| Abstract/Description or Keywords |
The distribution and abundance of juvenile chinook salmon (Oncorhynchus tshawytscha) in the upper 100 km of the Nechako River, BC in 2010 were evaluated through sampling using electrofishing and rotary screw traps as part of the twentysecond year of the Nechako Fisheries Conservation Program (NFCP), commissioned by Rio Tinto Alcan. Mean daily water temperatures below the Cheslatta Falls in 2010 were close to, or above, the observed maximum between the years 1987 and 2004 for April but were close to the historic mean from June to mid-August. Flows at Cheslatta Falls in 2010 were lower than the 18-year median (1987-2004) from April to the end of July. Cumulative daily flows for 2010 followed the same pattern as in previous years but were lower than 10 of the 18 years on record. Based on the data on fish size versus time, emergence of chinook fry in 2010 had ceased by early June. Monthly electrofishing surveys along the length of the upper river in April, May, June, July and November captured 86,000 fish from 12 species or families. Juvenile chinook salmon were the most common species, accounting for 38% of all captures or 32,456 fish (32,232 0+ and 224 1+), of which 61% were captured at night. As in previous years, juvenile chinook captured at night tended to be longer and heavier than daytime-captured fish during the primary growth period of May – July. The catch-per-unit-effort of electrofished 0+ chinook peaked in May for both day and night catches. Spatial distribution of 0+ chinook along the length of the upper Nechako River reflected a general upstream movement of 0+ chinook from May to July and a large overall drop in abundance of fish residing in the river in November consistent with the historical trend. CPUE of 0+ chinook ranged from 0 to 421 fish/100m2 and peaked in either May (night) or June (day) and then decreased. CPUE of 1+ chinook ranged from 0 to 11 fish/100 m2 and decreased with date. The number of outmigrating 0+ chinook (8,926) captured by rotary screw traps at Diamond Island between April 11 and July 15, 2010, was bimodal, with an initial peak on May 9 and a secondary peak on June 20. Fish captured at night were both longer and heavier thann those captured during the day. Compared to the historic data, the 0+ fish captured in 2010 were larger than the 14-year mean (1991-2004) in April but smaller in May, June and July. Condition indices in 2010 were slightly lower than the historical mean but higher than the historical minimum. The index of juvenile downstream migration was 154,433 for 0+ chinook and 9,599 for 1+ chinook. The combined estimate (164,032) was the 3rd highest on record. The index of 0+ outmigrants for the years 1992 to 2004 and 2010 was positively and significantly correlated with the number of parent spawners upstream of Diamond Island in the previous year. The 2010 results do not fall outside the data envelope identified in the NFCP 5 year plan (2007-2012) and therefore additional evaluation and changes to the program schedule are not considered necessary. |
