| Abstract/Description or Keywords |
The goal of the 2009 Nechako River white sturgeon monitoring program was to use egg mat, drift nets, telemetry and observational techniques (e.g. underwater camera, DIDSON sonar) to precisely identify spawning locations within the more broadly defined spawning area located in Vanderhoof, BC. The brood stock program captured and assessed a total of 71 fish, 20 of which were considered ready to spawn. The tracking of fish movements in the spring through aerial and base station telemetry, along with monitoring of water temperatures were used to identify the approximate spawning window. Artificial substrate mats were deployed throughout the spawning area on May 29th with eggs collected on June 2nd, 3rd, 5th, 7th, 9th and 11th. The subsequent timing of the captured eggs hatching suggests spawning occurred in 4 events: May 31st - June 3rd; June 3rd – 5th; June 5th-7th; and June 7th - 9th. This is later then in 2004 and 2006 (May 18th and 19th, respectively) but similar timing to 2007 and 2008 (June 4th, and June 2nd - 9th, respectively). The location of spawning varied between the events. The initial two spawning events occurred primarily in the vicinity of the Stoney Creek confluence with eggs also being collected around the top island. Alternatively the 3rd and 4th events occurred both at the upstream end (i.e. above the top island) and downstream end (i.e. upstream of the Burrard Ave. Bridge) of the spawning area. The initial spawning event (May 31st – June 3rd) occurred at a mean daily temperature of 11°C, which is 2°C cooler then the temperature at which spawning occurred in 2004, 2006, 2007 and 2008. While micro-habitat conditions downstream of Stoney Creek could have resulted in slightly warmer conditions at the spawning site, the fact that eggs were also collected upstream suggests an environmental variable in addition to water temperature is likely involved in spawn timing. This variable, likely photoperiod, would ensure that spawning still occurs if threshold temperatures are not achieved by a particular date. Habitat surveys completed throughout the spawning area identified that while depths and velocities are considered suitable at the sites, the presence of fine sediments and infilling of interstitial spaces is likely detrimental to egg and larval survival. The percent composition of fine sediment was lowest at the upstream end of the site, which corresponded to the area of highest velocity, and increased at the downstream end. Specific spawning locations in 2009 did not necessarily correspond to the areas with favourable substrates. This suggests that while substrate composition may play a role in defining the general spawning area, specific sites are likely selected based on other parameters such as depth and velocity. Lastly, since spawning continues to occur in the area it suggests habitat restoration may be required to restore habitat and ensure better survival of eggs and larvae. |
