Patterns in reef fish assesmblages:insights from the Chagos Archipelago

<div><p>Understanding the drivers of variability in the composition of fish assemblages across the Indo-Pacific region is crucial to support coral reef ecosystem resilience. Whilst numerous relationships and feedback mechanisms between the functional roles of coral reef fishes and reef benthic composition have been investigated, certain key groups, such as the herbivores, are widely suggested to maintain reefs in a coral-dominated state. Examining links between fishes and reef benthos is complicated by the interactions between natural processes, disturbance events and anthropogenic impacts, particularly fishing pressure. This study examined fish assemblages and associated benthic variables across five atolls within the Chagos Archipelago, where fishing pressure is largely absent, to better understand these relationships. We found high variability in fish assemblages among atolls and sites across the archipelago, especially for key groups such as a suite of grazer-detritivore surgeonfish, and the parrotfishes which varied in density over 40-fold between sites. Differences in fish assemblages were significantly associated with variable levels of both live and recently dead coral cover and rugosity. We suggest these results reflect differing coral recovery trajectories following coral bleaching events and a strong influence of ‘bottom-up’ control mechanisms on fish assemblages. Species level analyses revealed that <i>Scarus niger</i>, <i>Acanthurus nigrofuscus</i> and <i>Chlorurus strongylocephalos</i> were key species driving differences in fish assemblage structure. Clarifying the trophic roles of herbivorous and detritivorous reef fishes will require species-level studies, which also examine feeding behaviour, to fully understand their contribution in maintaining reef resilience to climate change and fishing impacts.</p></div

Confirmed Sighting of a Spawning Aggregation of the Brown-marbled Grouper, Epinephelus fuscoguttatus, in Kenya

The occurrence of spawning aggregations at fixed sites and times is well documented for several species of reef fish. These aggregations are known to attract fishers and such species may therefore be vulnerable to overfishing. This is particularly true in the case of groupers which have intrinsically vulnerable life history traits. The brown-marbled grouper, Epinephelus fuscoguttatus, distributed throughout the Indo-Pacific region and classified by IUCN as Near Threatened, is reported to form spawning aggregations but little is known about its spawning behaviour; in the Western Indian Ocean this has only been reported for the Seychelles. This study confirmed spawning aggregation behaviour in E. fuscoguttatus in Kenya based on underwater observations and fishers’ knowledge of the phenomenon. We showed that E. fuscoguttatus forms short aggregations for ~5 days linked to the new moon for a 3-4 month period during the northeast monsoon (austral summer).  The numbers of aggregating fish appear to be low, however, and the species is currently not managed in Kenya. Considering the fact that only small areas of the Kenyan coastline are under total protection (8.6% of the country’s coral reefs), these factors suggest that there is an urgent need for additional management of E. fuscoguttatus if it is to survive in Kenya

Variola louti, Yellow-edged Lyretail

Variola louti is a widely distributed, reef-associated species that is common and abundant in parts of its range. There are emerging fisheries that target this species in some areas. There is some evidence for localized population declines in the Maldives and Mariana Islands due to overfishing, but this is not considered a major threat on a global-level at this time. Therefore, it is listed as Least Concern. Actions that reduce fishing effort and monitor populations are recommended and research on its life history is needed

Applying a social-ecological systems approach to understanding local marine management trajectories in northern Mozambique

UIDB/04647/2020 UIDP/04647/2020This study applied the social-ecological systems framework (SESF) to six fishing communities in northern Mozambique where marine resource management is being implemented through the Our Sea Our Life project. Data on 11 variables and 27 indicators were organised using the SESF to represent the key system dimensions (Governance system, Actors, Resource units and Resource system). Variables within each dimension were weighed to a cumulative score of one. High scores (> 0.50) for Governance system occurred where communities had fisheries management rules and good knowledge of fishing gear regulations. High scores for Actors were evident in communities with few migrant fishers and high participation in village savings and loans associations. Elevated scores of the Resource units occurred where fishers targeted a variety of fish taxa. A healthy Resource system was found in communities neighbouring highly productive and resilient reefs, characterised by high fish biomass and diversity. The status of social and ecological conditions coupled with initial levels of project support and quality of technical support were linked with project achievements. Application of the SESF is therefore valuable in understanding interdependent linkages between social and environmental conditions to inform the design of localised management interventions for social-ecological sustainability.publishersversionpublishe

