New Zealand Journal of Marine and Freshwater Research abstracts

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River residence of juvenile chinook salmon {Oncorhynchus tshawytscha) in the Rakaia River, South Island, New Zealand

CERI L. HOPKINS

MARTIN J. UNWIN

Freshwater Fisheries Centre Ministry of Agriculture and Fisheries P.O. Box 8324, Riccarton Christchurch, New Zealand

Abstract Most chinook salmon in the Rakaia River spawn in upland tributaries. In spring very large numbers of fry emigrate from side streams to the main river. It has been thought that most of these fry do not survive, and thus do not contribute to the adult population. In contrast, we found that many fry take up residence in the river and, after a period of growth, proceed slowly seawards, reaching the coast in late spring to early summer. By the time fry recruitment to the upper river ceases (November), juvenile salmon are abundant throughout the river, ranging in fork length (FL) from 35 mm in the upper reaches to 80 mm near the river mouth. Most fingerlings enter the sea at 60-90 mm FL. From November the residual population in the upland tributaries enters the river as fingerlings 50-60 mm FL. In the absence of severe flooding, these "stream residents" are probably outnumbered by "river residents".

Keywords chinook salmon; Oncorhynchus tshawytscha; juvenile behaviour; rearing; river residence; migration; Rakaia River; New Zealand

New Zealand Journal of Marine and Freshwater Research, 1987, Vol. 21: 163-174 0028-8330/87/2102-0163$2.50/0 © Crown copyright 1987 Received 3 February 1986; accepted 17 September 1986 Fisheries Research Publication 547

PDF file of entire paper: medium quality (871K); (scanned from paper original: notes about this process)

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