Fishery Ecology of Seychelles' Sea Cucumber Fishery.

摘要

Sustainable fisheries productions have been an important factor for human livelihoods, yet the number of overfished fisheries have increased over the years. With strong market demand, sea cucumber fishery has a trend of initial rapid growth followed by a collapse due to the local depletion of the stock. Seychelles enjoys one of the few long-term tropical sea cucumber fishery owing to its strong management capacity. Using Seycelles as a case study, this dissertation explored possible sustainable management options for tropical sea cucumber fisheries. First, I studied the ecology of sea cucumber in Seychelles, then examined their fishery pattern, and determined the sustainable catch limit for the fishery. In Seychelles' unique granitic plateau system, most of the commercially targeted sea cucumbers were found in mid-depth zone. However, the depth range of these species were capped around 40m, where bottom substrate changed from sand to silt lacking biological cover. Marine protected areas in Seychelles were mainly designed to protect shallow coral reef habitat thus did not have significant effect in protecting the targeted sea cucumber species. The analysis of the fishery showed that fishermen have been fishing further from port and spent longer time at the sea. The target species have expanded to lower value species as the time progressed. Despite trip costs have increased from further fishing grounds and longer fishing days, fishermen's net gain per trip increased over the years since the market growth surpassed the trip cost increase. Combining the ecological findings and fishery pattern, I created a spatially explicit surplus production model to account for spatial expansion and different habitat quality across the Seychelles waters. The model showed that H. fuscogilva has hardly recruited from 2002 to 2011. The carrying capacity of the specie showed differences among depth and upwelling zone. Based on the extremely low recruitment rate, we propose that H. fuscogilva be removed from the list of species allowed to harvest in Seychelles.