Effects of small-scale and recreational fisheries on the Gran Canaria ecosystem

A mass-balance trophic model was built in order to describe the impact of the different fleets that operate in the Gran Canaria marine ecosystem between 2005 and 2010. This is the first food-web model developed in the Canary Islands, and results were presented and compared with other ecosystems that have been modeled in Atlantic and Mediterranean coastal areas. Thirty-four functional groups were defined, corresponding to benthic, demersal, and pelagic domains, also including the deep scattering layer (DSL) and detritus. Keystone index and mixed trophic impacts matrix showed a bottom-up control in the benthic-demersal area while in the pelagic zone intermediate predators such as cephalopods, are more relevant to the ecosystem. Primary production required to sustain the fishery was higher when taking into account the detritus and the primary producers, suggesting the importance of detritivorous organisms such as crustaceans, DSL, molluscs, and other benthic species in the catches. Recreational fishermen exert high impacts on most groups of the ecosystem, especially in breams and epidemersal fishes. Benthic sharks, groupers, breams, parrotfishes, leatherjacket fishes, and common pandora showed high exploitation rates, suggesting that these species are overexploited.