Spatial Predator-Prey Dynamics: A Model of Tuna Longline Fishery Development in the Pacific Ocean

Theory regarding populations, communities, and ecosystems increasing relies upon an explicit consideration of space.  Recent research has demonstrated the importance of understanding the dynamics fishing intensity over time (termed “effort dynamics”) when interpreting catch data.  However, previous effort-dynamics models have neglected any consideration of spatial variation in densites of targetted fish populations.  We therefore develop a generic reaction-advection-diffusion model that approximates local dynamics and movement of a fishing effort as a mobile predator.  This model is demonstrated using the Japanese longline fishery for Pacific tunas (bigeye, yellowfin, albacore, and bluefin) from 1952-1974, a well-known example of spatial expansion in fishing effort.  We conduct a predictive evaluation of model performance, fitting the model to data for 1952-1969 and predicting data 1970-1974.  This model evaluation demonstrates the ability of spatial effort-dynamics models to predict changes in the spatial distribution of the longline fishery over moderate (5 year) time scales.  We conclude by discussing the potential importance of spatial effort-dynamics models. In particular, we propose that future research explore these methods to reconstruct the spatial distribution of fishing effort when only spatially aggregated information are available for some years, or for exploring the response of fisheries to spatially localized depletion of target species.