Physical trauma

Capture techniques can result in physical trauma to cephalopods. Specifically, physical trauma might arise from rough handling, causing the mantle to detach from the head (AK Schnell, personal observation 2013). Raising benthic species from depth too quickly can lead to buoyancy malfunction due to rapid changes in pressure (Forsythe et al. Reference Forsythe, Hanlon, DeRusha and Boucaud-Camou1991; Sherrill et al. Reference Sherrill, Spelman, Reidel and Montali2000; McDonald Reference McDonald2011). However, unlike the swim bladder of fish, the buoyancy mechanism in cuttlefish (the cuttlebone) is unpressurised, so its volume is not markedly altered as the animal changes depth (Denton & Taylor Reference Denton and Taylor1964; Sherrard Reference Sherrard2000). Nevertheless, rapid vertical movement may cause air to be trapped inside the mantle cavity (AK Schnell, personal observation 2013) resulting in potential discomfort or pain.

During capture methods that involve nets, individuals might be pursued to exhaustion and then suffocate and become crushed under the weight of other animals. However, further research is required to determine the severity of this risk. Finally, collision with other animals or the side of the net routinely causes skin damage (Boyle Reference Boyle, Hubrecht and Kirkwood2010). Cephalopods have soft skin and are particularly susceptible to skin ulcerations and fin injuries (i.e. specific to cuttlefishes and squids as octopuses do not have fins) that can result in permanent damage. These injuries encourage bacterial growth (Gestal et al. Reference Gestal, Pascual, Guerra, Fiorito and Vieites2019) and can lead to disease or death (Hanlon et al. Reference Hanlon, Forsythe, Cooper, Dinuzzo, Folse and Kelly1984; Boyle Reference Boyle, Hubrecht and Kirkwood2010; Gestal et al. Reference Gestal, Pascual, Guerra, Fiorito and Vieites2019).

Although most netted animals will die during or quickly after being hauled up, skin and fin injuries become a welfare concern if: (i) live individuals are left in nets for hours or days prior to landing (as can be the case with trawl and drift nets); if (ii) live undersized animals are released back into the water with injuries; and/or (iii) if the skin injuries cause the animals to experience pain prior to death. Skin plays a vital role in the survival of cephalopods as they use body patterns for both concealment and communication (Hanlon & Messenger Reference Hanlon and Messenger2018). Moreover, minor injuries in squid increases the risk of predation (Crook et al. Reference Crook, Dickson, Hanlon and Walters2014), and squid with skin and fin injuries respond poorly to temperature and salinity changes compared to uninjured squid (Hanlon et al. Reference Hanlon, Hixon and Hulet1983). Using soft netting material or alternative capture methods (i.e. traps or jigging) might decrease some risk of physical trauma involved in netting capture methods (Iglesias et al. Reference Iglesias, Sánchez, Bersano, Carrasco, Dhont, Fuentes, Linares, Munoz, Okumura, Roo, Van der Meeren, Vidal and Villanueva2007), but this has not been systematically tested.

Aggression and cannibalism

Except for a few species, both octopods and cuttlefish are relatively solitary animals. Confinement in a small space with conspecifics, such as a pot or trap, might not only cause stress but also fighting. Indeed, limb amputation is commonly observed in wild-caught octopuses (Florini et al. Reference Florini, Fiorito, Hague and Andrews2011), which might be a result of either autophagy/auto-mutilation (Reimschuessel & Stoskopf Reference Reimschuessel and Stoskopf1990; Budelmann Reference Budelmann1998) or fighting. Another risk is cannibalism; all coleoid cephalopod groups have cannibalistic tendencies, particularly between individuals that are not size-matched and when insufficient food is provided (Aguado-Gimémenz & Garcia Garcia Reference Aguado Giménez and García García2002; Hayter Reference Hayter2005; Moltschaniwskyj et al. Reference Moltschaniwskyj, Hall, Lipinski, Marian, Nishiguchi, Sakai, Shulman, Sinclair, Sinn, Staudinger, Van Gelderen, Villanueva and Warnke2007; Budelmann Reference Budelmann, Hubrecht and Kirkwood2010; Ibáñez & Keyl Reference Ibáñez and Keyl2010; Pierce et al. Reference Pierce, Allcock, Bruno, Bustamante, González, Guerra, Jereb, Lefkaditou, Malham, Moreno, Pereira, Piatkowski, Rasero, Sanchez, Santos, Begona, Santurtun, Seixas, Sobrino and Villanueva2010; Jacquet et al. Reference Jacquet, Franks, Godfrey-Smith and Sánchez-Suárez2019).

Consequently, fisheries that include traps or pots to detain live individuals together should ensure that their devices are large enough for the species in question, baited with sufficient prey to sustain the maximum number of captive individuals and be checked frequently. Leaving the devices in situ for several days can result in discomfort, stress, and even death, as the confined space can provoke trapped animals to fight or eat each other. The frequency of checking octopus traps varies depending on local regulations, fishing practices, and environmental conditions. In False Bay, South Africa, for example, soak time, trap density, and sea surface temperature are considered when determining optimal intervals (Sanjay Reference Sanjay2022). Additionally, variations in octopus behaviour, such as differences in trap interaction and escape attempts, suggest that checking frequency may need to be adjusted to account for activity patterns and catch efficiency (Dominguez-Lopez et al. Reference Dominguez-Lopez, Follana-Berná and Pablo Arechavala-Lopez2021).

Exposure to inappropriate salinity and temperatures

Cephalopods are highly stenohaline and stenothermal (Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015), meaning they can only tolerate a narrow range of salinity and temperature (Moltschaniwskyj et al. Reference Moltschaniwskyj, Hall, Lipinski, Marian, Nishiguchi, Sakai, Shulman, Sinclair, Sinn, Staudinger, Van Gelderen, Villanueva and Warnke2007). Changes in salinity can result in visual indicators of stress or discomfort, such as blanching of the skin and excessive inking, and can lead to death (AK Schnell, personal observation 2012). While stratification or mixing can sometimes buffer the effects of freshwater run-off, cephalopods in shallow or enclosed inshore environments remain vulnerable to sudden salinity changes. A single overnight rainfall event of over 60 mm caused salinity fluctuations severe enough to result in up to 70% mortality in cuttlefish held in open-air, pot-like aquarium traps exposed to the elements (AK Schnell, personal observation 2012). Such conditions, likely to become more frequent with extreme weather, highlight the need for frequent trap checks to minimise mortality.

Slaughter methods

Trawled or netted animals are usually brought aboard dead, whereas trapped or jigged animals are often landed alive (industry sources). If the animal is still alive, it will die from asphyxiation before being iced. Time of death via asphyxiation on boats is not well-documented but can take minutes to hours, which raises welfare concerns, especially since cephalopods are likely to experience distress during the process. Anecdotal evidence suggests that potentially inhumane methods are sometimes used on fishing vessels, such as clubbing, slicing the brain, and reversing the mantle (Pereira & Lourenco Reference Pereira and Lourenço2014).

There is currently an evidence gap regarding humane slaughter methods that are commercially practical and available. There are efforts to improve and standardise euthanasia for captive cephalopods used in scientific experiments (Andrews et al. Reference Andrews, Darmaillacq, Dennison, Gleadall, Hawkins, Messenger, Osorio, Smith and Smith2013; Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015; Butler-Struben et al. Reference Butler-Struben, Brophy, Johnson and Crook2018). Currently, the only recommended method of humane slaughter for cephalopods is terminal overdose of an anaesthetic (typically magnesium chloride and ethyl alcohol), often followed by decerebration (Boyle Reference Boyle, Hubrecht and Kirkwood2010; Andrews et al. Reference Andrews, Darmaillacq, Dennison, Gleadall, Hawkins, Messenger, Osorio, Smith and Smith2013; Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015; Abbo et al Reference Abbo, Himebaugh, DeMelo, Hanlon and Crook2021). However, this would be inappropriate for cephalopods slaughtered for human consumption. Furthermore, mechanical methods that do not involve contamination, such as cutting or puncturing of the brain, require skilled practitioners to ensure they are performed correctly (Boyle Reference Boyle, Hubrecht and Kirkwood2010; Andrews et al. Reference Andrews, Darmaillacq, Dennison, Gleadall, Hawkins, Messenger, Osorio, Smith and Smith2013; Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015) and are inefficient for large-scale practices. Further research is needed to determine the optimal slaughter methods for commercial cephalopod fisheries. We have been unable to find any codes of best practice or voluntary guidelines specific to cephalopod fisheries. Even though cephalopods are often caught as by-catch, it would be sensible to develop codes of best practice for circumstances in which cephalopods are alive when landed.

