Clupea harengus is a schooling species that inhabits the Atlantic ocean and the Baltic Sea. It forms big schools of similar sized IND, although sometimes ADULTS and JUVENILES get mixed in the same school. The schools are especially large during migrations to spawning grounds. Due to its small size and its schooling behaviour, C. harengus is one of the most frequently fished species in the world in terms of number of IND. Many countries have regulated the landings and some have closed the spawning grounds to ensure a restoration of the decimated populations that were suffering from overexploitation. C. harengus has an important role in the ecosystem, since it incorporates zooplankton into the trophic chain and is then predated by a vast number of larger species.

Fisheries target ADULTS, SPAWNERS, and JUVENILES. The most common fishing method nowadays is purse seine. JUVENILES are also traditionally caught by different types of methods. Decreasing distance to neighbours – especially during crowding – and contact with the gear are the most frequent welfare hazards during catching with purse seine. Avoiding crowding or keeping it short – particularly at the peak density – may avoid a steep decrease in welfare. Usually, IND are pumped out of the net onto the vessel which allows them to stay in water, but the arrival on deck may be accompanied by injuries and stress. If not already crushed, the most common ways to die are by asphyxia or hypothermia. A protocol for stunning and slaughter is urgently needed.

To find the fishes in their habitat, there are different techniques to localise them (e.g., echosound/sonar, chasing).

What is the probability of avoiding a decrease in welfare during the process of searching for the species?

Likelihood

Potential

Certainty

Catching methods differ in the way they are set up and consequently in the time it takes for setting them.

What is the probability of avoiding a decrease in welfare during the process of setting the catching method?

Likelihood

Potential

Certainty

Given the principle of the catching method, the gear (with the fishes caught) may be hauled vertically or horizontally in the water for a certain amount of time and distance.

What is the probability of avoiding a decrease in welfare during catching?

Likelihood

Potential

Certainty

The process of bringing the fishes out of the water also depends on the catching method and may, thus, differ in duration and impact (e.g., netting, brailing, pumping, lifting).

What is the probability of avoiding a decrease in welfare during emersion?

Likelihood

Potential

Certainty

There are different ways to remove the fishes from the gear (e.g., unhooking, disentangling, dropping).

What is the probability of avoiding a decrease in welfare during release from the gear?

Likelihood

Potential

Certainty

Not all specimens of the target species are equally sought after, e.g., when they are undersized, of wrong sex, wrong age, damaged or over quota. Measures to prevent this bycatch still in the water may include slipping in purse seine, window in net, opening in trap, etc.

What is the probability of avoiding a decrease in welfare with the help of bycatch-avoiding measures?

Likelihood

Potential

Certainty

Given the species specificity of the method, sorting might be necessary once the catch arrives on deck.

What is the probability of avoiding a decrease in welfare during sorting?

Likelihood

Potential

Certainty

If bycatch of the target species could not be prevented, the individuals could still be returned from the gear/deck to the water.

What is the probability of avoiding a decrease in welfare during discarding?

Likelihood

Potential

Certainty

Given how long it takes the vessel to return to the harbour, the caught fishes have to be stored for a certain amount of time. This storing happens most frequently with the fishes still being alive, but differing in the type of storage containers and medium (ice, brine, air, etc.).

What is the probability of avoiding a decrease in welfare during storing?

Likelihood

Potential

Certainty

Ideally, slaughter a) immediately follows stunning (i.e., while the individual is unconscious), b) happens according to a clear and reproducible set of instructions verified under catching conditions, and c) avoids pain, suffering, and distress.

What is the probability of avoiding a decrease in welfare during stunning/slaughter?

Likelihood

Potential

Certainty

Sometimes the literature does not specify the welfare hazards and the catching step that lead to hazard consequences.

What are consequences that decrease welfare during uncategorised steps of the catching process?

The focus of this WelfareCheck | catch is the welfare of the target species. There could be improvements to the catching method that are not covered by the criteria and could include prevention of overexploitation, prevention of bycatch of non-target species, e.g., pingers to deter cetaceans, and avoiding damage to the environment, though.

What are these improvements?

