Tonic immobility in the zebra shark Stegostoma fasciatum and its use for capture methodology

Mj Williamson,R Slade,C Dudgeon

doi:10.3354/ab00687

Abstract

When conducting biological investigations on shark species, capture and brief restraint procedures may be required in order to collect ecological, behavioral and physiological data. Tonic immobility is an innate, reversible, coma-like stasis displayed by a large number of taxa, including sharks, and has been used for brief restraint, but is rarely used during capture itself. Here, we present a novel, non-lethal capture method of zebra sharks, Stegostoma fasciatum, using tonic immobility, in the field. Zebra sharks were caught by free diving, and on SCUBA, inducing a state of tonic immobility by quickly applying tight-fisted manual pressure to the caudal fin, instead of the dorso-ventral inversion method. Divers were then able to collect tissue samples for genetic analysis, and in some cases, maintain the animals in a state of tonic immobility during transport up to the research vessel for additional data collection. Decreased duration of anthropogenic intervention, and minimal physical struggle associated with this capture and restraint method is expected to reduce physiological markers of distress. Tonic immobility induction and other methods of non-lethal capture deserve continued investigation.

Highlights

Over the past half century there has been a dramatic increase in worldwide catches of shark species (Baum et al 2003; Burgess et al 2005)
Longline and drumline capture are the most frequent methods used. Both techniques are potentially less stressful than some other capture methods, they may still result in captured animals struggling dramatically and thrashing violently (Brooks et al 2012), which can lead to potentially lethal physiological consequences (Hoffmayer and Parsons 2001; Manire et al 2001; Skomal 2007; Mandelman and Skomal 2008)
The duration of tonic immobility onset in this species was tested on three animals, which were tail grabbed and maintained in position for ten minutes while the capture team were on SCUBA

Summary

Introduction

Over the past half century there has been a dramatic increase in worldwide catches of shark species (Baum et al 2003; Burgess et al 2005). Longline and drumline capture are the most frequent methods used. Both techniques are potentially less stressful than some other capture methods, they may still result in captured animals struggling dramatically and thrashing violently (Brooks et al 2012), which can lead to potentially lethal physiological consequences (Hoffmayer and Parsons 2001; Manire et al 2001; Skomal 2007; Mandelman and Skomal 2008). There is a need for the exploration of other non-lethal methods of capture of shark species, which cause less impact to the stress and welfare of captured animals (Barnett et al 2010)

Methods

Results

Conclusion