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Assessment of Seychelles’ Sea Cucumber Fishery

2017

Seychelles sea cucumber survey 2021/22 – sample design, analysis of survey data and management recommendations

The commercialization of sea cucumber fishery in Seychelles began in the early 1990s and has since provided livelihood and income to fishers and communities involved in their processing and trade. However, the industry experienced declines in catch in the latter years of the succeeding decade, prompting the Seychelles Fishing Authority (SFA), in 1999, to introduce management measures for the industry, including limiting the number of non-transferrable fishing licenses to 25, limiting the number of divers per license to four, and requiring licensees to submit catch data. 

The first full-scale stock study, conducted in 2004 at 246 sites across the Amirantes and Mahe Plateau, concluded that the two sea cucumber species, sandfish (Holothuria scabra) and surf redfish (Actinopyga mauritiana), were overexploited, while the white teatfish (Holothuria fuscogilva) and flower teatfish (Holothuria sp. type pentard) were fully exploited. The succeeding stock surveys, which were limited in scope and relied on mandated logbook data, revealed an overall decline in several species of sea cucumber with the number of pentard appearing stable.

This study conducted in 2021-2022 aims to update stock data and inform the development of new management measures for the sea cucumber fishery industry.

The survey estimated the white teatfish population to be only 8.3% of the 2004 stock estimate, continuing the declining trend observed in 2011. The 2021 catch-per-unit-effort (CPUE) also decreased significantly to 14.4% of its value in 2004 and is at its lowest level in all surveys conducted from 2004. The decline in white teatfish densities in the survey sites, low population, and all-time low CPUE indicate that the species may be below the level of recruitment impairment.

Focusing on the flower teatfish species, the survey found that its population has declined to 59% of its original estimate in 2004. Meanwhile, the CPUE exhibits greater variability compared with the survey estimates but shows an overall downward trend and currently is at 47.4% of its 2004 value. Despite the decrease in these values, however, they still represent a remarkably stable population given the fishery focus on this particular species of sea cucumber, especially compared to the white teatfish. Still, with the downward trajectory of its population numbers, the current fishing levels are likely to be unsustainable.

Displaying an increase of 52% over its 2004 estimate, the prickly redfish (Thelenota ananas) was the only major sea cucumber species surveyed to have gotten a boost in its population. However, the CPUE was more variable and showed a very weak temporal trend with the 2021 value landing on the lower end of the scale. Overall, the high population increase indicates that current fishing levels would not have a significant detrimental effect on the prickly redfish population.

The survey also found that the black teatfish (Holothuria nobilis) population has decreased to 84% of its 2004 value and continued a downward trend first observed during the 2011 survey. The CPUE data, only available up until 2016, showed a 91% decrease from its 2004 value. These figures indicate that the black teatfish is still in a depleted state, despite ceasing fishing of this species in 2018. However, higher densities were monitored compared to the all-time low observed in 2017, suggesting that the population is recovering.

Overall, the sea cucumber population estimate in 2021-2022 is 77.7 million, a 30% decrease from the value recorded in 2004. While it is fortunate that some species, such as the prickly redfish, appear to become resilient to heavy fishing pressure, most of sea cucumbers experienced a decline in their populations and show signs of overexploitation. 

Therefore, the study recommends putting in place species management measures to ensure a sustained catch over the long term. For the white teatfish, an immediate cessation of fishing activities is recommended to allow for the population to recover to sustainable levels and monitor its recovery after 3 years for another assessment. Meanwhile, to prevent the flower teatfish from sliding down to a level where recruitment impairment could occur, a 10% reduction in the fishing quota is recommended. This assessment should be used as the basis to develop specific management actions for the pentard population. Despite the increase in prickly redfish population, additional stock modeling must be carried out using current surveys and fishery logbook data to see the impacts of possible increases in fishing pressure for this particular species. With the black teatfish population still continuing to slide down, the study recommends continuous monitoring with eventual fishing reopening once the population reaches sustainable levels. For underexploited and recovered species, experimental quotas can be reintroduced, contingent on additional catch reporting requirements.

Concerning crafting strategies and plans, the study recommends introducing and promoting standard species names and crafting a comprehensive fisheries species identification guide to help future research and management endeavors. Additionally, the study urges authorities to develop multispecies harvest strategies that outline the objectives, performance indicators, reference levels, and control measures to guide sustainable fishing practices. Implementing a system of closed areas in deeper non-reef regions, targeting 30% of each fishery area, is recommended to protect fish stocks. Finally, the study recommends that the authorities look into the potential of rotational harvest schemes and stock enhancement approaches, such as reseeding and broodstock aggregation, to ensure the long-term viability of the sea cucumber fishery in Seychelles.