Authors: Jenny Volstorf, Caroline Marques Maia

Scomber scombrus is a marine species naturally inhabiting North Atlantic waters, including the Mediterranean. In fisheries, it is of commercial importance to many Atlantic fisheries, being extensively targeted by purse seine fisheries in European waters from the northern Norwegian Sea to waters off the Portuguese coast.

Slipping the whole or parts of a catch has traditionally been used in pelagic fisheries if catches are too large or the size and/or quality of the FISHES are regarded as unsatisfactorily, although high post-slipping mortalities have been reported. S. scombrus is delicate and particularly vulnerable to stress which explains the very high mortality rates following the stress of capture, handling, and retention in nets, with excessive crowding in the net being considered the principal stress mechanism. Transfer to the vessel mainly happens via pumps which avoids contact with air, but the arrival on deck or in the storage containers is most likely stressful and may lead to injuries. Further research is needed on welfare hazards and their consequences. S. scombrus is brought to land without prior stunning or slaughter. Stunning and slaughtering protocols are on the table, but validation in field studies are still 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?

• non-target species: given the principle of purse seine to catch whole schools 1089, there is the risks to also include co-existing, preyed-on, and predating species 1112. Welfare hazards including mortality are best avoided by preventing bycatch. For methods of bycatch prevention in the target species that might also work on non-target species → 6.2. Contact with the gear. Further research needed on co-existing, preyed-on, and predating species.
  • How to improve: slipping through discharge opening might work
• non-target species: given the principle of purse seine to catch at the surface (avoid the bottom) 1089, seabed damage or impact on benthos respectively is unlikely 1112. When fishing takes place over the shelf or in shallower water, the bottom may be touched 1112. The net is not dragged along the seafloor 1089, though, so huge impact on benthos is unlikely 1112.
  • How to improve: impact on benthos unlikely

How much is this species targeted annually?

Authors: Jenny Volstorf, Caroline Marques Maia

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 may occur most frequently during decreasing distance to neighbours, contact with the gear, and handling. To avoid it during catching/hauling and emersion, a) take especially care to avoid high densities during crowding in the last 20% of retrieving the purse seine – before the IND dissolve schooling, start dashing at the surface, and turn blue, b) keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches), and c) prefer lower pumping velocity (1.2-1.8 t/min versus 7.4-8.6 t/min), shorter pumping time (27-85 min versus 56-165 min), and lower catch volume (55-80 tons versus 132-250 tons). To avoid it during bycatch release, a) slip the bycatch before 80% of the seine is hauled in, b) avoid crowding beyond 92 kg/m³ before slipping, and c) slip through a discharge opening, as it works and keeps the IND in the water and in school formation, but encouraging earlier escape would benefit welfare even more. Further research needed.

1.1 Barotrauma

Extruded eyes/guts: no data found yet.

Ruptured swim bladder: no data found yet.

Bleeding: no data found yet.

• Given catching during the day or – if at night – luring IND to the surface with the help of artificial light 13 and therefore catching at the surface 1089 with hauling speed 0.2-0.3 m/s 7, there is no risk of barotrauma 1415.
  • Catching step:  Catching
  • How to improve: no risk of barotrauma

1.2 Damages/abrasions/lacerations/wounds

Eye damage: no data found yet.

• As the seine was hauled, school density slighted increased 16.
  With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND - less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t) 17. >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  Norwegian legislation: slipping best before 7/8 (87.5%) of net pumped out 19↶20.
  Above critical crowding level (here: 187 kg/m³), panic behaviour: dissolving schooling, rushing to surface, dashing 6.
  LAB: crowding trial: decreased schooling at estimated 25 or 62-63 IND/m³ in response to predator model; no additive effect when additionally under hypoxic conditions (2.8-3.3 mg/L or 40% oxygen saturation at estimated 13, 37, 63, 78 IND/m³). Probably <1% mortality presumably through skin injuries 21. 
  LAB: crowding trial: increased tail beat frequency at estimated 30 kg/m³ for 2 h indicating increased swimming speed; no additive effect when additionally under hypoxic conditions (3.0-3.3 mg/L or 36.9-38.7% oxygen saturation) 22. 
  LAB: after 15 min of simulated purse seining at 82-100 kg/m³, no differences in blood lactate, glucose, cortisol probably due to IND being subjected to a second stressor (being put in a net) shortly after a first stressor (being hooked and put in a tank) 23.
  LAB: crowding trial: after 34-60 min intense crowding, increased plasma ion, cortisol, glucose, lactate, decreased muscle pH. Earlier onset of rigor mortis, more stiff, higher latency to resolve. Slightly more gaping and worse texture but only after 2 days on ice, not 7 24. 
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25. 
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve:
    • take especially care to avoid high densities during crowding in last 20% of retrieving purse seine before IND dissolve schooling, start dashing at surface, and turn blue
    • slipping best before 80% of seine is hauled in before IND dissolve schooling, start dashing at surface, and turn blue
• With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND – less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t). >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  LAB: crowding trial: following 15 min crowding, increasing cortisol, lactate, osmolality with increasing density (92-179.9 kg/m³) – even more so after 60 min crowding at 182.8 kg/m³. Lactate levels back to normal 2 hours later under 92-146.2 kg/m³, 24 h under 179.9 kg/m³. Cortisol recovered in all conditions 24 h later, glucose still elevated. Dying IND with extremely high lactate, extremely low glucose levels. When checked during the trial, IND were not injured. Injuries were discovered 8-20 days later (→ 6.3. Decreasing distance to neighbour (continuum up to crushing)) 26.
  LAB: crowding trial: lower vitality the longer and more densely crowded (182.8 kg/m³ at 1.1-1.2 h versus 92-179.9 kg/m³ at 0.2-0.3 h) where vitality contained swimming behaviour and reflexes and indicated the welfare state. Under fisheries conditions, after crowding (30-406.5 tonnes, mean 151 tonnes catch size) and pumping on board (0.1-1.2 h, mean 0.4 h), lower vitality the longer exposure to crowding. No effect of dissolved oxygen on vitality score 27.
  LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4.
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25.
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve: keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches)
• Ca 1/2 catch was pumped from purse seines into first vessel, remaining 1/2 into secondary vessel – with 45° and/or 90° bend. Pumped through 12-18 inch ∅ hose for 27-85 min (each vessel) over 7-30 m length and 4-9.5 m height into refrigerated sea water tanks resulting in 81.3-95.7% fin injuries, 0.3-9.5% pressure injuries, 87.0-98.3% discolouration of fins. Higher damage to skin with higher pumping velocity (0.7-3.0% damage to skin at 1.2-1.8 t/min versus 7.0-44.2% damage at 7.4-8.6 t/min). Large variation in discolouration of gills (0-91.2%), discolouration of skin (0-51.8%), discolouration of eyes (0-40%) with maximum value each at second vessel of highest catch volume and highest pump velocity. Higher mortality at second than first vessel, i.e. with increasing pumping time (46.8-62.7% after 27-85 min versus 82.5-96.2% after another 29-80 min), except no difference and generally lower mortality with lower total catch (23-24% mortality at 55-80 tons versus 132-250 tons) 29.
  • Catching step:  Emersion
  • How to improve: prefer lower pumping velocity (1.2-1.8 t/min versus 7.4-8.6 t/min), shorter pumping time (27-85 min versus 56-165 min), lower catch volume (55-80 tons versus 132-250 tons)
• Some IND may be entangled in the net. Given dropping from a certain height, landing hard on deck, being kicked or stood on by fishing folks 10, hazard consequences are probable 1112. Further research needed on gear settings, on mortality rate, and on how to avoid mortality.
  LAB: crowding trial: IND that were crowded, handled, or dropped developed blue skin almost immediately. Abrasion (e.g., contact with the net, rubbing against each other, struggling on deck) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  • Catching step:  Release from gear
• LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., contact with the net, rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  LAB: crowding trial: 8-20 days after 15 min simulated crowding, increasing number of injured IND and increasing mortality with increasing density from 0.2% injured IND and 0% mortality at 92 kg/m³ to 0.6% injured IND and 30% mortality at 179.9 kg/m³. Injuries probably from contact with the net or other IND. All dying or dead IND had injuries 26. 
  • Catching step:  Bycatch avoidance
  • How to improve: LAB: avoid crowding beyond 92 kg/m³ before slipping
• Size selection via stiff netting fitted 25 m from the breast of a purse seine when crowded close to vessel lead to IND being gilled in the netting and blocking the mechanism. Size selection via metal grid lowered into the purse seine took ca 20 min for 400 t catch and worked for many small IND. Not all approached grid, though. Some IND got stuck in the metal bars. Selection process decreased with increasing mortality, probably due to lack of oxygen 28.
  Size selection via metal grid lowered into the purse seine resulted in IND "panicking", jumping out of the water, dashing in all directions with increasing hauling probably leading to stress and skin injuries. In many IND, skin turned blue after towing to sheltered place. Mortality after 1 month 0.5-1.6% in small-scale experiments, 44-82% under fisheries conditions depending on how long IND were towed in purse seine to sheltered position and whether sea was rough or calm. Results indicate negative outlook of effectiveness of size sorting in terms of mortality of escapees 13.
  • Catching step:  Bycatch avoidance