• target species: closure of spawning grounds on Trinity Ledge and in Scots Bay 28.
  • How to improve: closure of spawning grounds
• target species: in Canada, in 2017, quota reduction in Southwest Nova Scotia management area as part of a population recovery plan, although the outcome was not the desired one 48. Decline of key spawning components and stability of the allowable catch (at low levels from 2011-2016) in 2018 48.
  • How to improve: quota reduction
• target species: in the US, control of catching areas and limitation of landings 49.
  • How to improve: control of catching area
• target species: in Norway, sizes <25 cm are prohibited in the spawning season 50.
  • How to improve: catch restriction during spawning season
• non-target species: in Canada, mitigation measures are in place to reduce harm, mortality or harrassment of the following species at risk with which the C. harengus fisheries interact 51: 
  • Northern wolffish (Anarhichas denticulatus) – threatened
  • Spotted wolffish (Anarhichas minor) – threatened
  • Atlantic wolffish (Anarhichas lupus) – special concern
  • Leatherback sea turtle (Dermochelys coriacea) – endangered
  • Loggerhead sea turtle (Caretta caretta) – endangered
  • White shark (Carcharodon carcharias) – endangered
  • North Atlantic right whale (Eubalaena glacialis) – endangered
  • Northern bottlenose whale (Hyperoodon ampullatus) – endangered
  • Sowerby’s beaked whale (Mesoplodon bidens) – special concern. 
  • How to improve: mitigation measures
• non-target species: river herring (including Alosa pseudoharengus and Alosa aestivalis) and shad (including Alosa sapidissima and Alosa mediocris) are harvested as non-target species, as they may co-occur seasonally with C. harengus52. River herring are either discarded at sea (bycatch) or, because they closely resemble C. harengus, they are retained and sold as part of the herring catch (incidental catch) 52. Catch caps are enacted in the US to protect these species 52.
  • How to improve: catch caps

How much is this species targeted annually?

As a consequence of welfare hazards, fishes may suffer from physical damage (e.g., barotrauma, abrasions/lacerations/wounds, ecchymosis, desiccation).

Where in the catching process does physical damage occur and how to avoid it?

Physical damage occurs most frequently during decreasing distance to neighbours and contact with the gear or storing containers. To avoid it during catching/hauling, prefer mesh size that avoids catching JUVENILES, decrease bycatch by slipping and fishing in groups of fishing folks, prefer catching at night, hauling the purse seine slowly, taking especially care to avoid high densities during crowding in last 20% of retrieving the purse seine. To avoid it during storing, prefer live-storing in ≥4,000 m³ net pens in calm waters or in onboard cooling tanks in ice.

1.1 Barotrauma

Extruded eyes/guts: no data found yet.

• IND can adjust to pressures greater than surface pressure when anaesthetised in nature thanks to the unusual swimbladder anatomy 13. IND can also survive pressure increases of 115% from their adjusted pressure at a rate of 6 cm Hg/s 13. IND "rising at a rate of 11 m/min at 100 m depth, at 6 m/min at 50 m or at 2 m/min at 10 m would have no limit placed on the extent of their upward movement by too great an increase in buoyancy or through rupture of the swimbladder” 13.
  • Catching step:  Catching
  • How to improve: not faster than 11 m/min at 100 m depth, 6 m/min at 50 m or 2 m/min at 10 m

Bleeding: no data found yet.

1.2 Damages/abrasions/lacerations/wounds

• Given that IND are observed at the surface 16, eyes adapting to the change in light during the catching process is probable 10. Further research needed on eye damage related to exposure to environmental light or UV light.
  • Catching step:  Emersion

• Possible risk of abrasion against the netting for IND on the outer edge of the shoal during crowding 20.
  • Catching step:  Emersion

• De-scaling is a cause of mortality within 1-4 days 11.
  • Catching steps:  Catching Emersion Release from gear
• IND caught at night with artificial light might reduce the physical contact with the net and therefore lethal scale loss because they might behave more carefully than those caught during daylight 12. 
  • Catching step:  Catching
  • How to improve: prefer catching at night
• Scale loss and skin injuries (bruises and lacerations) after 10 min of crowding in purse seine 20. Crowded groups had significantly higher scale loss than control groups 21. <10% scale loss after 10 min crowding at 79.8, 203.5, and 367.1 kg/m³ of crowding, without significant differences among groups 21. Intact scale pockets even when the scales were lost, suggesting that the osmoregulatory capabilities of the skin may not have been severely compromised by the scale loss 21.
  • Catching step:  Emersion
• Transfer from vessels to net pens and stored there alive for several weeks before delivery to processing plants 12. For 60 kg catch in 30 m³ netpen pulled up for 3 min: immediate scale loss in average 75% of skin, probably followed by lethal osmoregulation difficulties, 95% mortality in the next 24 h, no survivors after 120 h (5 days) 12. For 700 kg catch in 1,000 m³ netpen pulled up for 3 min: immediate scale loss in average 75% of skin, probably followed by lethal osmoregulation difficulties, 30% mortality in 48 h, 95% mortality after 9 days 12.
  • Catching steps:  Emersion Storing
• If stored in onboard cooling tanks, loose scales due to friction between IND and therefore less shiny skin than IND stored in ice 41↶42.
  • Catching step:  Storing
  • How to improve: store in ice
• Transfer from vessels to net pens and stored there alive for several weeks before delivery to processing plants 12. For 100 kg catch hold in 30 m³ net pen and without any net pull-up: 1% mortality in 24 h, 98% mortality in 120 h (5 days), dead IND had scale loss in 40% of skin 12. For 2,300 kg catch in 1,000 m³ net pen and without any net pull-up: 12% mortality after 9 days, dead IND had scale loss in 25% of skin 12. Lower mortality the larger the net pen: from 70-98% mortality after 120 h in 30 m³ net pens to 10-80% mortality in 1,000 m³ net pens to 0-20% mortality in 4,000 or 7,000 m³ net pens; no correlation with density and only marginal influence of mesh quality 12. Herring that die during the storage period in net pens are usually discarded 12.
  • Catching step:  Storing
  • How to improve: prefer net pens ≥4,000 m³ for storage

