213 



Abstract.— Because of their tendency 

 to return to natal streams, salmonid 

 populations have often been viewed in 

 ecological isolation, although the notion 

 of an evolutionarily significant unit 

 (ESU) recognizes dispersal on evolu- 

 tionary time scales. We investigated the 

 consequences of dispersal ( straying) on 

 an ecological time scale where straying 

 creates a metapopulation structure for 

 salmonid streams within an ESU. We 

 developed a simple model for salmonid 

 metapopulations. focusing on source 

 and sink populations, and used the 

 model to highlight the dangers of ignor- 

 ing this structure in conservation ef- 

 forts. We show that exactly the wrong 

 conservation efforts may occur if 

 metapopulation structure exists but is 

 ignored. 



The dangers of ignoring metapopulation 

 structure for the conservation of salmonids 



Andrew B. Cooper 



Quantitative Ecology and Resource Management 



University of Washington 



Box 357980 



Seattle, Washington 98195-7980 



E-mail address andy acqs Washington edu 



Marc Mangel 



Department of Environmental Studies 



and 



Institute of Marine Sciences 

 University of California 

 Santa Cruz, California 95064 



Manuscript accepted 5 Mav 1998, 

 Fish, Bull. 97:213-226 1 1999), 



The U.S. National Marine Fisher- 

 ies Service (NMFS) Status Review 

 of Coho Salmon (Oncorhynchus 

 kisutch ) from Washington, Oregon, 

 and California (Weitkamp et al., 

 1995) formalized the agency's ap- 

 proach to defining both the bound- 

 aries and conservation status of dis- 

 tinct segments of salmonid popula- 

 tions for potential listing under the 

 Endangered Species Act. With this 

 approach, originally developed by 

 Waples (1991), a population or 

 group of populations is considered 

 distinct if they are". . . substantially 

 reproductively isolated from conspe- 

 cific populations," and if they are 

 considered ". . . an important com- 

 ponent of the evolutionary legacy of 

 the species" (Weitkamp et al., 1995, 

 p. 3). A distinct population or group 

 populations is referred to as an evo- 

 lutionarily significant unit (ESU) of 

 the species. 



For a group of populations to be 

 classified as an ESU, the popula- 

 tions must be reproductively iso- 

 lated from other populations but not 

 from each other. An ESU also im- 

 plies successful dispersal and repro- 

 duction between populations on an 

 evolutionary time scale. A meta- 

 population is a group of populations 

 (demes) linked by dispersal of indi- 



viduals on a shorter ecological time 

 scale such that dispersal affects 

 both the genetics of the individual 

 demes and their abundance and 

 dynamics (Levins, 1969; Ruxton, 

 1996; Ruxton and Doebeh, 1996). To 

 maintain consistency with the eco- 

 logical literature, we have used the 

 term "metapopulation" to refer to 

 the group of populations or demes, 

 and the term "population" or "deme" 

 (often used interchangeably, see 

 Policansky and Magnuson, 1998) to 

 refer to one of the individual popu- 

 lations that make up the metapopu- 

 lation. ESUs and metapopulations 

 overlap on the continuum of popu- 

 lation structures. Although a meta- 

 population will always compose 

 part of, or the entire, ESU, an ESU 

 does not have to contain any meta- 

 population structure. Dispersal be- 

 tween demes within a metapopu- 

 lation must be great enough to af- 

 fect the dynamics of the demes and 

 the recolonization of habitats of ex- 

 tinct demes. Within an ESU, dis- 

 persal must only be great enough to 

 contribute to the genetic make-up of 

 component populations; it does not 

 have to lead to recolonization events 

 or affect the population dynamics. 



Salmon typically return to their 

 natal streams to spawn. However, 



