Physiological parameters of farmed Nile crocodiles (Crocodylus niloticus) captured manually and by electrical immobilisation

Abstract

During the past 15 years crocodile farming has become more important and sophisticated all over the world. In South Africa there are currently an estimated one million Nile crocodiles (Crocodylus niloticus) on commercial farms, mostly for leather production. The management, especially of crocodiles that are close to slaughter, is very intensive as the skins of these animals have to be in immaculate condition to achieve good prices on the international markets. In this regard, the electric stunner is often used on a daily basis on most farms in South Africa to safely handle crocodiles. However, this technique (electrical immobilisation) has only been scientifically evaluated in the Australian saltwater crocodile (C. porosus). As crocodilian species might react differently to the electrical immobilisation procedure, the aim of the project was to compare certain physiological parameters of Nile crocodiles captured by either electrical immobilisation (stunning) or captured manually by noosing. This study was conducted during the summer of 2012 on a commercial crocodile farm near Pongola, South Africa. In total 45 crocodiles were used of which 23 crocodiles were captured by electrical immobilisation and 22 by means of noosing. Physiological parameters chosen for monitoring were serum corticosterone, blood lactate, blood glucose, as well as alanine aminotransferase (ALT), alkaline phosphatase (ALP), aspartate aminotransferase (AST) and creatinine kinase (CK). The concentrations and activities of these parameters were determined in blood samples collected immediately after capture by the two methods. Animals were then tied and blind-folded and kept in a quiet place. Four hours later blood samples were collected again from each animal to monitor changes in concentrations and activities of these parameters. In all cases the time was recorded that it took to capture each animal. In addition, total handling time until blood collection was also recorded on an individual basis. Our results indicate that although corticosterone increased greatly within the four hour interval in both groups, there was no difference (p> 0.05) between the two methods of capture. Lactate did not increase significantly within the four hour period in both groups, but was higher when animals were noosed. Glucose concentrations rose within four hours, but no significant differences could be detected between the two capture methods. While ALT and ALP did not show any clear trend, increased activities were detected for AST and CK in the four hour period after capture. Both, AST and CK levels were higher in noosed animals. Noosing a crocodile took longer to restrain the animal when compared to the stunning method. On average stunning took 118 seconds from start of capture until an animal was under control while noosing took 186 seconds per animal. As a consequence the noosed animals struggle for a longer time, which most probably caused exhaustion and muscle damage; explaining the higher levels of blood lactate, AST and CK. One helper was injured (bite wound) trying to control a crocodiles using the noose method. Electrical immobilisation is therefore considered to be the better option for commercial farms, from a physiological perspective, as well as an animal welfare and human safety viewpoint.