Hatchling mortality

One of the currently limiting issues in captive management of octopus is hatchling mortality. As well as limiting the viability of cephalopod farming, this can also be a welfare issue. For O. vulgaris, survival rates are, at best, around 30–40% at day 40 (Iglesias et al. Reference Iglesias, Sánchez, Bersano, Carrasco, Dhont, Fuentes, Linares, Munoz, Okumura, Roo, Van der Meeren, Vidal and Villanueva2007) and < 10% by day 60 (Vaz-Pires et al. Reference Vaz-Pires, Seixas and Barbosa2004). This is primarily due to problems with temperature, water quality, and nutrition (Vaz-Pires et al. Reference Vaz-Pires, Seixas and Barbosa2004; Boyle Reference Boyle, Hubrecht and Kirkwood2010; Navarro et al. Reference Navarro, Monroig, Sykes, Iglesias, Fuentes and Villanueva2014). Moreover, hatchlings require a large amount of live food (larval shrimp and other crustacea), which can be difficult to obtain (Iglesias et al. Reference Iglesias, Sánchez, Bersano, Carrasco, Dhont, Fuentes, Linares, Munoz, Okumura, Roo, Van der Meeren, Vidal and Villanueva2007; Pierce et al. Reference Pierce, Allcock, Bruno, Bustamante, González, Guerra, Jereb, Lefkaditou, Malham, Moreno, Pereira, Piatkowski, Rasero, Sanchez, Santos, Begona, Santurtun, Seixas, Sobrino and Villanueva2010). Young animals dying of poor nutrition and inappropriate housing conditions are highly likely to suffer poor welfare.

Capture and transport

As captive breeding efforts and rearing have tended to fail, octopus aquaculture often takes the form of ‘ranching’ or ‘rearing’, in which young animals are captured and grown in captive tanks for eventual sale. As noted above, many capture and transport methods can harm cephalopods. Cephalopods require highly oxygenated water, and prolonged transport can lower oxygen and increase nitrogenous waste. An air stone or aerator should be used whenever possible (Iglesias et al. Reference Iglesias, Sánchez, Bersano, Carrasco, Dhont, Fuentes, Linares, Munoz, Okumura, Roo, Van der Meeren, Vidal and Villanueva2007; McDonald Reference McDonald2011; Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015). Additionally, if the animals ink in the water and it is not subsequently cleaned (or the animal transferred), the ink can coat the gills and cause asphyxiation (Hayter Reference Hayter2005; McDonald Reference McDonald2011). Several species of octopus show stress-related biomarkers after being caught by trawl, such as a compromised immune system, but they typically recover within 24 h (Barragán-Méndez et al. Reference Barragán-Méndez, Sobrino, Marín-Rincón, Fernández-Boo, Costas, Mancera and Ruiz-Jarabo2019). Some species appear more suited than others to these procedures – for example, O. vulgaris and S. officinalis show some resistance to stress from handling and transport (Vaz- Pires et al. Reference Vaz-Pires, Seixas and Barbosa2004; Cooke et al. Reference Cooke, Tonkins, Mather, Carere and Mather2019).

A working group through FELASA (Federation of European Laboratory Animal Science Associations) has recently published a set of best-practices for capture and transport of cephalopods (Sykes et al. Reference Sykes, Galligioni, Estefanell, Hetherington, Brocca, Correia, Ferreira, Pieroni and Fiorito2024), though this is primarily for research purposes and may not reflect larger-scale commercial operations.

Poor nutrition

Poor nutrition is one of the primary obstacles to establishing large-scale octopus aquaculture, as the animals are carnivorous and typically require live prey (Boyle Reference Boyle, Hubrecht and Kirkwood2010; Pierce et al. Reference Pierce, Allcock, Bruno, Bustamante, González, Guerra, Jereb, Lefkaditou, Malham, Moreno, Pereira, Piatkowski, Rasero, Sanchez, Santos, Begona, Santurtun, Seixas, Sobrino and Villanueva2010; Navarro et al. Reference Navarro, Monroig, Sykes, Iglesias, Fuentes and Villanueva2014). Although work has been done on developing suitable alternatives, none has been successful enough for widespread use (Pierce et al. Reference Pierce, Allcock, Bruno, Bustamante, González, Guerra, Jereb, Lefkaditou, Malham, Moreno, Pereira, Piatkowski, Rasero, Sanchez, Santos, Begona, Santurtun, Seixas, Sobrino and Villanueva2010). As it stands, there is insufficient understanding of the metabolism and nutritional needs of cephalopods to formulate complete diets (O’Brien et al. Reference O’Brien, Roumbedakis and Winkelmann2018). Animals which fail to thrive on food sources provided will experience a range of welfare harms, such as hunger as well as nutritional and metabolic diseases.

Inappropriate housing

The quality of the aquatic environment is critical to cephalopod health and welfare. Cephalopods have precise environmental needs, requiring strict monitoring of oxygen, pH, CO₂, nitrogenous waste, and salinity levels, as well as rapid removal of ink as necessary (Vaz-Pires et al. Reference Vaz-Pires, Seixas and Barbosa2004; Hayter Reference Hayter2005; McDonald Reference McDonald2011; Sykes et al. Reference Sykes, Baptista, Gonçalves and Andrade2012; Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015; Cooke et al. Reference Cooke, Tonkins, Mather, Carere and Mather2019). Inadequate water conditions can lead to health issues, infections, respiratory problems, agitation, frequent inking and jetting, and even death (Hanley et al. Reference Hanley, Shashar, Smolowitz, Bullis, Mebane, Gabr and Hanlon1998; Hayter Reference Hayter2005; Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015).

Other environmental factors, such as lighting, temperature, and noise or vibrations, also significantly impact their welfare (Hayter Reference Hayter2005; Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015). Cephalopods possess unique sensory abilities, such as detecting polarised light, and advanced mechanoreception and chemosensory capabilities, which demand specific environmental conditions (Browning Reference Browning2019; Cooke et al. Reference Cooke, Tonkins, Mather, Carere and Mather2019). Temperature appears particularly important, impacting feeding, growth, and lifespan (Aguado-Giménez & García García Reference Aguado Giménez and García García2002; Sherrill et al. Reference Sherrill, Spelman, Reidel and Montali2000).

Inadequate shelter in captivity is a major stressor for cephalopods. In their natural habitat, these soft-bodied molluscs use hiding and rapid escape strategies against predators (Cooke & Tonkins Reference Cooke and Tonkins2015). A lack of sufficient or appropriate shelter can cause behaviours associated with fear and stress, such as inactivity and anorexia (Sherrill et al. Reference Sherrill, Spelman, Reidel and Montali2000). Moreover, stress in octopus can even result in autophagy: the consumption of their own limbs (Hayter Reference Hayter2005). Providing ample hiding spots, such as shelters or caves, is essential for their welfare (Vaz-Pires et al. Reference Vaz-Pires, Seixas and Barbosa2004).

Furthermore, as discussed above, appropriate social grouping is crucial. Most octopus species are solitary and prone to stress when overcrowded. Housing them individually is important, as crowding can trigger aggression, cannibalism (Aguado-Giménez & García García Reference Aguado Giménez and García García2002; Hayter Reference Hayter2005; Budelmann Reference Budelmann, Hubrecht and Kirkwood2010; Pierce et al. Reference Pierce, Allcock, Bruno, Bustamante, González, Guerra, Jereb, Lefkaditou, Malham, Moreno, Pereira, Piatkowski, Rasero, Sanchez, Santos, Begona, Santurtun, Seixas, Sobrino and Villanueva2010; Jacquet et al. Reference Jacquet, Franks, Godfrey-Smith and Sánchez-Suárez2019) and increased stress, affecting their resting and feeding habits (Cooke et al. Reference Cooke, Tonkins, Mather, Carere and Mather2019).

Lack of cognitive stimulation

There is also the potential for poor psychological welfare for captive octopus, due to their behavioural and cognitive complexity (Cooke & Tonkins Reference Cooke and Tonkins2015; Jacquet et al. Reference Jacquet, Franks, Godfrey-Smith and Sánchez-Suárez2019). Octopus are even able to recognise and form relationships with caregivers, and the presence of familiar people can impact their welfare (Narshi et al. Reference Narshi, Free, Justice, Smith and Wolfensohn2022). Jacquet et al. (Reference Jacquet, Franks, Godfrey-Smith and Sánchez-Suárez2019) are concerned about lack of cognitive stimulation for farmed octopus. They worry that the “tightly controlled and monotonous environments” typical of farming do not allow for the cognitive stimulation, exploration, and environmental control necessary for psychological welfare. Cephalopods regularly show signs of stress in poor captive environments, such as irregular swimming patterns, lethargy, agitation, and anorexia (McDonald Reference McDonald2011).