• LAB: electrical stunning induced spine breaks in ≤60% of IND as well as hematomas in the fillets 47. Given this outcome and given that immedate slaughter after stunning has not been studied yet, electrical stunning cannot be recommended 10. 
  • Catching step:  Slaughter

• Given the principle of purse seine to haul the net close to the ship and crowd the IND before suctioning them into the storage space of the ship 6789, hazard consequences are probable 10. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching step:  Catching
• JUVENILES getting stuck in the net is probable 78.
  • Catching steps:  Catching Emersion Release from gear Bycatch avoidance
  • How to improve: prefer mesh size that avoids catching JUVENILES given body diameter in season and region
• Below-critical densities in median (190 t) and large (620-1,100 t) catches until 80% of seine is hauled 14. >80% hauling: highly uncertain predictions about seine volume 14 due to complex shapes with large folds that seine may take 15↶14; unexpectedly high densities possible as seine is hauled in completely 14. Further research needed for types of hazard consequences.
  • Catching steps:  Catching Emersion
  • How to improve: take especially care to avoid high densities during crowding in last 20% of retrieving purse seine
• Given that JUVENILES aggregate with ADULTS in schools 28, aggression between conspecifics is unlikely 10.
  • Catching step:  Emersion
• Probably no sorting but direct pumping into the storage space of the ship 789 (although can also be lifted with scoop net out of purse seine 7). Given the speed with which IND arrive on deck or slide down chutes respectively and based on the crowding density, hazard consequences are probable 10. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching steps:  Emersion Sorting
• Escaping behaviour of IND in slipping events is influenced by the vessel releasing the IND, the amount of IND being slipped, how long the discharge opening had been open, and the particular slipping event 33. No escapes in 73% of observed slippling events; if IND escaped, then a) in orderly way in large groups (59%) – good for welfare due to low probability of injuries by touching each other or the gear – or b) in unorderly way in large groups (24%) – bad for welfare due to a higher chance of getting damage by collisions with each other or the gear; IND escaping individually or in small groups was rare (15%) 33.
  • Catching step:  Bycatch avoidance
• Although usually similar-sized IND in schools 37, sometimes mix of small and larger size, resulting in slipping small IND21. Slipping also when school in purse seine very dense 21. Slipping itself is stressful, e.g., by combining increased swimming activity with physical damage, which may result in delayed mortality 23. Swimming to more favourable environment may make recovery possible 23. Slipping operations recommended as best practice to reduce stress and promote survival in released catches 38↶39.
  • Catching step:  Bycatch avoidance
  • How to improve: slipping
• In Canada, since 1976, fishing by groups of fishermen has been encouraged to avoid dumping and discarding 28.  
  • Catching step:  Bycatch avoidance
  • How to improve: fishing in groups of fishing folks
• 121 t discarded at sea in 84 trips in 1995-2006 40.
  In Canada, since 1976, fishing by groups of fishermen has been encouraged to avoid dumping and discarding 28.
  • Catching step:  Discarding
  • How to improve: fishing in groups of fishing folks
• In storage tanks with ice or ice water, rough handling, such as bad weather disturbances in the ship, cause collisions and thereby physical damages, resulting in bloodstains and dull skin 42.
  • Catching step:  Storing
  • How to improve: prefer calm waters

1.3 Ecchymosis

• Scale loss and skin injuries (bruises and lacerations) after 10 min of crowding in purse seine 20. Crowded groups had significantly higher scale loss than control groups 21. <10% scale loss after 10 min crowding at 79.8, 203.5, and 367.1 kg/m³ of crowding, without significant differences among groups 21. Intact scale pockets even when the scales were lost, suggesting that the osmoregulatory capabilities of the skin may not have been severely compromised by the scale loss 21.
  • Catching step:  Emersion

1.4 Desiccation (surface issue)

• Given emersion to air, desiccation is probable 10.
  • Catching step:  Emersion

Stress is a likely consequence of various welfare hazards. It may be measured via physiological parameters (cortisol, glucose, lactate, etc.) or behavioural observations (e.g., opercular movement).

Where in the catching process does stress occur and how to avoid it?