• With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND – less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t). >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  LAB: crowding trial: following 15 min crowding, increasing cortisol, lactate, osmolality with increasing density (92-179.9 kg/m³) – even more so after 60 min crowding at 182.8 kg/m³. Lactate levels back to normal 2 hours later under 92-146.2 kg/m³, 24 h under 179.9 kg/m³. Cortisol recovered in all conditions 24 h later, glucose still elevated. Dying IND with extremely high lactate, extremely low glucose levels. When checked during the trial, IND were not injured. Injuries were discovered 8-20 days later (→ 6.3. Decreasing distance to neighbour (continuum up to crushing)) 26.
  LAB: crowding trial: lower vitality the longer and more densely crowded (182.8 kg/m³ at 1.1-1.2 h versus 92-179.9 kg/m³ at 0.2-0.3 h) where vitality contained swimming behaviour and reflexes and indicated the welfare state. Under fisheries conditions, after crowding (30-406.5 tonnes, mean 151 tonnes catch size) and pumping on board (0.1-1.2 h, mean 0.4 h), lower vitality the longer exposure to crowding. No effect of dissolved oxygen on vitality score 27.
  LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4.
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25.
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve: keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches)
• Some IND may be entangled in the net. Given dropping from a certain height, landing hard on deck, being kicked or stood on by fishing folks 10, hazard consequences are probable 1112. Further research needed on gear settings, on mortality rate, and on how to avoid mortality.
  LAB: crowding trial: IND that were crowded, handled, or dropped developed blue skin almost immediately. Abrasion (e.g., contact with the net, rubbing against each other, struggling on deck) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  • Catching step:  Release from gear
• LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., contact with the net, rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  LAB: crowding trial: 8-20 days after 15 min simulated crowding, increasing number of injured IND and increasing mortality with increasing density from 0.2% injured IND and 0% mortality at 92 kg/m³ to 0.6% injured IND and 30% mortality at 179.9 kg/m³. Injuries probably from contact with the net or other IND. All dying or dead IND had injuries 26. 
  • Catching step:  Bycatch avoidance
  • How to improve: LAB: avoid crowding beyond 92 kg/m³ before slipping

Broken spine: no data found yet.

• Given the principle of purse seine to encircle the IND, haul the net close to the ship, and crowd the IND before transferring them into the storage space of the ship 1089, taking 40-50 min/haul 4, 1.5 h/haul 7, hazard consequences are probable 1112. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching steps:  Catching Emersion
• Given that IND school 16321162, aggression between conspecifics is unlikely 1112.
  • Catching step:  Emersion
  • How to improve: attacks by con-specifics unlikely
• If not pumped, IND are lifted out of the purse seine into the storage space of the ship with a scoop net or brailer 716822. Given the force with which the net is dipped into the purse seine, exposure to air, and the crowding density, hazard consequences are probable 1112. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching step:  Emersion
• Probably no sorting but direct pumping into the storage space of the ship 42810729165302224292725 for 0.1-1.2 h, mean 0.4 h 27 (although can also be lifted with scoop net out of purse seine 716822). Given the speed with which IND arrive on deck or slide down chutes respectively and based on the crowding density, hazard consequences are probable 1112. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching steps:  Emersion Release from gear Sorting
• If not pumped, after scooping the IND out of the purse seine, the scoop net is released above the storage space of the ship 716822. Given dropping from a certain height, landing hard in plastic containers, being catapulted away from the containers, kicked or stood on by fishing folks, and exposure to air, hazard consequences are probable 1112. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching steps:  Release from gear Sorting Discarding
• Some IND may be entangled in the net. Given dropping from a certain height, landing hard on deck, being kicked or stood on by fishing folks 10, hazard consequences are probable 1112. Further research needed on gear settings, on mortality rate, and on how to avoid mortality.
  LAB: crowding trial: IND that were crowded, handled, or dropped developed blue skin almost immediately. Abrasion (e.g., contact with the net, rubbing against each other, struggling on deck) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  • Catching steps:  Release from gear Sorting Discarding
• Slipping through ≥18 m opening of bunt end of seine. Most of the time, IND did not escape – positive because keep school formation, but negative because of constraint in net. Of those escaping, they rather did in an orderly way (47%), staying in school formation without collisions. If escaping disorderly (39%), broke the school and collided with net or each other probably resulting in injuries. IND breaking away from school on their own or in small groups and escaping – only seldomly. Amount of IND escaping and way of escaping (orderly/disorderly) depending on vessel. Probability of escaping increased with increasing time of discharge left open – but so did escape in disorderly fashion, probably due to reluctance of leaving safety of school (e.g., towards predators) in threatening situation and only being forced out of the net as noise and proximity to net and conspecifics increased. Finding ways to increase orderly escapes – maybe with the help of visual stimuli – could benefit welfare 20.
  • Catching step:  Bycatch avoidance
  • How to improve: slipping through discharge opening works and keeps IND in the water and in school formation, but encouraging earlier escape would benefit welfare even more
• LAB: slipping trial: 30 min after simulated slipping (following 15 min crowding at 82 kg/m³), higher lactate and cortisol levels (not at 100 kg/m³), some IND turning blue. No difference in blood parameters between green and blue IND. 48 h after 15 min crowding (82-100 kg/m³), 5-7.7% mortality, 144 h after 147 kg/m³, 10.5% mortality 23.
  LAB: crowding trial: in simulated crowding, until 100 IND/m³, mortality only after 6 h crowding duration. 50% mortality estimated to appear under crowding at 30 IND/m³ (6.5 kg/m³) for 48 h 4. 
  LAB: crowding trial: 2.5-6 days after 10-15 min simulated crowding (max 187 kg/m³), higher mortality than in uncrowded IND; less crowded IND (ca 31 kg/m³) in between 6. 
  LAB: crowding trial: 8-20 days after 15 min simulated crowding, increasing number of injured IND and increasing mortality with increasing density from 0.2% injured IND and 0% mortality at 92 kg/m³ to 0.6% injured IND and 30% mortality at 179.9 kg/m³. Injuries probably from contact with the net or other IND. All dying or dead IND had injuries 26. 
  LAB: crowding trial: up to 27 days after 15 min simulated crowding (179.87 kg/m³), mortality ≤31% 25. 
  • Catching step:  Bycatch avoidance
  • How to improve: LAB: avoid crowding beyond 92 kg/m³ before slipping
• Size selection via stiff netting fitted 25 m from the breast of a purse seine when crowded close to vessel lead to IND being gilled in the netting and blocking the mechanism. Size selection via metal grid lowered into the purse seine took ca 20 min for 400 t catch and worked for many small IND. Not all approached grid, though. Some IND got stuck in the metal bars. Selection process decreased with increasing mortality, probably due to lack of oxygen 28.
  Size selection via metal grid lowered into the purse seine resulted in IND "panicking", jumping out of the water, dashing in all directions with increasing hauling probably leading to stress and skin injuries. In many IND, skin turned blue after towing to sheltered place. Mortality after 1 month 0.5-1.6% in small-scale experiments, 44-82% under fisheries conditions depending on how long IND were towed in purse seine to sheltered position and whether sea was rough or calm. Results indicate negative outlook of effectiveness of size sorting in terms of mortality of escapees 13.
  • Catching step:  Bycatch avoidance
• Rumours that fishers sort catch on deck and discard undersized IND. Would be detrimental for mackerel stock 28, and hazard consequences are probable 1112. Alternative could be size-grading while still in the water 28. For size grading through sorting grid → 6.2. Contact with the gear.
  • Catching steps:  Sorting Discarding

1.3 Ecchymosis

1.4 Desiccation (surface issue)

Unspecified: no data found yet.

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 may occur most frequently during decreasing distance to neighbours, contact with the gear or the storing container, and handling. To avoid it during catching/hauling and emersion, a) take especially care to avoid high densities during crowding in the last 20% of retrieving the purse seine – before the IND dissolve schooling, start dashing at the surface, and turn blue, b) keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches). To avoid it during bycatch release, a) identify bycatch through sampling, b) slip the bycatch before 80% of the seine is hauled in, and c) avoid crowding beyond 92 kg/m³ before slipping. To avoid it during storing, prefer immediate stunning followed by slaughter while still unconscious. Further research needed.

• As the seine was hauled, school density slighted increased 16.
  With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND - less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t) 17. >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  Norwegian legislation: slipping best before 7/8 (87.5%) of net pumped out 19↶20.
  Above critical crowding level (here: 187 kg/m³), panic behaviour: dissolving schooling, rushing to surface, dashing 6.
  LAB: crowding trial: decreased schooling at estimated 25 or 62-63 IND/m³ in response to predator model; no additive effect when additionally under hypoxic conditions (2.8-3.3 mg/L or 40% oxygen saturation at estimated 13, 37, 63, 78 IND/m³). Probably <1% mortality presumably through skin injuries 21. 
  LAB: crowding trial: increased tail beat frequency at estimated 30 kg/m³ for 2 h indicating increased swimming speed; no additive effect when additionally under hypoxic conditions (3.0-3.3 mg/L or 36.9-38.7% oxygen saturation) 22. 
  LAB: after 15 min of simulated purse seining at 82-100 kg/m³, no differences in blood lactate, glucose, cortisol probably due to IND being subjected to a second stressor (being put in a net) shortly after a first stressor (being hooked and put in a tank) 23.
  LAB: crowding trial: after 34-60 min intense crowding, increased plasma ion, cortisol, glucose, lactate, decreased muscle pH. Earlier onset of rigor mortis, more stiff, higher latency to resolve. Slightly more gaping and worse texture but only after 2 days on ice, not 7 24. 
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25. 
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve:
    • take especially care to avoid high densities during crowding in last 20% of retrieving purse seine before IND dissolve schooling, start dashing at surface, and turn blue
    • slipping best before 80% of seine is hauled in before IND dissolve schooling, start dashing at surface, and turn blue
• With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND – less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t). >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  LAB: crowding trial: following 15 min crowding, increasing cortisol, lactate, osmolality with increasing density (92-179.9 kg/m³) – even more so after 60 min crowding at 182.8 kg/m³. Lactate levels back to normal 2 hours later under 92-146.2 kg/m³, 24 h under 179.9 kg/m³. Cortisol recovered in all conditions 24 h later, glucose still elevated. Dying IND with extremely high lactate, extremely low glucose levels. When checked during the trial, IND were not injured. Injuries were discovered 8-20 days later (→ 6.3. Decreasing distance to neighbour (continuum up to crushing)) 26.
  LAB: crowding trial: lower vitality the longer and more densely crowded (182.8 kg/m³ at 1.1-1.2 h versus 92-179.9 kg/m³ at 0.2-0.3 h) where vitality contained swimming behaviour and reflexes and indicated the welfare state. Under fisheries conditions, after crowding (30-406.5 tonnes, mean 151 tonnes catch size) and pumping on board (0.1-1.2 h, mean 0.4 h), lower vitality the longer exposure to crowding. No effect of dissolved oxygen on vitality score 27.
  LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4.
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25.
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve: keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches)
• LAB: slipping trial: 30 min after simulated slipping (following 15 min crowding at 82 kg/m³), higher lactate and cortisol levels (not at 100 kg/m³), some IND turning blue. No difference in blood parameters between green and blue IND. 48 h after 15 min crowding (82-100 kg/m³), 5-7.7% mortality, 144 h after 147 kg/m³, 10.5% mortality 23.
  LAB: crowding trial: in simulated crowding, until 100 IND/m³, mortality only after 6 h crowding duration. 50% mortality estimated to appear under crowding at 30 IND/m³ (6.5 kg/m³) for 48 h 4. 
  LAB: crowding trial: 2.5-6 days after 10-15 min simulated crowding (max 187 kg/m³), higher mortality than in uncrowded IND; less crowded IND (ca 31 kg/m³) in between 6. 
  LAB: crowding trial: 8-20 days after 15 min simulated crowding, increasing number of injured IND and increasing mortality with increasing density from 0.2% injured IND and 0% mortality at 92 kg/m³ to 0.6% injured IND and 30% mortality at 179.9 kg/m³. Injuries probably from contact with the net or other IND. All dying or dead IND had injuries 26. 
  LAB: crowding trial: up to 27 days after 15 min simulated crowding (179.87 kg/m³), mortality ≤31% 25. 
  • Catching step:  Bycatch avoidance
  • How to improve: LAB: avoid crowding beyond 92 kg/m³ before slipping

