Simulation Study of Biological Reference Points for Summer Flounder

• Published in: Transactions of the American Fisheries Society (1900) 2012-03, Vol.141 (2), p.426-436
• Main Authors: Rothschild, Brian J, Jiao, Yue, Hyun, Saang-Yoon
• Format: Article
• Language: English
• Subjects: biomass; flounder; Marine; mortality; Paralichthys dentatus; population dynamics; simulation models; spawning
• ISSN: 1548-8659; 0002-8487; 1548-8659
• DOI: 10.1080/00028487.2012.667041

The biological reference point F ₓ% (i.e., the fishing mortality rate that maintains the spawning stock biomass per recruit at x % of its unfished value [where x is usually set to 40]) is a commonly used proxy for F MSY (the fishing mortality rate that results in the maximum sustainable yield). However, F ₓ% is not in general equivalent to F MSY. To investigate the difference between F ₓ% and F MSY, we developed a simple simulation model capable of representing the relationship between yield and fishing mortality, maximum spawning potential (%MSP), and the curvature of the stock–recruitment (S–R) curve (parameterized as β) for a stock similar to summer flounder Paralichthys dentatus (a high- β species). The model demonstrates that the dynamic trajectories of the stock are heavily dependent on β . The model confirmed the dependence of equilibrium yield on β and produced a specific relationship between the magnitude of β and yield. A decision-theoretic approach was used to suggest that setting x to 40 reduces yield and that smaller values of x produce greater yields for high- β stocks. The analysis focuses attention on the fact that the choice of F ₓ% as a management tool places extreme reliance on the least known and understood component of fish population dynamics: the S–R relationship. Our conclusion (to use a value of x considerably less than 40 to obtain MSY) was supported by (1) our simulation results, (2) averaging in a decision-theoretic approach, (3) the correspondence of the traditionally computed biomass at the maximum sustainable yield with high values of β , and (4) the values of x reported in the literature.