814 
Fishery Bulletin 95(4), 1997 
The South Island of New Zealand and the Rakaia River catchment, showing geographical features referred to in the text, the four main 
headwater tributaries used by spawning chinook salmon (1-4), and the 20-m and 30-m isobaths off the Rakaia mouth. 
August to October (late winter to mid spring), large 
numbers of newly hatched fry emerge from the gravel 
in Glenariffe Stream and other spawning areas and 
begin to move downstream within 24 h of emergence. 
This migration appears to be driven by population 
pressure; the rearing capacity of Glenariffe Stream 
has been estimated at less than 100,000 fry, whereas 
annual fry production can exceed 3.7 million (Unwin, 
1986). A second wave of larger fry, representing indi- 
viduals remaining in their natal stream for up to 3 
months, enters the upper river from November to 
January, but in Glenariffe Stream these fry repre- 
sent less than 10% of the total production. This pat- 
tern appears to be typical for chinook populations 
within their native range (e.g. Lister and Walker, 
1966; Reimers, 1973; Healey, 1991). 
Within the upper reaches of the Rakaia River, fry 
quickly take up residence along the margins of the 
braided channels, where there is an abundance of 
suitable rearing habitat (Glova and Duncan, 1985). 
Aquatic invertebrates, predominantly Deleatidium 
spp., are the primary prey in spring, but in summer 
the diet of fry is dominated by terrestrial species and 
chironomids (Sagar and Glova, 1987). From mid- 
August fingerlings gradually disperse downriver, 
growing steadily as the season progresses and reach- 
ing the lower river in mid-October at about 60-80 
mm fork length (FL) (Hopkins and Unwin, 1987). 
Fingerlings remain abundant in the lower river un- 
til early February but show little tendency to increase 
in size; thus there appears to be a steady emigration 
of 90-day fingerlings into marine waters with con- 
tinual replacement from upriver (Hopkins and 
Unwin, 1987). Similar patterns of movement have 
been observed in other New Zealand stocks (Davis 
and Unwin, 1989), in their ancestral Sacramento 
River (Kjelson et al., 1982), and elsewhere in North 
America (Healey, 1991). Mean FL at seawater entry 
