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Complementary use of density estimates and hunting statistics: Different sides of the same story?

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Eeva M Soininen at UiT The Arctic University of Norway
Eeva M Soininen
Eva Fuglei at Norwegian Polar Institute
Eva Fuglei
Åshild Ø. Pedersen at Norwegian Polar Institute
Åshild Ø. Pedersen
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Abstract and Figures

The use of hunting statistics for population monitoring has often been criticized because such data are affected by several sources of error. Still, for many harvested populations hunting statistics are the only available data source and cautious use of such data may be valuable for management. Here we assessed to what extent long-term monitoring of Svalbard rock ptarmigan spring densities and hunting statistics (bag size and proportion of juveniles in the hunting bag) reflect similar population fluctuations. We found a decreasing trend in both bag size and proportion of juveniles in the bag, but no trend in ptarmigan spring densities. However, annual fluctuations of ptarmigan spring density and bag size were correlated. Together, these time-series indicate that both population abundance (bag size) and recruitment (proportion of juveniles in the bag) are decreasing, but the reproductive component fraction (density of territorial males) is not yet compromised. This biological interpretation remains, however, uncertain due to lack of hunting effort data. Monitoring programs using hunting statistics should therefore critically discuss and evaluate what the hunting statistics reflect and fine-tune the hunter data collection to obtain maximum biological relevance. Still, our results illustrate that the combination of population estimates and hunting statistics can provide more nuanced information about the population status than the density estimates alone.
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ORIGINAL ARTICLE
Complementary use of density estimates and hunting statistics:
different sides of the same story?
Eeva M. Soininen
1
&Eva Fuglei
2
&Åshild Ø. Pedersen
2
Received: 29 September 2015 /Revised: 17 December 2015 /Accepted: 3 January 2016 /Published online: 13 January 2016
#Springer-Verlag Berlin Heidelberg 2016
Abstract The use of hunting statistics for population moni-
toring has often been criticized because such data are affected
by several sources of error. Still, for many harvested popula-
tions, hunting statistics are the only available data source and
cautious use of such data may be valuable for management.
Here we assessed to what extent long-term monitoring of
Svalbard rock ptarmigan spring densities and hunting statis-
tics (bag size and proportion of juveniles in the hunting bag)
reflect similar population fluctuations. We found a decreasing
trend in both bag size and proportion of juveniles in the bag,
but no trend in ptarmigan spring densities. However, annual
fluctuations of ptarmigan spring density and bag size were
correlated. Together, these time series indicate that both pop-
ulation abundance (bag size) and recruitment (proportion of
juveniles inthe bag) are decreasing, but the reproductive com-
ponent fraction (density of territorial males) is not yet com-
promised. This biological interpretation remains, however,
uncertain due to lack of hunting effort data. Monitoring pro-
grams using hunting statistics should therefore critically dis-
cuss and evaluate what the hunting statistics reflect and fine-
tune the hunter data collection to obtain maximum biological
relevance. Still, our results illustrate that the combination of
population estimates and hunting statistics can provide more
nuanced information about the population status than the den-
sity estimates alone.
Keywords Harvest .Lagopus muta .Long-term monitoring .
Point transect sampling .Time series
Introduction
Accurate estimation of population abundance is fundamental
to identify population fluctuation and changes, for manage-
ment and science alike. However, high-quality estimates of
population density (i.e., mark–recapture methods) are time-
consuming and expensive to achieve (Thompson et al.
1998), especially for spatial scales representative for large
hunting management units. Therefore, monitoring of harvest-
ed populations is commonly based on relative abundance in-
dices, i.e., index counts and hunting statistics (Cattadori et al.
2003; Lehikoinen et al. 2014; Pettorelli et al. 2007). Such
indices often include a substantial amount of uncertainty, as
they do not routinely account for imperfect and variable de-
tection (Pettorelli et al. 2007;Rosenstocketal.2002). Even
though many index count methods could easily incorporate
estimates of detection distance in the field protocols, and thus
achieve absolute population density estimates using the dis-
tance sampling framework, this is rarely done (Buckland et al.
2001;Matsuokaetal.2014;Rosenstocketal.2002). Hunting
statistics, on the other hand, are affected by both variable
detection probabilities and variable sampling effort and are
often interpreted without considering the effects of these
sources of error (Imperio et al. 2010;Ristetal.2008). There-
fore, hunting statistics are criticized for not giving meaningful
estimates of population abundance trends (Ranta et al. 2008;
Imperio et al. 2010; Willebrand et al. 2011, but see Cattadori
et al. 2003).
