The Greenland White-fronted Goose Anser albifrons flavirostris

8 Survival
8.1 Introduction
Almost all goose populations have increased in
the Western Palearctic in the last 45 years (Madsen
et al. 1999). Since many of these are discrete and
closed populations, the increases cannot be accounted
for by immigration of individuals from
elsewhere. These increases have not always been
brought about by enhanced reproductive output,
indeed for many populations, recruitment has
actually fallen with increasing abundance (e.g. the
Russian-breeding Barnacle Goose population
Ebbinge 1991, and see also chapter 6). Population
modelling and simulation demonstrates that
as relatively long-lived birds, northern nesting
geese are sensitive to small changes in annual
adult survival - very much larger changes in productivity
rates are necessary to effect similar
changes in the rate of population change (e.g.
Tombre et al. 1997, Pettifor et al. 1999). The size
of a population is determined by the relative annual
gain (birth rate and immigration) balanced
against loss (death and emigration), hence it is
natural to accredit recent increases in abundance
to declining mortality rates. As a very high proportion
of individually marked geese has been
recovered as a result of hunting, it is assumed that
hunting is responsible for a high proportion of
deaths (e.g. Ebbinge 1991). Restrictions and complete
banning of hunting on particular goose populations
have resulted in immediate increases in
some species including the Greenland Whitefronted
Goose (MS14). Others have shown less
immediate responses after protective legislation
(e.g. Russian Barnacle Geese Ebbinge 1991 and
Svalbard Barnacle Geese Owen & Black 1999).
Others still have shown long-term increases despite
apparent increasing mortality (e.g. Russian
White-fronted Geese Anser a. albifrons, Mooij et
al. 1999) or sudden rapid increases not linked in
any way to changes in hunting restriction (e.g.
the Iceland/Greenland Pink-footed Goose, Mitchell
et al. 1999). Hence, while it has been suggested
that increases in numbers of some goose populations
are primarily due to the decreased mortality
rates resulting from reduction in shooting, this
is unlikely to be the sole factor influencing
changes in population size. However, there is
evidence that adult annual survival rates have
been greater under protection than in earlier pe-
riods when the geese were subject to hunting exploitation
(Ebbinge 1991, MS14).
This relationship is important in order to understand
the nature of hunting mortality if restriction
on shooting kill is to be used justifiably as a
management tool to achieve nature conservation
management goals. It is necessary to understand
the extent to which the number of deaths caused
directly through hunting add to natural mortality
(additive mortality), rather than being compensated
for through a consequent reduction in
natural loss through some density-dependent
function (compensatory mortality, see discussion
in Anderson & Burnham 1976, Nichols et al. 1984,
Newton 1998). In order that hunting loss is directly
compensated for by reductions in natural
mortality, natural loss must already be density
dependent and the kill cannot take place after the
main period of natural loss. Hence the impact of
the hunting bag in terms of the mortality in addition
to natural loss depends on both the numbers
killed in the hunt, the seasonal timing of both
losses and the degree of density dependence involved
in natural mortality. However, to demonstrate
such a mechanism is important – if hunting
mortality were completely compensatory,
protection of a hunted population would not result
in an increase of numbers. Conversely, demonstrating
that mortality is completely additive
enables restriction of hunting kill to be used as a
tool to directly influence population size, controlling
for reproduction rates. Hunting mortality
may ultimately become partially additive to natural
losses, i.e. at low levels, this would have no
effect on the total annual death loss but above a
certain density threshold, extra hunting mortality
does contribute to a reduction in survival.
Serious declines in the numbers and range of the
Greenland White-fronted Goose were attributed
to habitat loss and the effects of hunting in the
1980s (Ruttledge & Ogilvie 1979). This led to the
protection of the population at most haunts on
the wintering grounds and ultimately to the drafting
of a management plan for the population
(Stroud 1992). The geese had been legal quarry
throughout its range (West Greenland breeding
grounds, Iceland staging areas and wintering
quarters in Britain and Ireland) until the early
65