Stress occurs most frequently during decreasing distance to neighbours and contact with the gear. To avoid it, fish in groups of fishing folks, use passive acoustics for prospection, slip bycatch preferably in an early phase, keep crowding as short as possible, preferably <10 min, taking especially care to avoid high densities during crowding in last 20% of retrieving the purse seine.

• Given possible oxygen shortage in IND in the middle of a shoal during crowding 22↶2324↶232021, hazard consequences are probable 10.
  LAB: hypoxic environments increased swimming activity, with a peak in velocity during severe hypoxia (at 15-34% oxygen saturation), followed by decrease in swimming speed until school disruption (at 12-25% oxygen saturation) 25.
  LAB: school dimensions (length, width, depth, area, volume) increased during severe hypoxia (20% oxygen saturation), but school dynamics were not affected: IND in the front tried to remain in the front, probably due to the cost of changing positions while in respiratory distress 18.
  LAB: decrease in water oxygen pressure increased plasma cortisol and plasma osmolality above the normoxic level at pressures ≤8.5 kPa 26. At 4.2 and 6.4 kPa, extremely high plasma cortisol with levels comparable to stressful exercise 26. At ≤12.7 kPa, reduced plasma glucose by hypoxia 26.
  • Catching steps:  Emersion Bycatch avoidance
• Reduced plasma glucose 21 and increased cortisol, lactate, chloride, sodium, and potassium ions 20 after 10 min of crowding, indicating an incapacity to restore homestasis and a sign of approaching physical exhaustion, which can be a cause of death 21. Increased stress (anaerobic muscle activity followed by increase in blood lactate) and muscle pH with increased crowding duration (0-30 min) 27. Lactate returns to control levels 2 days after crowding 21. Reduced physical condition lasts for at least 4 days 20. Cortisol and blood ion levels increase for at least 4-5 days after crowding while IND are caged in net pens 21.
  • Catching step:  Emersion
  • How to improve: keep crowding as short as possible, preferably <10 min

Opercular movement: no data found yet.

• WILD/LAB: schools release air from their swim bladder when they ascend and descend, and it forms clouds of bubbles that can be observed at the surface 4. This release is accompanied by sound which could be used by fishermen to detect them using passive acoustics 4.
  • Catching step:  Prospection
  • How to improve: passive acoustics
• Given the principle of purse seine to haul the net close to the ship and crowd the IND before suctioning them into the storage space of the ship 6789, hazard consequences are probable 10. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching step:  Catching
• Below-critical densities in median (190 t) and large (620-1,100 t) catches until 80% of seine is hauled 14. >80% hauling: highly uncertain predictions about seine volume 14 due to complex shapes with large folds that seine may take 15↶14; unexpectedly high densities possible as seine is hauled in completely 14. Further research needed for types of hazard consequences.
  • Catching steps:  Catching Emersion
  • How to improve: take especially care to avoid high densities during crowding in last 20% of retrieving purse seine
• Given the principle of purse seine to catch IND at the surface and slowly haul the seine close to the ship 6789 and thus no way of fleeing predators, there is the risk of stress by predators being present in or close to the net 10.
  • Catching step:  Emersion
  • How to improve: for ways to avoid predators in the net → 6.7. Other.
• Probably no sorting but direct pumping into the storage space of the ship 789 (although can also be lifted with scoop net out of purse seine 7). Given the speed with which IND arrive on deck or slide down chutes respectively and based on the crowding density, hazard consequences are probable 10. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching steps:  Emersion Sorting
• Given no evolutionary adaptation to experiencing own weight in air 29, hazard consequences following emersion are probable 10. Further research needed on type of hazard consequences.
  • Catching step:  Emersion
• Swimming activity is probably reliable behavioural indicator of stress in FISHES following crowding, particularly tail beat frequency 23. Measuring tail beat frequency before crowding would provide the baseline against which to compare tail beat frequency during crowding: Increasing beyond a threshold (20% in this study) likely increases mortality 23. In Norway, this catch cannot be discarded because laws prohibit to release dead or dying IND34↶23. Tail beat frequency below threshold indicates low mortality and allows for slipping 23. Further research needed on relationship between tail beat frequency and mortality during crowding to set up threshold 23.
  • Catching step:  Bycatch avoidance
  • How to improve: measure tail-beat frequency before crowding
• Escapees and surviving discarded IND will be prone to be predated since they are disoriented, stressed, and weakened after the catching process and release, and seabirds and other predators might gather near fishing boats 29.
  • Catching steps:  Bycatch avoidance Discarding
• Given that JUVENILES aggregate with ADULTS in schools 28 and the principle of purse seine is to catch whole schools 78, there is a risk of bycatch (accidental catch of undersized, wrong sex, wrong age, damaged, over quota IND) of the target species 10. In the US, bycatch is reported to be low, consisting mostly of undersized IND, SPAWNERS, or IND caught after the vessel has filled to capacity 35.  After setting the net and in the initial stages of hauling, skippers or captains can get an impression of the catch by looking at a sample of IND that come to the surface 36 or that they catch with pole and line 89. At that point, they can abort the process if the catch does not include the target species and before the school is crowded 36.
  • Catching step:  Bycatch avoidance
  • How to improve: sampling
• Although usually similar-sized IND in schools 37, sometimes mix of small and larger size, resulting in slipping small IND21. Slipping also when school in purse seine very dense 21. Slipping itself is stressful, e.g., by combining increased swimming activity with physical damage, which may result in delayed mortality 23. Swimming to more favourable environment may make recovery possible 23. Slipping operations recommended as best practice to reduce stress and promote survival in released catches 38↶39.
  • Catching step:  Bycatch avoidance
  • How to improve: slipping
• In Canada, since 1976, fishing by groups of fishermen has been encouraged to avoid dumping and discarding 28.  
  • Catching step:  Bycatch avoidance
  • How to improve: fishing in groups of fishing folks
• 121 t discarded at sea in 84 trips in 1995-2006 40.
  In Canada, since 1976, fishing by groups of fishermen has been encouraged to avoid dumping and discarding 28.
  • Catching step:  Discarding
  • How to improve: fishing in groups of fishing folks

