possible; - SHARK : reef sharks are in low density with low average sizes, probably following a recent overfishing; density and average size of tiger shark are good; no evidence of the presence of white shark in the area; - BIRDS : nesting populations are stable and the presence of several vulnerable species confirms the status of Chesterfield as an International Bird Area; - CETACEAN : no sign of replenishment of humpback whales stock; atypical occurrence of a large dolphin usually living close to continents or large islands; These main findings suggest the following recommendations for a sustainable management: - BAN on any kind of fishing for sharks; - BAN of commercial fishing of reef fish and trochus; - FISHING REGULATION (through quotas or ban of specific fishing techniques) of giant clams, lobsters and holothurians; - ENFORCMENT of regulation linked to the IBA status for birds and sanctuary area for cetacean; - MANAGEMENT of invasive species from the islets
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Knowledge of the habitat use and migration patterns of large sharks is important for assessing the effectiveness of large predator Marine Protected Areas (MPAs), vulnerability to fisheries and environmental influences, and management of shark-human interactions. Here we compare movement, reef-fidelity, and ocean migration for tiger sharks, Galeocerdo cuvier, across the Coral Sea, with an emphasis on New Caledonia. Thirty-three tiger sharks (1.54 to 3.9 m total length) were tagged with passive acoustic transmitters and their localised movements monitored on receiver arrays in New Caledonia, the Chesterfield and Lord Howe Islands in the Coral Sea, and the east coast of Queensland, Australia. Satellite tags were also used to determine habitat use and movements among habitats across the Coral Sea. Sub-adults and one male adult tiger shark displayed year-round residency in the Chesterfields with two females tagged in the Chesterfields and detected on the Great Barrier Reef, Australia, after 591 and 842 days respectively. In coastal barrier reefs, tiger sharks were transient at acoustic arrays and each individual demonstrated a unique pattern of occurrence. From 2009 to 2013, fourteen sharks with satellite and acoustic tags undertook wide-ranging movements up to 1114 km across the Coral Sea with eight detected back on acoustic arrays up to 405 days after being tagged. Tiger sharks dove 1136 m and utilised three-dimensional activity spaces averaged at 2360 km(3). The Chesterfield Islands appear to be important habitat for sub-adults and adult male tiger sharks. Management strategies need to consider the wide-ranging movements of large (sub-adult and adult) male and female tiger sharks at the individual level, whereas fidelity to specific coastal reefs may be consistent across groups of individuals. Coastal barrier reef MPAs, however, only afford brief protection for large tiger sharks, therefore determining the importance of other oceanic Coral Sea reefs should be a priority for future research.
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Widespread declines among many coral reef fisheries have led scientists and managers to become increasingly concerned over the extinction risk facing some species. To aid in assessing the extinction risks facing coral reef fishes, large-scale censuses of the abundance and distribution of individual species are critically important. We use fisheries-independent data collected as part of the NOAA Pacific Reef Assessment and Monitoring Program from 2000 to 2009 to describe the range and density across the US Pacific of coral reef fishes included on The International Union for the Conservation of Nature’s (IUCN) 2011 Red List of Threatened Species. Forty-five species, including sharks, rays, groupers, humphead wrasse (Cheilinus undulatus), and bumphead parrotfish (Bolbometopon muricatum), included on the IUCN List, were recorded in the US Pacific Islands. Most species were generally rare in the US Pacific with the exception of a few species, principally small groupers and reef sharks. The greatest diversity and densities of IUCN-listed fishes were recorded at remote and uninhabited islands of the Pacific Remote Island Areas; in general, lower densities were observed at reefs of inhabited islands. Our findings complement IUCN assessment efforts, emphasize the efficacy of large-scale assessment and monitoring efforts in providing quantitative data on reef fish assemblages, and highlight the importance of protecting populations at remote and uninhabited islands where some species included on the IUCN Red List of Threatened Species can be observed in abundance.
Chapter
Goliath grouper,1Epinephelus itajara, the largest grouper in the western North Atlantic, has been protected from all harvest in U.S. waters since 1990, after years of overexploitation at its spawning aggregations. We are currently assessing this species’ recovery by using a variety of tagging methods, including conventional tagging and acoustic telemetry. We have been monitoring the adult populations at offshore spawning aggregations and the juveniles at their nursery areas along mangrove shorelines. Conventional mark/recapture studies enabled us to predict juvenile goliath grouper population densities, growth rates and survival rates. Conventional tagging and recaptures of both adults and juveniles have given information on habitat use and movement patterns, while manually tracking acoustically tagged fish provided fine-scale habitat use and seasonal movements. Continuous data-logging hydrophones provided long-term data on site residency of both juveniles and adults. Future studies will include the use of satellite tracking to define large scale ontogenetic and spawning migrations to previously undescribed habitats. Each method of tagging has provided answers to key questions regarding goliath grouper population biology, but every method also has had its limitations. By starting with the most economical and simplest methods, we have built upon each study by adding complexity as it is warranted.