Seabirds are excellent ecosystem indicators and are amongst the most threatened taxa globally. Aldabra Atoll, Seychelles, supports significant breeding colonies of seabirds, especially red-footed boobies Sula sula. The population was surveyed by boat during 1968–1969 and in 2000, over which period the population grew from c. 6,500 to 10,000 breeding pairs. In 2022–2023, we monitored five subcolonies across Aldabra to determine breeding phenology and breeding success. In August 2022 and February 2023, we surveyed the atoll-wide population using the boat-based survey methodology followed in earlier studies. We also carried out unmanned aerial vehicle (UAV) surveys in February 2023 to compare the results with the boat-based counts and to quantify inland colonies undetectable by boat. Boat surveys revealed that Aldabra’s red-footed booby population had grown to 36,720 pairs by 2023, an increase that is intrinsically possible based on our population model but only if the much lower count in 2000 was an underestimate. The UAV and boat counts were closely aligned in our study, and aerial images captured a similar number of nests to boat surveys for shoreline colonies. However, UAV surveys revealed several undocumented inland colonies. An additional 5,574 inland breeding pairs of red-footed boobies were counted from images captured inland during aerial surveys in the 2023 wet season, bringing the atoll-wide population to at least 45,817 pairs. We recommend UAVs for surveys of large, conspicuous seabird species at low-lying mangrove colonies. Our study highlights the global importance of Aldabra as the most significant red-footed booby colony in the Indian Ocean and possibly the world.

Over the years as a part of many fishery surveys, considerable number of stomiiform fishes were collected by the Centre for Marine Living Resources and Ecology (CMLRE) Research Vessel ‘Sagar Sampada’. The collection came from throughout the Indian EEZ and some from the western Indian Ocean. However, a systematic identification of these fishes had never been carried out prior to this paper. Thirty-four species were identified and it was found that eight species were new records to India and one to peninsular India. Among the records, two species, Photonectes paxtoni Flynn and Klepadlo, 2012 and Photonectes barnetti Klepadlo, 2011, are collected from the Indian Ocean for the first time. The paper provides a detailed report on all the new records and a list of stomiiform species collected during these surveys. Differences in barbel morphology observed for many of the stomiids are discussed.

We report two separate sightings of the ornate eagle ray Aetomylaeus vespertilio (Bleeker, 1852) in the Bazaruto Seascape of southern Mozambique. In May 2021, a single individual was encountered at a depth of 30 m during an in-water survey in the Bazaruto Archipelago National Park. Another solitary individual was documented ~55 km away during an aerial survey in the Vilanculos Coastal Wildlife Sanctuary three days later. These represent the first documented sightings of A. vespertilio in the Inhambane Province of Mozambique, confirming the presence of the species in the region and extending the known range northward along the south-east African coastline. Given the rarity of reported sightings, additional records are particularly valuable for these threatened and elusive rays in order to expand current knowledge of their distribution and range.

A total of 5478 fishes were sampled between 2009 and 2020 to assess length–weight, length–length and weight–weight relationships in 39 marine species from 10 families caught in the Seychelles waters by the artisanal fishery. Two types of length (total length TL, fork length FL) and three types of weight (whole weight WT, gutted weight GW and gilled-gutted weight GGW) were measured. The parameters of the relationships were estimated using the log-transformed allometric model with bias correction. Our results include length–weight, length–length and weight–weight relationships for 39, 20 and 18 species, respectively. Our length–weight data and resulting relationships were compared against FishBase database for 36 species and were in the Bayesian 95% confidence interval of the relationships available for 33 species and above for Gnathanodon speciosus, Lutjanus gibbus and Variola louti. Finally, for five abundant and widely dispersed species we tested for spatial differences in morphometric relationships between the Mahé Plateau and three southern atoll groups. Significant differences were found for two species only, but their magnitude was small. We thus argue for the regression relationships based on pooled data to be used for most types of population and community analyses. The availability of these morphometric relationships will support the application of accurate size-based analyses for Seychelles fisheries survey data, and so enhance understanding of the ecology of the reef-associated fish component of marine ecosystems and food webs, and improve fisheries research management.

