Indicators of fishing mortality on reef shark populations
Gabriel Vianna, Jessica Meeuwig | Mar 25, 2016
Incidental catch remains a dominant source of mortality in reef sharks within Palau’s sanctuary.
Photo: USFWS – Pacific Region.
Vianna GMS, Meekan MG, Ruppert JLW, Bornovski TH, Meeuwig JJ. 2016. Indicators of fishing mortality on reef shark populations in the world’s first shark sanctuary: the need for surveillance and enforcement. Coral Reefs, 35(3): 973-977.
- The density of reef sharks was an order of magnitude lower and individuals were significantly smaller in remote areas of the Palau shark sanctuary when compared to populated areas.
- There was strong evidence that the lower density of sharks observed in remote areas was a consequence of illegal, unreported and unregulated fishing. This is a consequence of Palau’s limited infrastructure capacity to enforce fishery regulations across its very large Economic Exclusive Zone.
- Shark sanctuaries are a promising instrument for shark conservation however, there is an urgent need for better regulation, enforcement and surveillance that targets both illegal and licensed commercial fisheries to provide effective protection for sharks.
- Baseline surveys must be an essential part of the establishment of sanctuaries because without them, we lack any means to judge the effectiveness of these areas as a management tool or to identify problems that could be hampering strategic goals.
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.
The (log-transformed) mean density of reef sharks (species combined) sighted in belt transects decreases steeply with increased prevalence of derelict fishing gear on entangled reefs. Figure extracted from Vianna et al. 2016.
FUNDING & ACKNOWLEDGEMENTS
The authors acknowledge the Save Our Seas Foundation and a private donor for financial support. We also thank the staff and divers of Fish ‘n’ Fins and the Ocean Hunter III. We acknowledge the support of Micronesian Shark Foundation and the Koror State Rangers, in particular M. Moros, Bohemian Companies, T. Wynn, and H. Wuyts. We are also thankful to N. Bornovski, J. White, B. Oh, T. Hofmeister and F. Toribiong.
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