Comparative analysis of the spatial distribution of fishing effort contrasting ecological isodars and discrete choice models

Abstract

The spatial dynamics of catch and effort data are often overlooked in fisheries research despite its well-documented utility in understanding the distribution and abundance of fish. We apply a recently developed fisheries isodar model to an otter trawl groundfish fishery on the Scotian Shelf and compare its predictive performance with a more traditional discrete choice model random utility model. Isodars represent the expected distribution of foragers between two habitats when fitness is equal and can be a representation of the ideal free distribution. Here, fitness was defined with relative catch rates, cost differentials, and interference effects between habitats. Random utility models were constructed as mixed logit models to give the expected probability of fishing in a particular area based on a collection of predictors. The predictions of the isodar models consistently outperformed the mixed logit for both in-sample and out-of-sample forecasts and the isodar was determined to be the preferred model based on its increased accuracy and simplicity. The isodar model can provide a statistically powerful and easily implemented tool in effort studies, especially in situations of aggregated or limited data, which can inform conservation and management decisions.