Risk of capture-related mortality in large free-ranging mammals: experiences from Scandinavia

Abstract

Chemical capture and anaesthesia of free-ranging mammals will always involve some risk of mortality even in healthy animals. Deaths may be directly or indirectly attributable to the anaesthetic event itself (e.g. drug overdose, drowning during induction and dart trauma) or may be caused by secondary effects from the capture (e.g. stress, myopathy, trauma or instrumentation with radio-transmitters). In long-term research projects on five major wildlife species in Scandinavia, the capture-related mortality rates (number of captures) were: moose Alces alces 0.7% (N = 2,86), brown bears Ursus arctos 0.9% (N = ,079), wolverines Gulo gulo 2.8% (N = 46), Eurasian lynx Lynx lynx 3.9% (N = 380), and gray wolves Canis lupus 3.4% (N = 89). We suggest that wildlife professionals should strive for a zero mortality rate but adopt the standard that a mortality rate of > 2% probably should not be accepted in any large mammalian species. This can be achieved by: ) using an experienced professional capture team, 2) developing and following a capture protocol specific to each species, and 3) requiring that a mortality assessment be undertaken after any capture-related death. This assessment should re-evaluate the capture protocol, including how changes in anaesthetics and methodological approaches could have prevented the mortality.

The use of box-traps for wild roe deer: behaviour, injuries and recaptures

“…Second, it would increase the total handling time substantially. Third, mortality rates as a direct effect of sedation (typically respiratory depression) seems generally to be higher than what we report here (Arnemo et al 2006). However, this only applies for this specific method.…”

“…Typically, capturing wild animals causes stress and can potentially cause injuries, behavioural and physiological disorders and in some cases death (Arnemo et al 2006;Iossa et al 2007). To date several different methods have been used to capture different deer species such as drive nets (roe deer; Morellet et al 2009), net guns (whitetailed deer; Jacques et al 2009), remote drug delivery by darting (moose; Arnemo et al 2006), netted cage traps (white-tailed deer; VerCauteren et al 1999), drop-nets (mule deer;D'Eon et al 2003), cannon nets (Hawkins et al 1968), corrals (Rempel and Bertram 1975) and box-traps (roe deer; Heurich et al 2012). Several variables should be taken into consideration when decisions about which capture and handling methods are used, as some methods are not suitable in adverse weather conditions, in differing habitat types and population sizes.…”

How safe is mist netting? evaluating the risk of injury and mortality to birds

“…While researchers often assume that the benefits of information gained outweigh the potential risk to individual animals, the impacts are not always quantified (Wilson & McMahon 2006). Some methods such as blood and diet sampling in birds (Carlisle & Holberton 2006;Brown & Brown 2009;Voss, Shutler, & Werner 2010), branding and tagging in seals (McMahon, van den Hoff, & Burton 2005;Baker & Johanos 2006) and radiotelemetry in mammals and birds (Kock et al 1987;Bailey et al 1996;Del Giudice et al 2005;Arnemo et al 2006;Barron, Brawn, & Weatherhead 2010) have been scrutinized carefully to determine potential effects on survival, reproduction and behaviour, whereas other methods such as the use of mist nets to capture wild birds have rarely been evaluated (Wilson & McMahon 2006;Jennings et al 2009). Procedures that affect the welfare of animals raise ethical considerations and can compromise research objectives by introducing bias into data collection and should be considered when interpreting results (Dugger et al 2006;Wilson & McMahon 2006;Saraux et al 2011).…”

Detecting capture-related mortality in radio-marked birds following release

“…Short-term effects, in contrast, may result from a variety of factors associated with capture, handling, and/or marking. Following release, a bird may succumb to injuries (either observed or latent) that were incurred during capture , may die as a result physiological complications due to capture and handling, i.e., capture myopathy (Arnemo et al 2006), or may die via indirect causes, such as predation, that occur because the bird is disoriented after release or is acclimating to presence of the mark. Hereafter we will use the term capture effects to refer to this suite of potential short-term impacts associated with capture, handling, marking, and release.…”