Opercular movement: no data found yet.

• Echosounder/sonar (pulse repetition frequency of about 0.5 H 2) is commonly used to search for schools 42 and then to evaluate their size and biomass 152 while encircling them 2; sonar prospection used during the day 67, at night 78. Further research needed on types of hazard consequences.
  • Catching step:  Prospection
• Given the principle of purse seine to encircle the IND, haul the net close to the ship, and crowd the IND before transferring them into the storage space of the ship 1089, taking 40-50 min/haul 4, 1.5 h/haul 7, hazard consequences are probable 1112. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching steps:  Catching Emersion
• Given the principle of purse seine to catch IND at the surface and slowly haul the seine close to the ship 10 and thus no way of fleeing predators, there is the risk of stress by predators being present in or close to the net 1112.
  • Catching step:  Emersion
• If not pumped, IND are lifted out of the purse seine into the storage space of the ship with a scoop net or brailer 716822. Given the force with which the net is dipped into the purse seine, exposure to air, and the crowding density, hazard consequences are probable 1112. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching step:  Emersion
• Probably no sorting but direct pumping into the storage space of the ship 42810729165302224292725 for 0.1-1.2 h, mean 0.4 h 27 (although can also be lifted with scoop net out of purse seine 716822). Given the speed with which IND arrive on deck or slide down chutes respectively and based on the crowding density, hazard consequences are probable 1112. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching steps:  Emersion Release from gear Sorting
• If not pumped, after scooping the IND out of the purse seine, the scoop net is released above the storage space of the ship 716822. Given dropping from a certain height, landing hard in plastic containers, being catapulted away from the containers, kicked or stood on by fishing folks, and exposure to air, hazard consequences are probable 1112. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching steps:  Release from gear Sorting Discarding
• Some IND may be entangled in the net. Given dropping from a certain height, landing hard on deck, being kicked or stood on by fishing folks 10, hazard consequences are probable 1112. Further research needed on gear settings, on mortality rate, and on how to avoid mortality.
  LAB: crowding trial: IND that were crowded, handled, or dropped developed blue skin almost immediately. Abrasion (e.g., contact with the net, rubbing against each other, struggling on deck) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  • Catching steps:  Release from gear Sorting Discarding
• Size selection via stiff netting fitted 25 m from the breast of a purse seine when crowded close to vessel lead to IND being gilled in the netting and blocking the mechanism. Size selection via metal grid lowered into the purse seine took ca 20 min for 400 t catch and worked for many small IND. Not all approached grid, though. Some IND got stuck in the metal bars. Selection process decreased with increasing mortality, probably due to lack of oxygen 28.
  Size selection via metal grid lowered into the purse seine resulted in IND "panicking", jumping out of the water, dashing in all directions with increasing hauling probably leading to stress and skin injuries. In many IND, skin turned blue after towing to sheltered place. Mortality after 1 month 0.5-1.6% in small-scale experiments, 44-82% under fisheries conditions depending on how long IND were towed in purse seine to sheltered position and whether sea was rough or calm. Results indicate negative outlook of effectiveness of size sorting in terms of mortality of escapees 13.
  • Catching step:  Bycatch avoidance
• Given that IND school 16321162, and given the principle of purse seine to catch whole schools 1089, there is a risk of bycatch (accidental catch of undersized, wrong sex, wrong age, damaged, over quota IND) of the target species 1112.
  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 fishes that come to the surface. At that point, they can abort the process if the catch does not include the target species and before the school is crowded 14.
  • Catching step:  Bycatch avoidance
  • How to improve: sampling
• Slipping when catch exceeds size or IND are mixed, of wrong size, or bad quality 67.
  • Catching step:  Bycatch avoidance
• Rumours that fishers sort catch on deck and discard undersized IND. Would be detrimental for mackerel stock 28, and hazard consequences are probable 1112. Alternative could be size-grading while still in the water 28. For size grading through sorting grid → 6.2. Contact with the gear.
  • Catching steps:  Sorting Discarding
• Given live storage in containers with (ice?) water 8, hazard consequences are probable. Further research needed on types of hazard consequences.
  Pumped into refrigerated sea water tanks 29302427 of 41-62 m³ with -1.1--0.3 °C and stored for 21-60 h with 82.5-96.2% mortality after 56-165 min 29.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious

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 exposure to (ice) water. To avoid it during storing and slaughter, prefer immediate stunning followed by slaughter while still unconscious. Further research needed.

