18 



Fishery Bulletin 



1990 



patterns of age-related mortality and growth; "impossi- 

 ble" size-frequency distributions are indicative of spe- 

 cific violations of the assumptions. Even though model 

 assumptions impose severe restrictions upon the shape 

 of size distributions, the shape of an observed distribu- 

 tion, coupled with marginal information concerning 

 recruitment and growth for the species, can be used 

 to infer age-related changes in growth, mortality, or 

 both, leading to better directed research efforts on the 

 population. This is particularly important for species 

 such as red urchins which show strong geographical 

 variation in their population dynamics (Tegner and 

 Barry llnpubl.); fishery managers often must rely on 

 easily collected size-frequency information to infer 

 demogT'aphic parameters, rather than costly jiopulation 

 studies at several locations. 



Acknowledgments 



We thank P. Dayton, J. Enright, C. Lennert, A. McCall, 

 T. Ragen, W. Stockton, G. Sugihara, W. Wakefield, 

 W. Wright, and an anonymous reviewer for advice and 

 editorial help. This research was sponsored in part by 

 the National Science Foundation, National Sea Grant 

 College Program, Department of Commerce, under 

 grant NOAA 04-8-M()M89, project number R/F-36, 

 through the California State Resources Agency. The 

 U.S. Government is authorized to reproduce and dis- 

 tribute for governmental purposes. 



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