The difference between temperature in water and air may induce a thermal shock.

Where in the catching process does temperature shock occur and how to avoid it?

Temperature shock may occur during catching/hauling and storing. To avoid it, prefer air temperatures ≥0 °C and ≤18 °C as well as immediate stunning followed by slaughter while still unconscious.

• IND have been observed behaving normally at temperature range -0.3-18 °C 16. Upper lethal temperature (i.e., 50% of tested IND died when they were exposed to that temperature for 48h): 19.5 °C or 21.2 °C depending on size (larger IND die faster at higher temperature than smaller ones) 16. In a preliminary study, 87% survived temperatures of -1 °C 16.
  Given this information, encountering IND at the ocean surface, the change in temperature between water and boat surface will probably not cause temperature shock in most cases, except temperature on board <-1 °C or >21 °C 10. Given that in some seasons, IND live below the thermocline 171819, it is possible that they cannot adapt to the rapid change in temperature that would occur during the lifting of the net from below the thermocline to the surface and therefore suffer from temperature shock 10. Further research needed on the rate that C. harengus can adapt to temperature changes without decreasing welfare.
  • Catching step:  Catching
  • How to improve: prefer air temperatures ≥0 °C and ≤18 °C
• Given pumping on board into tanks with refrigerated sea water (-1 °C) 4327 and transporting to shore for 12 h 44↶2845↶28 or 2-3 days 43, temperature shock is probable 10.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious

The quick transition from one salinity level to another may lead to osmoregulatory distress.

Where in the catching process does osmoregulatory distress occur and how to avoid it?

Osmoregulatory distress may occur during catching/hauling, emersion, and storing. Further research needed for ways to avoid it.

• Given that IND may be found just below or in the halocline, in areas with stratified water column 17, osmoregulatory distress is possible when they are brought to the surface 10. Further research needed on the rate C. harengus adapts to osmotic changes without decreasing welfare and on reports of osmoregulatory distress after purse seining.
  • Catching step:  Catching
• Unable to regain osmoregulatory ability and homeostasis in at least 4 days after 10 min of crowding 20.
  • Catching step:  Emersion
• Transfer from vessels to net pens and stored there alive for several weeks before delivery to processing plants 12. For 60 kg catch in 30 m³ netpen pulled up for 3 min: immediate scale loss in average 75% of skin, probably followed by lethal osmoregulation difficulties, 95% mortality in the next 24 h, no survivors after 120 h (5 days) 12. For 700 kg catch in 1,000 m³ netpen pulled up for 3 min: immediate scale loss in average 75% of skin, probably followed by lethal osmoregulation difficulties, 30% mortality in 48 h, 95% mortality after 9 days 12.
  • Catching steps:  Emersion Storing

Removing an individual from its home ground and social group and subjecting it to a potentially stressful catching event may result in disorientation.

Where in the catching process does disorientation occur and how to avoid it?

Disorientation may occur during displacement. Further research needed for ways to avoid it.

• Escapees and surviving discarded IND will be prone to be predated since they are disoriented, stressed, and weakened after the catching process and release, and seabirds and other predators might gather near fishing boats 29.
  • Catching steps:  Bycatch avoidance Discarding

Lack of oxygen is a likely consequence for aquatic species facing removal from the water.

Where in the catching process does asphyxia occur and how to avoid it?

