Spatial distribution of sea cucumbers in protected and exploited areas of Ungula island, Zanzibar

Zanzibar long term fisheries catch statistics show that sea cucumber catches are declining in most of the shallow coastal waters around Unguja Island. This observation, however, is not verified or backed up by field data. In this study, the distribution pattern and stock sizes (density) of sea cucumber in zones open for collection in Menai Bay and in Chumbe marine reserve was assessed. Information was obtained through interviewing local fishers and visual census (manta tows and scuba dives). ArcMAP 9.3 software was used to visualize the distribution patterns and production of thematic maps for different sea cucumber species with respect to their respective habitat characteristics. The Shannon Weaver Diversity for sea cucumber species was highest in Chumbe reserve (H′=1.585). High and medium valued commercial species (Holothuria fuscogilva, Stichopus herrmanni, Thelenota ananas and Thelenota anax) were only encountered in Chumbe reserve while the other sites were mainly composed of low valued species (Holothuria atra and Holothuria edulis). The ANOVA Single factor showed significantly higher densities of Holothuria atra (F = 5.132, DF = 5, P = 0.0004) and Bohadschia graeffei (F = 2.815, DF = 4, P = 0.028) in the reserve. However, there was no significant difference in densities of Holothuria edulis and Stichopus monotuberculatus among the sites. This study provides field evidence that commercially important sea cucumber species in the study areas are restricted to Chumbe reserve, and are over-exploited outside the reserve. There is an urgent need for devising a proper management scheme to protect sea cucumbers (the high value species in particular) from high exploitation levels and facilitate their recovery.