Impact of hunting along the migration corridor of pink‐footed geeseAnser brachyrhynchus– implications for sustainable harvest management

Abstract

Summary1. Hunting can potentially affect population size, age composition, sex-ratio, behaviour and distribution of natural populations, and understanding its impacts is a prerequisite to manage quarry species sustainably. Harvest management relies strongly on the existence of both strictly regulated hunting efforts and efficient monitoring of populations, their demography and harvest. These conditions are rarely met in practice. 2. For the Svalbard-breeding population of the pink-footed goose Anser brachyrhynchus, an internationally coordinated adaptive harvest management framework enables a flyway-based assessment of harvest impact. Based on 25 years of population assessment and harvest data, we evaluate the differential impact of harvest along the migration corridor of the population. 3. The analysis reveals that (i) total harvest and harvest rate (proportion of the population killed by hunting) have increased substantially in recent years, (ii) compared to adult geese, juveniles were overrepresented in the hunting bag by a factor of 3Á7, (iii) the proportion of juveniles in the hunting bag differed between the two countries (Norway and Denmark) with an open season, and was more than twice as high in the former compared to the latter, and (iv) the increase in harvest rate seemed to be driven by increased hunting mortality of juvenile birds, with no clear impact on the growth rate of the population. However, this may partly relate to the transient dynamics and population inertia commonly seen in long-lived species such as geese, and a 3-year consecutive decline towards the end of our study period might be the first signs of an impending decline. 4. Synthesis and applications. Our findings highlight that the impact of harvest varies along the migration corridor and between age classes of a single species and suggest that allocation of hunting effort in time and space is important to optimise harvest. Our example demonstrates the need for internationally coordinated, detailed population and harvest data which are essential for sustainable harvest management.

Highly dynamic wintering strategies in migratory geese: Coping with environmental change

“…The increasing probability of changing wintering strategy during the last 25 years might relate to a growing impact of intra‐ and interspecific competition on the wintering grounds, but might also be the result of increasing benefits from an exploratory behaviour among individual geese in a time of global change. The foraging opportunities (Madsen et al., ), roosting possibilities (Clausen & Madsen, ), spring weather conditions (Tombre et al., ) and hunting pressure (Clausen et al., ) experienced by pink‐footed geese have all changed rapidly recently, and might increasingly favour exploratory traits over traditional philopatric ones. Further evidence of recent exploratory behaviours can be seen from an expanding distribution into Sweden and Finland (Madsen, Cottaar et al., ), and the use of new staging areas in Jutland (Madsen et al., ).…”

“…As explanatory variables of changes in site use both hunting pressure (positively associated with wintering proportions in Denmark) and winter temperature (insignificant for all three regions) were weak predictors, indicating that neither was very important in shaping strategy choice. Harvest rate has increased substantially in Jutland recently (Clausen et al., ), and hunting has been used to control numbers as part of an international adaptive management strategy to stabilize population size (Madsen, Clausen, Christensen, & Johnson, ). However, this does not seem to have had any negative effect on goose usage of this region.…”

“…hunting pressure (Clausen et al, 2017) experienced by pink-footed geese have all changed rapidly recently, and might increasingly favour exploratory traits over traditional philopatric ones. Further evidence of recent exploratory behaviours can be seen from an expanding distribution into Sweden and Finland (Madsen, Cottaar et al, 2016), and the use of new staging areas in Jutland .…”

“…As a measure of hunting pressure in Denmark (pink‐footed geese do not have an open season in the Netherlands and Belgium) we used the annual harvest rate (proportion of the population being shot, Clausen, Christensen, Gundersen, & Madsen, ). Average annual winter temperatures (Dec–Feb) were acquired from weather stations in Esbjerg (Jutland), Leeuwarden (Friesland) and Oostende (Flanders), representing each of the three major stopover regions.…”

Making do with less: must sparse data preclude informed harvest strategies for European waterbirds?

“…Although no data specific to Taiga Bean Geese are available, we assumed that young-of-theyear are twice as vulnerable to harvest as older birds based on studies of other goose species (Frederiksen et al 2004, Madsen 2010, Alisauskas et al 2011, Clausen et al 2017. Therefore, we assumed annual, population-level harvest quotas in increments of 1,000 from 0 to 30,000, with the assumption that harvest could be regulated with this degree of precision.…”