Village-Based Larviculture and Stock Enhancement of Sea Cucumbers (Echinodermata: Holothuroidea) on the Kenyan Coast. Final Technical Report

Abstract

Marine protected areas were initiated in Kenya for biodiversity conservation in marine parks and as fisheries management areas in marine reserves. Unfortunately overexploitation of marine resources in unprotected areas is beginning to erode the gains made by MPAs, creating an environment of conflict with marine parks that are no-take zones. In order to resolve this conflict, viable resource use alternatives have to be explored. The holothurian fishery is a potentially very valuable fishery with characteristics that allow low income fishers to have gainful employment. However little is known about this fishery in Kenya. This study therefore investigates the status of the holothurian fishery in Kenya including the diversity and distribution of holothurians, the reproductive patterns of holothurians as a prelude to culture and stock enhancement trials, and identifies communities adjacent to MPAs that could participate in a pilot stock enhancement project for holothurians This is the first set of data available on the holothurian resources of the Kenyan coast. Holothurians were distributed throughout the Kenyan coast from Kiunga in the north to Kisite in the south. A total of 31 species were recorded with one new species tentatively named Holothuria arenacava not previously described in the Western Indian Ocean (WIO). This is a relatively high diversity and is comparable to holothurian diversity in other locations in the WIO region. The most common species was H. atra and H. leucospilota which are also common in the WIO region. Seventeen species were of commercial value including the high value species H. fuscogilva, H. nobilis and H. scabra. Sandy channels and hard substrate channels had the highest abundance of holothurians (5 – 15 individuals/250m2) and seagrass areas the lowest (2 individuals/250m2). The reproductive patterns of two high value species H. fuscogilva and H. scabra and the new species H. arenacava were investigated. H. fuscogilva had a relatively short spawning period between October and December. Peak spawning occurred during the hottest months of the year although there was no correlation between spawning and sea water temperature or light. H. scabra also exhibited a short spawning period between August and December. The reproductive pattern of H. scabra also did not show a relationship with sea water temperature or light. The reproductive patterns of both these species are similar to records from New Caledonia. Holothuria arenacava on the other hand, had a characteristic annual reproductive pattern with spawning occurring between September and March of the following year. By April spawning has ended and gametogenesis commences in July. This is the first time a seasonal reproductive pattern has been recorded on the East African coast. The reproductive pattern of H. arenacava had a significant correlation with sea water temperature and light. The correlation with light however was very strong (r = 0.96) suggesting that light is a controlling factor in the reproduction of this species. The species occurs most of the time buried in the sand so light could act as a powerful cue to induce spawning. The socio-economic study revealed that the fisher communities of many villages in the south coast of Kenya are engaged in holothurian fishing concentrated between Gazi and Shimoni. The main occupation is fishing although farming is carried out on a subsistence basis. The community has a low level of education and are classified in the low income group. The community depends mainly on natural resources for food, fuel, building materials and medicines. The level of awareness of conservation and environmental issues was high which is not surprising as there are three protected areas, Shimba hills national reserve and Kisite-Mpunguti marine park and reserve and Diani-Chale marine reserve in the district. These communities were keen on the prospect of culture and stock enhancement of holothurians. Unfortunately the results from rearing holothurians were not so encouraging. In most cases spawning was successful through thermal stimulation. Fertilisation trials for H. atra and were also successful. However rearing of the larval stages beyond the doliolaria stage proved more difficult. This was possibly due to the microalgal diet but also to logistical problems. A great deal more research in required before a viable pilot project can be initiated. Compilation of fisheries statistic, interviews and perusal of old records in the National Archives reveals that this fishery is over exploited. Catches have been declining from a high of 90 metric tons to a low of less then 20 metric tons. Size frequencies of H. fuscogilva and H. scabra collected from the catch indicate that a sizeable portion of the catch is sexually immature. Interviews with fishers have also indicated that large high value species are becoming more difficult to collect and the catch is increasingly dominated by mid value and low value species. All these indicate that the fishery is in urgent need of intervention. We have provided information from this study to the fisheries department and an initial management intervention has been instituted requiring all District Fisheries officers to stop licensing any traders and collectors. We have further recommended a moratorium in marine reserves where enforcement would be more effective. This could be carried out for a period of three years with a monitoring program to record recovery. We have also recommended a comprehensive monitoring program that requires reporting on species, sizes and effort. This information will be key in developing effective management interventions for this potentially valuable fishery.