Shoot, shovel and shut up: cryptic poaching slows restoration of a large carnivore in Europe - PubMed (original) (raw)

Shoot, shovel and shut up: cryptic poaching slows restoration of a large carnivore in Europe

Olof Liberg et al. Proc Biol Sci. 2012.

Abstract

Poaching is a widespread and well-appreciated problem for the conservation of many threatened species. Because poaching is illegal, there is strong incentive for poachers to conceal their activities, and consequently, little data on the effects of poaching on population dynamics are available. Quantifying poaching mortality should be a required knowledge when developing conservation plans for endangered species but is hampered by methodological challenges. We show that rigorous estimates of the effects of poaching relative to other sources of mortality can be obtained with a hierarchical state-space model combined with multiple sources of data. Using the Scandinavian wolf (Canis lupus) population as an illustrative example, we show that poaching accounted for approximately half of total mortality and more than two-thirds of total poaching remained undetected by conventional methods, a source of mortality we term as 'cryptic poaching'. Our simulations suggest that without poaching during the past decade, the population would have been almost four times as large in 2009. Such a severe impact of poaching on population recovery may be widespread among large carnivores. We believe that conservation strategies for large carnivores considering only observed data may not be adequate and should be revised by including and quantifying cryptic poaching.

PubMed Disclaimer

Figures

Figure 1.

Figure 1.

Posterior (solid black line) and prior (dotted black line) densities for (a) cryptic poaching rate c (posterior median = 0.103 ± 0.106, shown by vertical thin line), (b) non-poaching mortality rate m (posterior median = 0.142 ± 0.027) and (c) verified poaching rate v (posterior median = 0.046 ± 0.016). Overlap between prior and posterior densities is shown by the grey area. Parameters m and v were given informative priors based on radio-tracking data. Their posterior median estimates were very similar to rates from radio-tracking data (non-poaching mortality rate = 0.148 ± 0.028, verified poaching rate = 0.049 ± 0.017). The prior for cryptic poaching rate was on the contrary left uninformative. Still, its posterior median estimate was remarkably similar to the independent estimate of cryptic poaching rate from radio-tracking data (0.085 ± 0.023). The posterior density of cryptic poaching poorly overlapped with its prior and reveals that an unobserved source of mortality was present in the population.

Figure 2.

Figure 2.

Model and census estimates of the wolf population in Scandinavia during 1999–2009. Filled black triangles are census data. Squares are median of posterior distribution of the fitted model, with its 95% credible interval shown by dashed lines. Circles are the median posterior distribution of the simulated population without poaching assuming no density-dependence. This reveals a decade of poaching scaled down population size from 990 to 263 wolves in 2009. Lozenges are the median posterior distribution of the simulated population without cryptic poaching assuming no density-dependence. The grey area indicates the number of wolves theoretically lost due to cryptic poaching.

Similar articles

Cited by

References

    1. Gavin M. C., Solomon J. N., Blank S. G. 2010. Measuring and monitoring illegal use of natural resources. Conserv. Biol. 24, 89–10010.1111/j.1523-1739.2009.01387.x (doi:10.1111/j.1523-1739.2009.01387.x) - DOI - DOI - PubMed
    1. Agnew D. J., Pearce J., Pramod G., Peatman T., Watson R., Beddington J. R., Pitcher T. J., Sandin S. A. 2009. Estimating the worldwide extent of illegal fishing. PLoS ONE 4, e4570.10.1371/journal.pone.0004570 (doi:10.1371/journal.pone.0004570) - DOI - DOI - PMC - PubMed
    1. Fulton E. A., Smith A. D. M., Smith D. C., Van Putten I. E. 2011. Human behaviour: the key source of uncertainty in fisheries management. Fish Fish. 12, 2–1710.1111/j.1467-2979.2010.00371.x (doi:10.1111/j.1467-2979.2010.00371.x) - DOI - DOI
    1. Hilborn R., Arcese P., Borner M., Hando J., Hopcraft G., Loibooki M., Mduma S., Sinclair A. R. E. 2006. Effective enforcement in a conservation area. Science 314, 1266.10.1126/science.1132780 (doi:10.1126/science.1132780) - DOI - DOI - PubMed
    1. Redpath S., Thirgood S. 2009. Hen harriers and red grouse: moving towards consensus? J. Appl. Ecol. 46, 961–96310.1111/j.1365-2664.2009.01702.x (doi:10.1111/j.1365-2664.2009.01702.x) - DOI - DOI

Publication types

MeSH terms

LinkOut - more resources