Research Document - 2000/152
Evaluation of utility of aerial overflight based estimates versus mark-recapture estimates of chinook salmon escapement to the Nicola River, B.C.
By R.E. Bailey, C.K. Parken, J.R. Irvine, B. Rosenberger, and M.K. Farwell
Abstract
We surveyed adult chinook salmon (Oncorhynchus tshawytscha) in the Nicola River from a helicopter and examined our count data to determine their statistical properties. Replicated counts were compared and variances estimated for reach counts using regression and quartile approaches. Reach counts were highly repeatable. Expansions of peak counts indexed abundance well among years, however, when using the standard expansion factor (π=1.538), estimates were biased low for three of four years when compared to Petersen mark-recapture estimates. AUC (area-under-the curve) estimates of spawner-days described the spawner abundance in a more robust manner than peak counts. Apparent redd residence times were stable among years (mean = 5.81 d, range 5.34 - 6.37 d). Retrospective AUC estimates, calculated using observed spawner data and the mean apparent redd residence time, adequately estimated spawner abundances for all four years. While at this time, we are unsure of the minimum number of overflights required to produce scientifically defensible AUC escapement estimates, it is likely that four or more flights may be required on many systems. We recommend similar studies be conducted in other watersheds in order to examine: 1) The repeatability of aerial counts; 2) spatial and temporal variability in survey life; and 3) degree of bias associated with aerial overflight-based estimates.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: