Capture Related Stress in Mackerel #2
In Norway, 1.3 million tonnes of fish were landed by commercial purse seiners in 2017. However, during the capture and slaughter process, fish are exposed to stresses such as crowding, hypoxia and rapid temperature change. Such stressors have the potential to negatively impact upon the animals’ short and long-term welfare. The purpose of these experiments is to increase our understanding of how current purse seine capture and slaughter practices affect the behaviour, physiology and resulting meat quality of Atlantic mackerel (Scomber scombrus). Mackerel supports an important purse seine fishery in Norway, but is a delicate species that is highly susceptible to stress. By understanding how mackerel responds to stress we hope to promote welfare friendly fishing practices that maximise: 1) survival potential if the catch is to be released and: 2) meat quality if the catch is to be retained, contributing towards a more sustainable and profitable Norwegian fishing industry.
This application is in support of the FHF project “Fangstkontroll in Notfiske”. Three replicates of three small schools of mackerel (consisting of 100 individuals in aquaculture net pens) will be exposed to typical purse seine capture crowding densities of either ~50 kg/m3 or ~180 kg/m3 (achieved by reducing the volume of the net pen) or a control (no crowding) for either 15 or up to a maximum of 60 minutes. Resulting behavioural, physiological and meat quality responses will be determined using camera observation, as well as blood, tissue and meat quality sampling. Mortality outcomes will be monitored in the control and ~50kg/m3 crowded groups.
The effect of slaughter method on meat quality will also be investigated after stressor treatments for subsamples of 10 fish taken from the net pen. Slaughter methods investigated will be: 1) a blow to head followed by brain spiking; 2) immersion in cold hypoxic seawater and 3) electrical stunning followed by immersion in cold hypoxic seawater. These experiments will also be replicated three times. Optimal field strength and duration for effective mackerel electrical stunning will be determined by examination of behavioural and reflex responses on 25 additional fish post stunning.
The number of mackerel involved in all experiments will total 900. Simulation of commercial conditions during capture and slaughter of pelagic fish can be regarded as “Considerable distress” as fish are exposed to hypoxic environments, rapid temperature changes and crowding to relatively high densities, inducing a level of distress and perhaps death. As we intend to study physiology and behaviour, there is no replacement for the use of live animals. We have therefore focused on reducing the number of animals required to an absolute minimum, by use of power analysis. Furthermore, as much data as possible will be collected from each experimental subject. The project will also reduce the severity of the experiments by avoiding chronic and acute suffering, by defining early stage endpoints. For the development of effective future legislation, these experiments are required in order to reveal, understand and compare the implications of current commercial fishing practices upon animal welfare.
This application is in support of the FHF project “Fangstkontroll in Notfiske”. Three replicates of three small schools of mackerel (consisting of 100 individuals in aquaculture net pens) will be exposed to typical purse seine capture crowding densities of either ~50 kg/m3 or ~180 kg/m3 (achieved by reducing the volume of the net pen) or a control (no crowding) for either 15 or up to a maximum of 60 minutes. Resulting behavioural, physiological and meat quality responses will be determined using camera observation, as well as blood, tissue and meat quality sampling. Mortality outcomes will be monitored in the control and ~50kg/m3 crowded groups.
The effect of slaughter method on meat quality will also be investigated after stressor treatments for subsamples of 10 fish taken from the net pen. Slaughter methods investigated will be: 1) a blow to head followed by brain spiking; 2) immersion in cold hypoxic seawater and 3) electrical stunning followed by immersion in cold hypoxic seawater. These experiments will also be replicated three times. Optimal field strength and duration for effective mackerel electrical stunning will be determined by examination of behavioural and reflex responses on 25 additional fish post stunning.
The number of mackerel involved in all experiments will total 900. Simulation of commercial conditions during capture and slaughter of pelagic fish can be regarded as “Considerable distress” as fish are exposed to hypoxic environments, rapid temperature changes and crowding to relatively high densities, inducing a level of distress and perhaps death. As we intend to study physiology and behaviour, there is no replacement for the use of live animals. We have therefore focused on reducing the number of animals required to an absolute minimum, by use of power analysis. Furthermore, as much data as possible will be collected from each experimental subject. The project will also reduce the severity of the experiments by avoiding chronic and acute suffering, by defining early stage endpoints. For the development of effective future legislation, these experiments are required in order to reveal, understand and compare the implications of current commercial fishing practices upon animal welfare.
Begrunnelse for etterevalueringen
Forsøket er klassifisert som betydelig belastende og må etterevalueres av Mattilsynet.
