Use of the Spawning Potential Ratio for the Upper Mississippi River Channel Catfish Fishery

Abstract

We used simulation modeling to identify the conditions of growth and recruitment overfishing that were associated with a decline in the Upper Mississippi River (UMR) commercial fishery for channel catfish Ictalurus punctatus prior to 1984, when the minimum length limit was increased from 330 to 381 mm total length. The spawning potential ratio (SPR)—an index developed by marine fisheries scientists to identify and prevent recruitment overfishing—is simply a ratio of the average lifetime production of mature eggs per recruit in a fished population to what it would have been if the population had never been fished. We identified a critical minimum SPR that could be used as a biological reference point in the management of a highly exploited channel catfish fishery. Simulation modeling predicted that the SPR, which ranged from 3% to 12% under the 330-mm minimum length limit, would increase to 10–20% with a 381-mm minimum length limit for exploitation rates of 45–80%. Our predicted increase in the SPR corresponded well to the three- to fourfold increase in age-0 channel catfish abundance. Prior to the higher length limit, the reduction in commercial yield was primarily due to recruitment overfishing and not growth overfishing. The critical minimum SPR of 10–20% for the UMR channel catfish population is lower than the critical levels of 20–30% typically reported for pelagic marine species and is likely due to the life history characteristics and spawning strategy of channel catfish.