Points of view
Introduction of spawning potential:
improvement in the threshold management
Division of Population Dynamics of Marine Organisms, Ocean Research Institute, University of Tokyo,
Minamidai 1-15-1, Nakano-ku, Tokyo 164, Japan. E-mail: firstname.lastname@example.org
Introduction page 285
Does biomass really indicate the future productivity? 285
Fisher’s reproductive value 286
Spawning potential 286
Comparison between biomass threshold and SP threshold 287
Current and future usage 288
To avoid overfishing, we must maintain sufficient productivity of the fish population.
Threshold or limit reference point management is widely used for this purpose. In many
cases, a minimum biomass level is used in conjunction with other management measures
that control exploitation above the threshold (Myers et al., 1994). In this study, I explore
a possible threshold other than biomass, which to the best of my knowledge has never
Does biomass really indicate the future productivity?
Threshold is the minimum biologically acceptable level that ensures sustainability of the
stock. Therefore threshold must serve as the criterion of the future productivity of the
resource. However, it is doubtful whether biomass or spawning biomass is the proper
criterion of the future productivity. Let us denote some problems.
First, existence of the immature fish is ignored in spawning biomass. Although
immature at present, they will spawn in the future. As a result, they are expected to
have some effect on future reproduction. We should consider this future contribution.
Second, age composition is also ignored in spawning biomass. Biological parameters,
Reviews in Fish Biology and Fisheries 7, 285–289 (1997)
1997 Chapman & Hall