Size based dynamics of the pelagic fish community off Northern Chile

The well-being of humans and their societies depends on goods and services from marine ecosystems. Management of the fish stocks off Northern Chile is based on a single species approach. However, the fish species are not independent, and there is a need to understand the species interactions within the community and with the 3climate variability and human pressures. In this thesis I studied the size-based dynamics of pelagic fish community off Northern Chile. I investigated temporal effects of climate variability on size-based indicators from the pelagic fishery. I found that catches from the pelagic community have been declining and have become composed of smaller fish. The main signals from the environment were short-term effects, but the trends found were probably combined consequences of climate variability and fishing. I developed a multispecies size-spectrum model to explore the dynamics of the pelagic community. The model examined the effect of cannibalism and intraguild predation on anchovy and sardine dynamics under different environmental conditions. I found that climate variability and predation interactions are both needed to understand the coexistence and extinction of anchovy and sardine. The effect of fishing on anchovy dynamics was also explored through the model. Preliminary results showed that fishing below maturity has lower impact on anchovy dynamics than current fishing pattern off northern Chile. In addition the approach of a balanced harvest strategy would be more beneficial for anchovy only when it follows the relative growth rate of the species. Indicators and models are key tools in implementing the ecosystem-based approach. This thesis has combined these tools with emerging ecological theory about the role of size in the structuring marine ecosystems and, in this way, has set up a basic framework to work towards the ecosystem-based fishery management off Northern Chile.