Cooper and Mangel: Metapopulation structure in the consen/ation of salmonids 



225 



cess uncertainty (Hilborn and Mangel, 1997) in the 

 model will not change any of the main conclusions. 

 These factors will make recognizing the problem even 

 more difficult, as is the case in the real world. To 

 uncover metapopulation dynamics, one must explore 

 two aspects of each population's life history in refer- 

 ence to its habitat: dispersal (in the form of immi- 

 gration and emigration ) and the per-capita reproduc- 

 tive rate (defined by survival and reproduction). 

 Watershed-scale estimates of these rates, however, 

 are not appropriate. Given their reliance on index 

 stream counts, managers must know the rates of 

 immigration, emigration, and reproduction specific 

 to that stream to be able to understand the true dy- 

 namics of that stream. The dispersal of individuals 

 is important to determine the extent of the meta- 

 population structure. The focus should be both on 

 absolute numbers as well as on the effective migra- 

 tion rates that account for differences in survival and 

 productivity between the residents and the migrants. 

 Survival and reproduction estimates (the components 

 of the per-capita reproductive rate) will allow the 

 manager to assess the potential importance of the 

 metapopulation structure (i.e. to define sources and 

 sinks). As long as the risk exists for abundance and 

 density estimates to be disconnected from habitat qual- 

 ity and per-capita reproduction, all the above informa- 

 tion is required to make an accurate assessment of the 

 conservation status of the individual demes and to 

 choose the appropriate management actions. 



A great deal of time, money, and effort is currently 

 directed toward the conser\'ation and improvement 

 of salmonid populations and their habitats. The 

 NMFS report alludes to the fact that metapopulation 

 structure may exist between some salmonid popula- 

 tions, and the NRC (1996) report lists the mainte- 

 nance of metapopulation structure as one of its most 

 important recommendations. Without investigating 

 the possibility of metapopulation structure, research- 

 ers, managers, and policy makers are setting them- 

 selves up to fall into the traps described above: that 

 of either not seeing a problem that may exist or, if 

 they do see it, not knowing the true causes of such a 

 problem. 



Acknowledgments 



The initial phases of this work were supported by a 

 contract from the Southwest Fisheries Science Cen- 

 ter, Tiburon, CA, to MM. We thank Robin Waples 

 and Tom Wainwright for providing a conducive set- 

 ting where we could meet. We thank Michael Healey, 

 Andrew Hendry, and three anonymous reviewers for 

 comments on the manuscript. 



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