A Norwegian study1 recommended electrical stunning prior to killing, which can render the animal unconscious within a second, as the most humane way to dispatch crabs.
Research at Bristol University concluded that crabs and lobsters can be stunned with a current at 110 V, 50 Hz and an ampage of respectively 1.3 (edible brown crab) and 1.0 (lobsters)2 cited in 3. Robb argues these currents cause a sufficient period of insensibility for the crustaceans to be killed by immediate boiling.
The Crustastun machine, developed in the UK, has been in commercial use for several years. There is version for stunning in batch which can stun 2 tonnes of shellfish per hour (video available here) and a single stunner for restaurants (video available here). The following clip describes how the single stunner works:
The Crustastun employs a voltage of 110 V at 50 Hz and, according to a 2005 report3, delivers currents substantially greater than Robb’s recommendation. The duration of the stun is programmed at 10 seconds for crabs and 5 seconds for lobsters. According to this report, this kills as well as stuns the animal ensuring no recovery before death.
Further research conducted at Glasgow University suggests, according to the authors, that the Crustastun causes no additional measurable stress to the animal (as evidenced by blood lactate levels) above that caused by handling4 and that the result of the Crustastun is to silence the central nervous system 5,6 without recovery. This conclusion is based on electrophysiological readings of exposed nerves in Crustastunned crabs and lobsters and is supported by the finding that induced autotomy (shedding of legs in response to harmful stimuli or damage) never occurred and has been found not to occur when the device is used commercially.
The Crustastun is recommended by celebrity chefs, such as Raymond Blanc, and it is reported that Waitrose, Tesco and major supermarkets have insisted that all shellfish products supplied to them are dispatched using this method7.
Stansas commercial stunner
In a separate development, scientists in Norway have adapted the commercial dry stunner for fish (Stansas, from the equipment manufacturer Seaside) for the humane killing of edible crabs in bulk. This new technology is in line with new Norwegian animal welfare regulation and allows for easier handling of the animals during processing8.
According to a report on this stunner9, it was found that that in order to stun a crab within 1 second, the voltage must be 220 V at 50 Hz AC and this must be maintained for at least 10 seconds to prolong the period of unconsciousness. The researchers recommend that the stun duration should not exceed 20 seconds (to avoid local heating, a quality issue) but that the animals should be immediately killed, e.g. by boiling. The authors also concluded that crabs could be killed, following electrical stunning, by carving or by storage in ice or ice slurry, but it is not clear that these would in fact kill quickly enough to prevent any recovery of consciousness.
In contrast to the Crustastun, these recommended stun parameters for the Stansas do not kill. The stun also failed to avoid autotomy. Perhaps the reason for the difference in effects between the Stansas and Crustastun is the former involves a lower current. In the Stansas, current flow in the first second of stunning at 220 V AC varied between 0.65 to 2.2 Amps whereas the Crustastun reportedly delivers a higher current (average current ranging from 2.9 to 9.0 Amps for crabs3). Presumably design of the Crustastun avoids the local burning issue either because the duration is no longer than 10 seconds or because the design provides a wider area of electrical contact.
For more information on animal welfare aspects of killing crabs and lobsters, see Welfare during killing of crabs, lobsters and crayfish.
A Mood. January 2014.
1. Roth, B. and Øines, S., 2010. Stunning and killing of edible crabs (Cancer pagurus), Animal Welfare, Volume 19, Number 3, August 2010 , pp. 287-294(8). Universities Federation for Animal.
2. Robb, D., 1999. Unpublished research report, The humane slaughter of crustacea: Electrical stunning. Department of Food Animal Science, University of Bristol.
3. Sparrey, J., 2005. Testing of Crustastun single crab and lobster stunner.
Accessed on 16 November 2013 at http://crustastun.com/assets/files/Sparrey_2005-Crustastun_tests.pdf.
4. Neil, D. and Thompson, J., 2012. The stress induced by the Crustastun™ process in two commercially important decapod crustaceans: the edible brown Cancer pagurus and the European lobster Homarus gammarus. Scientific report. Institute of Biodiversity, Animal Health and Comparative Medicine at the School of Medical Veterinary and Life Sciences, University of Glasgow. Accessed on 16 November 2013 at http://eprints.gla.ac.uk/81433/1/81433.pdf.
5. Neil, D., 2012. The effect of the Crustastun™ on nerve activity in crabs and lobsters. Scientific report. Institute of Biodiversity, Animal Health and Comparative Medicine at the School of Medical Veterinary and Life Sciences, University of Glasgow. Accessed on 16 November 2013 at http://eprints.gla.ac.uk/81428/1/81428.pdf.
6. Neil, D., 2012. The effect of the Crustastun™ on nerve activity in two commercially important decapod crustaceans: the edible brown Cancer pagurus and the European lobster Homarus gammarus. Scientific report. Institute of Biodiversity, Animal Health and Comparative Medicine at the School of Medical Veterinary and Life Sciences, University of Glasgow. Accessed on 16 November 2013 at http://eprints.gla.ac.uk/81430/1/81430.pdf.
7. Anonymous, 2013. Selective Seafoods website. Accessed on 16 November 2013 at http://www.selectiveseafoods.com/crustastun.htm.
8. Berg-Jacobsen, J., 2012. Nofima technology gives crab success, Nofima website, Norwegian Institute of Food, Fisheries and Aquaculture Research. Accessed on 16 November 2013 at http://www.nofima.no/en/nyhet/2012/11/nofima-technology-gives-crab-success.
9. Electrical stunning of edible crabs, Report no: 18/2013, Nofima, ISBN 978-82-8296-0279-3 (pdf). Accessed on 16 November 2013 at http://www.nofima.no/filearchive/Rapport%2018-2013.pdf.