POPULATION-SPECIFIC VARIATION IN BODY DIMENSIONS OF ADULT CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA) FROM NEW-ZEALAND AND THEIR SOURCE POPULATION, 90 YEARS AFTER INTRODUCTION

Chinook salmon (Oncorhynchus tshawytscha) transplanted from the Sacram ento River, California, U.S.A., to New Zealand in the 1900s colonized many South Island rivers, which now show significant population-specif ic phenotypic variation. To characterize this variation, we conducted a morphometric analysis of two New Zealand populations and the fan-run Battle Creek population at the Coleman Hatchery, the apparent ancestr al stock. Variation in length at age, weight at length, fin lengths, h ump depth, snout length, and caudal peduncle width was detected among populations. Sexually mature Battle Creek and New Zealand chinook salm on were consistently identifiable from morphometric data (97.7% classi fication accuracy), largely through differences in caudal peduncle wid th and hump depth. The two New Zealand spawning populations, although distinguishable in morphology in 1994 (mean of 80% correct classificat ion), did not classify as well using the same discriminant functions i n 1995 (mean of 62.7% correct), suggesting interannual multivariate ef fects. Little variation was observed between the two mainstem river po pulations in adults collected shortly after entering freshwater. Altho ugh the genetic or environmental causes for the differences between po pulations have yet to be determined, our results provide empirical evi dence of phenotypic divergence over decadal time scales. This work may be relevant to considerations in the development and monitoring of sa lmon recovery and conservation programs.