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Contribution to the biological inventory and resource assessment of the Chesterfield reefs
Abstract
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
... The Coral Sea is a vast tropical/sub-tropical region in the Southwest Pacific comprising both significant coral reef systems around its boundary and open oceanic habitat with sea mounts and reef aggregations across its basin [39], [40]. Connectivity of reefs across the Coral Sea relies on sparse seamounts and reef aggregations, both in the Australian and French Exclusive Economic Zones (EEZ) [41]. Recent work suggest that these isolated seamounts, such as the Osprey and Shark reefs in the Australian EEZ, require urgent protection in order to conserve reef-associated shark populations [42]. ...
... Recent work suggest that these isolated seamounts, such as the Osprey and Shark reefs in the Australian EEZ, require urgent protection in order to conserve reef-associated shark populations [42]. Moreover, demonstrated interactions between large sharks and commercial long-lining and illegal shark-fining occur across the Coral Sea [41]. Despite this, information on the movement of large sharks in coastal coral reefs and open oceanic and seamount habitats in the Coral Sea is scant and as such the protection of large sharks in this region is of concern, particularly for wide ranging species that undertake large scale movements. ...
... The abundance and diversity of suitable prey available in the Chesterfields lagoon, in contrast to the sparsely distributed resources found on coastal reefs, may explain tiger shark residency. The Chesterfield reefs sustain large turtle populations including seasonal aggregations of breeding green turtles, populations of numerous sea snake species and breeding colonies of different species of sea bird (.200,000 individuals) in addition to teleost populations [41], [72]. For example, the stomach contents of one tiger shark (TS 19) tagged in the Chesterfield Islands contained hawksbill turtle (Eretmochelys imbricata), seabird and sea snake remains; prey items consistent with prey availability in the Chesterfields. ...
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.
... They have been uninhabited 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) published a checklist of the fishes of the Chesterfield Islands. ...
... Artisanal 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). The data provided 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 Chesterfield Islands. ...
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.
... It is a 8.1 ha low-lying carbonate islet, with low and grassy vegetation, housing 8 breeding seabird species for a total of >40,000 breeding pairs 34 . Both islets are surrounded by coral reefs supporting hard coral dominated benthic assemblages 38,39 . As all islands in the region are hosting seabirds, it was not possible to get control samples at corresponding distances from a seabird-free island. ...
Seabirds concentrate nutrients from large marine areas on their nesting islands playing an important ecological role in nutrient transfer between marine and terrestrial ecosystems. Here we investigate the role of guano on corals reefs across scales by analyzing the stable nitrogen isotopic (δ15N) values of the scleractinian coral Pocillopora damicornis on fringing reefs around two Pacific remote islets with large seabird colonies. Marine stations closest to the seabird colonies had higher nitrate + nitrite concentrations compared to more distant stations. Coral and zooxanthellae δ15N values were also higher at these sites, suggesting that guano-derived nitrogen is assimilated into corals and contributes to their nitrogen requirements. The spatial extent of guano influence was however restricted to a local scale. Our results demonstrate that seabird-derived nutrients not only spread across the terrestrial ecosystem, but also affect components of the adjacent marine ecosystem. Further studies are now needed to assess if this nutrient input has a positive or negative effect for corals. Such studies on remote islets also open fresh perspectives to understand how nutrients affect coral reefs isolated from other anthropogenic stressors.
Although juvenile anguillid eels live in freshwater/estuarine habitats, and marine eels live in diverse ocean environments ranging from shallow-to-deep continental shelf areas and around islands to deep-benthic habitats and deeper meso- and bathy- pelagic zones, the larvae (leptocephali) of all species mix together in the ocean surface layer. All types of eel habitats are present in the western South Pacific (WSP), so it is a unique region for studying long-lived leptocephali, especially because the westward flowing South Equatorial Current (SEC) and several countercurrents pass through many different WSP island groups and deep waters where both anguillid and marine eels live and spawn. Large mouth-opening IKMT sampling surveys for leptocephali were conducted in the southwest Pacific extending to French Polynesia in Jan-Mar 2013 (99 tows, 78 stations, 1052 larvae) and Jul-Sept 2016 (187 tows, 111 stations, 3976 larvae) that collected about 152 species of 18 anguilliform and elopomorph families. The larvae of mesopelagic serrivomerid eels were the most abundant taxa in all oceanic areas, and they were particularly abundant at northern SEC or equatorial latitudes. Australian and New Zealand anguillid eels had spawned in the western SEC areas, as previously detected, and the larvae of tropical anguillids were also only caught in western areas. The larvae of the mesopelagic nemichthyid and derichthyid eels were also widely distributed at lower abundances and with more patchy distributions, but larvae of Eurypharyngidae, Cyematidae, and Mongnathidae were rare. Shallow-water eel larvae were most abundant west of New Caledonia near the banks of the Chesterfield Islands, or near other island-groups, but they were rare in the 2 easternmost 2016 transects passing by both sides of Tahiti. Some conger eels were suggested to have spawned in offshore areas in the western region. Congrid Ariosoma and various shallow-water or slope eels had spawned in the region near the Chesterfield Islands or near New Caledonia where current jets can transport larvae westward, and eastward countercurrents exist. Some taxa of larvae of coastal species (muraenesocids, and elopomorphs) were extremely rare, all non-mesopelagic eel larvae were rare in the far-eastern transects, but the New Caledonia region with large shelf areas appears to be a high biodiversity region for marine eels, as it is for reef/shore fish in general.
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