Disease

Several factors, including stress, suboptimal water quality, and inadequate nutrition, can predispose cephalopods to disease. Stress, in particular, weakens their immune systems, increasing susceptibility to bacterial, viral, and fungal infections (Sherrill et al. Reference Sherrill, Spelman, Reidel and Montali2000; McDonald Reference McDonald2011). The cephalopod immune system is not well understood (Sykes & Gestal Reference Sykes, Gestal, Iglesias, Fuentes and Villanueva2014; O’Brien et al. Reference O’Brien, Roumbedakis and Winkelmann2018). Whilst viral infections have rarely been reported, bacterial infections commonly occur in skin lesions (as above), and gills (Sykes & Gestal Reference Sykes, Gestal, Iglesias, Fuentes and Villanueva2014; Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015). Parasites are common in wild animals and can appear in captive stocks if live prey are used (Sykes & Gestal Reference Sykes, Gestal, Iglesias, Fuentes and Villanueva2014). Additionally, the current lack of comprehensive knowledge of cephalopod analgesia and anaesthesia poses welfare concerns, particularly when animals are injured or need to undergo medical interventions (Fiorito et al. Reference Fiorito, Affuso, Basil, Cole, De Girolamo, D’Angelo, Dickel, Gestal, Grasso, Kuba, Mark, Melillo, Osorio, Perkins, Ponte, Shashar, Smith, Smith and Mark2015).

Slaughter methods

There is, at present, no established method to humanely slaughter farmed cephalopods; a major evidence gap. Proposals for commercial octopus farms in the Canary Islands have suggested slaughter through immersion in ice slurry, but there is no evidence that this is a humane method for octopus. The use of ice slurry for slaughtering fish has faced criticism due to its potential to cause prolonged distress and pain (Marshall Reference Marshall2023). This occurs as the fish’s body temperature gradually decreases. Additionally, the sudden immersion in extreme cold can lead to thermal shock. In some instances, this method also results in asphyxiation, as fish struggle to get sufficient oxygen from the water (Marshall Reference Marshall2023). As noted in the previous section, other more humane methods are not appropriate for use on a commercial scale.

Accidental injury

It is generally in the interests of the shellfish industry to avoid damaging the decapods they catch, with intact animals fetching a much higher value than injured ones would, especially in larger species. Therefore, industry guidance already emphasises careful handling as good practice (e.g. Jacklin & Combes Reference Jacklin and Combes2005; Seafish et al. 2024). Risk of physical damage is greater for catches that are intended for markets with less emphasis on the quality of individual animals, such as trawl-caught species. Accidental physical injuries to decapods include cracked carapaces, damaged antennae, and loss of limbs. Haemolymph can rapidly leak from cracks, killing the animal. In species intended for relatively prolonged live storage or transport, industry guidance recommends that animals are carefully inspected, and those with damaged limbs should be prompted to cast off the limbs via autotomy (Jacklin & Combes Reference Jacklin and Combes2005). It is unclear what the relative welfare impact of external injury versus autotomy is to decapods, because injuries vary greatly, but risk of infection or rapid death is lessened with autotomy. Crabs with claws that were manually twisted off showed more defensive behaviour in contests, more frothing at the mouth and more haemolymph loss, compared with those whose claws were autotomised following an incision to the joint above the merus (McCambridge et al. Reference McCambridge, Dick and Elwood2016).

The risk of accidental injury can be reduced by refined capture methods, such as using smooth plastic inserts in creels to prevent limb tearing when crabs are pulled from netting (Jacklin & Combes Reference Jacklin and Combes2005), avoiding rapid haulage of lobsters from deeper waters (Basti et al. Reference Basti, Bricknell, Hoyt, Chang, Halteman and Bouchard2010), or where it is not possible to alter commercial haulage speeds or capture depths allowing recovery in recirculating seawater (rather than damp storage) (Basti et al. Reference Basti, Bricknell, Hoyt, Chang, Halteman and Bouchard2010). Studies on species caught using both creels and trawling (e.g. langoustine [Nephrops norvegicus] and shrimp [Pandalus borealis]) have shown trawling causes greater physiological stress, risk of injury, and mortality, especially when trawl times were longer (Ridgway et al. Reference Ridgway, Taylor, Atkinson, Chang and Neil2006; Albalat et al. Reference Albalat, Gornik, Atkinson, Coombs and Neil2009; Larssen et al. Reference Larssen, Dyb, Woll and Kennedy2013). Alongside discussions about the economic and environmental effects of trawling for decapods (e.g. Williams & Carpenter Reference Williams and Carpenter2016), the welfare risks should also be considered.

There is risk of physical injury (such as crushing) during transport and storage, which can be reduced by using well-designed species-appropriate containers. Containers should be resistant to crushing, not allow limbs to become caught, and not contain so many animals that those above do not crush those below (Barrento et al. Reference Barrento, Marques, Vaz-Pires and Nunes2010). When lobsters are stored onboard in totes, they should be packed with their tails curled beneath them to protect their ventral surface from puncture, face in the same direction, and be at a density that aids stability, but without pressing the animals too tightly together (Basti et al. Reference Basti, Bricknell, Hoyt, Chang, Halteman and Bouchard2010).

At all stages, handling decapods causes physiological stress (Jacklin & Coombes Reference Jacklin and Combes2005) and should be performed with care and kept to a minimum. If decapods are ‘thrown’ (e.g. Barrento et al. Reference Barrento, Marques, Pedro, Vaz-Pires and Nunes2008) or ‘tossed’ (Lavallee et al. Reference Lavallee, Spangler, Hammell, Dohoo and Cawthorn2000) into containers, this increases the risk of physical injury and loss of vigour compared with more careful placement. Careless and rough handling is a welfare risk and should be avoided.

Declawing

Declawing is the practice of manually twisting or snapping the claws off a decapod, and evidence suggests this may be painful for the animals. Declawing can be contrasted with inducing the animals to autotomise their own claws, usually by making an incision in the limb at certain locations. Declawed crabs will tend their wound, shield it, and in some cases display a ‘shudder’ response (McCambridge et al. Reference McCambridge, Dick and Elwood2016). They also show a physiological stress response (as indicated by glucose and lactate in the haemolymph) for at least 24 h after the injury, which is more severe for manual declawing than induced autotomy (Patterson et al. Reference Patterson, Dick and Elwood2007). Declawed crabs may be thrown back to sea (the claw being the most valuable product in some cases) but without their claws, they are at a competitive disadvantage in contests with other crabs and unlikely to mate (McCambridge et al. Reference McCambridge, Dick and Elwood2016), as well as less able to gain access to bivalves, one of their main food sources (Patterson et al. Reference Patterson, Dick and Elwood2009; Duermit et al. Reference Duermit, Kingsley-Smith and Wilber2015). Larger wounds can also lead to death within days (Duermit et al. Reference Duermit, Kingsley-Smith and Wilber2015).

It is reasonable to conclude (with high confidence) that declawing true crabs (infraorder Brachyura) causes suffering. UK industry codes of practice discourage declawing (Seafish et al. 2024), but declawing is largely unregulated, with bans in place only in some states within the US. The practice was banned in the UK from 1986 until 2000, when the relevant legislation was overridden by a European Union regulation (No 850/98). Banning declawing would be an easy, low-cost intervention to improve the welfare of decapods.

Disabling pincers (including nicking)

Decapod pincers or large claws usually require disabling in some way, to prevent injury to both human handlers and other animals sharing the same container. For clawed lobsters, the usual method is to restrain the claws using elastic bands or cable ties (Jacklin & Combes Reference Jacklin and Combes2005; Seafish et al. 2024). Research into the welfare effects of banding is yet to provide any conclusive evidence that this practice compromises lobster welfare compared with the harms of leaving the claws unrestricted. When comparing the haemolymph parameters of group-housed banded American lobsters (Homarus americanus) with those of individually housed non-banded lobsters, there was a significant lasting increase in calcium levels but not of glucose and lactate, which are more typically taken to indicate stress (Coppola et al. Reference Coppola, Tirloni, Vasconi, Anastasio, Stella and Bernardi2019). There is therefore no reason at this stage to consider regulating this procedure.

