Introduction
The snow crab fishery takes place in the Barents Sea far from land and therefore majority of the crabs are slaughtered on board the fishing vessels. A common slaughter method is the use of a splitting machine. This machine works by fixating the crab’s walking legs and claws and flipping off the carapace before splitting the crab in two using either a knife blade or a water jet. Despite the widespread use of this method, there is little evidence as to whether this renders the crab unconscious, or if there could be alternative methods that may be more humane. In our study we aimed to investigate three different slaughter techniques (chemical, mechanical and electrical) and assess the welfare using behavioural and neurological (EEG of thoracic ganglion) measurements to examine response and loss of consciousness and death.
Materials and methods
Three slaughtering techniques were tested; chemical, mechanical and electric. The chemical method was injecting saturated potassium chloride (KCl) directly into the heart using a syringe. Welfare was evaluated by scoring responsiveness of eyes, antenna, mandibula, chelae, walking legs, claw and tail along with EEG. The mechanical method was splitting the crab in two using a large kitchen knife. Welfare was evaluated as above. The electric stunning was carried out using a dry stunner 50 Hz, 220 V AC. The crab was placed on a metal plate and the electrodes were placed either on the carapace or fixated on the legs to simulate the splitting machine onboard fishing vessels.
Results
Of the three methods, correct splitting gave what appeared to be a quick epileptic seizure followed isoelectric line indicating a cessation of nerve signa i.e. death. However, if the splitting was only slightly off the middle, signal would continue, even when the crab was non responsive during the behaviour tests. KCl had varying results from fast cessation of signal to continuing signal until euthanasia. Eyes, antenna, mandibula, chelae, walking legs, claw and tail were all negative on the responsiveness test, but EEG could still sometimes show signals during the test. Electrical stunning also gave epileptic seizure, but some individuals appeared to regain a “normal signal” after 3-4 minutes which coincided with increased response to stimulation, whereas other did not regain either normal signals or responsiveness. With electric stunning there was in general good correlation between behavioural response during stimulation and increased amplitude and frequencies of signal measured by EEG.
Conclusion
The preliminary data indicates that here is not always a good correlation between behavioural responses and neural activity (indication of potential consciousness) during slaughter of snow crab when using splitting or injection of KCl. Of the three methods, splitting and electrical stunning appears to be the most promising. We propose a combination of the two, - a stun splitter, to be a potential new and humane method for slaughtering snow crabs.