Going against the flow: Effects of river damming in Cuban fisheries

Abstract

Over the last decade eutrophication of freshwater artificial reservoirs in Cuba occurred in parallel to oligotrophication of estuarine and coastal waters. These two processes influenced both freshwater and marine fisheries. A dramatic shift in species composition in freshwater fisheries has occurred, from dominance by cichlids (tilapia) to dominance by cyprinids. The high fishery yield from some reservoirs, and shift in species composition, seems related to progressive eutrophication of reservoirs by nutrient subsidies from different anthropogenic activities; particular those related to the size of urban areas within their watersheds. On the other hand, marine landings of estuarine-dependent species declined more significantly than for other groups associated with seagrass beds–coral reefs and oceanic waters. The ratio between catches of estuarine-dependent species and those associated with seagrass beds and coral reefs, decreased significantly over the last 20 years. The decrease in landings was more evident in typical estuarine species, such as shrimps ( Litopenaeus schmitti and Farfantopenaeus notialis), mangrove oyster ( Crassostrea rhizophorae) and mullets ( Mugil spp.). River damming increased during the same period and is significantly correlated with these decreases. It is hypothesized that two different processes acted synergistically, leading to dramatic decreases of several orders of magnitude, in the catches of estuarine species over the last decade: the trapping of nutrients and sediments by river damming, and a drastic reduction in nutrient inputs from land-based sources due to reduced fertilizer use. These are postulated to have affected not only estuarine resources, but also the whole coastal ecosystem.