• Given live storage in containers with (ice?) water 8, hazard consequences are probable. Further research needed on types of hazard consequences.
  Pumped into refrigerated sea water tanks 29302427 of 41-62 m³ with -1.1--0.3 °C and stored for 21-60 h with 82.5-96.2% mortality after 56-165 min 29.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious
• Given no sorting but direct pumping into the storage space of the ship 42810729165302224292725 – or given lifting with scoop net out of purse seine 716822 – into (ice?) water 8, ice slurries 30, or refrigerated sea water 29302427, probably no stunning and slaughter but asphyxia or hypothermia 1112.
  • Catching step:  Slaughter
  • 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?

There is no conclusion yet.

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?

There is no conclusion yet.

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 through lack of oxygen. To avoid it from emersion on, prefer immediate stunning followed by slaughter while still unconscious. Further research needed.

• LAB: crowding trial: oxygen decreased by 1-2 g/L 26.
  LAB: hypoxia trial: no difference in swimming speeds and no change to schooling at 2.8-3.3 mg/L or 40% oxygen saturation at estimated density 27 and 44 IND/m³. Decreased schooling when additionally crowded (estimated 13, 37, 63, 78 IND/m³) 21. 
  LAB: hypoxia trial: tendency of increased tail beat frequency at 2.8-3.3 mg/L or 36.4-38.3% oxygen saturation for 2 h indicating increased swimming speed; no additive effect when additionally crowded (estimated 30 kg/m³) 22. 
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25. 
  • Catching steps:  Emersion Bycatch avoidance

• LAB: crowding trial: oxygen decreased by 1-2 g/L 26.
  LAB: hypoxia trial: no difference in swimming speeds and no change to schooling at 2.8-3.3 mg/L or 40% oxygen saturation at estimated density 27 and 44 IND/m³. Decreased schooling when additionally crowded (estimated 13, 37, 63, 78 IND/m³) 21. 
  LAB: hypoxia trial: tendency of increased tail beat frequency at 2.8-3.3 mg/L or 36.4-38.3% oxygen saturation for 2 h indicating increased swimming speed; no additive effect when additionally crowded (estimated 30 kg/m³) 22. 
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25. 
  • Catching steps:  Emersion Bycatch avoidance
• If not pumped, IND are lifted out of the purse seine into the storage space of the ship with a scoop net or brailer 716822. Given the force with which the net is dipped into the purse seine, exposure to air, and the crowding density, hazard consequences are probable 1112. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching step:  Emersion
• If not pumped, after scooping the IND out of the purse seine, the scoop net is released above the storage space of the ship 716822. Given dropping from a certain height, landing hard in plastic containers, being catapulted away from the containers, kicked or stood on by fishing folks, and exposure to air, hazard consequences are probable 1112. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching steps:  Release from gear Sorting Discarding
• Given no sorting but direct pumping into the storage space of the ship 42810729165302224292725 – or given lifting with scoop net out of purse seine 716822 – into (ice?) water 8, ice slurries 30, or refrigerated sea water 29302427, probably no stunning and slaughter but asphyxia or hypothermia 1112.
  • 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 may occur during decreasing distance to neighbours. To avoid it during catching/hauling, emersion, and bycatch release, keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches). Further research needed.

• With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND – less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t). >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  LAB: crowding trial: following 15 min crowding, increasing cortisol, lactate, osmolality with increasing density (92-179.9 kg/m³) – even more so after 60 min crowding at 182.8 kg/m³. Lactate levels back to normal 2 hours later under 92-146.2 kg/m³, 24 h under 179.9 kg/m³. Cortisol recovered in all conditions 24 h later, glucose still elevated. Dying IND with extremely high lactate, extremely low glucose levels. When checked during the trial, IND were not injured. Injuries were discovered 8-20 days later (→ 6.3. Decreasing distance to neighbour (continuum up to crushing)) 26.
  LAB: crowding trial: lower vitality the longer and more densely crowded (182.8 kg/m³ at 1.1-1.2 h versus 92-179.9 kg/m³ at 0.2-0.3 h) where vitality contained swimming behaviour and reflexes and indicated the welfare state. Under fisheries conditions, after crowding (30-406.5 tonnes, mean 151 tonnes catch size) and pumping on board (0.1-1.2 h, mean 0.4 h), lower vitality the longer exposure to crowding. No effect of dissolved oxygen on vitality score 27.
  LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4.
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25.
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve: keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches)

Oxidative stress: no data found yet.

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?

Fear up to panic may occur most frequently during decreasing distance to neighbours. To avoid it during catching/hauling and emersion, take especially care to avoid high densities during crowding in the last 20% of retrieving the purse seine before the IND dissolve schooling, start dashing at the surface, and turn blue. To avoid it during bycatch release, a) slip the bycatch before 80% of the seine is hauled in, b) slip through a discharge opening, as it works and keeps the IND in the water and in school formation, but encouraging earlier escape would benefit the welfare even more. Further research needed.

9.1 Fear (continuum up to panic)

Freeze: no data found yet.

• When circling schools with a vessel at 90-340 m distance from the school centre, schools avoided the vessel and the sound emission pattern of the vessel horizontally – with increasing speed at increasing distance. During pursing, some schools maintained depth of ca 20-30 m when in net, others avoided capture by diving away under vessel, probably during leadline lifting 1.
  Encircling schools repeatedly at 100-200 m distance resulted in IND swimming closer to one another 2.
  • Catching step:  Prospection
• When confronted with a sequence of frequency pulses of 50-600 Hz of up to 171 dB re 1 μPa peak-to-peak at 10-35 m depth, schools mainly dived deeper quickly, some dispersed or changed density. Increasing probability to react with increasing sound level, with 50% schools reacting to 163.3 dB re 1 μPa peak-to-peak (particle velocity level of -80.4 dB re 1 m/s), 142.0 dB re 1 μPa² s for single strike (particle velocity level -101.7 dB re 1 m²/s) 3. Further research needed on types of hazard consequences.
  • Catching step:  Prospection