Epinephelus malabaricus, Malabar Grouper

This widely distributed species inhabits a variety of nearshore habitats. It can be common in parts of its range and is relatively fast-growing. Adults and juveniles are exploited by fisheries, especially for the live reef fish food trade based in Hong Kong. Population declines have occurred in the Andaman Islands, New Caledonia and the Philippines, and probably elsewhere in areas of heavy fishing pressure, but the level is not known or quantified. Even anecdotal information is missing from large areas of the range of this grouper, including Indonesia, most of East Africa, the Red Sea and New Guinea. Populations are considered to have remained healthy in Australia. Overfishing is a threat on a localised basis, and is not known to be driving global-level population declines that would approach a 'threatened' level. Therefore, it is listed as Least Concern. It is strongly recommended that fishery management and data collection is improved to monitor population trends, as well as additional research on its life history. The change in status from the previous assessment reflects an improved application of the Red List categories and criteria, as well as a better understanding of available data

Characteristics of shallow and mesophotic environments of the Pemba Channel, Tanzania : implications for management and conservation

Information on the spatial distribution of habitats and vulnerable species is important for conservation planning. In particular, detailed knowledge on connectivity of marine ecosystems in relation to depth and seafloor characteristics is crucial for any proposed conservation and management actions. Yet, the bulk of the seafloor remains undersampled, unstudied and unmapped, thereby limiting our understanding of connections between shallow and deep-water communities. Recent studies on mesophotic coral ecosystems (MCEs) have highlighted the western Indian Ocean as a particularly understudied marine region. Here we utilise an autonomous underwater vehicle (AUV) to collect in-situ temperature, oxygen concentration, bathymetry, acoustic backscatter and photographic data on benthic communities from shallow (<30 m) and mesophotic (30-150 m) depths at selected sites in the Greater Pemba Channel, Tanzania . Further, we use generalised additive models (GAMs) to determine useful predictors of substratum (hard and sand) and benthic community type (coral, turf algae, fleshy algae, fish). Our results revealed the presence of a complex seafloor characterised by pockmarks, steep slopes, submarine walls, and large boulders. Photographs confirmed the presence of MCE composed of corals, algae and fishes on the eastern margins of the Pemba Channel. The GAMs on the presence and absence of benthic community explained 35% to 91% of the deviance in fish and fleshy algae assemblages, respectively. Key predictors of the distribution of hard substrata and the coral reef communities were depth, showing the upper boundary of MCEs present at 30-40 m, and seafloor slope that showed more occurrences on steep slopes. The upper 100 m of water column had stable temperatures (25-26°C) and oxygen concentrations (220- 235 μmol/l). We noted the presence of submarine walls, steeply inclined bedrock, which appeared to support a highly bio-diverse community that may be worthy of particular conservation measures. Our results also highlight the capability of using marine robotics, particularly autonomous vehicles, to fill the knowledge gap for areas not readily accessible with surface vessels, and their potential application in the initial survey and subsequent monitoring of Marine Protected Areas

Epinephelus malabaricus, Malabar Grouper

This widely distributed species inhabits a variety of nearshore habitats. It can be common in parts of its range and is relatively fast-growing. Adults and juveniles are exploited by fisheries, especially for the live reef fish food trade based in Hong Kong. Population declines have occurred in the Andaman Islands, New Caledonia and the Philippines, and probably elsewhere in areas of heavy fishing pressure, but the level is not known or quantified. Even anecdotal information is missing from large areas of the range of this grouper, including Indonesia, most of East Africa, the Red Sea and New Guinea. Populations are considered to have remained healthy in Australia. Overfishing is a threat on a localised basis, and is not known to be driving global-level population declines that would approach a 'threatened' level. Therefore, it is listed as Least Concern. It is strongly recommended that fishery management and data collection is improved to monitor population trends, as well as additional research on its life history. The change in status from the previous assessment reflects an improved application of the Red List categories and criteria, as well as a better understanding of available data