Humane Slaughter For Decapods
Not unlike our use of terrestrial animals or fishes, the consumption of decapod crustaceans including lobsters, prawns, crayfish and crabs is on the rise. Historically, not much heed has been paid to ensuring high welfare for billions of these animals caught or farmed annually. Why you might ask? Crustaceans were considered unable to experience pain until very recently. And even today, the scientific community is divided on whether decapods are sentient. We are sure that the animals do possess sensory cells, can perceive noxious stimuli, and show corresponding behavioral responses, though.
However, there is reason to suspect that such averse reactions go beyond impulses and nociception. Some decapods have brains as large as those of some fishes which allow for remarkably advanced cognitive processes. Shore crabs, for instance, are known for their capacity to rapidly associate specific locations with unpleasant stimuli and pay a cost to avoid adverse sensations. Hermit crabs and glass prawns show long-term changes in behaviour where the former choose not to retain old shells and the latter rub and groom injured antennae for a prolonged period of time, a behavior that is alleviated upon application of a local anaesthetic. Such behavioral responses are consistent with the experience of pain.
Drawing from what we know about pain in mammals, its aversive nature, and the powerful emotional responses that it evokes, painful experiences are expected to trigger stress — a specific physiological state of response to unfavorable changes. Rapid stress responses, as measured via the observed increases in concentrations of certain biological compounds, are seen in crabs after one of their claws gets removed by force. In fact, studies on the nervous system, behaviour, and stress responses in decapods fulfill 14 of the 17 criteria for pain perception, where the last three are not fulfilled yet simply because they are yet to be tested in these animals. However, as in any other animal, we will never be able to prove the subjective experiences of pain or consciousness definitively.
In this study, a group of European researchers joined forces in an effort to review the slaughter methods currently practised in the industry and point out which of them are the most humane. They highlight that despite the lack of absolute proof, there are regulations already in place that protect decapod crustaceans to a varying extent in New Zealand, Norway, Switzerland, Australia, France and Italy, effectively employing the precautionary principle. On the other hand, decapods are still excluded from U.K. animal welfare legislation. This means that retailers, processors, and consumers are not obliged to take welfare into consideration during storage, handling, or slaughter. However, the U.K. government has recently asked the Department for Environment, Food and Rural Affairs (DEFRA) to reevaluate the current scientific literature on crustacean sentience and provide evidence-based recommendations.
The authors of the present review note that there are many techniques used for slaughtering crustaceans, and they vary greatly due to the vast physiological and anatomical differences across the many species humans consume. Therefore, the methods must be species-specific to ensure that the highest levels of welfare are attained. Slaughter methods should take into account stress responses and consider metabolism, respiration, and tolerance to hypoxia in all affected species. Finally, the method should ensure that the animal loses sensibility as quickly as possible. However, given the resilience of the animals, judging welfare solely based on being insensible is not optimal, thus the chosen slaughter method should be equally humane. Below is a summary of the methods currently used in the industry and their suitability:
- Out of all common methods, electrical stunning is the most advanced. The Crustastun™ device, for instance, was developed to enable stress-free rapid stunning of various crustaceans in water. Similarly, a large-scale dry electrical stunning system was developed throughout the project “StunCrab”. The authors concluded that even dry electrical stunning is a very efficient method.
- Although crustaceans may become immobile already at air temperatures of 4 degrees Celsius, stunning and slaughter by cold is not seen as a humane means to render these animals insensitive. Previous research found that chilling is ineffective when stunning Australian giant crabs, a species used to living in temperate waters. Other research determined that crabs can respond behaviorally to stimuli even after 100 min at 0 degrees Celsius. Moreover, it can take more than half an hour in the freezer for the animals to lose all behavioural signs of sensibility. Also, crabs often autotomize (shed deliberately) two or more of their legs, suggesting high-stress levels before death. Chilling in ice slurries can also be problematic as despite causing sedation within minutes in crayfish and shrimps, crabs can retain functional neural circuitry for much longer.
- Drowning in freshwater, submerging the animals into salt baths and performing carbon dioxide narcosis were all deemed inhumane means of stunning.
- Splitting crustaceans can result in a swift death of the animals as brain destruction is instant and thorough when performed correctly. However, a highly skilled operator is required.
- Accurate spiking can also quickly destroy the brain and thus should be a humane method. Likewise, however, adequately trained personnel is crucial to ensure that proper technique is applied consistently.
- High-pressure killing via pressurised steam could represent an effective means of slaughter as the animals are said to die within 6 seconds. However, the researchers found no data to support such claims. The method is likely to become more common due to its straightforward technological implementation and low cost. However, the researchers call for more information on the speed of killing and possible suffering to evaluate the welfare implications of this technique.
- Declawing has been defended historically, with claims that crabs survive and regenerate their limbs, leading to a sustainable fishery practice. However, there is no experimental evidence to support the claim. Furthermore, the difficulties that such released animals face when feeding and gaining resources are significant, rendering the method even more inhumane.
- Boiling is still a commonly used slaughter method. However, it is shown to cause physiological shock and the animals show aversive behavior. Some crabs were shown to perceive the heat for at least 2.5 min and even longer if the animals had been pre-chilled before boiling. This inhumane practice can also lead to chilled crabs regaining their senses.
So what does the future hold? Given the more abundant evidence for possible decapod sentience and pain perception, the researchers argue that we must embrace precautionary principles when dealing with such crustaceans. This should be the case especially when drafting new legislation aimed at reducing suffering. An important limitation is that we have little knowledge of how smaller crustaceans such as shrimp and prawns handle the procedures highlighted above. It is an important issue as despite the estimated quicker stunning times, we consume many more of these small-bodied animals.
Animal advocates must keep pressing for more national and regional legislation to include decapod crustaceans under the umbrella of animal protection. Luckily, now we know better which stunning and slaughter methods are more effective and thus should be promoted to minimize the harm caused to our tough aquatic fellows. Furthermore, it is critical that the legislation protecting the wellbeing of these animals would be based on standardized, species-specific methods. Finally, campaigning to ensure that only highly-skilled, well-rested personnel are involved in the transportation, handling and slaughter procedures, and that all equipment is maintained and monitored regularly, could be an ask to prioritize.