No abstract

Tourism is a growing activity in Cape Verde, which can lead to more intensive and uncontrolled fishing and diving activities, affecting the quality of marine habitats. To mitigate this biodiversity problem, a private diving operator, supported by the local authorities, decided to deploy the first artificial reefs (ARs) in the Archipelago just off Santa Maria Bay (Sal Island). To evaluate the ARs capacity to promote marine fish biodiversity in Santa Maria Bay, the fish assemblages were compared to those from nearby natural reefs (NRs), located at the same depth (10 and 28 m depth), by means of visual census. All study sites were surveyed by visual census in August 2009. A total of 64 species were recorded, mostly consisting of sedentary and/or benthophagous demersal species, followed by highly-sedentary benthic cryptic species. 'Tchuklassa' NR showed the highest species richness (58 species), while the lowest was recorded at 'Santo Antão' AR (48 species). An overall positive relationship was observed between habitat rugosity and mean species richness. The results showed a high percentage of common species on both reef types. Higher mean values of community descriptors (number of species, Shannon-Weaver diversity index, Simpson dominance index and equitability) and fish density were found on the ARs, with slightly higher densities recorded on the deeper reefs. These results suggest that ARs can have an important role promoting the local fish biodiversity and supporting local sustainable development of diving tourism.

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Summary In the present paper there was a twofold hypothesis, i.e. that the deployment of artificial reefs adds value to natural features by diversifying diving sites and thus be a certain propensity concerning the type of added value (either of non‐extractive direct or indirect use). Two vessels were used as artificial reefs off Sal Island (Cape Verde) in 2006 and 2008, with the aim of bolstering the local economy through ecotourism. The additional economic value anticipated was to: (i) enhance fish aggregation as well as other marine organisms, and (ii) mitigate human pressure on natural reefs by diverting divers. The supply‐side view of diving trips was tested and analysed over a 4‐year period (2008–2011) in the choice of divers between natural and artificial reefs, as well as such reef attributes as reef depth, reef distance from the main pier in Santa Maria Bay, and the year‐season as well as combinations thereof. Data were also analysed to determine if the deployed reefs off Sal Island had a complementary or a substitute function. It was observed that the presence of artificial reefs created more dive users, but that divers who used these reefs were not deterred from diving at natural reefs. This resulted in a low‐diversion effect (low substitutability). Thus, dive operators can offer additional options to divers (moderate to highly complementary). The distance to diving sites was the most influential factor in diving decisions (linear model results indicated 15 more divers at distances closer to Santa Maria Bay than elsewhere). From the log‐linear model the number of divers would be expected to change, the distance being the most influential factor (11.7 times higher at closer sites); reef type and depth were less influential (0.2 times fewer divers at artificial reefs; 2.3 times more divers in shallower waters). Also apparent was that the depth of the reef was fundamental in the diver niche allocation throughout the seasons.

A B S T R A C TThe African hind Cephalopholis taeniops (Valenciennes, 1828) is one of the most important commercial demersal species caught in the Cape Verde archipelago. The species is closely associated with hard substrate and is one of the main attractions for SCUBA divers. In January 2006 a former Soviet fishing vessel -the Kwarcit -was sunk off Santa Maria Bay (Sal Island). Young C. taeniops are commonly observed in this artificial reef (AR). In order to investigate the species' use of the AR, 4 specimens were captured and surgically implanted underwater with Vemco brand acoustic transmitters. The fish were monitored daily with an active telemetry receiver for one week after release. Simultaneously, an array of 3 passive VR2 / VR2W receivers was set for 63 days, registering data that allowed an analysis of spatial, daily and short term temporal activity patterns. The results showed site fidelity to the AR, with no migrations to the nearby natural reef. The method used allowed to register a consistent higher activity during daytime and a preference for the area opposite the dominant current. R E S U M OA garoupa-de-pintas Cephalopholis taeniops (Valenciennes, 1828) é uma das espécies demersais comerciais mais importantes no Arquipélago de Cabo Verde. Esta espécie está fortemente associada ao substrato rígido e constitui uma das principais atracções para os mergulhadores. Em Janeiro de 2006 um antigo navio de pesca soviético -Kwarcit -foi afundado ao largo da Baía de Santa Maria (Ilha do Sal). É comum observar juvenis de C. taeniops neste recife artificial (AR). Para investigar a utilização dos AR por esta espécie, foram capturados 4 exemplares nos quais foi implantado um transmissor acústico da marca Vemco, através de cirurgia realizada debaixo de água. Os peixes foram monitorizados através de um receptor de telemetria activo na semana após libertação. Simultaneamente foi instalada uma rede de 3 receptores passivos tipo VR2 / VR2W que registou dados durante 63 dias, permitindo analisar os padrões de actividade espaciais, diários e temporais de curto-prazo. Os resultados obtidos mostram que os peixes são fiéis ao habitat no AR, não realizando migrações para o recife natural próximo. O método utilizado permitiu registrar um padrão consistente de maior actividade diurna e uma preferência pela área do navio oposta à corrente dominante.