FECUNDITY AND THE STOCK RECRUITMENT RELATIONSHIP

The stability of fishery population models often depends upon the form of the underlying stock-recruitment (SR) relationship, yet this relationship generally cannot be defined from actual fishery data. I use a simple SR model to show that the ability to characterize a SR relationship depends upon both natural mortality (M) during the prerecruit period, which is associated with a species' fecundity (F), and the variability of M. The SR relationship may be readily determined in species with low fecundities (e.g. higher vertebrates: F less-than-or-similar-to 10), even if the variability of M is relatively high. However, the SR relationship generally cannot be defined in species, such as teleosts, with high fecundities (F on the order of 10(6)) if prerecruit M exhibits even moderate variability because small variations in M lead to large changes in survivorship. Thus, the concept of a simple deterministic SR relationship does not appear applicable to organisms with high fecundities. The use of fishery population models dependent upon such functions needs to be reexamined. Adaptive management strategies (i.e experimental manipulations of stock size) are likely to succeed in defining the form of the SR relationship only for stocks characterized by low recruitment variability.