Asphyxia may occur during decreasing distance to neighbours as well as during slaughter. To avoid it during slaughter, prefer immediate stunning followed by slaughter while still unconscious. For the other case, further research needed for ways to avoid it.

• Given possible oxygen shortage in IND in the middle of a shoal during crowding 22↶2324↶232021, hazard consequences are probable 10.
  LAB: hypoxic environments increased swimming activity, with a peak in velocity during severe hypoxia (at 15-34% oxygen saturation), followed by decrease in swimming speed until school disruption (at 12-25% oxygen saturation) 25.
  LAB: school dimensions (length, width, depth, area, volume) increased during severe hypoxia (20% oxygen saturation), but school dynamics were not affected: IND in the front tried to remain in the front, probably due to the cost of changing positions while in respiratory distress 18.
  LAB: decrease in water oxygen pressure increased plasma cortisol and plasma osmolality above the normoxic level at pressures ≤8.5 kPa 26. At 4.2 and 6.4 kPa, extremely high plasma cortisol with levels comparable to stressful exercise 26. At ≤12.7 kPa, reduced plasma glucose by hypoxia 26.
  • Catching steps:  Emersion Bycatch avoidance

• Given direct pumping into the storage space of the ship 6789, probably no stunning and slaughter but asphyxia 10. Given storing on ice, asphyxia 4327. Given storing in ice 42 or ice water 424327, probably hypothermia 10.
  • Catching step:  Slaughter
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious

Loss of water is another likely consequence of exposing aquatic species to air.

Where in the catching process does dehydration occur and how to avoid it?

There is no conclusion yet.

Unspecified: no data found yet.

In an attempt to escape the situation of being caught, many individuals struggle and resist until they are exhausted.

Where in the catching process does fatigue/exhaustion occur and how to avoid it?

Fatigue/exhaustion may occur at prospection, after slipping, and during emersion. To avoid it during prospection, use submerged light shortly after dusk, but only for short times and in colder waters. To avoid it during emersion, keep crowding as short as possible, preferably <10 min. For the other case, further research needed for ways to avoid it.

• Escapees and surviving discarded IND will be prone to be predated since they are disoriented, stressed, and weakened after the catching process and release, and seabirds and other predators might gather near fishing boats 29.
  • Catching step:  Bycatch avoidance

Oxidative stress: no data found yet.

• LAB: submerged light was more effective at attracting IND than light above the surface, and fishing with light is more effective shortly after dusk 5. A few IND influenced by the light might lead the whole shoal to it 5. Continued exposure to light to attract IND might cause them fatigue 5. Increased temperature results in weakened attraction to light, therefore fishing in warmer waters (depending on season or fishing area) might affect the success of the attracting technique 5.
  • Catching step:  Prospection
  • How to improve: submerged light shortly after dusk, but only for short times and in colder waters
• Reduced plasma glucose 21 and increased cortisol, lactate, chloride, sodium, and potassium ions 20 after 10 min of crowding, indicating an incapacity to restore homestasis and a sign of approaching physical exhaustion, which can be a cause of death 21. Increased stress (anaerobic muscle activity followed by increase in blood lactate) and muscle pH with increased crowding duration (0-30 min) 27. Lactate returns to control levels 2 days after crowding 21. Reduced physical condition lasts for at least 4 days 20. Cortisol and blood ion levels increase for at least 4-5 days after crowding while IND are caged in net pens 21.
  • Catching step:  Emersion
  • How to improve: keep crowding as short as possible, preferably <10 min
• Escapees and surviving discarded IND will be prone to be predated since they are disoriented, stressed, and weakened after the catching process and release, and seabirds and other predators might gather near fishing boats 29.
  • Catching step:  Discarding

The process of being caught probably induces states not unlike emotions.

Where in the catching process do emotion-like states occur and how to avoid them?

IND may be startled during prospection. To avoid it, prefer active sonar in low frequencies (not >100 Hz).

9.1 Fear (continuum up to panic)

Freeze: no data found yet.

Avoidance behaviour: no data found yet.

Escape manoeuvres: no data found yet.

• LAB: startled by a 10 cycle of a sine wave of 100 Hz 2, by sounds above 4 kHz 3.
  • Catching step:  Prospection
  • How to improve: LAB: avoid sound from 100 Hz on upwards

Unspecified: no data found yet.

9.2 Other

Unspecified: no data found yet.

Although killing is the ultimate goal of fisheries, many mortalities happen unwanted - even resulting in discards - and unregulated, without avoiding prolonged suffering.

Where in the catching process does mortality occur and how to avoid it?

Mortality occurs most frequently during decreasing distance to neighbours and contact with the gear. To avoid it during catching/hauling and emersion, prefer IND of ≥30 cm, keeping crowding as short as possible, preferably <10 min at densities <51 kg/m³, and taking especially care to avoid high densities during crowding in last 20% of retrieving the purse seine. To avoid it for bycatch species, prefer fishing in groups of fishing folks, use slipping in an early phase, and ban discarding of dead IND. To avoid it during storing, prefer live-storing in ≥4,000 m³ net pens in calm cold waters outside hibernating areas in autumn and towing them inshore slowly (≤0.5-0.6 m/s). 

