Kinnison, Michael. 1997. Population differentiation of chinook salmon populations introduced to New Zealand: Evidence from morphological, reproductive and early life history characters. M.S.
The issues of local population structure and genetic adaptation are of central concern to the conservation and rehabilitation of salmon populations. The time frames and the mechanisms associated with the initial stages of development of population divergence and local adaptation are fundamental to these issues and yet they have no been studied in detail for salmonids. One way of studying these topics is the detailed investigation of introduced populations, in which the time since population establishment is known and in which divergent character states can be readily identified. Introductions of anadromous Pacific salmon have proven largely unsuccessful even within their native ranges. The introduction of anadromous chinook to New Zealand represents the longest standing and most expansive "success".
Inspired by observations of significant degrees of phenotypic differences that appear to have arisen within the last century among populations in New Zealand, a long term project was initiated to further document phenotypic variation and to determine the genetic and environmental basis for it. This thesis represents the results from the early stages of this research program. Morphological traits, size at age, weight to length relationship, egg size and fecundity of maturing adult chinook were compared among two New Zealand populations and their closest related North American counterparts (from a tributary of the Sacramento River, CA). Early development, fry growth, salinity tolerance and incidence of freshwater parr maturation were compared between the two New Zealand populations under common controlled conditions to determine if genetic differences in early phenotypic traits exist between the populations.
Phenotypic differences among populations were found for each of the characters measured from mature adults. Differences were generally more pronounced in comparisons between the New Zealand fish and their North American Relatives than between the New Zealand populations. Differences between the New Zealand populations in early life history characters were not apparent or slight, though early fry growth showed indications of genetic divergence. These results suggest that genetic differences in early life history traits, arising from local adaptation or other mechanisms, has not occurred between the New Zealand populations in the 90 years since introduction, to the extent implied by adult trait variation. The results of this study are discussed with respect to local adaptation, genetic drift and pre-existing adaptive characters, and to the restoration and conservation of anadromous Pacific salmon.