The recently established large reservoirs Manantali on the river Bafing, tributary to the Senegal River and Selingue, located on the river Sankarani, tributary to the Niger River, have followed similar changes in limnology and fish populations as those established in West Africa 20 to 30 years ago. Basic water parameters, such as oxygen content, pH, electrical conductivity and temperature show seasonal variations largely determined by the changes in wet and dry seasons. Both waterbodies are monomictic, with water mixing taking place in January, the coldest period ofthe year. Pre-impoundment forest clearence ofthe future reservoir bottom in the shallow SelinguC reservoir was carried out only in the proximity of the dam site. In the deeper reservoir Manantali the savanna forest was cleared from an area of about 25 percent, and the tree gallery was cleared along the river. The initial filling of Manantali reservoir was followed by a nearly complete drainage of the reservoir. After refilling some months later, the dissolved oxygen content stayed reasonably high and therefore there was no fish mortality. Also no hydrogen sulphide or a large-scale spread of noxious aquatic plants developed. At present the fish fauna is dominated by cichlids and pelagic species, i.e. at SelinguC by clupeids, and at Manantali by cyprinids (Lepfocypris niloticus). In both reservoirs was the genus Citharinus considerably reduced. At Selinguk reservoir disappeared Proroprerus annectens. The fish yield estimate is 27 kg/ha/year for Manantali, and 40 kg/ha/year for Selingue. Both rerservoirs have recorded a slight increase in electrical conductivity. They both serve as a valuable water resource and fish supply for the Sahel region.

The prop roots of mangroves play an important role as habitat for juvenile fishes. Revisit studies (>10 yrs apart) provide rare and valuable insights into the structure and stability of these systems in the face of escalating pressure from coastal development, climate change, and fisheries. We compared assemblages of juvenile fishes in the mangroves of a Caribbean estuary from 1991 to 1993 and 2018 to 2019 using trap collections to quantify changes and identify their potential drivers. Although the environmental and physical properties of the mangrove landscape were similar between the two periods, there were significant changes in many aspects of the fish assemblage. Compared to 25 yrs earlier, overall fish abundance (catch-per-unit-effort) was 3 to 7 times higher but overall biodiversity was 30% lower at the species level and 50% lower at the genus level. Taxa with dramatic changes in CPUE were mojarras (Gerreidae, 84% lower CPUE in 2018–2019), snappers (17 times higher CPUE), puffers (Tetraodontidae, 14 times higher CPUE), and moray eels (>200 times higher CPUE). Traps in 2019 also captured the first documented invasive Indo-Pacific swimming crab (Charybdis helerii) in the US Virgin Islands. The observed changes in the fish assemblage may be due to natural variations in recruitment, environmental influences, and/or hurricane disturbance, but for some species likely relate to declines in adult reef fish populations in the region.

Fish assemblages associated with patch reefs, rubble, seagrass, algal plain, and sandy habitats types were sUldied at St Croix's Southeastern barrier reef lagoon using underwater visual census techniques. Higher species richness and fish density were observed over patch reefsJrubble habitat followed by seagrass, algal plain, and unvegetated sandy habitat types. Thalassoma bifasciatum, HaemuJon flavolineatum, and Acanthul1l$ chirurgus were the most common fishes in highly structured habitat types (patch reef, rubble). Halichoeres bivittatus, Sparisoma radian.v. newly settled grunts (l.e., Haemulon spp.), and juveniles of Dcyumr chrysurus were mainly associated with vegetated habitat types (seagrass, algal beds), while Xyrichtys martinicensis and Coryphopterus glaucofraenum were common over unvegetated sandy habitat types. Cluster ana1ysis among backreeflagoon habitat types based on the entire fish density data showed distinct associations of fish assemblages by habitat type, regardless of season. Fish assemblages in the more structured habitat types were similar to each other but different from unstructured vegetated, and unvegetated habitat types. These results suggest that differences in fish species richness and density in the backreef lagoon are related to habitat type. The ecological importance and need far protection of backreef lagoon habitat types are discussed in relation to their potential role as nurseries for many fish species.

Considerable knowledge has been gained regarding fish use of nearshore habitats such as seagrass meadows or mangrove lagoons in the Caribbean (e.g., evaluation of nursery value, trophic linkages). However, few studies have been conducted on fish recruitment to seagrass habitat around the Caribbean. Juvenile reef fish in seagrass meadows at Teague Bay, St Croix, U.S. Virgin Islands were surveyed from October 1998 through September 1999 using a visual census technique. Grunts (Haemulidae) were the most abundant juveniles observed (60% of all fish), followed by wrasses (Labridae, 20%) and parrotfishes (Scaridae, 13%). French grunt, Haemulon flavolineatum, were the most numerous species (59.5% of all fish), followed by slippery dick, Halichoeres bivittatus (18.5%), and bucktooth parrotfish, Sparisoma radians (10.4%). Most numerically abundant fish species demonstrated peaks in recruitment during late summer and fall. Our results imply that the functioning of seagrass beds incorporates strong seasonal patterns of small-fish abundance that need to be accommodated in any study wishing to understand their importance to fisheries.

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