Acoustic Telemetry Validates a Citizen Science Approach for Monitoring Sharks on Coral Reefs

Citizen science is promoted as a simple and cost-effective alternative to traditional approaches for the monitoring of populations of marine megafauna. However, the reliability of datasets collected by these initiatives often remains poorly quantified. We compared datasets of shark counts collected by professional dive guides with acoustic telemetry data from tagged sharks collected at the same coral reef sites over a period of five years. There was a strong correlation between the number of grey reef sharks (Carcharhinus amblyrhynchos) observed by dive guides and the telemetry data at both daily and monthly intervals, suggesting that variation in relative abundance of sharks was detectable in datasets collected by dive guides in a similar manner to data derived from telemetry at these time scales. There was no correlation between the number or mean depth of sharks recorded by telemetry and the presence of tourist divers, suggesting that the behaviour of sharks was not affected by the presence of divers during our study. Data recorded by dive guides showed that current strength and temperature were important drivers of the relative abundance of sharks at monitored sites. Our study validates the use of datasets of shark abundance collected by professional dive guides in frequently-visited dive sites in Palau, and supports the participation of experienced recreational divers as contributors to long-term monitoring programs of shark populations.


Environmental Influences on Patterns of Vertical Movement

Environmental Influences on Patterns of Vertical Movement and Site Fidelity of Grey Reef Sharks (Carcharhinus amblyrhynchos) at Aggregation Sites Gabriel M. S. Vianna , Mark G. Meekan, Jessica J. Meeuwig, Conrad W. Speed Published: April 10, 2013 We used acoustic telemetry to describe the patterns of vertical movement, site fidelity and residency of grey reef sharks (Carcharhinus amblyrhynchos) on the outer slope of coral reefs in Palau, Micronesia, over a period of two years and nine months. We tagged 39 sharks (mostly adult females) of which 31 were detected regularly throughout the study. Sharks displayed strong inter-annual residency with greater attendance at monitored sites during summer than winter months. More individuals were detected during the day than at night. Mean depths of tagged sharks increased from 35 m in winter to 60 m in spring following an increase in water temperature at 60 m, with maximum mean depths attained when water temperatures at 60 m stabilised around 29°C. Sharks descended to greater depths and used a wider range of depths around the time of the full moon. There were also crepuscular cycles in mean depth, with sharks moving into shallower waters at dawn and dusk each day. We suggest that daily, lunar and seasonal cycles in vertical movement and residency are strategies for optimising both energetic budgets and foraging behaviour. Cyclical patterns of movement in response to environmental variables might affect the susceptibility of reef sharks to fishing, a consideration that should be taken into account in the implementation of conservation strategies.


Indicators of fishing mortality on reef-shark populations

Indicators of fishing mortality on reef-shark populations in the world’s first shark sanctuary: the need for surveillance and enforcement Authors: Gabriel M. S. Vianna, Mark G. Meekan, Jonathan L. W. Ruppert, Tova H. Bornovski, Jessica J. Meeuwig Shark sanctuaries are promoted as a management tool to achieve conservation goals following global declines of shark populations. We assessed the status of reef-shark populations and indicators of fishing pressure across the world’s first shark sanctuary in Palau. Using underwater surveys and stereophotogrammetry, we documented large differences in abundance and size structure of shark populations across the sanctuary, with a strong negative relationship between shark densities and derelict fishing gear on reefs. Densities of 10.9 ± 4.7 (mean ± SE) sharks ha−1 occurred on reefs adjacent to the most populated islands of Palau, contrasting with lower densities of 1.6 ± 0.8 sharks ha−1 on remote uninhabited reefs, where surveillance and enforcement was limited. Our observations suggest that fishing still remains a major factor structuring shark populations in Palau, demonstrating that there is an urgent need for better enforcement and surveillance that targets both illegal and licensed commercial fisheries to provide effective protection for sharks within the sanctuary.


Wanted Dead or Alive?

Arguments for conservation of sharks based on their role in the maintenance of healthy marine ecosystems have failed to halt a worldwide decline in populations of these top-order predators. This decline is driven by the economic value of sharks as a fishery and the growing market for shark fin products. An alternative approach for conservation stresses the economic value of sharks as a focus of dive tourism. In this context, sharks may have a greater value as a non-harvested resource than as a fishery. Our study quantified the economic benefits of the shark-diving industry to the community and Government of Palau. A series of questionnaires were used to survey the demographics, income and expenditure of divers visiting Palau, the markets, income and expenditures of dive tour operators and the income and interactions with shark fishers. The results of these questionnaires and recent statistics of tourism and revenues published by the Government of Palau were used to calculate the contribution of shark diving. The shark-diving industry attracts 8,600 divers each year or approximately 21% of the divers visiting Palau. The value of sharks to the Palauan economy was estimated to be US$18 million per year, accounting for approximately 8% of the gross domestic product of Palau. An individual reef shark in Palau was estimated to have an annual value of US$179,000 and a life-time value of US$1.9 million to the tourism industry. The annual income in salaries paid by the shark-diving industry to the local community was estimated to be US$1.2 million. The annual tax income to the Government of Palau generated by shark diving was estimated to be US$1.5 million or 14% of the business tax revenue. A fishery targeting the same 100 sharks that are interacting with the tourism industry in Palau would obtain a maximum of US$10,800, or 0.00006% of the life-time value of these animals as a non-consumptive resource. VALUE OF REEF SHARKS IN PALAU VIANNA ET AL. iv The tax revenues collected from shark diving were roughly 24 times higher than those from the fishing industry. The creation of the shark sanctuary could play an important role on the selection of Palau as a diving destination by tourists. WANTED DEAD OR ALIVE? The relative value... (PDF Download Available)

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