Assessing mammal trapping standards in wild boar drop-net capture

Abstract

Applying contemporary trapping standards when managing wildlife should no longer be an option, but a duty. Increasing wild boar populations originate a growing number of conflicts and hunting is the only cost-effective management option in most cases. However, new scenarios where hunting is unfeasible emerge and trapping necessities cope with lacking regulatory frameworks and technical guidelines. In this research, we evaluated drop nets, a capture method not considered by the international trapping standards, to capture Eurasian wild boar (Sus scrofa), a wildlife species not included in the list of mammal species under the scope of the Agreement on International Humane Trapping Standards (AIHTS). Less than 20% of the captured wild boars presented moderate or severe injuries attributable to the capture method, hence fulfilling the acceptance thresholds of the outdated AIHTS. Based on the new standards thresholds of acceptance, the humaneness of drop-nets in our study ranged 66-78%, under the 85% required. The capture success and selectivity were 100%, as ensured by operator-driven triggering, which should be considered the main strengths of this method, together with the minimization of animal suffering owing the short duration of the stressful situation. Additionally, in spite of the socially adverse environment, with people contrary to wild boar removal, no disturbances against the capture system or operations occurred. This is the first assessment of a drop-net capture method according to internationally accepted mammal trapping standards, with unconclusive results. However, there is a need for adapted procedures and thresholds of acceptance aimed at not-mechanical traps in general, and specifically at drop-nets. Compared to other live-capture methods, drop-nets minimize the duration of the stressful situation -at the expense of a strong adrenergic acute response-, maximize the probabilities of capturing entire sounders of prosocial species, which may be also considered as more humane, and has the ability to coordinate higher values of capture success, absolute selectivity and adaptability to difficult environments.

Figure 1

The ESTRATEKO drop-net trap deployed in a peri-urban location of Barcelona city at dusk, ready to run. Corn kernels are used as bait to attract wild boars to the central area under the net.

Figure 2

Heat map of the wild boar-related incidences recorded by the Barcelona city police department from 2010 to 2019, and approximate location of specific trap sites in the boundaries between the urban area of Barcelona and the natural area of Collserola. Generated with QGIS version 3.22.7 Bialowieza (https://qgis.org/en/site/).

Figure 3

(a) Severe, deep gingival laceration with external haemorrhage exposing the maxillary bone. (b) Sampling of longissimus dorsi. (c) Sampling of semitendinosus and semimembranous muscles. (d) Acute skeletal muscle degeneration. A central myofiber is swollen and hypereosinophilic (arrow) and a fragmented segment of another myofiber is also present (arrowhead).