Maximum Economic Yield and Non-Linear Catchability
June 24, 2021
This study presents a revised bioeconomic model that bridges the gap between fishery management goals, and the realities of fisheries by improving Schaefer’s (1957) bioeconomic model to derive maximum economic yield (MEY).
Maximum economic yield (MEY) as derived from Schaefer’s (1957) bioeconomic model was potentially a major contribution to fishery management, but it has been hard to apply to fishery management in reality. Schaefer’s model with fixed catchability and associated linear CPUE does not match the variable nature of catchability resulting from technological progress and schooling behavior, leading to a biased estimation of MEY or economic optimal biomass (BMEY). This study improves on Schaefer’s model by incorporating nonlinear CPUE, where MEY depends on biomass relationships with catchability and with CPUE. When CPUE is constant, MEY is shown analytically to be the same as the biological optimal yield (maximum sustainable yield [MSY]) and the related optimal biomasses are equivalent (BMEY = BMSY). However, in cases of nonlinear CPUE, MEY might be closer to or further away from MSY. The less sensitive the CPUE is in response to changes in biomass, the closer the economic optimum BMEY is to the biological optimum BMSY. When CPUE is sensitive to changes in biomass, the benefit of leaving more fish in water (the stock effect) is more noticeable. Hence, this revised model can become an important component in matching fishery management goals to the realities of fisheries. Simulation analyses further illustrate that the traditional Schaefer economic optimum does not apply to all fisheries. This model provides the basis for fishery management to set a total catch limit (as a fishery management reference point) that could achieve MEY but also defines how MEY could be equal to, closer to, or further away from MSY based on characteristics of an individual fishery. For a fishery in overfished status, it helps fishery managers to decide a rebuilding target at BMSY or at a higher abundance than BMSY in order to achieve MEY and still meet biological reference points.
Pan M. 2021. Maximum Economic Yield and Non-Linear Catchability. North American Journal of Fisheries Management. http://doi.org/10.1002/nafm.10661.