• As the seine was hauled, school density slighted increased 16.
  With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND - less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t) 17. >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  Norwegian legislation: slipping best before 7/8 (87.5%) of net pumped out 19↶20.
  Above critical crowding level (here: 187 kg/m³), panic behaviour: dissolving schooling, rushing to surface, dashing 6.
  LAB: crowding trial: decreased schooling at estimated 25 or 62-63 IND/m³ in response to predator model; no additive effect when additionally under hypoxic conditions (2.8-3.3 mg/L or 40% oxygen saturation at estimated 13, 37, 63, 78 IND/m³). Probably <1% mortality presumably through skin injuries 21. 
  LAB: crowding trial: increased tail beat frequency at estimated 30 kg/m³ for 2 h indicating increased swimming speed; no additive effect when additionally under hypoxic conditions (3.0-3.3 mg/L or 36.9-38.7% oxygen saturation) 22. 
  LAB: after 15 min of simulated purse seining at 82-100 kg/m³, no differences in blood lactate, glucose, cortisol probably due to IND being subjected to a second stressor (being put in a net) shortly after a first stressor (being hooked and put in a tank) 23.
  LAB: crowding trial: after 34-60 min intense crowding, increased plasma ion, cortisol, glucose, lactate, decreased muscle pH. Earlier onset of rigor mortis, more stiff, higher latency to resolve. Slightly more gaping and worse texture but only after 2 days on ice, not 7 24. 
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25. 
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve:
    • take especially care to avoid high densities during crowding in last 20% of retrieving purse seine before IND dissolve schooling, start dashing at surface, and turn blue
    • slipping best before 80% of seine is hauled in before IND dissolve schooling, start dashing at surface, and turn blue
• Slipping through ≥18 m opening of bunt end of seine. Most of the time, IND did not escape – positive because keep school formation, but negative because of constraint in net. Of those escaping, they rather did in an orderly way (47%), staying in school formation without collisions. If escaping disorderly (39%), broke the school and collided with net or each other probably resulting in injuries. IND breaking away from school on their own or in small groups and escaping – only seldomly. Amount of IND escaping and way of escaping (orderly/disorderly) depending on vessel. Probability of escaping increased with increasing time of discharge left open – but so did escape in disorderly fashion, probably due to reluctance of leaving safety of school (e.g., towards predators) in threatening situation and only being forced out of the net as noise and proximity to net and conspecifics increased. Finding ways to increase orderly escapes – maybe with the help of visual stimuli – could benefit welfare 20.
  • Catching step:  Bycatch avoidance
  • How to improve: slipping through discharge opening works and keeps IND in the water and in school formation, but encouraging earlier escape would benefit welfare even more

• As the seine was hauled, school density slighted increased 16.
  With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND - less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t) 17. >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  Norwegian legislation: slipping best before 7/8 (87.5%) of net pumped out 19↶20.
  Above critical crowding level (here: 187 kg/m³), panic behaviour: dissolving schooling, rushing to surface, dashing 6.
  LAB: crowding trial: decreased schooling at estimated 25 or 62-63 IND/m³ in response to predator model; no additive effect when additionally under hypoxic conditions (2.8-3.3 mg/L or 40% oxygen saturation at estimated 13, 37, 63, 78 IND/m³). Probably <1% mortality presumably through skin injuries 21. 
  LAB: crowding trial: increased tail beat frequency at estimated 30 kg/m³ for 2 h indicating increased swimming speed; no additive effect when additionally under hypoxic conditions (3.0-3.3 mg/L or 36.9-38.7% oxygen saturation) 22. 
  LAB: after 15 min of simulated purse seining at 82-100 kg/m³, no differences in blood lactate, glucose, cortisol probably due to IND being subjected to a second stressor (being put in a net) shortly after a first stressor (being hooked and put in a tank) 23.
  LAB: crowding trial: after 34-60 min intense crowding, increased plasma ion, cortisol, glucose, lactate, decreased muscle pH. Earlier onset of rigor mortis, more stiff, higher latency to resolve. Slightly more gaping and worse texture but only after 2 days on ice, not 7 24. 
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25. 
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve:
    • take especially care to avoid high densities during crowding in last 20% of retrieving purse seine before IND dissolve schooling, start dashing at surface, and turn blue
    • slipping best before 80% of seine is hauled in before IND dissolve schooling, start dashing at surface, and turn blue
• Size selection via stiff netting fitted 25 m from the breast of a purse seine when crowded close to vessel lead to IND being gilled in the netting and blocking the mechanism. Size selection via metal grid lowered into the purse seine took ca 20 min for 400 t catch and worked for many small IND. Not all approached grid, though. Some IND got stuck in the metal bars. Selection process decreased with increasing mortality, probably due to lack of oxygen 28.
  Size selection via metal grid lowered into the purse seine resulted in IND "panicking", jumping out of the water, dashing in all directions with increasing hauling probably leading to stress and skin injuries. In many IND, skin turned blue after towing to sheltered place. Mortality after 1 month 0.5-1.6% in small-scale experiments, 44-82% under fisheries conditions depending on how long IND were towed in purse seine to sheltered position and whether sea was rough or calm. Results indicate negative outlook of effectiveness of size sorting in terms of mortality of escapees 13.
  • Catching step:  Bycatch avoidance

9.2 Other

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 may occur most frequently during decreasing distance to neighbours, contact with the gear, and handling. To avoid it during catching/hauling and emersion, a) take especially care to avoid high densities during crowding in the last 20% of retrieving the purse seine – before the IND dissolve schooling, start dashing at the surface, and turn blue, b) keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches), c) prefer lower pumping velocity (1.2-1.8 t/min versus 7.4-8.6 t/min), shorter pumping time (27-85 min versus 56-165 min), and lower catch volume (55-80 tons versus 132-250 tons). To avoid it during bycatch release, a) slip the bycatch before 80% of the seine is hauled in, b) avoid crowding beyond 92 kg/m³ before slipping, and c) keep the crowding duration as short as possible. To avoid it during storing, prefer immediate stunning followed by slaughter while still unconscious. Further research needed.