For brown crabs (Cancer pagurus), banding is considered unsuitable within the shellfish industry (Jacklin & Combes Reference Jacklin and Combes2005; Seafish et al. 2024), due to the claws’ tapered conformation. Instead, if live storage or transportation of the crabs is necessary, the tendon connecting the two parts of each claw is cut. This procedure is known as ‘nicking’. There is evidence that this has negative welfare effects. Nicking causes elevated glucose and lactate in the haemolymph and increases the risk of muscle necrosis and pathology (Welsh et al. Reference Welsh, King and MacCarthy2013). These effects are worsened at warmer temperatures, whilst colder temperatures helped reduce the risk of physiological stress and pathology (Johnson et al. Reference Johnson, Coates, Albalat, Todd and Neil2016). Due to the health and welfare risks to crabs, alternatives to nicking should be developed and implemented. One potential alternative is immobilisation using elastic bands as is sometimes practised for brown crabs in Norway (Woll et al. Reference Woll, Larssen and Fossen2010). In blue crabs (Callinectes sapidus), elastic bands can be successfully used for binding claws if a small block or dowel is first gripped between the two dactyls of each claw and then left in place (Haefner Reference Haefner1971). Another solution to prevent fighting could be to use individual compartments for storing crabs, equivalent to the ‘tubes’ used for Nephrops (langoustine).

Social stress and aggression

Aggression and stress can occur in decapods that are usually solitary in the wild, such as lobsters, when many animals are kept in close proximity, such as being trapped in the same creel or housed in live storage tanks at food retailers. Social aggression can cause ‘anxiety-like’ states in crayfish (P. clarkii) (Bacqué-Cazenave et al. Reference Bacqué-Cazenave, Cattaert, Delbecque and Fossat2017), and it is reasonable to assume that social aggression will produce similar states in other decapods. While socially grouping lobsters with bound pincers did not significantly increase haemolymph glucose or lactate compared to individual holdings (Coppola et al. Reference Coppola, Tirloni, Vasconi, Anastasio, Stella and Bernardi2019), this could be due to the protection from injurious aggression or because the stress measures used were not sensitive to the effects. To prevent aggression and associated stress during capture, the Seafish code of good practice for handling crustaceans recommends the use of creels with a second chamber and with escape gaps or a large mesh net (where practical) to allow by-catch to escape (Jacklin & Combes Reference Jacklin and Combes2005).

Though low stocking density may be important in preventing social stress, one survey conducted in Portugal showed that stocking densities can be very high (maximum reported: 300 kg m⁻³) and sometimes exceed recommendations (120 kg m⁻³; Barrento et al. Reference Barrento, Marques, Pedro, Vaz-Pires and Nunes2008). Carder (Reference Carder2017) investigated live lobster storage conditions at nine UK food retailers and found that lobsters were stocked at densities that caused some individuals to be on top of each other in eleven of the 26 display tanks observed. Indeed, in four tanks, there were at least two full layers of lobsters. Similarly, Crustacean Compassion (2020) reported lobsters fighting in a wholesaler display tank, and up to 50 lobsters being displayed within a single tank (dimensions not given). High stocking densities of socially stored decapods could represent a risk to welfare.

Exposure to inappropriate temperatures

The thermal preferences of decapods differ between species and depend to some extent on what temperature they are acclimated to. For most species, their upper and lower temperature tolerance is currently unknown (Lagerspetz & Vainio Reference Lagerspetz and Vainio2006). However, there are potential welfare risks from exposing animals to temperatures that are too high or low.

Physiological stress, disease susceptibility, and mortality are higher in decapods transported or stored at excessively warm temperatures. This can occur whenever vessel- or shore-based storage containers cannot be cooled to an optimal temperature, such as during warm weather (Lavallee et al. Reference Lavallee, Spangler, Hammell, Dohoo and Cawthorn2000; Jacklin & Combes Reference Jacklin and Combes2005). Studies of decapod transport at different temperatures have shown negative health, behaviour and physiological stress effects at higher temperatures for brown crabs (C. pagurus) (Woll et al. Reference Woll, Larssen and Fossen2010; Barrento et al. Reference Barrento, Marques, Vaz-Pires and Nunes2011; Johnson et al. Reference Johnson, Coates, Albalat, Todd and Neil2016), shrimps (P. borealis) (Larsson et al. Reference Larssen, Dyb, Woll and Kennedy2013) and Asian tiger prawns (Penaeus monodon) (de la Vega et al. Reference de la Vega, Hall, Wilson, Reverter, Woods and Degnan2007). Decapods in both immersed and damp storage must, therefore, be kept below a maximum temperature threshold appropriate for their species (Jacklin & Combes Reference Jacklin and Combes2005). This is the case even for temporary storage (e.g. onboard vessels or awaiting transfer) – for example, lobsters landed on sunny days showed greater loss of vigour than those on cloudy days, presumably because of exposure to sunlight (Lavallee et al. Reference Lavallee, Spangler, Hammell, Dohoo and Cawthorn2000). Use of shade covers, running seawater hoses, and planning capture times to avoid the hottest parts of the day can all reduce excessive heat exposure. UK codes of practice recommend storing decapods between 4 and 8^oC (Seafish et al. 2024).

Excessively cold temperatures may also be a problem. Ice or ice-packs are sometimes used to cool decapod environments on board vessels and during live transport, because they reduce the animals’ activity levels and oxygen requirements, helping prolong their lives (Jacklin & Combes Reference Jacklin and Combes2005). However, ice should not be placed in direct contact with decapods (Seafish et al. 2024). Fishing industry reports suggest that the sudden cold can stress and even kill many decapod species from UK waters (Jacklin & Combes Reference Jacklin and Combes2005). In some countries, including Italy and Switzerland, displaying and transporting live crustaceans on ice or in icy water is illegal. Most marine decapods do not inhabit polar regions (the exception being certain caridean shrimp species), so they would rarely encounter ice in nature, and most become immobile at or below about 2°C (Frederich et al. Reference Frederich, Sartoris, Pörtner, Arntz and Clarke2002). The reduced activity in decapods when cooled to near freezing is sometimes termed ‘torpor’. It reduces the metabolic rate, which helps them survive short cold periods and regain activity once temperatures increase again. For decapods fished in waters that rarely reach temperatures below 4°C (such as the UK; Morris et al. Reference Morris, Pinnegar, Maxwell, Dye, Fernand, Flatman, Williams and Rogers2018), torpor is unlikely to be a ‘natural’ behaviour.

Whether near freezing temperatures cause nociception or pain in decapods is unknown. Research into this is urgently needed, especially because there is the assumption that extreme cooling has anaesthetic effects, which is in direct conflict with the possibility that it could cause avoidance, nociception, or pain. Even in humans, this paradox exists, because very cold temperatures can cause pain, but can otherwise numb certain other sources of pain (Yin et al. Reference Yin, Zimmermann, Vetter and Lewis2015), so the situation may also be complex in decapods, and current evidence is inconclusive. Cold shock did not influence haemolymph serotonin or octopamine levels in either crabs or shrimp (Weineck et al. Reference Weineck, Ray, Fleckenstein, Medley, Dzubuk, Piana and Cooper2018). Lobsters (H. americanus), spiny lobsters (Panulirus japonicus), and prawns (Penaeus japonicus) have cold-sensitive neurons in their ventral nerve cord, which increase their firing rate within a temperature range of 0.5–5.5°C (Tani & Kuramoto Reference Tani and Kuramoto1998). Puri and Faulkes (Reference Puri and Faulkes2015) found no evidence for cold-sensitive nociceptors in crayfish (P. clarkii), but this study used a much colder stimulus (−78°C) than either conventional chilling methods or ecologically relevant conditions. Cold nociception in general is not well understood across species, and it may have evolved later than heat nociception (Smith & Lewin Reference Smith and Lewin2009). This is an important evidence gap: there is a need for better knowledge of the lowest temperature that commercially important species of decapod can tolerate without harming health and welfare.

Storage and transport out of water or in marine vivier vehicles

Another potential welfare risk is the open-air storage and transport of aquatic decapods. For instance, rock lobsters (Panulirus cygnus) will tail-flip (thought to be a behavioural sign of stress) as soon as they are removed from the water (Paterson & Spanoghe Reference Paterson and Spanoghe1997). Some decapods, especially brown crabs, green crabs, and lobsters, can typically survive for 2–3 days in ‘dry’ storage, as long as the conditions are sufficiently damp. This is sometimes known as damp storage or semi-dry storage. Industry guidance suggests that decapods in dry storage should be covered with wet seaweed, fabric, paper or hessian and kept between 4 and 8^oC (Seafish et al. 2024). The welfare effects of dry storage are not well known. One study investigating the effects of damp storage on brown crabs (C. pagurus) reported that waste products, such as ammonia, started to accumulate in the haemolymph, since seawater is needed to remove them (Woll et al. Reference Woll, Larssen and Fossen2010). This accumulation of waste products may or may not cause suffering — this is an evidence gap.

