Factors affecting the bag size of the common eider Somateria mollissima in Denmark, 1980–2000

Abstract

Based on data compiled from the official Danish Bag Record and from the annual wing surveys of waterfowl, analyses of long-term trends in the bag of common eiders Somateria mollissima were performed for the period 1958–2000, while more detailed analyses of factors affecting bag size were made for the period 1980–1999. The bag size increased from ca 100,000 in the late 1950s to ca 140,000 in the 1970s and 1980s. During the 1990s, the bag size decreased to ca 83,000 in parallel with a decrease in the number of eiders wintering in Danish waters and in parallel with a significant decrease in the number of eider hunters. Assessed from both national and regional developments in bag size, hunter numbers and numbers of eiders bagged per hunter during 1980–1999, there were no indications that bag size was related to the number of wintering eiders. Stepwise multiple regression on data from 1983–1999 showed that the number of eider hunters significantly explained 71.3% of the variation in bag size, and the annual juvenile:adult female ratio in October significantly explained 10.6% of the variation. Marked decreases in the number of eider hunters during the mid-1980s and between the hunting seasons of 1992/93 and 1993/94 coincide with public debates and introductions of legislative restrictions on waterfowl hunting in Denmark. My results stress the importance of detailed analyses of factors contributing to variation in the bag size of waterfowl before accepting an apparent correlation between bag size and population size.