Monitoring of nesting beaches is often the only feasible and low-cost approach for assessing sea turtle populations. We investigated spatio-temporal patterns of sea turtle nesting activity monitored over 17 successive years in the Lamu archipelago, Kenya. Community-based patrols were conducted on 26 stretches of beach clustered in five major locations. A total of 2,021 nests were recorded: 1,971 (97.5%) green turtle Chelonia mydas nests, 31 (1.5%) hawksbill Eretmochelys imbricata nests, 8 (0.4%) olive ridley Lepidochelys olivacea nests and 11 (0.5%) unidentified nests. Nesting occurred year-round, increasing during March–July, when 74% of nests were recorded. A stable trend in mean annual nesting densities was observed in all locations. Mean clutch sizes were 117.7 ± SE 1 eggs (range 20–189) for green turtles, 103 ± SE 6 eggs (range 37–150) for hawksbill turtles, and 103 ± SE 6 eggs (range 80–133) for olive ridley turtles. Curved carapace length for green turtles was 65–125 cm, and mean annual incubation duration was 55.5 ± SE 0.05 days. The mean incubation duration for green turtle nests differed significantly between months and seasons but not locations. The hatching success (pooled data) was 81.3% (n = 1,841) and was higher for in situ nests (81.0 ± SE 1.5%) compared to relocated nests (77.8 ± SE 1.4%). The results highlight the important contribution of community-based monitoring in Kenya to sustaining the sea turtle populations of the Western Indian Ocean region.

The Livingstone's fruit bat Pteropus livingstonii is endemic to the small islands of Anjouan and Mohéli in the Comoros archipelago, Indian Ocean. The species is under threat from anthropogenic pressure on the little that remains of its forest habitat, now restricted to the islands’ upper elevations and steepest slopes. We report the results of the most comprehensive survey of this species to date, and present recommendations for ongoing field conservation efforts and monitoring. Morning counts were conducted at roost sites in the wet and dry seasons during 2011–2013. Habitat structure around the roosting sites was characterized and roost numbers compared, to investigate the potential effect of habitat loss and degradation. We estimate the population to comprise c. 1,260 individuals distributed across 21 roosts on the two islands. All occupied roosting sites were restricted to a narrow altitudinal range, and roosting populations in agroforestry areas were smaller than those found in degraded and undisturbed forest. Only one of the 16 roosts on Anjouan was found in undisturbed, old-growth forest with no nearby signs of clearance for agriculture or landslides following tree-felling upslope. Following a suspected severe population decline as a result of widespread and long-term forest loss Livingstone's fruit bat has been recategorized as Critically Endangered on the IUCN Red List.

Madagascar is an important foraging ground for marine turtles in the Western Indian Ocean, yet the status of the country's nesting aggregations remains poorly documented. We assess the current status and trend in nesting throughout Madagascar, including data recorded by a community-based monitoring project in the Barren Isles (western Madagascar). We contextualize the findings in comparison with data from Madagascar's closest neighbouring states. Reports indicate that nesting levels have declined at many coastal sites, with no known recordings since 2000 at > 40 nesting sites. We estimate there are a minimum of 1,200 nests per year in Madagascar, with the largest recorded nesting aggregation (< 1,000 nests per year) found on islands off the west and northern coasts. The majority of nesting aggregations, including those recorded by the community-based monitoring project in the Barren Isles, are relatively small, in the order of < 50 nests per year, yet they are potentially important sources of regional genetic diversity. Nesting on many of the islands (e.g. Tromelin, Europa) around Madagascar has increased over the last 20 years, despite the fact that thousands of turtles probably originating from these sites are taken by fishers in the waters of Madagascar annually. We discuss the importance of protecting small nesting populations, and how community-based monitoring could be an important tool for conserving remote and vulnerable populations and building capacity for natural resource management.

