Dabbling duck harvest dynamics in the Central Valley of California--implications for recruitment

Abstract

Age and sex ratios and body weights were obtained for northern pintails (Anas acuta), mallards (A. platyrhynchos), American wigeon (A. americana), green-winged teal (A. crecca), and northern shovelers (A. clypeata) shot at Mendota State Wildlife Area in the San Joaquin Valley (SANJV) and at Sacramento National Wildlife Refuge in the Sacramento Valley (SACV) during 1982-83 and 1983-84. Age ratios were determined for pintails at four locations during 1980-83. Cooperative Waterfowl Parts Collection Survey (1982-84; U.S. Fish and Wildlife Service) and California preseason-banding data (1973-77, for mallards and pintails) also were used to measure age ratios of the California harvest. Harvest rate (ducks shot per day) was obtained and summed from all SACV and SANJV public hunting areas in 1982-84. All species except female wigeon and adult female mallards lost weight between October and January. Except for wigeon, harvest rate was high in October when hunting began. Harvest rates were low in November and December but rose markedly in January in the SACV for all species and for all except pintails in the SANJV. Proportion of adults in the bag as measured by all methods increased progressively through the hunting season. Proportion of adults in the harvest was higher in 1982-83 than in 1983-84 and was greater in the SACV than the SANJV both years for most species. Adult females formed a small component of total kill but 50% or more of female kill. The harvest of pintails at a SACV and a SANJV location consistently contained about half as many immatures per adult as that at two other California locations for 1980-83. The substantial harvest of adults in January eliminates the most productive breeders from the population. Thus, winter hunting mortality may influence age composition of the spring flight and, hence, recruitment potential of the breeding population.