Spawning migrations and reproduction of landlocked sockeye salmon (Oncorhynchus nerka) in the Waitaki catchment, New Zealand

Abstract

The spawning migrations of landlocked sockeye salmon (Oncorhynchus nerka) within the Waitaki catchment from 1975 to 1992 are described. In late February and early March an overlapping succession of spawning runs, consisting of fish of different origins and ages, spawned in cool (8–12°C) spring‐fed tributaries of lakes Ohau and Benmore. The size, age, and sex compositions of the runs were highly variable. Mature fish ranged in age from 2 to 5 years and in length from 138 to 462 mm. Redds were constructed in gravel (15–30 mm diam.) in water 0.15–0.50 m deep, flowing at 0.20–0.50 m s‐1. Runs increased during the 1970s, reaching a peak number of over 18 000 in 1979. Dam construction that was completed in late 1979 blocked spawning migrations from Lake Benmore to Lake Ohau; spawning runs are now fewer than 100 fish per annum and may be insufficient to maintain the wild stock. Attempts to increase the spawning runs by liberating hatchery‐reared juveniles and by the transfer of mature fish into warm (14–19°C) rain‐fed streams have failed, possibly because of the premature emergence of fry in mid winter.

Keywords:

• sockeye salmon
• Oncorhynchus nerka
• spawning migrations
• Waitaki River
• hydroelectric development