An inventory has been made of the decapod fauna of the Glorieuses Islands, western Indian Ocean (WIO), following the BIORECIE 2 Expedition to the Islands, 5–17 December 2012. Field data are complemented by a review of taxonomic studies for these islands. Overall 157 species are now reported from the Glorieuses Islands, including 61 new records. The presence of the coconut crab, Birgus latro, is confirmed from these islands, for the first time since 1884, and the WIO distribution of this endangered species is updated, based on observations made in the region since 2006.

Records of the anthiine fish genus Meganthias are rare and most species are only known from few specimens. On 17 February 2012 a specimen of Meganthias natalensis, ~400 mm standard length was caught in 150 m depth about 10 nautical miles off Watamu, Kenya. This is the first record of the species from Kenyan waters.

The genetic diversity of haematozoan parasites in island avifauna has only recently begun to be explored, despite the potential insight that these data can provide into the history of association between hosts and parasites and the possible threat posed to island endemics. We used mitochondrial DNA sequencing to characterize the diversity of 2 genera of vector-mediated parasites (Plasmodium and Haemoproteus) in avian blood samples from the western Indian Ocean region and explored their relationship with parasites from continental Africa. We detected infections in 68 out of 150 (45 3%) individuals and cytochrome b sequences identified 9 genetically distinct lineages of Plasmodium spp. and 7 lineages of Haemoproteus spp. We found considerable heterogeneity in parasite lineage composition across islands, although limited sampling may, in part, be responsible for perceived differences. Two lineages of Plasmodium spp. and 2 lineages of Haemoproteus spp. were shared by hosts in the Indian Ocean and also on mainland Africa, suggesting that these lineages may have arrived relatively recently. Polyphyly of island parasites indicated that these parasites were unlikely to constitute an endemic radiation and instead probably represent multiple colonization events. This study represents the first molecular survey of vector-mediated parasites in the western Indian Ocean, and has uncovered a diversity of parasites. Full understanding of parasite community composition and possible threats to endemic avian hosts will require comprehensive surveys across the avifauna of this region.

This study assessed the Zanzibar sea cucumber fishery using a multidisciplinary approach.Data was collected by (i) interviewing various groups of actors in the fishery andreviewing management documentation and legislation, (ii) by monitoring catches and (iii)through a visual census of coastal sea cucumber populations in areas open and closed tofishing. The fishery showed clear signs of being unsustainable with high fishing effort,and weak formal and informal management institutions. The fishery operation wascharacterised by an intricate cross-scale structure with both fishers and sea cucumberproducts being transported across national borders. The visual census of commercial seacucumber stocks at three sites open to fishing around Zanzibar showed low densities acrossthe range of sea cucumber value groups including low value species. Furthermore, thediversity of commercial sea cucumber species was lower in fished reefs than on a protectedreef. The poor status of the sea cucumber populations was confirmed by the perception ofan overfished resource by the interviewed actors active in the fishery. This was alsodepicted by the paucity of high value species, and high representation of low value andnewly commercialised species in fishers catch. We conclude that the current state ofZanzibar’s sea cucumber populations is compromising the fisheries self-replenishment andexistence and that the fishery is in urgent need of a complete management reform.

Cymbastela sodwaniensis sp. nov. (order Halichondrida: family Axinellidae) is described from the subtropical waters of Sodwana Bay on the north-east coast of South Africa. The genus was previously unknown from southern Africa or the western and eastern parts of the Indian Ocean. This record represents the westernmost extent of this predominantly Indo-Pacific to Australasian genus. This new species record brings the number of Cymbastela species described to a total of nine.

