Quinn et al Origin and genetic structure of Oncorhynchus tshawytscha 



509 



(Fig. 2), three of the four major salmon-producing 

 rivers in NZ (McDowall, 1990). Collection sites in the 

 Waimakariri, Rakaia, and Waitaki rivers were 55, 

 18, and 57 km above the river mouths, respectively. 

 All collections were made in mid-late summer (12 

 January to 2 February 1993), early enough in the 

 season to ensure that both ocean-type and stream- 

 type juveniles (Healey, 1991) would have been 

 present (Hopkins and Unwin, 1987; Unwin and 

 Lucas, 1993). Mean fork lengths (FL) ranged from 

 61 mm (Waitaki) to 76 mm (Waimakariri). Only 63 

 parr were caught in the Rakaia River mainstem, so 

 another 38 (83 mm mean FL) were collected from the 

 downstream trap on Glenariffe Stream, a major spawn- 

 ing tributary 94 km upstream from the mouth (Unwin, 

 1986). We also sampled 62 landlocked adults (409 mm 

 mean FL) from Lake Dunstan, a hydroelectric impound- 

 ment in the upper Clutha River formed in 1992. 



Allozyme analysis 



Samples collected from NZ were frozen on dry ice 

 and transported to the National Marine Fisheries 



Service Auke Bay Laboratory where they were stored 

 at -80°C. Tissue extraction and protein electrophore- 

 sis procedures followed those described in Aebersold 

 et al. (1987). Following initial screening for activity 

 and variation at 71 loci, 24 polymorphic loci (Table 

 1) were selected for comparison with parallel allelic 

 data reported for five Sacramento River populations 

 by Bartley et al. ( 1992 ): fall chinook salmon from the 

 Coleman Hatchery (Battle Creek), the Nimbus 

 Hatchery (American River), and the Feather River 

 Hatchery (all on tributaries of the lower Sacramento 

 River); fall chinook salmon from the Merced River 

 Hatchery on a tributary of the San Joaquin River; 

 and wild winter-run chinook salmon from the upper 

 Sacramento River. To provide additional perspective 

 on the levels of genetic variation observed, we also 

 analyzed data on fall chinook salmon from the South 

 Fork of the Eel River, which enters the Pacific Ocean 

 north of the Sacramento River (Bartley et al., 1992; 

 Fig. 1). Compatible data within a subset of 10 out of 

 the 24 polymorphic loci for three Sacramento River 

 samples (Coleman Hatchery fall-run and both fall- 

 run and spring-run from the Feather River Hatch- 