• Given the principle of purse seine to encircle the IND, haul the net close to the ship, and crowd the IND before transferring them into the storage space of the ship 1089, taking 40-50 min/haul 4, 1.5 h/haul 7, hazard consequences are probable 1112. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching steps:  Catching Emersion
• As the seine was hauled, school density slighted increased 16.
  With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND - less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t) 17. >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  Norwegian legislation: slipping best before 7/8 (87.5%) of net pumped out 19↶20.
  Above critical crowding level (here: 187 kg/m³), panic behaviour: dissolving schooling, rushing to surface, dashing 6.
  LAB: crowding trial: decreased schooling at estimated 25 or 62-63 IND/m³ in response to predator model; no additive effect when additionally under hypoxic conditions (2.8-3.3 mg/L or 40% oxygen saturation at estimated 13, 37, 63, 78 IND/m³). Probably <1% mortality presumably through skin injuries 21. 
  LAB: crowding trial: increased tail beat frequency at estimated 30 kg/m³ for 2 h indicating increased swimming speed; no additive effect when additionally under hypoxic conditions (3.0-3.3 mg/L or 36.9-38.7% oxygen saturation) 22. 
  LAB: after 15 min of simulated purse seining at 82-100 kg/m³, no differences in blood lactate, glucose, cortisol probably due to IND being subjected to a second stressor (being put in a net) shortly after a first stressor (being hooked and put in a tank) 23.
  LAB: crowding trial: after 34-60 min intense crowding, increased plasma ion, cortisol, glucose, lactate, decreased muscle pH. Earlier onset of rigor mortis, more stiff, higher latency to resolve. Slightly more gaping and worse texture but only after 2 days on ice, not 7 24. 
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25. 
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve:
    • take especially care to avoid high densities during crowding in last 20% of retrieving purse seine before IND dissolve schooling, start dashing at surface, and turn blue
    • slipping best before 80% of seine is hauled in before IND dissolve schooling, start dashing at surface, and turn blue
• With increasing hauling, net volume decreased from 1,300,000 m³ at 5-15% hauled to 130,000 m³ at 70-80% hauled or 1.4 m³/IND to 0.5 m³/IND – less space per IND with a larger catch. Extrapolation for 90% hauled: 0.03 m³/IND at 500 t catch or 0.02 m³/IND at 1,000 t catch. Shoal density independent of hauling rate: 6-31 IND/m³7.
  Below-critical densities to be expected in median-sized catches (270 t) until 80% of seine is hauled in, whereas critical crowding levels were reached in large catches (650-985 t). >80% hauling: highly uncertain predictions about seine volume 17 due to complex shapes with large folds that seine may take 18↶17; unexpectedly high densities possible as seine is hauled in completely 17.
  LAB: crowding trial: following 15 min crowding, increasing cortisol, lactate, osmolality with increasing density (92-179.9 kg/m³) – even more so after 60 min crowding at 182.8 kg/m³. Lactate levels back to normal 2 hours later under 92-146.2 kg/m³, 24 h under 179.9 kg/m³. Cortisol recovered in all conditions 24 h later, glucose still elevated. Dying IND with extremely high lactate, extremely low glucose levels. When checked during the trial, IND were not injured. Injuries were discovered 8-20 days later (→ 6.3. Decreasing distance to neighbour (continuum up to crushing)) 26.
  LAB: crowding trial: lower vitality the longer and more densely crowded (182.8 kg/m³ at 1.1-1.2 h versus 92-179.9 kg/m³ at 0.2-0.3 h) where vitality contained swimming behaviour and reflexes and indicated the welfare state. Under fisheries conditions, after crowding (30-406.5 tonnes, mean 151 tonnes catch size) and pumping on board (0.1-1.2 h, mean 0.4 h), lower vitality the longer exposure to crowding. No effect of dissolved oxygen on vitality score 27.
  LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4.
  LAB: crowding trial: skin of IND turned blue - even more so when crowded at higher density and longer (1 h 10 min at 182.8 kg/m³ versus 15 min at 92 kg/m³). More blue at 2 h after crowding. Good correlation of blueness with plasma lactate, not with glucose or cortisol, indicating possible link to hypoxia 25.
  • Catching steps:  Catching Emersion Bycatch avoidance
  • How to improve: keep the duration of crowding as short as possible (LAB: ≤0.3 h, best by focusing on smaller catches)
• Given that IND school 16321162, aggression between conspecifics is unlikely 1112.
  • Catching step:  Emersion
  • How to improve: attacks by con-specifics unlikely
• If not pumped, IND are lifted out of the purse seine into the storage space of the ship with a scoop net or brailer 716822. Given the force with which the net is dipped into the purse seine, exposure to air, and the crowding density, hazard consequences are probable 1112. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching step:  Emersion
• Probably no sorting but direct pumping into the storage space of the ship 42810729165302224292725 for 0.1-1.2 h, mean 0.4 h 27 (although can also be lifted with scoop net out of purse seine 716822). Given the speed with which IND arrive on deck or slide down chutes respectively and based on the crowding density, hazard consequences are probable 1112. Further research needed on gear settings, on types of hazard consequences, and on how to avoid a decrease in welfare.
  • Catching steps:  Emersion Release from gear Sorting
• Ca 1/2 catch was pumped from purse seines into first vessel, remaining 1/2 into secondary vessel – with 45° and/or 90° bend. Pumped through 12-18 inch ∅ hose for 27-85 min (each vessel) over 7-30 m length and 4-9.5 m height into refrigerated sea water tanks resulting in 81.3-95.7% fin injuries, 0.3-9.5% pressure injuries, 87.0-98.3% discolouration of fins. Higher damage to skin with higher pumping velocity (0.7-3.0% damage to skin at 1.2-1.8 t/min versus 7.0-44.2% damage at 7.4-8.6 t/min). Large variation in discolouration of gills (0-91.2%), discolouration of skin (0-51.8%), discolouration of eyes (0-40%) with maximum value each at second vessel of highest catch volume and highest pump velocity. Higher mortality at second than first vessel, i.e. with increasing pumping time (46.8-62.7% after 27-85 min versus 82.5-96.2% after another 29-80 min), except no difference and generally lower mortality with lower total catch (23-24% mortality at 55-80 tons versus 132-250 tons) 29.
  • Catching step:  Emersion
  • How to improve: prefer lower pumping velocity (1.2-1.8 t/min versus 7.4-8.6 t/min), shorter pumping time (27-85 min versus 56-165 min), lower catch volume (55-80 tons versus 132-250 tons)
• If not pumped, after scooping the IND out of the purse seine, the scoop net is released above the storage space of the ship 716822. Given dropping from a certain height, landing hard in plastic containers, being catapulted away from the containers, kicked or stood on by fishing folks, and exposure to air, hazard consequences are probable 1112. Further research needed on types of hazard consequences and on how to avoid them.
  • Catching steps:  Release from gear Sorting Discarding
• Some IND may be entangled in the net. Given dropping from a certain height, landing hard on deck, being kicked or stood on by fishing folks 10, hazard consequences are probable 1112. Further research needed on gear settings, on mortality rate, and on how to avoid mortality.
  LAB: crowding trial: IND that were crowded, handled, or dropped developed blue skin almost immediately. Abrasion (e.g., contact with the net, rubbing against each other, struggling on deck) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  • Catching steps:  Release from gear Sorting Discarding
• LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., contact with the net, rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  LAB: crowding trial: 8-20 days after 15 min simulated crowding, increasing number of injured IND and increasing mortality with increasing density from 0.2% injured IND and 0% mortality at 92 kg/m³ to 0.6% injured IND and 30% mortality at 179.9 kg/m³. Injuries probably from contact with the net or other IND. All dying or dead IND had injuries 26. 
  • Catching step:  Bycatch avoidance
  • How to improve: LAB: avoid crowding beyond 92 kg/m³ before slipping
• Size selection via stiff netting fitted 25 m from the breast of a purse seine when crowded close to vessel lead to IND being gilled in the netting and blocking the mechanism. Size selection via metal grid lowered into the purse seine took ca 20 min for 400 t catch and worked for many small IND. Not all approached grid, though. Some IND got stuck in the metal bars. Selection process decreased with increasing mortality, probably due to lack of oxygen 28.
  Size selection via metal grid lowered into the purse seine resulted in IND "panicking", jumping out of the water, dashing in all directions with increasing hauling probably leading to stress and skin injuries. In many IND, skin turned blue after towing to sheltered place. Mortality after 1 month 0.5-1.6% in small-scale experiments, 44-82% under fisheries conditions depending on how long IND were towed in purse seine to sheltered position and whether sea was rough or calm. Results indicate negative outlook of effectiveness of size sorting in terms of mortality of escapees 13.
  • Catching step:  Bycatch avoidance
• LAB: slipping trial: 30 min after simulated slipping (following 15 min crowding at 82 kg/m³), higher lactate and cortisol levels (not at 100 kg/m³), some IND turning blue. No difference in blood parameters between green and blue IND. 48 h after 15 min crowding (82-100 kg/m³), 5-7.7% mortality, 144 h after 147 kg/m³, 10.5% mortality 23.
  LAB: crowding trial: in simulated crowding, until 100 IND/m³, mortality only after 6 h crowding duration. 50% mortality estimated to appear under crowding at 30 IND/m³ (6.5 kg/m³) for 48 h 4. 
  LAB: crowding trial: 2.5-6 days after 10-15 min simulated crowding (max 187 kg/m³), higher mortality than in uncrowded IND; less crowded IND (ca 31 kg/m³) in between 6. 
  LAB: crowding trial: 8-20 days after 15 min simulated crowding, increasing number of injured IND and increasing mortality with increasing density from 0.2% injured IND and 0% mortality at 92 kg/m³ to 0.6% injured IND and 30% mortality at 179.9 kg/m³. Injuries probably from contact with the net or other IND. All dying or dead IND had injuries 26. 
  LAB: crowding trial: up to 27 days after 15 min simulated crowding (179.87 kg/m³), mortality ≤31% 25. 
  • Catching step:  Bycatch avoidance
  • How to improve: LAB: avoid crowding beyond 92 kg/m³ before slipping
• LAB: slipping trial: in a 1 m keep net, higher cumulative mortality the longer the crowding duration – even if lower density (e.g., 4.2% mortality after 0.2 h at 142 IND/m³ versus 5% mortality after 0.4 h at 100 IND/m³). Crowding by the side of the boat ca 10-20 min until skipper decides to slip catch or retain it. Duration of crowding before slipping will increase if skipper starts pumping and only after reaching the allowed catch size decides to slip part of the catch. Given a pumping capacity of 100-150 t/h and an allowable catch of 100 t, IND will be crowded for ≤1 h before being slipped. At 1,000 IND/m³ for 0.5 h, 74% mortality expected after 48 h 4. 
  • Catching step:  Bycatch avoidance
  • How to improve: keep crowding duration as short as possible
• Rumours that fishers sort catch on deck and discard undersized IND. Would be detrimental for mackerel stock 28, and hazard consequences are probable 1112. Alternative could be size-grading while still in the water 28. For size grading through sorting grid → 6.2. Contact with the gear.
  • Catching steps:  Sorting Discarding
• Given live storage in containers with (ice?) water 8, hazard consequences are probable. Further research needed on types of hazard consequences.
  Pumped into refrigerated sea water tanks 29302427 of 41-62 m³ with -1.1--0.3 °C and stored for 21-60 h with 82.5-96.2% mortality after 56-165 min 29.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious

