Phase III – Genetic Connectivity and its Implications for the Design and Management of Marine Protected Areas in the East African Ecoregion

Genetic studies on stock structure and dispersal and connectivity patterns are essential for the design of management strategies for coral reef fisheries. The overall aim of the project was to assess the population structure and genetic stock composition of reef associated fish species along the Eastern seaboard of Africa (Kenya and Tanzania) and islands of the WIO (Mauritius, Rodrigues, Seychelles). Specific objectives of this project were (i) to evaluate the potential impact of genetic flow among the islands, between the islands and the East African mainland coasts through dispersal by the South Equatorial Current (SEC), and along the East African coastline via the East African Coastal Current (EACC); and (ii) to generate data on commercially important fish species for use at national fisheries departments for sustainable fish stock management through identification of local breeding populations. The project targeted to benefit scientific communities, policy and decision makers.

During the study, a series of activities were undertaken; (i) examination of genetic stock composition of Scarus ghobban and Siganus sutor using Amplified Fragment Length Polymorphism (AFLP), (ii) assessment of genetic connectivity of S. ghobban and S. sutor using DNA sequence analysis using (mtDNA), (iii) creation of bathymetric data using GeoMap App (www.geomapapp.org/) and study of population structure (FST) based on calculations of genetic distances between pairs of populations using ARLEQUIN v3. The project was implemented in five countries in the WIO region, comprising of two mainland countries (Kenya and Tanzania) and three WIO islands (Mauritius, Rodrigues, Seychelles).

The project revealed important scientific findings.including (i) S. ghobban and S. sutor displayed a high degree of population genetic structuring, (ii) S. ghobban showed a high diversity of mtDNA, a condition that signifies the species long-term survival and adaptability in the region, (iii) based on mismatch analysis, S. ghobban exhibited a recent demographic expansion in the region and displayed a relatively high level of gene flow which is a consistent condition for reef fishes with a pelagic larval phase, (iv) in combination, different genetic markers AFLP and mtDNA for S. ghobban revealed two events of range expansions (70-130 Ka) forming two major mtDNA clades found at most of the study sites and (v) mtDNA data for S. sutor showed that the oceanic islands of Mauritius and Rodrigues are genetically different from mainland sites in Kenya, with less genetic diverse island population indicating negative implications for resilience to environmental perturbations.

This project has produced significant information relative to management options of S. ghobban and S. sutor in the WIO region. Of the such tangible outputs include (i) the evidence of genetic structure showing that both S. ghobban and S. sutor exhibit several genetically defined stocks with limited genetic exchange over an ecological time-scale (tens to hundreds of years) and that islands specifically show evidence of restricted migration between neighboring sites; hence, high fishing pressure can lead to local loss of the species, which may have consequences both for human food consumption, economy and ecosystem function, (ii) the less intensively fished species, S. ghobban, showed evidence of mixed stock fisheries, particularly along the East African coast and in most sites they occurred in high stocks indicating relatively high degree of resilience against local depletion, (iii) Siganus sutor, which is an intensively fished species had comparatively fewer stocks per site. Fisheries that target spawning aggregations of this species may lead to local extinction of this specie.

Spin-off of the project include the development of an infrastructure for molecular work (regional network of marine scientists and laboratories), which serves to expose students from the region to applications of genetics in conservation and management.

The projects recommended future genetic research in Madagascar and Mozambique and also to consider other species, particularly those that are economically important. Furthermore, for sustainable management of fish stocks in the region, especially on island sites like Mauritius and Rodriguez with few dominant stocks, it is recommended that a number of small marine protected areas, preferably no take zones, be established around these islands for protecting fish populations at the local scale. Moreover, fish spawning aggregations should be identified and given the necessary protection.