Contrasting Different Classes of Connectivity Among Salmon Populations: Syntheses and Synergism of Genetics and Demographics

Human activities have fundamentally altered connectivity among fish populations in general and in salmonids in particular.  Physical connectivity has changed as a result of river and estuarine engineering for impoundment, diversion, reclamation, and channelization.  Genetic and demographic connectivity are continually influenced by artificial propagation, whether through hatchery broodstock development, altered mortality schedule, out-of-basin stocking and straying, or altered reproductive success of emigrants.  Although there is wide agreement on the pervasive nature of human impacts, “connectivity” can take a wide variety of meanings.  Moreover, the meaning and significance of connectivity are often case-specific.  In this study, we explore recent ideas on connectivity and apply them to selected eastern Pacific salmon populations.  Using a variety of landscape genetic methods, we examine recent data sets that provide both fine-scale depth and large geographic breadth.  We find expected isolation-by-distance patterns, however, we also note some potentially interesting basin effects and other departures from expectation.  These departures are attributed to both earth-history events and anthropogenic effects.  Finally, individual assignment to population of origin, combined with radio tagging, help quantify and contrast genetic and demographic connectivity.  Synthesizing multiple studies suggests that emigrants (including, in many cases, hatchery out plants) have significantly reduced reproductive success relative to native, natural-origin fish.  Our results are relevant to conservation and recovery, as well as more general fishery management, artificial propagation, and habitat restoration.  Powerful new ecological genetic methods, applied to large data sets, provide valuable new insights into connectivity and human impacts, especially when combined with direct measures of the movement of individual fish.