Periodicity of spawning aggregations of coral trout Plectropomus leopardus (Pisces: Serranidae) on the northern Great Barrier Reef

I investigated seasonal, lunar and diel patterns in the spawning behaviour of a serranid, the common coral trout Plectropomus leopardus, on the Great Barrier Reef, Australia, using underwater visual census surveys. The study was conducted at Scott and Elford Reefs, 2 mid-shelf reefs off Cairns, for 4 and 3 yr, respectively. At each reef, coral trout aggregated and spawned at the same \'primary\' aggregation site in each year. Primary sites are defined as those with the largest aggregations of coral trout. Spawning activity, though not limited to, was concentrated at primary sites. The aggregation site at Scott Reef measured 1700 m2 in area, and that at Elford Reef 3200 m2. Maximum numbers of coral trout recorded in these sites were 128 fish at Scott Reef and 59 at Elford Reef. Coral trout aggregated and spawned at the primary sites around 3 consecutive new moons each year within the period August-December, 1991 to 1993. In 1990 only 2 aggregations were detected at Scott Reef, both around the new moon. The largest aggregations were recorded at the primary site at Scott Reef: numbers of fish at the aggregation site rose from an average pre-spawning density of 3.9 fish 1000m-2 to aggregation densities ranging from 37.1 to 75.3 fish 1000m-2. The median size class of aggregating fish was 41 to 45 cm FL (forklength) at both reefs in all years, with a maximum range of 16 to 80 cm FL at Scott Reef, and 16 to 65 cm FL at Elford Reef. The onset of the spawning season corresponded with a rise in water temperature (>24.00°C) after the austral winter. Spawning aggregations occurred for an average of 5 d, however aggregations were not found at the sites throughout the day. The aggregations appeared to disperse in the morning and re-establish after 13:00 h. Coral trout spawned in pairs predominantly on flooding tides and when current flow at the spawning sites was minimal. Ninety-four spawning rushes were observed which only occurred during a 33 (±4 SE) min period spanning sunset. The spatial and temporal predictability of P. leopardus spawning aggregations makes them vulnerable to overfishing, but also amenable to specialised management through seasonal and/or spatial closures

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

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

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

Complex transboundary movements of marine megafauna in the Western Indian Ocean

Transboundary marine species have an increased risk of overexploitation as management regimes and enforcement can vary among states. The complex geopolitical layout of exclusive economic zones (EEZs) in the Western Indian Ocean (WIO) introduces the potential for migratory species to cross multiple boundaries, consequently a lack of scientific data could complicate regional management. In the current study, we highlight both the relative lack of spatial data available in the WIO, and the prevalence of transboundary movements in species that have previously been studied in the region. Five tiger sharks Galeocerdo cuvier were tracked with near real‐time positioning (SPOT) satellite tags to determine individual shark movements relative to EEZs within the WIO. Concurrently, a literature search was performed to identify all satellite telemetry studies conducted to date in the WIO for marine megafaunal species, and the results compared to global satellite telemetry effort. Finally, the satellite tracks of all marine species monitored in the WIO were extracted and digitized to examine the scale of transboundary movements that occur in the region. Tiger sharks exhibited both coastal and oceanic movements, with one individual crossing a total of eight EEZs. Satellite telemetry effort in the WIO has not matched the global increase, with only 4.7% of global studies occurring in the region. Species in the WIO remained within the EEZ in which they were tagged in only three studies, while all other species demonstrated some level of transboundary movement. This study demonstrates the lack of spatial data available for informed regional management in an area where transboundary movements by marine megafauna are highly prevalent. Without more dedicated funding and research, the rich biodiversity of the WIO is at risk of overexploitation from the diverse threats present within the various political regions