HOMING AND STRAYING PATTERNS OF CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA) FROM A NEW-ZEALAND HATCHERY - SPATIAL-DISTRIBUTION OF STRAYS AND EFFECTS OF RELEASE DATE

Homing and straying patterns of fall chinook salmon (Oncorhynchus tsha wytscha) released from the Glenariffe Salmon Research Station on the R akaia River, New Zealand, are reported, based on coded-wire tag recove ries from the 1978-84 brood years. Of 17 671 tagged adults recovered, 87.9% returned to the Rakaia, and the rest were recovered from 12 othe r catchments up to 500 km away. The number of strays entering a given river increased with discharge and with proximity to the Rakaia, but m ost strays were recorded in catchments north of the Rakaia. A higher p roportion of salmon released in winter, when the downriver migration o f naturally produced chinook is a minimum, strayed to other catchments (14.9-20.6%) than did those released at other times of the year (3.6- 7.6%). However, straying within the Rakaia catchment was largely unaff ected by release date, suggesting that imprinting by fry to the natal tributary is separate from imprinting by smolts to the mainstem river. There was a complex interaction between age at maturity, release date , and straying rates; straying of 4-yr-old fish was more strongly infl uenced by release date than straying of younger fish. Notwithstanding this interaction, straying was more prevalent among older fish.