Juan De Nova Research Articles

Ocean control of the breeding regime of the sooty tern in the southwest Indian Ocean

Food availability, which is often seasonal, is regarded as a key factor in the breeding success of seabirds. In oceanic tropical areas, the resources are mostly patchy and ephemeral at the surface, and the seasonality is less marked than at higher latitudes. Such a situation influences greatly the breeding strategies of the oceanic seabird species. We conducted a comparative study of the breeding phenology of the sooty tern ( Sterna fuscata) in relation to the local and regional oceanographic conditions around the four major colonies (Europa, Juan de Nova, Lys and Bird Islands) of the southwest Indian Ocean. Over the 1997–2003 period, around all the studied locations, the sea-surface temperature (SST) and the chlorophyll concentration in the Mozambique Channel and the Seychelles area showed clear seasonal differences related to the southern climate and the monsoon phenomena. The breeding activity is synchronized at each studied colony, but the timings are very different. Seasonal reproduction occurs in austral winter at Europa and Bird Island and in austral summer at Juan de Nova; at Lys Island the reproduction is non-seasonal. For the seasonal colonies, there is a large monthly change in SST just before the beginning of reproduction, which is a proxy indicating the annual phytoplankton bloom. This variation is accompanied by the development of oceanic features such as fronts that favour aggregation of prey, and may also play an important role in the presence of schools of surface tuna, which are very important for the foraging success of sooty terns. Conversely, around Lys Island the seasonal variations of the marine environment do not lead to pronounced development of oceanic structures, and consequently, the longer-lasting phytoplankton bloom could explain the non-seasonal breeding regime there. Further studies will help discern the advantages and disadvantages of seasonal and non-seasonal reproduction regime in response to unpredictable fluctuations of the marine environment.

Assessment of the seabird community of the Mozambique Channel and its potential use as an indicator of tuna abundance

Tropical seabirds are known to associate with aggregations of surface dwelling predators, like tunas when feeding. Some species are even regarded as near obligate commensals of tunas. As food is one of the main factors that shape breeding strategies and determine breeding success of seabirds, it is of interest to test the hypothesis that variations in tuna abundance may have effects on foraging success and thus on breeding parameters of tropical seabirds. The Mozambique Channel is appropriate for such a study because relative tuna abundance is assessed annually (through fishery catches) and seabird populations are abundant. A regional synopsis shows that at least 3.034 million pairs of seabirds breed on islands of the Mozambique Channel, 99.3% being sooty terns. This super-abundant seabird is strongly associated with tuna and marine mammals when feeding. More than 99% of the sooty tern population of the Mozambique Channel breeds at three remote coralline islands, namely Juan de Nova (66%), Europa (25%) and Glorieuses (9%). Various breeding parameters (breeding population size, breeding time, growth rate of the chicks, daily food intake, diet) are studied at these three sites in order to investigate their relation to the marine environment (including tuna abundance). A preliminary estimate is made of the quantity of food eaten by the sooty tern population.

Gestion ou cogestion des « réserves naturelles » créées sur les îles Eparses de la zone sud-ouest de l'océan Indien et du canal de Mozambique ? (Le cas spécifique du récif de Tromelin, de l'archipel des Glorieuses et des îlots Juan de Nova, Europa et Bassas da India)

Pursuant to a regulation dated 18 November 1975 issued by the Préfet of La Réunion in his capacity as representative of the French Government, a nature reserve was created on the terrestrial part of the "Iles Eparses" scattered around Madagascar in the eastern Indian Ocean and coming under French sovereignty : these include the reef of Tromelin, the archipelago of the Glorieuses and the islands of Europa and Bassas de India. The island of Juan de Nova was implicitly placed under the same regime, which entails the prohibition of any industrial, agricultural or tourist activity and any hunting or fishing in the islands' lagoons as well as a prohibition on movements in these "pockets handkerchiefs". Other rigourous measures were subsequently taken to ensure the protection of the marine environment of the Iles Eparses, which now constitute refuges for their characteristic flora and strict sanctuaries for many colonies of resident birds (frigate birds, certain gannets) and migratory birds (pink flamingos, Antarctic terns) as well as sea turtles of the species Chelonia mydas.