A key welfare risk to (non-amphibious) decapods is hypoxia (lack of oxygen), which causes lactate to build up in the tissues due to anaerobic respiration. In humans, this build-up of lactate is painful. Whether it is also painful in decapods is unknown — another evidence gap. For animals held in vivier vehicles (lorries, boats or trailers adapted to transport marine life in seawater), industry guidance suggests that oxygen saturation should not fall below 85%, which is a risk over time, at higher stocking densities, and under warmer temperatures (Seafish et al. 2024). Hypoxia can occur when an animal is removed from water, because the gills can collapse. Decapods are exposed to air during damp storage, but also sometimes whilst awaiting transfer to vehicles or storage containers. For example, a study of crabs transported from the UK to Portugal found that crabs held in the buckets for longer showed increased haemolymph L-lactate, acidity, and haemocyanine before the journey, and lasting lowered haemolymph pH throughout the entire journey (Barrento et al. Reference Barrento, Marques, Vaz-Pires and Nunes2010). Since hypoxia can also occur in viviers with seawater low in oxygen, in some cases, decapods will have equivalent or even better experiences in damp storage than storage in poor-quality seawater (Lorenzon et al. Reference Lorenzon, Giulianini, Libralato, Martinis and Ferrero2008; Barrento et al. Reference Barrento, Marques, Vaz-Pires and Nunes2011, Reference Barrento, Marques, Vaz-Pires and Nunes2012). However, the focus should be on ensuring higher-quality seawater transport, good water quality, and appropriate temperature. Keeping seawater clean and well-aerated can be challenging but is very important (Jacklin & Combes Reference Jacklin and Combes2005; Seafish et al. 2024). However, where this is not possible, it may sometimes be preferable to use temporary damp storage. The maximum duration of damp storage should be investigated for key species to help prevent suffering.

Lack of food

Decapods in medium-term storage, such as lobsters, are often not fed (Seafish et al. 2024), partly to prevent contamination and soiling of the water with uneaten food and waste products. They can survive without obvious weight loss or increased mortality risk for several weeks without food (e.g. Siikavuopio et al. Reference Siikavuopio, Johansson, James and Lorentzen2018), although there are species differences (Sacristán et al. Reference Sacristán, Rodríguez, De los Angeles Pereira, Lopez Greco, Lovrich and Fernandez Gimenez2017). In the wild, decapods have periods of fasting as part of their moult cycle (Lipcius & Herrnkind Reference Lipcius and Herrnkind1982). Recently moulted decapods are usually avoided in the fishing industry, because their flesh is very watery and their soft shells make them vulnerable to damage, so stored individuals will mostly comprise animals between moults that would be motivated to feed, and a smaller proportion that may have been preparing to moult and therefore would not feed. Housing animals in colder water may help them cope with lack of food, as indicated by physiological markers (Albalat et al. Reference Albalat, Johnson, Coates, Dykes, Hitte, Morro, Dick, Todd and Neil2019; Siikavuopio et al. Reference Siikavuopio, Johansson, James and Lorentzen2018). The resilience to starvation at cool temperatures in terms of bodyweight and mortality suggests that lack of food might pose little welfare concern for some species over the short- to medium-term, although this has not been tested directly, and fasting does confer some gradual physiological effects.

Lack of access to dark shelters

Decapods in the wild will spend substantial amounts of time in dark shelters. Given a choice between a light area and a dark shelter, crabs will typically prefer the dark shelter (e.g. Barr & Elwood Reference Barr and Elwood2011; Hamilton et al. Reference Hamilton, Kwan, Gallup and Tresguerres2016). Crayfish (P. clarkii) in an anxiety-like state will avoid bright areas (Fossat et al. Reference Fossat, Bacqué-Cazenave, De Deurwaerdère, Delbecque and Cattaert2014, Reference Fossat, Bacqué-Cazenave, De Deurwaerdère, Cattaert and Delbecque2015). Given this aversion to light, good practice for handling decapods must involve providing them with access to dark environments. This is already recommended by Seafish as one of their “10 golden rules” for handling crustaceans and in their codes of practice (Jacklin & Combes Reference Jacklin and Combes2005; Seafish et al. 2024). Yet there is evidence (obtained by the campaign group Crustacean Compassion) that supermarkets selling live lobsters in the UK commonly do not provide access to dark shelters (Carder Reference Carder2017) and display lobsters under bright lighting (Crustacean Compassion 2020).

Live purchase

Live decapods can be ordered from Amazon and other online retailers in countries such as the UK and US, sometimes travelling internationally. There is no way to ensure welfare-sensitive handling when a live animal is delivered to a private home. This practice carries an inherent risk of poor handling and inappropriate slaughter methods (see also the following section). Ending this practice would be a simple intervention to avoid this specific set of risks for poor decapod welfare.

A report by the campaign group Crustacean Compassion (2020) described highly inconsistent advice given to customers purchasing live lobsters in UK wholesalers on how to effectively transport, store or slaughter the animals. There is a need for enforceable codes of good practice regarding the advice and training that is provided in these settings. Live animals should only be sold to customers who are trained in appropriate handling and slaughter methods. Industry codes of practice suggest that animals should only be dispatched by competent persons (Seafish et al. 2024), but currently it is difficult to define or enforce this.

Stunning

Effective stunning not only immobilises the animal but also abolishes sentience (see discussion in Conte et al. Reference Conte, Voslarova, Vecerek, Elwood, Coluccio, Pugliese and Passantino2021). Electrical stunning has the potential to be an effective method. Electric shocks of sufficiently high voltage and long duration can stun (and, at even higher voltages or longer durations, kill) crustaceans. Pre-dispatch stunning is a legal requirement in New Zealand and Switzerland. There are now several manufacturers producing electrical stunning equipment (e.g. Crustastun® [Mitchell and Cooper Ltd, Uckfield, UK] and Polar Systems Ltd [Kings Lynn, UK]) and include both single-animal units for the hospitality sector and a large-scale stunner for processors.

Electrical stunning appears to be the most humane method for stunning and/or slaughter. Roth and Øines (Reference Roth and Øines2010) compared electrical stunning, chilling, boiling, and CO₂ gassing for slaughter of crabs (C. pagurus), and found that electrical stunning was the only method effective within 1 s. Crustastun® units are effective for a range of species, such as brown crabs (C. pagarus), lobster (H. gammarus), Norway lobster (N. norvegicus), and shore crab (Carcinus maenas), rapidly causing loss of consciousness (as measured by cessation of behavioural and neuronal activity) without creating stress (as measured by sampling L-lactate in haemolymph and occurrence of autotomy [Neil Reference Neil2010, Reference Neil2012; Neil & Thompson Reference Neil and Thompson2012; Neil et al. Reference Neil, Albalat and Thompson2022]; though other work [Roth & Øines Reference Roth and Øines2010; Roth & Grimsbø Reference Roth and Grimsbø2016] has found autotomy in response to electroshock of insufficient voltage). We note that only the first of these two latter studies has been peer-reviewed. In other work, electric shock immobilised and reduced heartrate in P. clarkii and Litopenaeus vannamei (Weineck et al. Reference Weineck, Ray, Fleckenstein, Medley, Dzubuk, Piana and Cooper2018) A non-peer-reviewed study also found that Crustastun® reliably kills Norway lobster (Albalat et al. Reference Albalat, Gornik, Theethakaew and Neil2008).

However, a degree of caution is needed in interpreting these results. While they suggest that Crustastun® did not cause extreme physiological stress, we cannot conclude from this that it is painless (Stevens et al. Reference Stevens, Arlinghaus, Browman, Cooke, Cooke, Cowx, Diggles, Key, Rose, Sawynok, Schwab, Skiftesvik, Watson and Wynne2016). Stress responses can indicate pain (Elwood Reference Elwood2016), but this study should be considered in the context of how Crustastun® affects other (neural) indicators. A lack of significantly increased haemolymph lactate or autotomy, especially in experiments with small sample sizes, is insufficient evidence that high-voltage shocks do not induce pain. Elwood and Adams (Reference Elwood and Adams2015) found that shore crabs (C. maenas) exposed to a weak electric shock for a short time exhibited higher levels of haemolymph lactate than controls. Fregin and Bickmeyer (Reference Fregin and Bickmeyer2016) found that the Crustastun® induced a seizure-like pattern of increased neural activity, combined with an absence of responsiveness to mechanical stimulation (interpreted as total anaesthesia), but when crayfish were dropped into boiling water after stunning, the neural response – though much reduced relative to controls – was not abolished. We do not know what the seizure-like neural activity induced by electrical stunning feels like for decapods though, in humans, epileptic seizures involving the whole brain (as opposed to a specific region) result in loss of consciousness, so the same may be true for these animals.

