Title:

MICE in space:  Using spatio-temporal ecosystem models to explore density-dependent range shifts, species interactions, and the standardization of fishery catch-rate data

 

Authors:

James Thorson

 

Abstract:

Fisheries managers must increasingly cope with changes over time in fish productivity (e.g., changing individual growth and juvenile survival rates).  One hypothesis for changing productivity is that interactions among species will be modified by climate change and fishing impacts, and that changes in these interactions cause the parameters of single-species models to be nonstationary.  Estimating community dynamics and species interactions has historically been difficult using time-series data.  However, recent research suggests that spatio-temporal analyses have greater statistical efficiency than previous time-series approaches because they use spatial variation as a form of replication. In this talk, I discuss ongoing collaborations to estimate community dynamics and interactions using multivariate spatio-temporal models.  I start with a global meta-analysis of a classic hypothesis for nonstationary catch rates, i.e., that fish populations collapse to a core habitat during declines in population size.  Using bottom trawl data for 120 populations worldwide, colleagues and I estimate a 0.6% decrease in “effective area” for every 10% decline in abundance, but also show that this relationship varies widely among populations and regions.  I then use “spatial dynamic factor analysis” to estimate an abundance index for Petrale sole based on catch-rates in a multispecies bottom trawl fishery.  This case study illustrates how to simultaneously estimate fisher targeting and fish densities, and yields an index with good simulation and case-study performance.  Finally, colleagues and I propose a new procedure for estimating the matrix of pairwise species interactions, where this approach bridges between unregulated (“neutral”) and highly-regulated (“niche”) approaches to community ecology.  Using the marine community in the Gulf of St. Lawrence as case study, we show a mixture of regulated and unregulated dynamics, where the unregulated component is associated with a recovering grey seal population that is negatively impacting productivity for three prey species of fish.  I end by discussing important research topics to enable development of spatial ecosystem models using widely-available data for marine systems.