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

Key climate change stressors of marine ecosystems along the path of the east african coastal current

For the countries bordering the tropical Western Indian Ocean (TWIO), living marine resources are vital for food security. However, this region has largely escaped the attention of studies investigating potential impacts of future climate change on the marine environment. Understanding how marine ecosystems in coastal East Africa may respond to various climatic stressors is vital for the development of conservation and other ocean management policies that can help to adapt to climate change impacts on natural and associated human systems. Here, we use a high-resolution (1/4°) ocean model, run under a high emission scenario (RCP 8.5) until the end of the 21st century, to identify key regionally important climate change stressors over the East African Coastal Current (EACC) that flows along the coasts of Kenya and Tanzania. We also discuss these stressors in the context of projections from lower resolution CMIP5 models. Our results indicate that the main drivers of dynamics and the associated ecosystem response in the TWIO are different between the two monsoon seasons. Our high resolution model projects weakening of the Northeast monsoon (December–February) winds and slight strengthening of the Southeast monsoon (May–September) winds throughout the course of the 21st century, consistent with CMIP5 models. The projected shallower mixed layers and weaker upwelling during the Northeast Monsoon considerably reduce the availability of surface nutrients and primary production. Meanwhile, primary production during the Southeast monsoon is projected to be relatively stable until the end of the century. In parallel, a widespread warming of up to 5 °C is projected year-round with extreme events such as marine heatwaves becoming more intense and prolonged, with the first year-long event projected to occur as early as the 2030s. This extreme warming will have significant consequences for both marine ecosystems and the coastal populations dependent on these marine resources. These region-specific stressors highlight the importance of dynamic ocean features such as the upwelling systems associated with key ocean currents. This indicates the need to develop and implement a regional system that monitors the anomalous behaviour of such regionally important features. Additionally, this study draws attention to the importance of investment in decadal prediction methods, including high resolution modelling, that can provide information at time and space scales that are more directly relevant to regional management and policy making

Seasonal and Long-Term Changes in Relative Abundance of Bull Sharks from a Tourist Shark Feeding Site in Fiji

Shark tourism has become increasingly popular, but remains controversial because of major concerns originating from the need of tour operators to use bait or chum to reliably attract sharks. We used direct underwater sampling to document changes in bull shark Carcharhinus leucas relative abundance at the Shark Reef Marine Reserve, a shark feeding site in Fiji, and the reproductive cycle of the species in Fijian waters. Between 2003 and 2009, the total number of C. leucas counted on each day ranged from 0 to 40. Whereas the number of C. leucas counted at the feeding site increased over the years, shark numbers decreased over the course of a calendar year with fewest animals counted in November. Externally visible reproductive status information indicates that the species' seasonal departure from the feeding site may be related to reproductive activity

Global Spatial Risk Assessment of Sharks Under the Footprint of Fisheries

Effective ocean management and conservation of highly migratory species depends on resolving overlap between animal movements and distributions and fishing effort. Yet, this information is lacking at a global scale. Here we show, using a big-data approach combining satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively) and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of high-seas fishing effort. Results demonstrate an urgent need for conservation and management measures at high-seas shark hotspots and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real time, dynamic management

Artisanal fish fences pose broad and unexpected threats to the tropical coastal seascape

Gear restrictions are an important management tool in small-scale tropical fisheries, improving sustainability and building resilience to climate change. Yet to identify the management challenges and complete footprint of individual gears, a broader systems approach is required that integrates ecological, economic and social sciences. Here we apply this approach to artisanal fish fences, intensively used across three oceans, to identify a previously underrecognized gear requiring urgent management attention. A longitudinal case study shows increased effort matched with large declines in catch success and corresponding reef fish abundance. We find fish fences to disrupt vital ecological connectivity, exploit > 500 species with high juvenile removal, and directly damage seagrass ecosystems with cascading impacts on connected coral reefs and mangroves. As semi-permanent structures in otherwise open-access fisheries, they create social conflict by assuming unofficial and unregulated property rights, while their unique high-investment-low-effort nature removes traditional economic and social barriers to overfishing

fisheries and tourism social economic and ecological trade offs in coral reef systems

Coastal communities are exerting increasingly more pressure on coral reef ecosystem services in the Anthropocene. Balancing trade-offs between local economic demands, preservation of traditional values, and maintenance of both biodiversity and ecosystem resilience is a challenge for reef managers and resource users. Consistently, growing reef tourism sectors offer more lucrative livelihoods than subsistence and artisanal fisheries at the cost of traditional heritage loss and ecological damage. Using a systematic review of coral reef fishery reconstructions since the 1940s, we show that declining trends in fisheries catch and fish stocks dominate coral reef fisheries globally, due in part to overfishing of schooling and spawning-aggregating fish stocks vulnerable to exploitation. Using a separate systematic review of coral reef tourism studies since 2013, we identify socio-ecological impacts and economic opportunities associated to the industry. Fisheries and tourism have the potential to threaten the ecological stability of coral reefs, resulting in phase shifts toward less productive coral-depleted ecosystem states. We consider whether four common management strategies (unmanaged commons, ecosystem-based management, co-management, and adaptive co-management) fulfil ecological conservation and socioeconomic goals, such as living wage, job security, and maintenance of cultural traditions. Strategies to enforce resource exclusion and withhold traditional resource rights risk social unrest; thus, the coexistence of fisheries and tourism industries is essential. The purpose of this chapter is to assist managers and scientists in their responsibility to devise implementable strategies that protect local community livelihoods and the coral reefs on which they rely

Movement in a large predatory fish: coral trout, Plectropomus leopardus (Pisces: Serranidae), on Heron Reef, Australia

Movement by the larger more mobile species of coral reef fish plays a significant role in determining patterns in abundance and population structure. Fish movement is also relevant to the use and effectiveness of marine reserves in managing fish populations. Coral trout are large piscivorous serranids supporting major fisheries on the Great Barrier Reef (GBR). This study reports on the within-reef movement of the common coral trout, Plectropomus leopardus, at Heron Reef, southern GBR, over a twelve month period, investigated by tagging and underwater tracking. Tracking of coral trout revealed no apparent relationship between the area moved and stage of tide or time of day. However, movement areas were affected by the size of fish: in spring a linear relationship between fish size and area of movement was measured, but in summer the largest (male) fish moved over significantly smaller areas than medium-sized fish. Movement of males may be related to cleaning behaviour and spawning. Fifty nine percent (n = 101) of the tagged fish were resighted over periods of 4-5 months, in 'home sites' measuring ~2000 m. Coral trout were not restricted to home sites, but moved on average 2 km along the reef slope; maximum distances of 7-7.5 km were measured. Coral trout appear to range as mobile, opportunistic predators, but also maintain home sites for access to shelter and cleaning stations