Juvenile salmonid production in a Lake Erie nursery stream

Abstract

Normandale Creek (2531m 2 ) provides spawning and nursery grounds for lake‐run rainbow trout, Salmo gairdneri Richardson, brown trout, Salmo frutta L. , and coho salmon, Oncorhynchus kisutch (Walbaum). Upstream movements are significantly correlated with peak stream discharge (P < 0.05). In 1973–1974, 59 adult salmonids constructed 86 nests of which 60% were disturbed by re‐use or sand deposition. From a calculated deposition of 90 400 ova, 483 juveniles, 6 cm in fork length ( f.l. ), were resident in the stream when estimates by electrofishing first became valid. Estimated within‐stream (i.e. all sections combined) monthly densities of wild juveniles >6 cm f.l. ranged from six to 22 fish (100 m 2 ) −1 , and biomass from 1.3 to 3.1 gm −2 . The highest within‐section biomass was 8.3 gm −2 in November. Additions of hatchery‐reared rainbow trout temporarily increased monthly within‐stream juvenile density up to 23 fish (100 m 2 ) −1 , and biomass to 8.2 g m −2 . Density and biomass were positively correlated (P < 0.05) with both instream and bank cover, and biomass negatively correlated (P < 0.05) with gradient. The importance of substratum and flow characteristics on juvenile density and biomass was strongly indicated although not statistically significant. Annual within‐section production of juveniles > 6 cm f.l. ranged from 4.79 to 5.93 g m −2 year −1 in Sections III and IV, respectively. Inclusion of calculated probable numbers of fish < 6 cm f.l. increased within‐section production from 5.93 to 18.65 g m −2 year −l in upstream Section IV.