Is catch proportional to nominal effort? Conceptual, fleet dynamic, and statistical considerations in catch standardization.

Often, catch-per-unit-effort (CPUE) standardizations are used to reflect fish abundance. This implies that catch is directly proportional to effort. We examine this using 78 reported catch and effort series in a meta-analysis, correcting for errors-in-variables in the relationship. Though proportionality in the apparent relationship is the average, there is significant variation among fisheries. We then examine the Scotian Shelf haddock fishery in detail. We used a generalized linear mixed model (GLMM) predicting catch-per-set, accounting for annual and within-year variation in fish, fleet activity, aggregation, and vessel locations and differences. In individual trawls the catch was less than expected from a proportional relationship with effort. The GLMM revealed both interference and facilitation among vessels as well as autocorrelation among sets. The greatest impact on coefficient estimates was seen by allowing the effort coefficient to vary. Temporal aggregation made the catch-effort relationship ap...