Pacific Salmon Population Structure and Dynamics: a Perspective from Bristol Bay on Life History Variation across Spatial and Temporal Scales
Thomas P. Quinn
Abstract.—Pioneering scientists pointed out that conservation and management of salmon for human use and as a component of ecosystems depends on understanding their population structure. Many current controversies regarding exploitation rates, interceptions, and resuscitation of depleted populations hinge on issues of population structure. This paper examines the range of spatial scales over which salmon population structure can be defined, using Bristol Bay sockeye salmon Oncorhynchus nerka as the example. The region’s geology has created similar spawning habitats associated with different lakes, revealing the extent to which evolutionary processes repeat themselves. The life history patterns of the salmon reflect both genetic adaptations to their local environment, facilitated by homing to their natal site for spawning, and also the capability to respond to changing environmental conditions. This combination of variables may explain why similar environmental conditions result in different patterns of population dynamics among the lake systems, giving the Bristol Bay system as a whole more stability than is seen in any single lake. At still finer spatial scales, investigations show that sockeye salmon home not only to specific streams but even to habitat patches within a stream. Nevertheless, records of the presence of other salmon species, notably Chinook O. tshawytscha, chum O. keta, and pink salmon O. gorbuscha, seem to indicate more dynamic population structure, including straying and the possible establishment of new populations in streams where sockeye salmon are numerically dominant. The understanding of these patterns and processes stems largely from a well-conceived and persistent long term program of research and monitoring, and this provides lessons and cautions for research and management in systems where information is less extensive, such as in the Arctic-Yukon-Kuskokwim region.