Etterevaluering
Good catch welfare depends on the development of indicators of stress and welfare that are appropriate and measurable in a real capture scenario. Establishing such operational welfare indicators will enable fishers to make informed, real-time decisions regarding fishing practices to minimize impacts upon the animals and thereby reduce the likelihood of negative outcomes. This experiment, to identify practical and informative stress and/or welfare indicators (S/WIs), has investigated how crowding (a catch-related stressor) affects more than thirty different stress metrics in mackerel. S/WIs that provided near real-time data and/or intuitively interpreted results show most promise as potential operational S/WIs, like skin colour change and some behavioural indicators, e.g. nearest neighbour distance, swimming activity and vitality (Breen et al, 2020).
The introduction of good welfare practices to commercial capture fisheries is not only ethically sound, it has real potential to make fisheries more sustainable by promoting meat quality and product shelf life, as well as reducing unwanted catches and collateral mortality.
A total 934 mackerel were used in this experiment. Of these 934 mackerel, 253 experienced mild treatment (as part of the control treatments, or as pre-treatment removals) and 681 experienced moderate or severe treatments (as part of the crowding treatments).
The original estimate for number of animals to be used was approximately 900, based on an estimate of approximately 100 mackerel per replicate, of which we planned nine: 3 controls, 3 moderate crowding, and 3 high & prolonged crowding treatments. However, early in the experiment, it became evident that our estimates of the number of fish entering a replicate cage during the transfer from the large (12x12x12m) stock cage were inaccurate; with us generally underestimating the actual numbers of fish transferred. Only when each cage was terminated, and each fish counted and measured, was it possible to accurately determine the true population size and biomass of each cage. To account for this error, the final high & prolonged treatment was abandoned.
Replacement – there have been no developments in this field of research which could replace the use of some or all of the animals.
Reduction – the results of this pilot study can be used to improve power analysis and simulations to better define the required number of replicates for future experiments. An additional sampling team could double the number of animals sampled during each treatment. This would improve the precision of estimates per replicate, which would ultimately reduce the total number of replicates required. However, more replicates would improve our understanding of the between-replicate variation, making the results and inferences more applicable to a general population.
Refinement - these experiments have built on previous experience to develop sound procedures of catching and handling individual and schools of mackerel, so that the impact upon each fish is minimal. However potential for improvement has also been identified, including a method to monitor crowding density would be informative and enable better control of the crowding treatment. Future experiments should investigate the use of the alternative welfare metrics investigated in this experiment (eg. vitality and skin colour change) to better define the welfare status of experimental subjects, and thus enable more informative endpoints.
The introduction of good welfare practices to commercial capture fisheries is not only ethically sound, it has real potential to make fisheries more sustainable by promoting meat quality and product shelf life, as well as reducing unwanted catches and collateral mortality.
A total 934 mackerel were used in this experiment. Of these 934 mackerel, 253 experienced mild treatment (as part of the control treatments, or as pre-treatment removals) and 681 experienced moderate or severe treatments (as part of the crowding treatments).
The original estimate for number of animals to be used was approximately 900, based on an estimate of approximately 100 mackerel per replicate, of which we planned nine: 3 controls, 3 moderate crowding, and 3 high & prolonged crowding treatments. However, early in the experiment, it became evident that our estimates of the number of fish entering a replicate cage during the transfer from the large (12x12x12m) stock cage were inaccurate; with us generally underestimating the actual numbers of fish transferred. Only when each cage was terminated, and each fish counted and measured, was it possible to accurately determine the true population size and biomass of each cage. To account for this error, the final high & prolonged treatment was abandoned.
Replacement – there have been no developments in this field of research which could replace the use of some or all of the animals.
Reduction – the results of this pilot study can be used to improve power analysis and simulations to better define the required number of replicates for future experiments. An additional sampling team could double the number of animals sampled during each treatment. This would improve the precision of estimates per replicate, which would ultimately reduce the total number of replicates required. However, more replicates would improve our understanding of the between-replicate variation, making the results and inferences more applicable to a general population.
Refinement - these experiments have built on previous experience to develop sound procedures of catching and handling individual and schools of mackerel, so that the impact upon each fish is minimal. However potential for improvement has also been identified, including a method to monitor crowding density would be informative and enable better control of the crowding treatment. Future experiments should investigate the use of the alternative welfare metrics investigated in this experiment (eg. vitality and skin colour change) to better define the welfare status of experimental subjects, and thus enable more informative endpoints.