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?

• When circling schools with a vessel at 90-340 m distance from the school centre, schools avoided the vessel and the sound emission pattern of the vessel horizontally – with increasing speed at increasing distance. During pursing, some schools maintained depth of ca 20-30 m when in net, others avoided capture by diving away under vessel, probably during leadline lifting 1.
  Encircling schools repeatedly at 100-200 m distance resulted in IND swimming closer to one another 2.
  • Catching step:  Prospection
• When confronted with a sequence of frequency pulses of 50-600 Hz of up to 171 dB re 1 μPa peak-to-peak at 10-35 m depth, schools mainly dived deeper quickly, some dispersed or changed density. Increasing probability to react with increasing sound level, with 50% schools reacting to 163.3 dB re 1 μPa peak-to-peak (particle velocity level of -80.4 dB re 1 m/s), 142.0 dB re 1 μPa² s for single strike (particle velocity level -101.7 dB re 1 m²/s) 3. Further research needed on types of hazard consequences.
  • Catching step:  Prospection
• LAB: crowding trial: in simulated crowding with increasing density, IND left shoal at 15-20 IND/m³, swam individually at normal velocity until 150 IND/m³. Developed blue skin almost immediately. More body surface turning blue the longer the crowding. Abrasion (e.g., contact with the net, rubbing against each other) will result in loss of scales and mucus, leading within 2-3 days to skin loss and death 4. 
  LAB: crowding trial: 8-20 days after 15 min simulated crowding, increasing number of injured IND and increasing mortality with increasing density from 0.2% injured IND and 0% mortality at 92 kg/m³ to 0.6% injured IND and 30% mortality at 179.9 kg/m³. Injuries probably from contact with the net or other IND. All dying or dead IND had injuries 26. 
  • Catching step:  Bycatch avoidance
  • How to improve: LAB: avoid crowding beyond 92 kg/m³ before slipping
• Slipping through ≥18 m opening of bunt end of seine. Most of the time, IND did not escape – positive because keep school formation, but negative because of constraint in net. Of those escaping, they rather did in an orderly way (47%), staying in school formation without collisions. If escaping disorderly (39%), broke the school and collided with net or each other probably resulting in injuries. IND breaking away from school on their own or in small groups and escaping – only seldomly. Amount of IND escaping and way of escaping (orderly/disorderly) depending on vessel. Probability of escaping increased with increasing time of discharge left open – but so did escape in disorderly fashion, probably due to reluctance of leaving safety of school (e.g., towards predators) in threatening situation and only being forced out of the net as noise and proximity to net and conspecifics increased. Finding ways to increase orderly escapes – maybe with the help of visual stimuli – could benefit welfare 20.
  • Catching step:  Bycatch avoidance
  • How to improve: slipping through discharge opening works and keeps IND in the water and in school formation, but encouraging earlier escape would benefit welfare even more