Survival and productivity. Brief summary of available information on generation length, age of first breeding, clutch size, productivity, survival of the age classes (adult, juvenile, chick, nest) and factors affecting them.
Survival and productivity. Like most goose populations in the Northern Hemisphere, when not subject to hunting, individuals are typically long-lived, exhibiting annual adult survival rates of up to 90%, although first year survival is typically lower than that of adults. This has been shown to be the case amongst Greenland White-fronted Geese, where long time series of count and age ratio data show an average of 89% for the crude annual survival rate amongst adult birds (Fox 2003). Annual survival rates based on resightings of marked individuals during 1983-1997 was 79% for adults and 68% for juveniles (Fox 2003). This estimate was made during a period when autumn hunting was permitted in Iceland - which accounts for the overall difference to that calculated by census data. At Wexford Slobs, retrospective analysis of crude annual adult survival rate showed an inverse relationship with hunting mortality, and that the slope of this regression model did not differ significantly with that predicted if hunting mortality was completely additive to other sources of mortality (Fox 2003). In other words, the adults dying as a result of being shot were not a “harvestable excess” in the population that would have died of other causes anyway, potentially through some density-dependent mechanism, such as limited food supply. This finding is of considerable importance for management of the population, since with the cessation of winter hunting, the population increased at a rate of c. 4% per annum (in line with the theoretical prediction) and as a result of the survival of those birds that would have previously been shot prior to the hunting ban. This makes hunting regulation a powerful management tool with which to effect change in overall population size, since reduction of the winter hunting bag by a given number of individuals will likely increase the population size by that same amount at the end of the first closed hunting season. In this context, it is important to stress that during the period of expansion in the population during the 1980s, production was sufficiently high that the annual autumn kill in Iceland (over 3,200 individuals in 1995 – Statistics Iceland 2011) did not inhibit an increase in overall population size. However, following the prolonged subsequent period of decline in overall numbers since 1999, it was clear that this additive source of mortality (over 3,700 taken in 2001) was not assisting the recovery of the species towards favourable conservation status in very rec...
