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Solution Search Entry

Bycatch Escape Gaps for Fish Traps

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Wildlife Conservation Society

Bycatch Escape Gaps for Fish Traps

Tim McClanahan and Ayana Elizabeth Johnson

The majority of reef fish captured globally are caught in fish traps. Although traps target high-value fish such as groupers and snappers, any fish that enters but cannot escape through the mesh is retained. This results in high bycatch of juveniles, ornamental species, and ecologically important herbivores, and leads to overexploitation. However, studies in Curaçao and Kenya demonstrate that traps retrofitted with vertical, rectangular escape gaps allow narrow-bodied, compressible, and juvenile fish to escape, reducing bycatch up to 80%, without reducing (and potentially increasing) catch value. Escape gaps are a low-cost, low-tech solution to increase fishery selectivity and sustainability. Thus, we work with fishing communities to incorporate gaps as part of ongoing adaptive management.

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Biodiversity Impact

Describe how your solution creates sustainable fisheries and promotes ecosystem health.
Reducing bycatch is a key aspect of increasing fishery sustainability. The inclusion of escape gaps in fish traps allows juveniles and narrow-bodied species (i.e. bycatch) to exit, while larger, wider-bodied target species are retained, making this solution effective despite the diversity of fish caught with traps. Experimental results from Curaçao and Kenya showed the mean length of fish in traps with gaps is up to 31% greater than that of fish in control traps, due to a reduction in the catch of small fish. Reducing the catch of juveniles can increase long-term sustainability of the fishery by allowing fish to grow and reproduce before they are caught. Importantly, the presence of escape gaps has no significant effect on the number of targeted high-value species (i.e., groupers, snappers, emperors, rabbitfish) caught, thus profitability is maintained. Furthermore, relative to controls, traps with escape gaps can reduce catch of key herbivores (i.e., parrotfish and surgeonfish) by up to 58%. These herbivores are critical algal grazers who help maintain the coral dominance on reefs, so by reducing their capture, escape gaps can indirectly contribute to improved ecosystem health. In sum, by reducing the catch of juveniles and herbivores, escape gaps can promote both fishery sustainability and ecosystem health.

Describe how your solution protects biodiversity against local threats.
Escape gaps protect biodiversity by reducing the catch of the many narrow-bodied, ornamental species that are not targeted by fishermen and not desirable as food. Increasing the number of ornamental fish and the sustainability of the fishery may also promote increased ecotourism in these villages and fishing grounds. In the context of poverty, and poverty traps that prevent easy escape from poverty, this dual effect of increasing ornamentals and increasing ecotourism will provide a unique solution that can be adopted by fishing communities without undermining their wealth or creating considerable economic sacrifices.

How large is the surface area where your solution is being applied?
Escape gaps were tested at three sites on the southwest coast of Curaçao, and are now required island-wide. Near term future efforts to expand the use of this gear modification will focus on Kenya and poor fishing communities where prices of fish are influenced by the size of the fish. Subsequently, escape gaps were tested on the coast of Mombasa and Shimoni, Kenya. These are fishing communities near two national marine protected areas, the Mombasa and Kisite Marine National Parks. These communities have developed positive attitudes towards conservation and management restrictions, and can pilot adaptive management that may eventually spread to the entire East African coastline. The Mombasa marine park and reserve is an area of 30 km2 (-S4.001280°, E39.741740°; -S4.063740°, E39.712090°), while the Kisite fishing areas is ~100 km2 north of the national fisheries closure. Consequently, the total area for this pilot study is ~13,000 hectares. We plan to continue working with fishermen to expand the area in which escape gaps are used once the results of these community-level pilot studies have been completed. In the long term we hope escape gaps are used in coral reef trap fisheries all over the world.

Human Wellbeing and Livelihoods Impact

How does your solution improve human wellbeing or improve livelihoods and how many people are being impacted by your solution?
Escape gaps represent a win-win opportunity for fishers and coral reef conservation. Fishers’ current incomes are not reduced, and there is the potential that incomes will increase in both the short and long terms, through increased catch prices and increased ecotourism. For the short term, the Kenya study provided evidence that fish entry into traps is density-dependent – by reducing crowding in traps, escape gaps can result in greater retention of larger, high-value target fish. In the longer term, incomes will likely increase as the reduced catch of juveniles allows fish populations to increase. Improving the environmental sustainability of fish traps increases the likelihood of preserving and improving the jobs of the ~15,000 artisanal fishers in Kenya, and the ~800,000 individuals (family members, processors, traders and other service providers) whose incomes depend indirectly on fishing. Perhaps more importantly, escape gaps can make fish consumption more sustainable, which is critical to the approximately 500 million people globally who depend on fish as their primary source of protein. Additionally, there are important conservation benefits: reduced catch of herbivores can help control algal biomass on reefs, and reduced catch of ornamental species can increase local biodiversity. These conservation benefits can translate into livelihood benefits because improved ecosystem health translates into increased attractiveness to tourists. In these ways, escape gaps can help maintain and improve livelihoods and diets, while improving ecosystem health and biodiversity.


How many years has your solution been applied?
2 years

Have others reproduced your solution elsewhere?

Sustainability & Resilience

How do you manage your solution?
Escape gaps are low-tech, low-cost, and highly effective at reducing bycatch. Fish traps of any design can be easily and inexpensively retrofitted with escape gaps. Traps with escape gaps can be used in exactly the same manner as traditional traps. No training is required because fishermen do not need to alter their fishing methods. No new gear is required, so the number of active traps in the fishery is unlikely to change when use of escape gaps begins. To balance income impacts with conservation benefits, escape gap widths can start small and be increased with fish population recovery. Gaps can be made from and affixed with any number of materials, and constructed in any dimensions, making them adaptable to most locations, target catches, and budgets. Metal gaps made of rebar cost around USD 0.50 per trap, and take a maximum of 30 minutes per trap to install. Because metal gaps can be fabricated at a low cost, fishery departments or non-profits would be able to supply them to fishermen for a subsidized cost or no cost at all. Escape gaps constructed as holes in woven fiber traps (created from natural materials such as tree branches, palm fronds, and coconut fiber string) have essentially no equipment costs, and only increase the time to produce them by 10 to 15 minutes. Metal gaps were used in the first pilot experiments to assure that the gaps were inflexible, but preliminary tests of gaps made from branches and fiber indicated similar effectiveness. A trap has a life expectancy of six months but the gaps, if made of durable materials such as rebar, could be reused.


Describe the management and governance aspects of your solution as they relate to your local community.
In Kenya, various stakeholders are involved in the management of the local fishery. The Wildlife Conservation Society (WCS) is licensed to conduct research, and implemented this gear project through a public-private partnership. Fisheries in the Mombasa area are managed by Beach Management Units (BMUs), which are self-organized groups of fishers with elected representatives at each landing site. The management committee of each BMU develops local by-laws to manage the fishery, and several BMUs have already or are considering requiring escape gaps. WCS provides the BMUs with data to make management decisions, and escape gaps were presented as an option to the fishers after their effectiveness was demonstrated in local pilot studies run with local fishers. WCS holds annual meetings with fisheries leaders and government managers to describe the results of their science to these stakeholders. Approximately 120 fisheries leaders and the Director of the Fisheries Department attended the last meeting held in August 2011. The hope is that successful implementation of escape gaps in these first few BMUs will encourage other BMUs to consider adopting them and possibly making them the only legal trap through BMU bylaws.