Pharmacological anaesthesia is a potential alternative to electrical stunning, despite being limited to chemicals safe for human consumption. Two prime candidates are clove oil and AQUI-S®, a clove oil-based product without the former’s odour. In both, the active ingredient is eugenol (4-allyl-2- methoxyphenol). To our knowledge, pharmacological anaesthetics are rarely used on crustaceans in the UK. However, as a fish anaesthetic (Soto Reference Soto1995; Anderson et al. Reference Anderson, McKinley and Colavecchia1997; Keene et al. Reference Keene, Noakes, Moccia and Soto1998), AQUI-S® has been approved for human consumption in New Zealand, Australia, Chile, South Korea, Costa Rica, Honduras, and Norway, but not the EU or US (Priborsky & Velisek Reference Priborsky and Velisek2018).

Several studies suggest that clove oil and AQUI-S® stun crustaceans, though this can take some time. Eugenol temporarily immobilises blood-spotted crabs (Portunus sanguinolentus) in 14 min (Premarathna et al. Reference Premarathna, Pathirana, Rajapakse and Pathirana2016), and Australian giant crabs (Pseudocarcinus gigas) in 30 min (Gardner Reference Gardner1997) but up to 188 min in hairy shore crabs (Hemigrapsus oregonensis) (Morgan et al. Reference Morgan, Cargill and Groot2001). Eugenol also immobilises other crustaceans, including lobsters (H. americanus: Waterstrat & Pinkham Reference Waterstrat and Pinkham2005), langoustine (N. norvegicus; Cowing et al. Reference Cowing, Powell and Johnson2015), crayfish (Cherax quadricarinatus; Ghanawi et al. Reference Ghanawi, Saoud, Zakher, Monzer and Saoud2019), prawns (Macrobrachium rosenbergii; Coyle et al. Reference Coyle, Dasgupta, Tidwell, Beavers, Bright and Yasharian2005) and shrimps (P. monodon; Cai et al. Reference Cai, Dong, Wang and Su2012) (for more detailed reviews, see de Souza Valente [Reference de Souza Valente2022], Spoors et al. [Reference Spoors, James, Mendo, McKnight, Bønnelycke and Khan2023] and Rotllant et al. [Reference Rotllant, Llonch, García del Arco, Chic, Flecknell and Sneddon2023]). However, these pharmacological studies typically use behavioural indicators of stunning, which do not distinguish anaesthesia from paralysis. Eugenol’s mode of action is also poorly understood. Whilst pharmacological anaesthetics are potentially effective, more research is needed.

Chilling is another stunning technique, sometimes used for transport (as discussed previously in Handling of wild-caught decapods during capture, transport and sale). As crustaceans are ectothermic, they enter a state of torpor when external temperatures drop below a certain threshold. This renders them immobile, preventing autotomy and aggression between individuals. Torpor also facilitates nerve centre destruction, allowing a faster and more humane dispatch. Decapods are typically chilled by placing them into cold water or ice slurry. However, it is unclear whether chilling-induced inactivity is associated with loss of consciousness. Lobsters (H. gammarus and H. americanus) and crayfish (Astacus astacus and A. leptodactilus) both showed neural activity after an hour in cold water or ice slurry (Fregin & Bickmeyer Reference Fregin and Bickmeyer2016). Recordings of the number, amplitude, and rate of nerve impulses in Nephrops after 30 min of being immersed in ice were virtually the same as in the control animals, indicating no reduction of brain activity (Albalat et al. Reference Albalat, Gornik, Muangnapoh and Neil2022a). Blue crabs (C. sapidus), red swamp crayfish (P. clarkii), and white-leg shrimp (L. vannamei) held in ice slurry showed decreased heart rate, although most crabs still had a heart rate after five minutes and exhibited central neural processing for muscle reflexes after two minutes (Weineck et al. Reference Weineck, Ray, Fleckenstein, Medley, Dzubuk, Piana and Cooper2018). The effectiveness of chilling, even for inducing immobility, depends a lot on the cold tolerance of the particular species and appears to be ineffective for some (Rotllant et al. Reference Rotllant, Llonch, García del Arco, Chic, Flecknell and Sneddon2023). As discussed previously, there is also the potential for negative welfare experience associated with chilling. More research is needed to establish whether chilling itself is painful, but the existing literature suggests that cold-induced immobilisation leaves crustaceans susceptible to pain from subsequent procedures. Use of slush-ice presents another welfare concern: salinity drops as the ice melts, which can lead to osmotic shock before torpor is induced, although maintaining salinity can resolve this issue (AHAW 2005).

From a welfare perspective, crustaceans should be stunned before dispatch, and this is recommended in UK industry codes of practice (Seafish et al. 2024). Electric and pharmacological stunning are the most promising approaches. Future research could identify ways to make stunning more practical and effective. The Humane Slaughter Association is currently funding research into effective methods of stunning and slaughtering crustaceans. Chilling is not a humane stunning method if it merely paralyses crustaceans without anaesthetising them. This method has already been banned in Switzerland and parts of Italy.

Mechanical slaughter (dispatch)

The shellfish industry uses the term ‘dispatch’ to refer to the slaughter of decapods; here, we use the two terms interchangeably. Unlike vertebrates, crustaceans have a decentralised nervous system. Crabs have two main nerve clusters (ganglia), and lobsters have 13 interconnected ganglia down the ventral nerve cord. The result is that methods that target only the brain will not necessarily kill the animal quickly (Roth & Øines Reference Roth and Øines2010).

Spiking involves piercing the underside with a spike, destroying the ganglia. This method is recommended for crabs, because the brain (or cerebral ganglion) and ventral nerve mass (or thoracic ganglion) can both be spiked in rapid succession in a procedure known as ‘double spiking’. An early study for the Universities Federation for Animal Welfare (UFAW) recommended double spiking as the most humane method for slaughtering crabs (Baker Reference Baker1955). Although double spiking is relatively quick, it is not instantaneous. At present, most UK crab processors only destroy one ganglion (‘single spiking’). Single spiking creates a welfare risk because it is less likely to kill the animal quickly and reliably (Roth & Øines Reference Roth and Øines2010). UK codes of practice recommend double-spiking following stunning of crabs (Seafish et al. 2024), but regulations requiring double spiking (coupled with education about why this matters) would improve UK welfare standards; as would similar regulations globally.

Spiking is unsuitable for lobsters, because their chain of ganglia cannot be individually pierced quickly and accurately. To destroy all 13 ganglia, lobsters’ under-surface must be severed down the longitudinal midline using a knife. This process, known as splitting, is common in restaurants (industry sources) and is the recommended dispatch method following stunning according to UK industry guidance (Seafish et al. 2024). Due to the demand for whole lobsters, chefs typically only split the head (head splitting), rather than the whole body (complete splitting). However, head splitting leaves the posterior ganglia intact, raising the chance of continued survival. We cannot be confident that head splitting reliably abolishes consciousness immediately. From a welfare perspective, lobsters should be split from head to tail, destroying all 13 ganglia and killing the animal. Whole-body splitting should take less than 10 s when performed by a skilled practitioner.

Tailing involves separating the thorax from the abdomen. On Nephrops (langoustine) vessels, for instance, the abdomen is usually twisted away from the thorax (industry sources). Large vessels may chill the Nephrops beforehand, inducing immobility but without necessarily abolishing consciousness. As well as Nephrops, crayfish are slaughtered using tailing in the UK (industry sources). While spiking and splitting (properly performed) destroy all the animal’s ganglia, tailing does not. For this reason, it should not be recommended without prior effective stunning.

High-pressure processing involves crushing batches of crustaceans. It is claimed that high- pressure processing kills crustaceans in < 6 s, equivalent to spiking and splitting (industry sources). We have not been able to find robust scientific evidence confirming this. High- pressure processing without effective prior stunning has the potential to cause pain, even if it is over quickly. The use of this method varies by region – although it is the most common form of dispatch in the US, it is rare in the UK (industry sources).

Correctly practised, spiking and splitting are relatively quick dispatch methods. Quickly destroying every ganglion before further processing (e.g. boiling, freezing, or chopping up) ensures that the animal is dead and may not feel further pain. However, both tailing and routine spiking/splitting practices (especially single spiking and head splitting) do not destroy all ganglia. Double spiking crabs and completely splitting lobsters (as performed by competent and trained operators) should be considered best practice. Nevertheless, all mechanical dispatch methods take several seconds and may sometimes leave ganglia intact, especially when performed quickly or by untrained personnel. Crustaceans should therefore be effectively stunned beforehand.

