Productivity versus engineering-based approaches to measure effort creep over time

Abstract

Most fisheries stock assessments rely on fishery dependent data to a large extent, with catch per unit effort a key indicator of changes in stock conditions. However, increases in fishing efficiency due to changes in technology and physical fleet attributes distort the relationship between observable effort (e.g., days or hours fished), catch and biomass. To compensate, a key component of fisheries stock assessment is the estimation of changes in fishing power over time to adjust catch rate information for this “effort creep”. Two approaches have developed in parallel for estimating changes in efficiency of fishing vessels over time. An approach commonly applied in stock assessment is engineering-based, focusing on changes in physical inputs. In contrast, economic based approaches have developed for assessing efficiency change that also capture non-physical inputs such as fisher skill, management changes and resulting behavioural change. We apply both of these approaches to the Australian Northern Prawn Fishery (NPF) and test the degree to which the derived efficiency time series agree. We find that the two series are highly correlated and cointegrated, suggesting that both provide a consistent measure of efficiency change over time. In the case of the NPF, this validates the current method used to adjust for effort creep in the stock assessments.