Seabirds, i.e. species that spend a large part of their lives at sea, of the coast of mainland East Africa, associated islands and of the open sea are abundant and diverse, though they have received little attention in the region until the last 5-10 years. Recently, growing interest in how they can serve as indicators to patterns of oceanic productivity, and thereby to fisheries, has led to a rapid upsurge in studies. Further, the impacts of growing, ocean-wide fishing effort have led to greater concern about impacts, to the marine environment as well as to seabirds.
Globally, there are over 300 species of true seabirds, with about half this number reported for the WIO. The main groups of seabirds are albatrosses, petrels, shearwaters, tropicbirds, boobies, frigatebirds, gulls, terns, cormorants and penguins, many of which typically breed in large colonies on small islands or remote portions of continents. At least 31 species of seabird breed on WIO islands, and an additional number (such as African penguins and cormorants) are known also from the mainland coast of eastern and south-eastern Africa.

Breeding and nesting - A recent regional survey of the seabird species that breed in the WIO estimated a total seabird population of 7.4 million pairs, and found that the main breeding grounds are in the Seychelles (Aldabra and the granitic islands) and in the Mozambique Channel (Juan de Nova, Europa and Glorieuses). The Mascarene Islands also have significant breeding populations, at smaller numbers but for rarer species. In 2005, 16 species were recorded breeding in the Mozambique channel with an extraordinarily high density of over 3 million breeding pairs, of which 99% were sooty terns (Sterna fuscata), concentrated at Juan de Nova (66%, 2 million pairs), Europa (25%, 760,000 pairs) and Glorieuses (9%, 270,000 pairs). Thirteen thousand pairs spread among 13 seabird species breed on islets off the W coast of Madagascar, but population sizes are low and threatened by poaching. Europa is of particular conservation interest as it holds some of the last colonies of large Pelecaniforme birds (frigatebirds, red-footed boobies and red-tailed tropicbirds), which have experienced dramatic declines in most islands of the WIO.

Barau Petrel

Tropic birds

Sooty terns
all pictures © Mathieu le Corre

Masked booby

Foraging - Many tropical seabirds associate with tuna, as both groups feed in areas of high productivity, determined by ocean circulation patterns, and also because top predators such as tuna drive the primary seabird prey to the surface, where they become accessible to the birds. This interaction makes seabird populations highly dependent on the health of tuna and other open ocean top predators. They can also serve as indicators of the health of these top predators.
Based on foraging grounds, and their overlap with the nesting grounds, the following five areas were identified as priority regions for seabirds in the WIO:

Primary seabird breeding colonies in the WIO. The largest circles represent > 1,000,000 breeding pairs.
© Le Corre et al 2012

Seabird density based on tracking data, indicating major foraging grounds. Dark red indicates the highest density of seabirds.
© Le Corre et al 2012

Seychelles Basin - the Seychelles Plateau and a wide oceanic region around the Plateau is the main area occupied by wedge-tailed shearwaters (95,000 pairs that breed in the Seychelles) and white-tailed tropicbirds (6500 pairs). The Seychelles Archipelago (excluding Aldabra and Cosmoledo) supports the greatest abundance of seabirds in the tropical Indian Ocean with 14 breeding species totaling 2.2 million pairs.
Southern Mozambique Channel around Europa Island - Europa Island is one of the most important seabird breeding sites in the WIO, with 20, 40 and 8 of the great frigatebirds, red-tailed tropicbirds and red-footed boobies respectively. The southern Mozambique Channel is a major foraging area for all 3 species, as well as for most seabirds of the island.
Madagascar Plateau (Walters Shoals) – is a major foraging ground for two of seven tracked seabird species, the red-tailed tropicbird (many of which breed on islands in the S. Mozambique channel (Europa and Nosy Vé), and Barau’s petrel, which is endemic to Reunion and classified as endangered. With the limited sample size, the region is likely significant for several other seabird species.
Mascarene islands (Reunion, Mauritius, Rodrigues) and Tromelin Island - the only breeding ground of two endemic petrels, the Barau’s petrel (endangered) and the Mascarene petrel (Pseudobulweriaaterrima, critically endangered), and other species that breed on Reunion.
Central Indian Ocean – is a wide region for foraging for at least four migratory seabirds: Barau’s petrel, the red- tailed tropicbird, the wedge-tailed shearwater and the white-tailed tropicbird. There are two main subregions, both associated with seamounts and undersea topography that enhance upwelling, and therefore productivity.

Threats - The main threat to both resident and migrant birds in the WIO is habitat degradation, affecting breeding and nesting sites. Other threats are disturbance by fishers and tourists, egg collecting, and predators such as rats, cats, dogs and potentially oil spills. Invasive species such as rats and cats can decimate breeding bird populations on remote islands. Fisheries impact seabirds in various ways, the main impacts include direct mortality by fishing gear (bycatch) and competition when fisheries and seabirds target the same prey. Climate change is an increasing and more insidious threat to coastal birds. Rising sea-levels may swamp low-lying nesting colonies or lead to loss of shoreline feeding habitat. Warming and acidification of waters damages coral reefs, and may affect the distribution and abundance of key food species for some coastal and sea-birds.
Few species breeding in the WIO region are globally threatened (i.e. on the IUCN Red List, see sheet H1) because most seabirds have very wide distributions. However dependence on remote islands for breeding makes individual populations highly vulnerable to changes and threats. The Roseate tern is of particular concern in the WIO as populations have undergone major declines, as is the status of the Reunion Petrel (Critically Endangered) and Barau’s Petrel (Endangered) on Reunion.

Management and Conservation - Some of the large nesting seabird colonies and key roosting and feeding sites for coastal migrants lie within MPAs. For example, the Seychelles has a particularly large number of important breeding sites which are now protected e.g. Aldabra, Cousin Island, and Aride. Another mechanism for the protection of bird populations is through the designation of Ramsar sites under the Convention on Wetlands (Ramsar). For designation, a site must meet one of two criteria of importance to waterbirds: Criterion 5 for sites that regularly support at least 20,000 waterbirds; and Criterion 6 for sites that regularly support 1% or more of a waterbird species’ biogeographic population. Many of the key sites for bird species are now recognised internationally as Important Bird Areas (IBAs), under a scheme initiated by BirdLife International, and several of these are included either within or overlap with MPAs. The distribution of IBAs in the WIO reflects many of the most important breeding sites mentioned above, but further protection measures are necessary in many of them. BirdLife’s Global Seabird Programme, which started in 1997, focuses on specific objectives for seabirds, with a focus on fishery interventions and regional and global scale issues affecting seabirds. In 2004 the GSP launched a marine IBA programme, and work towards identifying marine IBAs in the WIO region is well underway.

Key References - Baker and Fison 1989; Chittenden) (2007); Grant (2010); Harrison 1989; Hayman et al. 1986; Jaquemet et al. (2005); Le Corre & Bemanaja (2009); Le Corre & Jaquemet (2005); Le Corre et al. (2012); Message & Taylor (2005); Newman (2010); Olsen & Larsson (2004); Sinclair & Ryan (2011); Sinclair et al. (2002); Soothill & Soothill 1982; Stevenson & Fanshawe (2004); Watson et al. 1963; ZICOMA (2001); Zimmerman et al. (2001). --> References