by Neha Vaingankar
Marine protected areas are a major cause of dispute especially in coastal and island regions like Seychelles, off the western coast of Africa. In recent times, tropical regions all over the world have experienced a huge boom in fishing of holothurians (sea cucumbers). Almost all of the holothurian fisheries are considered fully exploited, in decline, or entirely collapsed. The reason for the high demand is for the holothurian’s medicinal purposes as well as its supposed aphrodisiac qualities. In many tropical coral reef regions, locals rely on these invertebrates for their livelihoods. However, due to the density-dependent reproduction patterns and late maturing of these organisms, holothurians are very vulnerable to over-exploitation. Many MPAs were established in Seychelles 20 years ago that pre-date the wave of heavy exploitation in current times. Cariglia et al. (2013) aims to understand the effectiveness of these MPAs and measure the economic value of these holothurians.
Cariglia and her team at the School of Marine Science and Technology in Newcastle, UK looked at seven regions around the Seychelles islands: Cousin, Mahe E, Mahe NW, Mahe W, Ste. Anne, Praslin NE, and Praslin SW. These regions were chosen because they had been previously used by the Seychelles Fishing Authority for other studies. Within each region, 3 sites were chosen unsystematically, for a total of 21 sites. At each site, 16 count areas were delineated with a seven-meter rope, which acted as a radius for a circular area. The number of holothurians was counted in each circle and each holothurian was identified to the species level if possible. There were a total of 336 count circles total. The holothurians were then grouped into classes, which reflected their current economic value: low, medium and high. Only nine out of the 21 sites were located in MPAs. Cariglia et al. also realized that the type of habitat could affect distribution of marine organisms. Benthic composition was estimated and expressed as a percentage of cover.
Thirteen different species and a total of 978 holothurians were observed throughout this one month long study. Certain counts had over 100 holothurians while others had none. However, it is to be noted that counts where more than 15 holothurians were observed were all located in sites protected from fishing. Especially prominent were holothurians of high commercial value in the Cousin region (where fishing is not allowed). Low valued holothurians were found within the Praslin NE, Mahe NW, and Ste. Anne regions, where fishing is prohibited only at some sites. Overall, the probability of observing holothurians in counts in MPAs was twice as high as seeing them in counts subject to fishing. After separating them into their respective economic categories, holothurians with high or medium value were 10 times more likely to be observed in MPAs than areas subject to fishing.
Cariglia et al. found that habitat was a determinant of holothurian presence. Occurrence of high and medium value holothurians was associated with rocks and coral habitats. Among low value animals, sand was important in protected areas while rock was important in unprotected area. These results were obtained by using principal component analysis to correlate habitats with MPAs and unprotected areas.
Overall, Cariglia and her team found that the presence of MPAs was a significant determinant of high, medium and low value holothurian occurrence on the reefs. This same trend was noted in other projects, specifically in the Chagos Atolls and Maldives and Reunion Islands. In the discussion, the authors explain that closing fisheries as they expand and develop often leads to little success. The management process is done a little too late. In order to make MPAs successful, information regarding biological, ecological and behavioral patterns are required. Another aspect to consider is the gene flow of the species between MPAs. By having MPAs designed so that holothurians of different regions can interbreed, genetic diversity will be increased and the animals will become more resilient to changes. The main point is that successful MPAs can maintain a population at high densities despite high fishing pressure. All of the benefits of the target organism must be understood, authorities and fishermen must recognize this area, and the economic and ecological advantages should be acknowledged.
Cariglia N., Wilson, S., K., Graham, N., A., J., Fisher, R., Robinson, J., Aumeeruddy, R., Quatre, R., Polunin, N., V., C., 2013, Sea Cucumbers in the Seychelles: Effects of Marine Protected Areas on High-Value Species, Aquatic Conservation: Marine and Freshwater Ecosystems 23, 418–428. Abstract at http://bit.ly/1oFtsW8