Estimating the Population of Greater and Lesser Scaup during Winter in off-Shore Louisiana

• Main Author: Kinney, Sean David
• Other Authors: Alan Afton
• Format: Others
• Language: en
• Published: LSU 2004
• Subjects: Renewable Natural Resources
• Online Access: http://etd.lsu.edu/docs/available/etd-07032004-112854/

I analyzed data from an experimental aerial transect survey, using stratified random sampling, to estimate wintering populations of greater scaup (Aythya marila) and lesser scaup (Aythya affinis) (hereafter scaup) in off-shore waters along the coast of Louisiana during winters 2000-2002. My objectives were to evaluate anecdotal reports of large numbers of scaup in off-shore waters of Louisiana during winter, and to develop estimates and confidence intervals for numbers of scaup in this area. My analysis yielded estimates of 815,700, 420,600, and 791,000 scaup in off-shore Louisiana for years 2000-2002, respectively. Confidence intervals were 1,087,000 to 545,000, 594,300 to 247,000, and 1,351,900 to 230,200 for years 2000-2002, respectively. Although large numbers of scaup were observed off-shore each year, numbers observed in most strata varied widely from year to year. Coefficients of variation (CV) for these estimates ranged from 17 to 35 percent. Highest densities of scaup were found in bays off the central Louisiana coast followed by the southwest and southeast coasts. Highest CVs were found along the southwest and southeast coasts and in the area south of Atchafalaya Bay. The precision of population estimates in these areas could be improved by increasing the number of transects. Comparisons of the number of scaup estimated in off-shore waters and that in the standard midwinter survey indicate that off-shore areas comprise 51 to 85% of the wintering population of scaup each year in Louisiana. When off-shore estimates are combined with in-shore estimates, the annual variability in total scaup is reduced greatly. It is not known whether variation in the proportion of scaup counted off-shore occurred because scaup preference for off-shore and in-shore areas varied annually, or because shorter-term weather conditions differed during surveys. The resulting high variability therefore may mask true trends in wintering scaup populations. I recommend the addition of off-shore surveys for scaup to improve the accuracy of current mid-winter scaup estimates.