| Abstract/Description or Keywords |
The Nechako River supports a small population of white sturgeon genetically distinct from other stock groups within the Fraser River watershed. This population is provincially ranked as a “redlisted” and federally designated as “endangered” under Schedule 1 of the Species At Risk Act. A comprehensive study by RL&L (1995 – 1999) indicated that the reproductive success of the Nechako River population is low and that limited natural juvenile recruitment may be insufficient to maintain the population. The Recovery Plan for Nechako White Sturgeon, published in 2004 by the Nechako River White Sturgeon Recovery Initiative (NWSRI), specified that research should be conducted to identify early life history stages where juvenile recruitment is failing (NWSRI, 2004). Little is known about the early life history of white sturgeon, including larval and early juvenile stages, and their respective habitat use in the Nechako River; consequently, it is difficult to identify recruitment bottlenecks. A variety of factors, including flow regulation, substrate changes, and lack of suitable habitat (physical cover) for larvae, have been considered as possible causes of recruitment failure. This project is a continuation of various research experiments investigating potential causes of Nechako white sturgeon recruitment failure. The primary objective was to release hatchery-reared Nechako white sturgeon larvae (15 days-post-hatch) into the Nechako River and to monitor general drift rates through various habitat types. Approximately 60,000 larvae were released and monitored at four sites located within, or in close proximity to, a braided reach of the Nechako River near Vanderhoof, British Columbia. Three sites were monitored with D-ring drift-nets to assess general drift rates. A fourth site was sampled with a seine net to determine survival and growth rates of larvae. An additional 10,000 larvae were released at two other sites but were not monitored. It was hoped that these larvae would be detectable as feeding larvae later in the summer; however, sampling for these larvae was unsuccessful. In summary, an initial pulse of drifting larvae was observed after release at the three D-ring sampling sites. Generally, larvae released into a location with a substrate comprised mainly of sandy moved quickly through the monitoring sites. Larvae released into sites with substrates containing a mixture of gravels and fines tended to be detectable over a longer period of time at the monitoring sites. These results suggest that larvae were able to find resting / hiding habitat before drifting downstream when released into sites containing gravel. Larval growth and survival was monitored but was unsuccessful as no sturgeon were recovered from the fourth site. A secondary objective of this project was to sample a variety of sites with a beach seine to determine habitat use, growth rates and food of feeding sturgeon larvae and to determine the species and size of potential sturgeon predators in larval sturgeon habitat. Unfortunately, no larvae were recovered and consequently growth rates could not be determined. A variety of species of potential predators were captured and assessed including Northern pikeminnow (Ptychocheilus oregonensis), Prickly sculpin (Cotus asper), chinook (Oncorhynchus tshawytscha) and sockeye salmon (Oncorhynchus nerka). |