• Given the principle of purse seine to haul the net close to the ship and crowd the IND before suctioning them into the storage space of the ship 6789, hazard consequences are probable 10. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching step:  Catching
• De-scaling is a cause of mortality within 1-4 days 11.
  • Catching steps:  Catching Emersion Release from gear
• Below-critical densities in median (190 t) and large (620-1,100 t) catches until 80% of seine is hauled 14. >80% hauling: highly uncertain predictions about seine volume 14 due to complex shapes with large folds that seine may take 15↶14; unexpectedly high densities possible as seine is hauled in completely 14. Further research needed for types of hazard consequences.
  • Catching steps:  Catching Emersion
  • How to improve: take especially care to avoid high densities during crowding in last 20% of retrieving purse seine
• Reduced plasma glucose 21 and increased cortisol, lactate, chloride, sodium, and potassium ions 20 after 10 min of crowding, indicating an incapacity to restore homestasis and a sign of approaching physical exhaustion, which can be a cause of death 21. Increased stress (anaerobic muscle activity followed by increase in blood lactate) and muscle pH with increased crowding duration (0-30 min) 27. Lactate returns to control levels 2 days after crowding 21. Reduced physical condition lasts for at least 4 days 20. Cortisol and blood ion levels increase for at least 4-5 days after crowding while IND are caged in net pens 21.
  • Catching step:  Emersion
  • How to improve: keep crowding as short as possible, preferably <10 min
• Tail beat frequency (proxy for fish activity) increased with crowding density in a purse seine study under captive conditions: with lowest mean tail beat frequencies in the control groups (1.5-3.3 kg/m³ or 6.2-13.6 IND/m³) and lowest crowded group (51 kg/m³) and the highest mean frequency at the highest crowding density of 351 kg/m³ (1,565 IND/m³) 23. Mortality increased as tail beat frequency increased with largest increase at 200-247 kg/m³ during crowding with tail beat increasing by 0.1 tail beats/second, mortality increasing by 17% 23. Sample was taken on wild-caught IND that were kept in net for behaviour obsersations and least stressed IND, since the most stressed IND might have died in advance and therefore were not part of the study 23.
  • Catching step:  Emersion
  • How to improve: avoid densities >51 kg/m³
• Increasing mortality with increasing crowding density during 10 min of crowding: 1.6-1.8% mortality at 58-142 kg/m³, 27.9% mortality at 221 kg/m³, 50.7-52.0% mortality at 403-478 kg/m³20. Crowding densities <100 kg/m³ did not result in any additional mortality compared to control groups 21. Different results might be found in different weather conditions 2021.
  • Catching step:  Emersion
  • How to improve: keep crowding density as low as possible, preferably <100 kg/m³
• Mortality during crowding is size and body condition related 21: for IND sized 20-31 cm, smaller IND2021 and IND with lower condition were more susceptible 21.
  • Catching step:  Emersion
  • How to improve: prefer larger IND of ≥30 cm and maintain condition as best as possible
• Given that JUVENILES aggregate with ADULTS in schools 28, aggression between conspecifics is unlikely 10.
  • Catching step:  Emersion
• Transfer from vessels to net pens and stored there alive for several weeks before delivery to processing plants 12. For 60 kg catch in 30 m³ netpen pulled up for 3 min: immediate scale loss in average 75% of skin, probably followed by lethal osmoregulation difficulties, 95% mortality in the next 24 h, no survivors after 120 h (5 days) 12. For 700 kg catch in 1,000 m³ netpen pulled up for 3 min: immediate scale loss in average 75% of skin, probably followed by lethal osmoregulation difficulties, 30% mortality in 48 h, 95% mortality after 9 days 12.
  • Catching steps:  Emersion Storing
• Some IND are catapulted away from the chute and lie on deck, some IND are kicked or stood on by fishing folks 678. Further research needed on gear settings, on mortality rate, and on how to avoid mortality.
  • Catching steps:  Release from gear Sorting Discarding
• Escapees and surviving discarded IND will be prone to be predated since they are disoriented, stressed, and weakened after the catching process and release, and seabirds and other predators might gather near fishing boats 29.
  • Catching steps:  Bycatch avoidance Discarding
• Although usually similar-sized IND in schools 37, sometimes mix of small and larger size, resulting in slipping small IND21. Slipping also when school in purse seine very dense 21. Slipping itself is stressful, e.g., by combining increased swimming activity with physical damage, which may result in delayed mortality 23. Swimming to more favourable environment may make recovery possible 23. Slipping operations recommended as best practice to reduce stress and promote survival in released catches 38↶39.
  • Catching step:  Bycatch avoidance
  • How to improve: slipping
• Slipping in late phase of hauling may produce high rates of mortality that gets unaccounted for 21. Release in earlier phase may be acceptable, as C. harengus tolerates crowding well at lower densities 21.
  • Catching step:  Bycatch avoidance
  • How to improve: slipping in early phase
• In Canada, since 1976, fishing by groups of fishermen has been encouraged to avoid dumping and discarding 28.  
  • Catching step:  Bycatch avoidance
  • How to improve: fishing in groups of fishing folks
• 121 t discarded at sea in 84 trips in 1995-2006 40.
  In Canada, since 1976, fishing by groups of fishermen has been encouraged to avoid dumping and discarding 28.
  • Catching step:  Discarding
  • How to improve: fishing in groups of fishing folks
•  In Norway, laws prohibit to release dead or dying IND34↶23.
  • Catching step:  Discarding
  • How to improve: ban discards of dead IND
• Transfer from vessels to net pens and stored there alive for several weeks before delivery to processing plants 12. For 100 kg catch hold in 30 m³ net pen and without any net pull-up: 1% mortality in 24 h, 98% mortality in 120 h (5 days), dead IND had scale loss in 40% of skin 12. For 2,300 kg catch in 1,000 m³ net pen and without any net pull-up: 12% mortality after 9 days, dead IND had scale loss in 25% of skin 12. Lower mortality the larger the net pen: from 70-98% mortality after 120 h in 30 m³ net pens to 10-80% mortality in 1,000 m³ net pens to 0-20% mortality in 4,000 or 7,000 m³ net pens; no correlation with density and only marginal influence of mesh quality 12. Herring that die during the storage period in net pens are usually discarded 12.
  • Catching step:  Storing
  • How to improve: prefer net pens ≥4,000 m³ for storage
• Higher temperature increases general activity in C. harengus, which in turn tends to cause dispersal 5. Higher mortality after 120 h storing in net pens in autumn than winter could indicate lower activity in lower temperatures and therefore less contact with the net 12.
  • Catching step:  Storing
  • How to improve: prefer colder waters for fisheries, otherwise higher activity of IND may lead to more damage
• Higher mortality after 120 h storing in net pens in autumn at hibernating areas than in winter at spawning grounds could indicate higher ability to tolerate physical contact with the net during spawning 12.
  • Catching step:  Storing
  • How to improve: avoid catching at hibernating areas in autumn
• The lower the towing speed with which the 1,000 m³ storage net pens were towed inshore the lower the mortality after 120 h: 0-2% mortality at 0.5-0.6 m/s versus 10-20% mortality at 0.8-1.0 m/s 12.
  • Catching step:  Storing
  • How to improve: towing storage pens inshore slowly (≤0.5-0.6 m/s)