Vitellogenin (VTG) levels were measured in the plasma of 143 female skipjack tuna, Katsuwonus pelamis caught in the Western Indian Ocean. These levels were correlated with the gonadosomatic index (GSI) and with plasma 17β-estradiol (E2) levels during the reproductive cycle. VTG and E2 levels were measured using a competitive enzyme-linked immunosorbent assay (ELISA) and a radioimmunoassay (RIA), rcspectively. VTG was purified from a pool of plasma obtained from females with high GSI using a double chromatography method (gel filtration and ion exchange). A specific antibody was obtained in rabbits. The VTG immunoenzymeassay developed gave an assay detection limit (90% binding) of 15 ng.ml-1. Mean VTG levels ranged from 1.2 mg.ml−1 to 4 mg.ml−1. Mean monthly VTG values remained relatively elevated during the resting periods (1.2 mg.ml−1 in April and 1.9 mg.ml-1 in September), while maximum levels reached only 4 mg.ml−1 during the reproductive season. The highest GSI values were observed from November to March during the major reproductive season corresponding to the North monsoon and from early June to late August during the minor reproductive season corresponding to the East monsoon. Lowest GSI values were found in April-May and September-October. Mean E2 levels exhibited considerable variability among all females sampled ranging from 700 pg.ml−1 to 9 ng.ml−1. This study demonstrated that the sexual maturation was correlated with the monsoon seasons and that there was a positive correlation between monthly variations of GSI, VTG and E2 levels in the skipjack tuna population from the Western Indian Ocean.

Quelques aspects de la reproduction du listao (Katsuwonus pelamis) dans deux zones distinctes de l'ouest de l'océan Indien ont été étudiés de février 1989 à février 1994. A partir d'échantillonnages faits, soit à bord des thoniers senneurs sur du poisson frais (1 656 individus), soit à la conserverie de Maurice sur des thons décongelés (4 152 individus), les différents stades du cycle sexuel ont pu être précisés. La taille de première maturité sexuelle est atteinte à 41–42 cm (longueur à la fourche) chez les femelles et à 42-43 cm chez les mâles, correspondant à des individus âgés d'environ 1,5 an. L'évolution mensuelle de la proportion des différents stades macroscopiques de maturation des gonades montre que, quel que soit le mois considéré, il y a toujours plus de 70 % des femelles échantillonnées qui présentent des ovaires en fin de maturation (stade IV). Les variations du rapport gonado-somatique (RGS) montrent que la reproduction du listao a lieu toute l'année mais qu'il existe cependant plusieurs périodes d'activité sexuelle plus intense. L'observation histologique de 737 ovaires indique la présence de follicules post-ovulatoires (indicateur de ponte récente) pendant les 2 périodes de mousson, mousson de nord-ouest (novembre à mars) et mousson de sud-est (juin à août) tandis que la proportion d'ovaires présentant des follicules atrétiques est maximale aux 2 périodes d'inter-mousson (avril-mai et septembre-octobre). L'étude du sex-ratio montre que. pour l'ensemble de la période d'étude et pour les deux zones considérées, la proportion de mâles est significativement supérieure à celle des femelles. Ses variations mensuelles semblent indiquer une accentuation de la prédominance des mâles à chaque période de ponte plus intense.

La fécondité par acte de ponte du listao Katsuwonus pelamis de l'ouest de l'océan Indien a été étudiée à partir de 281 femelles dont les tailles (longueur à la fourche) sont comprises entre 43 et 73 cm et dont les ovaires étaient à un stade de maturité sexuelle avancé. Le liquide de Gilson, utilisé comme agent conservateur et dissociateur des ovocytes, a une action importante et rapide (5 jours) sur le rétrécissement des ovocytes. Des comptages effectués à l'aide d'une cuve de Dollfus sur des sous-échantillons d'ovocytes dissociés, montrent que pour une même période d'activité sexuelle (février), la fécondité du listao du canal de Mozambique est semblable à celle des listaos du sud du plateau des Seychelles. Bien qu'une activité sexuelle du listao soit notée tout au long de l'année, la fécondité individuelle varie d'une saison à l'autre et ce, pour un même secteur géographique. Cette fécondité individuelle par acte de ponte varie de 80 000 œufs pour des femelles de 44 cm provenant de la côte nord-ouest de Madagascar à 1,25 millions d'œufs pour des femelles de 75 cm pêchées autour des Seychelles. La fécondité relative correspondante évolue donc entre 40 et 130 œufs/g de poids de corps. Pour cette espèce, le nombre de pontes successives a été estimé à 4 par an.