For shrimp, representing “bottom-up” con- trol, no clear patterns emerged in this case, the same relevant stock and ecosystem attributes appear across all HRs applied. For sharks, representing “top-down” con- trol, a graphical arrangement of the first two components clearly shows a gradual pattern of response reflecting the transition from stock-level to ecosystem-level processes as HR increases. However, when a high HR was applied (higher than the maximum sustainable yield), ecosystem attributes emerged as relevant instead of stock attributes. For sharks, outputs indicate that under a low HR, group attributes govern the response to exploitation. Principal Components Analysis was applied, and outputs were obtained using ecosystems as variables and attributes as factors, and vice versa. For each simulation, only the target group was modified. Harvest rates (HR) varied along a gradient of HR = 0.4 to HR = 0.7 for sharks and HR = 0.3 to HR = 0.8 for shrimp. For both cases, a gradient of exploitation was simulated, and ecosystem attributes were estimated. A high trophic level group (sharks) and a low trophic level group (shrimp) were chosen to represent potential “top-down” and “bottom-up” control situations, respectively. Two cases were examined by selecting target species to be exploited during simulations experiments. Simulations were developed using different ecosystems models using the Ecopath with Ecosim suite of programs. So, the aim of this study is to identify and understand ecosystem processes governing their response to fishing in a more global sense. Most scientific contribu- tions have been based on case studies of particular ecosystems. “Top-down” and “bottom-up” control processes in exploited ecosystems have been characterised using their impacts on the mean trophic level of catches, changes in biomass, and certain ecosystem attributes.
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