Science for sustainable fisheries: Population diversity and the portfolio effect in Atlantic cod

Many fish populations world-wide are overexploited and now facing the additional threat of climate change. Fish stocks have traditionally been managed as single homogeneous units, but increasing evidence suggests that spatial population structure exists a t the sub-stock level, characterized by spatial diversity in life histories, habitats, and genetic adaptations. Maintaining this diversity has been suggested as a potential way to increase the sustainability of fisheries; however, the empirical evidence f or this remains to be explored. The applicant proposes a one year study to determine how spatial population structure and climate shape the population dynamics of Atlantic cod. She hypothesizes that population diversity confers a "portfolio effect" to A tlantic cod stocks by reducing the interannual variability in abundance and improving risk-adjusted performance, analogous to a diversified financial portfolio. She will further test whether population diversity buffers fish stocks through climate change, and determine which factors de-synchronize fluctuations in the abundance of neighboring populations, thus strengthening a portfolio effect. Hypotheses will be tested using a 91-year Norwegian time series on spatially-structured cod populations. Statistic al models of the underlying structure and dynamics of these populations will be constructed and confronted with data to test the support for alternative hypotheses. Support is requested for 12 months in residence as a post-doctoral researcher at the Centr e for Ecological and Evolutionary Synthesis, University of Oslo, to conduct this research, in collaboration with Professor Nils Christian Stenseth. This project will bring together Norwegian and American researchers with expertise in fisheries, ecology, a nd statistical modeling to contribute to the scientific groundwork needed for the successful management and sustainable harvest of spatially-structured populations in the face of ongoing climatic change.