Grouse represent an important ecosystem service in terms
of recreational and subsistence harvest in many countries
(Storch 2007b). Until recently, the population trends of
*Eeva M. Soininen
eeva.soininen@uit.no
1
UiT The Arctic University of Norway, 9037 Tromsø, Norway
2
Norwegian Polar Institute, Fram Centre, 9296 Tromsø, Norway
Eur J Wildl Res (2016) 62:151–160
DOI 10.1007/s10344-016-0987-z
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Under the reference condition, the endemic sub species Svalbard rock ptarmigan occurs in small, relatively stable or growing populations in suitable habitats (< 4 % of the land area in Svalbard), which locally support sustainable hunting (Fuglei et al. 2019a, Pedersen et al. 2012, Soininen et al. 2016). ...
... The understanding of links to these drivers has improved through recent studies ) and, although complex, are assessed as certain. Ptarmigan abundance can be affected negatively by several climatic and biotic drivers that act directly or indirectly, e.g. by changing grazing conditions, increasing goose populations and thus competition for important forage species, extreme weather that negatively affects reproduction and survival (more frequent "rain-on-snow" events), variable weather in spring, more frequent rain in summer, increased predation pressure from Arctic fox and increased hunting pressure (Fuglei et al. 2019a, Hansen et al. 2013, Henden et al. 2017, Soininen et al. 2016. ...
... Biological diversity Svalbard rock ptarmigan production Detailed data on production (i.e. number of juveniles generated by aged wing samples collected from the hunt) of Svalbard rock ptarmigan exist from 1997 until present (Soininen et al. 2016). At present, the estimated reproduction, based on wing samples, is compared to autumn line transect reproduction estimates to assess uncertainties in estimate (Fuglei et al. 2019b). ...
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... Control over the number of specimens hunted in private areas is done through the use of seals and rangers. Hunting statistics (Ruiz-Rodríguez et al. 2023) constitute a valuable information for monitoring and managing harvested populations (Maunder and Punt 2004;Aubry et al. 2020a, b;Bobek et al. 2021) and, in many cases, are the only available data source for such purposes (Soininen et al. 2016). On the other hand, the use of such statistics has often been criticized as these data are affected by several sources of error (e.g., lack of hunting effort, variable sampling effort, or variable detection probabilities, among others) and, therefore, they include a substantial amount of uncertainty (Rosenstock et al. 2002;Pettorelli et al. 2007). ...
... On the other hand, the use of such statistics has often been criticized as these data are affected by several sources of error (e.g., lack of hunting effort, variable sampling effort, or variable detection probabilities, among others) and, therefore, they include a substantial amount of uncertainty (Rosenstock et al. 2002;Pettorelli et al. 2007). The combination of population estimates and hunting statistics can provide more nuanced information about the population status than the density estimates alone (Soininen et al. 2016). Recent studies reveal a clear expansion of Iberian ibex populations which, locally, may show a strongly positive trend (Refoyo et al. 2015;Herrero et al. 2021;García-González et al. 2022); however, there are no studies at the national level characterizing and updating the status of the species. ...
Hunting Iberian ibex: from a threat factor to a conservation tool
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In this study we have compiled the information from official databases about Iberian ibex, Capra pyrenaica, hunting yields, hunting trophies and hunting licenses in the Spanish regions where the species is present and hunted. Such quotas showed an increasing trend between 2005–2021 and, on average, during this period, ≈ 6400 animals were yearly harvested. Despite this number decreased in 2019 and 2020 (in this last year, mainly due to the lock down caused by the COVID pandemia), the annual quota raised, reaching over 12,000 ibexes in 2021. The number of trophies increased since the 1970s and peaked in the period 2001–2005, and then declined during the period 2006–2020. At national level, the number of hunting licenses decreased from 2006 to 2021 by a 36.5%. The regional average hunting yield was significantly correlated with a regional-based ibex abundance estimation. The current situation of continued population increase together with the trophy reduction might suggest that the overall population is exceeding the carrying capacity. In this context, if hunting activity was one of the main factors involved in local extinction of the species, currently it should be considered a tool for sustainable managing of ibex populations in an scenario of increasing demographic trends and generalized absence of predators.