When it is difficult to assign an observed behaviour to one of the above categories, we report it here.

Where in the catching process do uncategorised behavioural changes occur and how to avoid them?

Increased swimming behaviour or tail beat frequency may occur during decreasing distance to neighbours. To avoid it during emersion, prefer densities <51 kg/m³. For bycatch species, further research needed for ways to avoid it.

• Shoaling and swimming behaviours not affected by Low-Frequency Active Sonar (1-2 kHz) nor Mid-Frequency Active Sonar (6-7 kHz) 1.
  • Catching step:  Prospection
  • How to improve: low- and mid-frequency sonar has no impact on shoaling and swimming
• Tail beat frequency (proxy for fish activity) increased with crowding density in a purse seine study under captive conditions: with lowest mean tail beat frequencies in the control groups (1.5-3.3 kg/m³ or 6.2-13.6 IND/m³) and lowest crowded group (51 kg/m³) and the highest mean frequency at the highest crowding density of 351 kg/m³ (1,565 IND/m³) 23. Mortality increased as tail beat frequency increased with largest increase at 200-247 kg/m³ during crowding with tail beat increasing by 0.1 tail beats/second, mortality increasing by 17% 23. Sample was taken on wild-caught IND that were kept in net for behaviour obsersations and least stressed IND, since the most stressed IND might have died in advance and therefore were not part of the study 23.
  • Catching step:  Emersion
  • How to improve: avoid densities >51 kg/m³
• Although usually similar-sized IND in schools 37, sometimes mix of small and larger size, resulting in slipping small IND21. Slipping also when school in purse seine very dense 21. Slipping itself is stressful, e.g., by combining increased swimming activity with physical damage, which may result in delayed mortality 23. Swimming to more favourable environment may make recovery possible 23. Slipping operations recommended as best practice to reduce stress and promote survival in released catches 38↶39.
  • Catching step:  Bycatch avoidance
  • How to improve: slipping