Chilling

Decapods are sometimes dispatched using extremely low temperatures in refrigerators, freezers, or on ice. The welfare issues outlined in the section on stunning also apply here: nervous system activity continues after chilling, melting slush-ice can cause osmotic shock, and death is slow. Gardner (Reference Gardner and Jones2004) argued that this method of dispatch is slow, inconsistent, and aversive. However, there is currently no evidence for cold-sensitive nociceptors in crustaceans (Puri & Faulkes Reference Puri and Faulkes2015). If future research confirms their absence at more realistic temperatures in more species, low temperatures could conceivably represent a humane method of slaughter.

Chilling is a rare slaughter method, because it reduces meat quality (industry sources; but see Albalat et al. Reference Albalat, Gornik, Muangnapoh and Neil2022a, who found no significant effect), but is common in domestic kitchens. This is concerning as, unlike commercial blast freezers, home freezers do not reduce temperature rapidly. Crustaceans in home freezers must, therefore, be left to die over a period of more than 1 h (Roth & Øines Reference Roth and Øines2010). Edible crabs autotomise during freezing, indicating distress (Roth & Øines Reference Roth and Øines2010). This prolonged suffering may be worse than rapid methods considered inhumane (e.g. boiling).

Boiling

Boiling is perhaps the most controversial dispatch method, having been banned in several jurisdictions (Switzerland, New Zealand, and parts of Italy). Immersion in boiling water is nonetheless common in UK restaurants and domestic kitchens for lobster, Nephrops (langoustine), small crabs, crayfish, shrimps, and prawns, as well as on-vessel for brown shrimp, although recent industry guidance has urged users to attempt to avoid processing or cooking crustaceans before stunning or killing them (Seafish et al. 2024).

Boiling elicits various behavioural and physiological symptoms of distress, such as unco-ordinated movements and escape attempts in crabs (C. pagurus; Baker Reference Baker1955). More recent work on lobsters and cuttlefish did not observe such behaviours but did find that intense neural activity continued for up to 30–150 s after immersion (Fregin & Bickmeyer Reference Fregin and Bickmeyer2016). This suggests a period of up to 2.5 min (this duration aligns with an estimate by Roth & Øines [Reference Roth and Øines2010], obtained by a different method) of continued sentience, potentially involving extreme suffering. Smaller individuals died more quickly than larger ones, suggesting that boiling involves less prolonged suffering for smaller crustaceans (e.g. shrimps). This has recently been supported through work by Lauridsen and Alstrup (Reference Lauridsen and Alstrup2024), who found more rapid heating curves for smaller species, suggesting they may reach stunning or killing temperatures in under 10 s; compared with several minutes for larger species.

To address welfare concerns regarding live boiling, a number of authors have recommended immersing crustaceans in cold water and slowly raising the temperature (e.g. 1°C per min). Evidence on the effectiveness and welfare effects of this method are mixed. Some studies have found that crabs, lobsters, and crayfish do not show behavioural responses indicating pain and distress (e.g. tail-flipping or escape behaviour; Gunter Reference Gunter1961; Fregin & Bickmeyer Reference Fregin and Bickmeyer2016) and that CNS activity disappeared above 32°C in lobsters (H. gammarus and H. americanus) and crayfish (A. astacus and A. leptodactilus) (Fregin & Bickmeyer Reference Fregin and Bickmeyer2016). However, other studies found that edible crabs (C. pagurus; Baker Reference Baker1955) and red swamp crayfish (P. clarkii; Adams et al. Reference Adams, Stanley, Piana and Cooper2019) displayed behaviours indicating distress, including escape attempts, unco-ordinated movements, and autotomy; and crayfish still showed a heartbeat and functional nervous system up to 44°C even when apparently unresponsive (Adams et al. Reference Adams, Stanley, Piana and Cooper2019). Hence, a lack of behavioural responses to boiling may not indicate a loss of consciousness. This evidence is therefore insufficient to suggest that gradually raising water temperature (without prior stunning) is more humane than dropping an animal into boiling water. There is still a serious risk that it causes suffering over a period of minutes.

Freshwater immersion

Crustaceans immersed (‘drowned’) in freshwater must usually be left overnight. This practice is rare in the UK, as it reduces meat quality, but is sometimes practised on lobster and brown crab (industry sources). From a welfare perspective, it cannot be recommended. Crabs immersed in freshwater have shown behavioural signs of distress, such as unco-ordinated movement and increased respiration (Baker Reference Baker1955), and even autotomising and tearing at their own legs and abdomen (Gardner Reference Gardner1997). Like chilling, freshwater immersion potentially leads to more prolonged suffering than faster methods considered inhumane, such as boiling.

Shrimps

Most of the decapods used in aquaculture are shrimp, with almost 10 million tonnes produced per year under increasing intensification (Wuertz et al. Reference Wuertz, Bierbach and Bögner2023). The most commonly farmed species is the whiteleg shrimp (L. vannamei). While there is currently little evidence one way or the other regarding sentience in penaeid shrimp (Birch et al. Reference Birch, Burn, Schnell, Browning and Crump2021), a precautionary approach based on the lack of research and their close taxonomic relationship to other decapods for which there is more convincing evidence means their welfare should be taken seriously and potential harms prevented where possible. Alongside problems of humane slaughter discussed above, one of the most pressing problems in shrimp aquaculture is the practice of eyestalk ablation, which poses a severe welfare risk if the animals are sentient.

Eyestalk ablation is a controversial practice that involves removing one or both of the eyestalks of a mature broodstock female prawn in order to induce egg production. It has a range of negative effects on the animals (for a review, see Albalat et al. Reference Albalat, Zacarias, Coates, Neil and Planellas2022b) and could be linked to suffering. Eyestalk ablation in L. vannamei causes recoil reactions (Taylor et al. Reference Taylor, Vinatea, Ozorio, Schuweitzer and Andreatta2004) and in M. americanum causes tail-flicking and rubbing of the wound site (Diarte-Plata et al. Reference Diarte-Plata, Sainz-Hernández, Aguinága-Cruz, Fierro-Coronado, Polanco-Torres and Puente-Palazuelos2012), all of which are dampened by the use of anaesthetic (lidocaine). In recent years, experiments with ablation-free approaches by Zacarias et al. (Reference Zacarias, Carboni, Davie and Little2019, Reference Zacarias, Fegan, Wangsoontorn, Yamuen, Limakom, Carboni, Davie, Metselaar, Little and Shinn2021) have suggested that eyestalk ablation may not be necessary for economically viable shrimp aquaculture, and that avoiding it leads to better reproductive performance from the breeding females and more resilient offspring with lower mortality rates. Banning eyestalk ablation will be a crucial part of high-welfare shrimp aquaculture. As it does not appear that shrimp aquaculture companies in the UK use eyestalk ablation (industry contacts) there would be no major downside to banning eyestalk ablation there, but any immediate welfare benefit would be limited. In the UK, the welfare benefits of such a ban would be limited due to the small size of the industry and the fact that UK shrimp aquaculture companies do not appear to use eyestalk ablation (industry contacts), though for the same reasons there would also be no major downside to a ban. However, in other regions where the practice is still common, such as the US and Asia, such bans could have a greater impact.

Alongside this direct welfare harm, shrimp can show physiological and behavioural signs of distress when housed under inappropriate conditions, such as inappropriate salinity, low oxygen, high water turbidity, low temperature, and high stocking density (which can even lead to cannibalism) (Albalat et al. Reference Albalat, Zacarias, Coates, Neil and Planellas2022b; Pedrazzani et al. Reference Pedrazzani, Cozer, Quintiliano, Tavares, da Silva and Ostrensky2023; Wuertz et al. Reference Wuertz, Bierbach and Bögner2023). Diseases are also common and have clear welfare implications depending on the disease (Albalat et al. Reference Albalat, Zacarias, Coates, Neil and Planellas2022b). Some diseases are non-transmissible and can be caused by suboptimal environmental conditions, toxicity or nutritional deficiencies. Others are caused by a variety of pathogens and parasites and can lead to epidemic outbreaks that lead to mass mortality. The most common diseases include white spot disease, yellow head virus, and Vibrio spp bacterial infections (El-Saadony et al. Reference El-Saadony, Swelum, Abo Ghanima, Shukry, Omar, Taha, Salem, El-Tahan, El-Tarabily and Abd El-Hack2022).