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... Since real monitoring data based on count data are rarely available and, especially, not in long time series, harvest data are frequently used as indicators of population abundance. Various studies with ungulates (Bender and Spencer, 1999;Imperio et al., 2010;Jędrzejewska et al., 1997;Liu et al., 2018), carnivores (Ozoliņš and Pilāts, 1995), lagomorphic species (Ferreira et al., 2010;Frylestam, 1980;Rödel and Dekker, 2012) and birds (Cattadori et al., 2003;Klansek, 2002;Martinoli et al., 2017;Ranta et al., 2008;Soininen et al., 2016) have shown that harvest data in long time series analyses are indeed suitable as estimates of population dynamics. Of course, attention is always advised when using harvest data as reference data for population abundance. ...
... First, our study was designed to capture the population dynamics based on harvest data. This relationship has already been tested for many game species and has proven to be effective for many species (Cattadori et al., 2003;Imperio et al., 2010;Jędrzejewska et al., 1997;Martinoli et al., 2017;Ozoliņš and Pilāts, 1995;Soininen et al., 2016). However, in hares and rabbits, but also in grouse species, there may well be deviations in the derived dynamics based on the counting and harvest data (Ferreira et al., 2010;Ranta et al., 2008). ...
Long-term game species dynamic as indicator for changing landscape quality
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Urban sprawl, increased traffic and modern forestry, as well as the globalisation of agriculture, have increasingly been affecting the landscape and its quality as habitat for species especially since the middle of the last century. Still, there are hardly any methods nor indicators which can measure the quality of the landscape for species over a long period. In this study, we investigated the influence of landscape structure and landscape quality on harvest data of 28 game species in South Tyrol, Italy, over the last 150 years. The harvest data were used to assess the population dynamics of individual species and habitat guilds since 1870. As a first result, we could show, on the examples of six species, that count population data were highly correlated with harvest data and are therefore well suited to estimate their population size. Second, the populations of ungulates consistently increased during the study period. The numbers of mesocarnivores as well as smaller forest and alpine game species increased strongly until the 1970s/80s of the last century, followed by a decline. The populations of farmland species and some synanthropic species have decreased substantially, and some species have even disappeared completely. Based on these results, we were able to show, in a third step, that the landscape quality for game species in South Tyrol has developed differently: In particular, the agriculturally used habitats have lost quality, whereas forests and alpine regions have initially gained quality due to the extensification of use; during the last five decades, the quality decreases again, at least for small game species. Our results thus provide concrete implications for the active improvement of the landscape quality for farmland and forest species, as well as indications for future priorities in funding support of alpine pasture management.
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... However, the population trends of polecat, stone marten and other mammal carnivores remains poorly understood due to lack of standardized long-term monitoring schemes to collect empirical data on these population trends (Gese, 2001;Croose et al., 2018). Estimates of species population trends based on hunting figures, for example, are affected by variable hunting intensity, which requires cautious interpretation of such statistics (McDonald and Harris, 1999;Soininen et al., 2016). For animals that occur in the wider landscape at relative low densities, citizen science-based monitoring schemes prove to be a suitable approach for the necessary long-term and large-scale data collection Kays et al., 2020). ...
... Long-term datasets of small-and medium sized carnivores that cover an extended area like our study does, are scarce. Moreover, most studies use hunting data, data of single sightings, or questionnaires and these data need to be interpreted with caution as they are sensitive to variable observation or sampling effort (McDonald and Harris, 1999;Baghli and Verhagen, 2003;Soininen et al., 2016;Croose et al., 2018). However, the use of road-killed animals was previously done e.g. by Grilo et al. (2009) to map which mammal species were hit by cars and by Clarke et al. (1998) to study the influence of road network density on the probability of badger collisions. ...
