New Zealand Journal of Marine and Freshwater Research abstracts

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Mortality and growth of juvenile brown and rainbow trout in a lake inlet nursery stream, New Zealand

JOHN W. HAYES*

Department of Zoology University of Canterbury Private Bag, Christchurch New Zealand

Abstract Density and growth of mixed populations of 0+ brown and rainbow trout, and population changes of the latter, were studied in Scotts Creek, a spawning/nursery inlet stream of Lake Alexandrina. Stream rearing capacity and the potential for interspecific competition between resident 0+ brown and rainbow trout were assessed. The 0+ trout populations were dominated by rainbow trout with maximum density of rainbow fry being 7.7 fry m~²; whereas that of brown fry usually was less than 0.16 frym~². Observed loss of 0+ rainbow trout over much of the summer was constant whereas mortality increased. Loss for the first six months of life was c. 96%. Mean length at the end of the summer growing season (April) was c. 114 mm and 69 mm for 0+ brown and rainbow trout, respectively. Size-selective emigration for large fish affected observed growth of 0+ rainbow trout in the autumn and early winter. Maximum biomass of 0+ fish ranged between 19.2 + 3.5 gm^²and 26.0 + 4.5 gm~² over the three summers. Brown trout obtained a size advantage over rainbow trout through earlier emergence, but they were too few in number to exert a competitive influence over rainbow trout.

Keywords Salmo gairdneri; Salmo trutta; fry; juveniles; mortality; growth; biomass; emigration; stream; rearing

New Zealand Journal of Marine and Freshwater Research, 1988, Vol. 22: 169-179 ; Crown copyright 1988Received 12 May 1986; accepted 23 June 1987

PDF file of entire paper: medium quality (769K); (scanned from paper original: notes about this process)

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