Development of Resources and Equipment to Promote Best Practices for the Humane Dispatch of Sharks in a Commercial Fishery

Abstract

This study aimed to identify best-practice methods and equipment for humane dispatch of 15 species of sharks commonly captured by commercial fishers in the Northern Territory (NT), Australia. Anatomical brain location was determined for each species using dissection, external photographs and radiographs (see www.ikijime.com website and Ikijime Tool phone apps). Eight dispatch methods were qualitatively evaluated for their effectiveness on sharks of various sizes. Electrical stunning equipment could not be used because it failed to meet Australian electrical safety standards. Field trials of 206 dispatch events found that penetrating captive bolt tools were most effective on medium-sized (120–210 cm) and large sharks (210–360 cm long), with mean total dispatch scores (MTDS) that ranged from 4.6 to 4.84 out of 5 and instantaneous death rate (IDR) that ranged from 88.57% to 95.45% (n = 79), while ikijime was most effective on small sharks (< 120 cm long), with an MTDS of 4.69 and IDR of 93.75% (n = 16). In contrast, percussive stunning (MTDS = 3.95, IDR = 80.95%, n = 42), shooting with a 12-gauge shotgun (MTDS = 2.92, IDR = 36.54%, n = 52) and spinal section (MTDS = 3, IDR = 0%, n = 2) were less effective, as shown by their lower IDR and MTDS scores. These preliminary findings may be useful for directing further research into best-practice dispatch methods for sharks in the NT, Australia, and elsewhere globally.