Tuesday, August 7, 2007 - 8:40 AM

OOS 7-3: Differential resilience of trophic structure to exploitation in continental shelf ecosystems

Kenneth Frank, Department of Fisheries and Oceans

Using data from twenty six studies in eighteen exploited marine ecosystems, we show that the type of trophic forcing, involving piscivores and their prey, depends on species richness and temperature throughout the north Atlantic. While very cold and species-poor areas in northern areas may readily succumb to top-down control and recover slowly (if ever), warmer areas with more species may oscillate between top-down and bottom-up control dependent on exploitation rates and, possibly, changing temperature regimes. This ocean-scale relationship translates directly to variation in the resilience to fishing pressure of piscivores and makes it possible to create ecosystem-level guidelines for sustainable fisheries. Given that top-down or bottom-up control reflects not only resilience to fishing, but also the underlying level of exploitation, we develop quantitative relationships linking exploitation, species richness and ocean climate variability. The analysis provides a direct measure of the limits to fishing necessary to prevent top-down forcing/predator-prey imbalances in different marine systems.