River residence of juvenile chinook salmon (oncorhynchus tshawytscha) in the rakaia River, south island, 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”. © Crown copyright 1987.