To prevent welfare issues, as well as the obvious production losses, there are many alternative actions that may be taken, which have been reviewed elsewhere (Seethalakshmi et al. Reference Seethalakshmi, Rajeev, Kiran and Selvin2021; Abdel-Latif et al. Reference Abdel-Latif, Yilmaz, Dawood, Ringø, Ahmadifar and Yilmaz2022; El-Saadony et al. Reference El-Saadony, Swelum, Abo Ghanima, Shukry, Omar, Taha, Salem, El-Tahan, El-Tarabily and Abd El-Hack2022). Prophylactic antimicrobials may be added to the ponds via the feed, but these can lead to resistant strains of pathogens that can ultimately harm the shrimps and other species, including humans. Probiotics, prebiotics, vaccines and other biotechnological solutions have been suggested as more sustainable alternatives for the future, and their impact on shrimp welfare should be taken into account during development (Seethalakshmi et al. Reference Seethalakshmi, Rajeev, Kiran and Selvin2021). Ultimately, because disease risk is increased by use of high stocking densities, excessively warm temperatures, and poor water quality, farming shrimp under optimal conditions for their health and welfare and using good biosecurity practices will help prevent diseases and their associated welfare compromises. This can be difficult in practice and work will be required to determine optimal conditions that are also feasible in reality.

Lethal ‘stress tests’ carried out on small samples of larvae to check the quality of the larvae batch carry obvious welfare harms if larvae are sentient, through exposure to environmental stressors such as changes in salinity and temperature or exposure to toxins such as ammonia and formalin (Wuertz et al. Reference Wuertz, Bierbach and Bögner2023). Harvesting of animals involves stressful capture using nets or pumps, which triggers flight behaviour and physiological stress responses (Wuertz et al. Reference Wuertz, Bierbach and Bögner2023).

Historically, shrimp standards and best practice guidelines have incidentally included welfare components, such as disease, stocking density, and water quality, but this has not been their focus (e.g. Aquaculture Stewardship Council [ASC] 2023). Since publication of our original report, however, several welfare-based best practice guidelines and reviews have been published (Albalat et al. Reference Albalat, Zacarias, Coates, Neil and Planellas2022b; Crustacean Compassion 2023; Pedrazzani et al. Reference Pedrazzani, Cozer, Quintiliano, Tavares, da Silva and Ostrensky2023; Shrimp Welfare Project [SWP] 2024). Moving forward, we recommend further strengthening these guidelines, using the peer-reviewed literature to make more specific recommendations, and (where this is lacking) carrying out welfare science to build a better evidence base. This would complement research into the development of shrimp sentience across all life stages.

Lobsters, crayfish and crabs

Crab, crayfish and lobster farming occur on a smaller scale than shrimp farming, but are increasing rapidly. Of global crustacean aquaculture production in 2022, the second most common species after the white leg shrimp at 62.2%, was the red swamp crayfish (P. clarkii) at 23.3%, followed by mitten crabs (Eriocheir spp) at 6.4% (FAO 2024). Many of the welfare risks associated with aquaculture of crabs, crayfish and lobsters are shared with those of shrimps. Disease is again a significant threat to the welfare of these animals, with the specific diseases differing somewhat between species, and being most common in intensive systems with suboptimal environments and high stocking densities. Common diseases and parasites of farmed crabs, including the commercially important Chinese mitten crab (E. sinensis), mud crabs (Scylla spp), swimming crabs (Portunus spp), blue crabs (C. sapidus) and shore crabs (C. maenas), have been extensively reviewed by Coates and Rowley (Reference Coates and Rowley2022). Depending on the specific disease, signs of poor welfare included lethargy, limb loss, tremors, loss of appetite, failure to moult and mortality. As with shrimp aquaculture, reducing stocking density and providing near optimal conditions are vital for preventing or minimising the spread of such diseases. Antimicrobial stewardship will be important here, as with shrimp aquaculture. One approach is to dip the tail or the whole of wild-caught berried female H. gammarus into antimicrobial solution before introducing them into a hatchery, but there are concerns that this may disrupt their microbiome (Hinchcliffe et al. Reference Hinchcliffe, Agnalt, Daniels, Drengstig, Lund, McMinn and Powell2022). Research is needed to further understand how to prevent and treat diseases in these, in some cases relatively newly cultured, decapod species.

There are also welfare risks associated with the demand for ‘soft-shell’ crabs. These are newly moulted crabs of species most commonly comprising mud crabs (Scylla spp) in Asia, the Atlantic Blue Crab (C. sapidus) in the US and the blue swimming crab (Portunus pelagicus) in India. For most of these species, there is only a short window of a few hours following moulting during which the crabs can be harvested for the soft-shell market. Therefore, there is commercial pressure to be able to induce moulting in these crabs, and although no single method is yet to prove entirely effective, many potential methods are being used and optimised, as reviewed by Waiho et al. (Reference Waiho, Ikhwanuddin, Baylon, Jalilah, Rukminasari, Fujaya and Fazhan2021). Eyestalk ablation is one such method, which seems relatively ineffective and carries similar welfare risk to that in shrimps, so should be discontinued. Induction of moulting by removal of the walking legs, the claws, or both was compared in Scylla olivacea (Rahman et al. Reference Rahman, Asaduzzaman, Zahangir, Islam, Nahid, Jahan, Mahmud and Khan2020); in that study, the claws were manually snapped off, whereas the legs were cut to induce autotomy. Ablation of both claws significantly hastened moulting and also appeared to increase crab body size following the moults. Crabs with limbs removed did not show significantly greater mortality rates than controls. However, no measures of animal welfare were included in that study, and as described previously in Handling of wild-caught decapods during capture, transport and sale, declawing is of animal welfare concern and has been shown to increase crab mortality in other studies (Waiho et al. Reference Waiho, Ikhwanuddin, Baylon, Jalilah, Rukminasari, Fujaya and Fazhan2021). Most other methods involve the injection of moult regulation hormones (ecdysteroids, e.g. E20), phytoecdysteroids, melatonin or other substances; these can be effective, although they are still at the experimental stage and the effects on crab welfare unknown (Waiho et al. Reference Waiho, Ikhwanuddin, Baylon, Jalilah, Rukminasari, Fujaya and Fazhan2021). Feeding crabs sufficiently also hastens moulting compared with restricted food rations (Gong et al. Reference Gong, Huang, Yu, Li, Zeng and Ye2022). A further cause for welfare concern for soft-shell crabs is that, when harvested, they are usually placed into –20°C while still alive to be frozen before their shells harden. The welfare risks of freezing as a slaughter method, especially without prior stunning, are described above (Waiho et al. Reference Waiho, Ikhwanuddin, Baylon, Jalilah, Rukminasari, Fujaya and Fazhan2021).

The welfare needs of species that are relatively new to aquaculture may not yet be well understood, creating welfare risks as industry develops. For example, insufficient or inadequate food may impair growth, risk deficiency diseases and hunger, and potentially cause cannibalism (Harlıoğlu & Farhadi Reference Harlıoğlu and Farhadi2017; Hinchcliffe et al. Reference Hinchcliffe, Agnalt, Daniels, Drengstig, Lund, McMinn and Powell2022; Nankervis & Jones Reference Nankervis and Jones2022). It was noted that individually housed H. gammarus larvae grew more slowly than communally housed ones fed the same ration of dry pellets, which are not readily accepted by the animals; this implies that communally housed larvae may have supplemented their diet – presumably through cannibalism. Unlike many shrimp species, some decapod species also require darkness or shelters to thrive and reduce aggression (Shelley & Lovatelli Reference Shelley and Lovatelli2011; Yu et al. Reference Yu, Xiong, Ye, Li, Xiong, Liu and Zhang2020; Zhang et al. Reference Zhang, Zhu, Yu and Wang2022). It will be important that research and development activities in decapod aquaculture evaluate welfare-relevant metrics beyond solely production or economic outcomes. This requires careful selection of species with fewer potential welfare risks (Chiang & Franks Reference Chiang and Franks2024) as well as development of species-specific welfare guidelines prior to commercial-scale use (for a recent example of the development of a comprehensive welfare index for whiteleg shrimp [P. vannamei], see Pedrazzani et al. Reference Pedrazzani, Cozer, Quintiliano and Ostrensky2024).

Where they are farmed, the concerns for handling and transport described in the previous section will apply. There are also some additional concerns regarding appropriate housing conditions. For instance, insufficient holding space for rearing lobsters can slow growth, and limit development of a normal behavioural repertoire (Latini et al. Reference Latini, Nascetti, Grignani, Bello, Polverino, Canestrelli and Carere2023).