Shifting dietary habits linked with contrasting population trends of two sympatric mustelids (Martes foina and Mustela putorius) over 16 years
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Despite widespread concern about biodiversity declines, few empirical studies exist on long-term population trends of mammal carnivores. In the context of global change, it is essential to understand the population trends and resource use of mammal carnivores. Mammal carnivores fulfil an important ecosystem function in terrestrial ecosystems as their top-down role directly and indirectly influences prey populations which affects the entire food web. The objective of this study was to evaluate whether and how the population trends of two sympatric mustelid species, stone marten and polecat, have changed between 1998 and 2013 in Flanders, Belgium. In addition, we explored temporal changes in their dietary habits. From 1998–2013, in collaboration with a citizen science network, we collected road-killed animals over the entire area of Flanders (13,682 km²). Based on the number of collected road-killed animals we detected a decrease in the polecat population during 1998–2013 whereas the stone marten population has increased. By subsequent identification of the stomach contents of the specimens, we detected fluctuations throughout the year of the consumption of certain food types. In addition, the consumption of certain food items decreased (stone marten: fruits, grains and nuts and lagomorphs; polecat: birds, rodents and other mammals) or increased (stone marten: edible waste and polecat: amphibians) throughout this period of opposite population trends. An increase of the degree of specialization of the diet throughout the sampling period was also detected for both mustelid species. In summary, our study concludes contrasting population trends coupled with clear changes in feeding habits of two sympatric carnivore species. Understanding these long-term relationships between species population trends and their dietary ecology is vital for biodiversity conservation and nature management.
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... • The distribution of wild ungulates in Saxony was not monitored. However, from the literature, a correlation between population sizes and hunting bags was verified for many game species (e.g., Cattadori et al., 2003;Imperio et al., 2013;Jędrzejewska et al., 1997;Soininen et al., 2016;Wagner et al., 2012). Therefore, we are convinced that it is valid to use changes in hunting bags as an indicator of abundance changes. ...
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... Harvest mortality was relatively constant during the study period except for high 566 estimates in the 2019-2020 winter season ( Figure S1.2). Including potentially relevant 567 covariates, such as harvest effort, will help interpret observed variation in harvest mortality 568 (Soininen, Fuglei, and Pedersen 2016). Immigration from source populations into harvested sink populations is a much discussed 572 mesopredator management issue (Beasley et al. 2013;Lieury et al. 2015;Kierepka, Kilgo, 573 and Rhodes 2017). ...
An integrated population modelling workflow for supporting mesopredator management
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Expanding populations of mesopredators threaten biodiversity and human health in many ecosystems across the world. Lethal control through harvest is commonly implemented as a mitigation measure, yet the effects of harvest and its interaction with environmental conditions on mesopredator population dynamics have rarely been assessed quantitatively due to data constraints. Recent advances involving integrated populations models (IPMs) have enabled promising alternative approaches for quantitative assessments. Efficient use of multiple datasets, together with the ability to account for bias and uncertainty, make IPMs ideal tools for studying impacts of management actions and environmental conditions on harvested populations for which limited data is available. Here we developed a versatile IPM workflow for studying mesopredator population dynamics under different harvest regimes and applied it to an expanding population of red foxes in Arctic Norway. Our model combined routinely collected data on age, reproductive status, and genetic variation from >3600 harvested red foxes with opportunistic field observations and information published on red foxes elsewhere. This allowed us to quantify population dynamics over a period of 18 years, and to identify the drivers of changes in population growth rates using retrospective (Life Table Response Experiments, LTREs) and prospective (population viability analyses, PVAs) perturbation analyses. We found no long-term trends in population size over the course of our study period, not least due to intense harvest limiting the growth potential of the population. On shorter, year-to-year timescales, however, the numbers of red foxes could change dramatically due to responses of natural mortality and immigration to fluctuations in the availability of rodent prey. Our study highlights the potential of integrated modelling approaches for studying population dynamics even when no structured surveys of living animals are available and illustrates the value of extracting and curating information from harvested animals. Our semi-automated and reproducible modelling workflow is ready to be re-run periodically when new data becomes available for our study population and can easily be transferred and adapted to other harvested species, contributing to the development of cost-effective population analyses that are of high relevance for informing management strategies and mitigating biodiversity loss in practice.
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... As wild boar in Sweden traditionally has the longest open hunting season of all ungulates, with few and small changes over time (see Results), we anticipate no such effects on data. Analysis of population development can be improved if additional and independent data series are available [69]. This is the case for wild boar in Sweden, as also the number of traffic accidents are available since 2003. ...
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... While variation in opening day of hunting is likely to have some effect, variation in CPUE of this magnitude is most likely dominated by changes in true population size. Harvest and population census data often gives a reasonable match (Small et al. 1993, Lindstrom et al. 1994, Cattadori et al. 2003, Ranta et al. 2008, Lampila et al. 2011, Soininen et al. 2016, especially when the annual variation in hunting bags as well as true populations size is large (Willebrand et al. 2011). We argue that this is the case for our willow ptarmigan time series. ...
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Behaviour and social structure in Svalbard rock ptarmigan Lagopus mutus hyperboreus.
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