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.