Authors: Jenny Volstorf, Joly Ghanawi

Merluccius merluccius is a DEMERSAL fish species that has been found in depths ranging from 30 to 1,075 m. It is heavily exploited in the northern Atlantic Ocean and is a target species in most Mediterranean fisheries for its high economic value. Although on a global level, the IUCN status is “least concern”, in the Mediterranean, it is considered an overfished species. Among all catching methods used to catch M. merluccius, set nets – more specifically gillnets – are the most frequently used in small-scale European fisheries.

The principle of gillnets is to catch and hold IND for hours, e.g., by the gills (called “gilling”), by the head region (called “snagging”), by the mid body (called “wedging”), or by wrapping the whole body or attaching protruding body parts including teeth (called “entangling”), resulting in stress and injuries up to mortality, so there is no way to avoid this decrease in welfare except for shorter soak times. This may be a solution to IND being depredated by predators, too. Since catching of M. merluccius takes place in great depths, there is the risk of barotrauma and osmoregulatory distress. After hauling the net, IND are subjected to exposure to air, contact with the gear, experiencing their own weight, and handling (including dropping and throwing) through emersion, release from the gear, and sorting. For storing, they might already be dead which prevents prolonged suffering by asphyxia or hypothermia, but a stunning step is missing.

Accidentally caught M. merluccius experience the same treatment until they are discarded after sorting. Avoiding bycatch may be managed through mesh size, although undersized IND may still be entangled by their teeth. Closure of fishing areas or seasons might be more successful. The set net’s impact on the benthos is relatively low, as set nets are usually not dragged along the seafloor.

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

Not all specimens of the target species are equally sought after, e.g., when they are undersized, of wrong sex, wrong age, damaged, over quota, or mixed with a high proportion of undersized or unwanted non-target fishes. 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

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

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: measures to manage population besides minimal landing size and minimum mesh size (→ 4.2. Contact with the gear 4.2. Contact with the gear): total allowable catch, closure of areas to prevent catch of JUVENILES because minimum mesh size cannot avoid entangling of small IND by teeth 6.
  Fishing season off the southern Portuguese coast (the Algarve): first semester 6, in Sea of Marmara: April-May 14, March-May 9. To avoid overexploitation, recommended to regulate length of nets, fishing days per year, close areas or seasons, especially during catching season winter-spring which corresponds with reproductive period in northern Tyrrhenian sea 8.
  In simulation of management strategies for Mediterranean coast off Spain, only 83% reduction in fishing days for multispecies and multigear fisheries (set nets, longline, bottom trawl) during 5 years of simulation achieved maximum sustainable yield, which the authors consider an unrealistic decrease in fishery activity throughout the year 26.
  • How to improve: total allowable catch, regulate net length and fishing days per year, closure areas or seasons
• Non-target species: given the principle of set nets to be passive gear floating or standing in habitat that other species use or traverse, there is the risk to also catch co-existing, preyed-on, and predating species 0.
  Usable bycatch: bottom gillnets in northern Atlantic off south-west of England and Ireland in 38-327 m depth with 100-150 mm, mostly 120 mm mesh sizes, caught Pollachius pollachius, Pollachius virens, Molva molva, Gadus morhua besides target M. merluccius 20.
  Gillnets off the southern Portuguese coast (the Algarve) in 500-700 m depth with 81 mm mesh size (commercially used): 14% of biomass commercially valuable of which very commonly Micromesistius poutassou, commonly Galeus melastomus, uncommonly Brama brama, Phycis blennoides, Ruvettus pretiosus, Scyliorhinus canicula, rarely Auxis rochei, Beryx decadactylus, Helicolenus dactylopterus, Lepidopus caudatus, Lophius piscatorius, Raja clavata, Nephrops norvegicus 10.
  Multispecies fisheries off western Portuguese coast, experimental gillnets in mostly <100 m depth: commercial species Pagellus acarne, Mullus surmuletus, Trisopterus luscus, Trachurus trachurus, almost no bycatch at 90 mm 12.
  In experimental gillnets in northern Tyrrhenian sea in 95-256 m depth with mesh sizes 53, 62.5, 70, 82 mm: decreasing biomass of Trachurus trachurus (72.5% → 36.1%), increasing biomass of Chelidonichthys lucerna (2.4-9.8%), small biomass of 16-20 other species 8.
  Bottom-set gillnets in south-eastern Sea of Marmara in 50-70 m depth with mesh size 28, 30, 32 mm contained commercial species Solea solea (39.4%) 14.
  Non-usable bycatch: bottom gillnets in northern Atlantic off south-west of England and Ireland in 38-327 m depth with 100-150 mm, mostly 120 mm mesh sizes, caught Phocoena phocoena (0.4-0.7 IND/trip or 15 IND/1,000 km net set), which were already dead or dying, detangled themselves or got detangled, and Delphinus delphis. Per year, estimated 2,200 Phocoena phocoena in vessels ≥15 m or 6.2% of porpoise population in Celtic sea 20 exceeds proposed 1% rate 27↶20.
  Gillnets off the southern Portuguese coast (the Algarve) in 500-700 m depth and 81 mm mesh size (commercially used): 1% of biomass non-commercial species of which commonly Todaropsis eblanae, rarely Benthodesmus elongatus, Centrolophus niger, Chimaera monstrosa, Dalatias licha, Etmopterus pusillus, Etmopterus spinax, Hoplostethus mediterraneus, Hymenocephalus italicus, Naucrates ductor, Illex coindetii 10.
  Multispecies fisheries off western Portuguese coast, experimental gillnets in mostly <100 m depth: at mesh size 40 mm mainly (84%) low (Dicologlossa cuneata, Scyliorhinus canicula) or non-commercial species (Citharus linguatula) 12.
  Bottom-set gillnets in south-eastern Sea of Marmara in 50-70 m depth with mesh size 28, 30, 32 mm contained non-commercial species Raja clavata (0.1%), Buglossidium luteum (0.1%) which were discarded and Trachurus mediterraneus (8.2%), Chelidonichthys lucerna (2.5%), Lophius piscatorius (0.2%) which fed the crew 14.
  Some bycatch (mackerel) fed the crew 2, large bycatch was disentangled and discarded 3 5, sometimes after being heavily tossed to the floor 2 (probable makeshift stunning 0) or half-eaten by predator 2 which makes survival improbable 0.
  Hazard consequences including mortality are best avoided by preventing bycatch 0. Further research needed on gear settings and on other co-existing, preyed-on, and predating species.
  • How to improve: prefer mesh size that avoids catching non-target species
• Non-target species: catching takes place at the bottom 20 7 14 9 24. The net is usually not dragged along the seafloor 28, though, so seabed damage or huge impact on benthos is relatively low 0. Recommended to monitor the benthic habitat before deploying the net 29.
  • How to improve: impact on benthos relatively low, recommended to monitor the benthic habitat before deploying the net
• Non-target species: non-usable bycatch: when gillnets get dragged by a trawl, they may get lost and become "ghost nets". Deliberately "lost" gillnets off the southern Portuguese coast (the Algarve) in 65-78 m depth with mesh size 81 mm (commercially used) started getting holes after 3 months, torn lines after 75 days when set in September or after 248 days when set in spring. May be dragged along the bottom. Catch of number of M. merluccius IND decreased by 5% after 30 days compared to normally fishing gillnets with 24 h soak time, 35% after 90 days, probably due to biofouling on net, amount of hake remains, or strong currents. No more catches after 248 days when set in May, after 75 days when set in autumn. Per year, estimated 7,139 IND or 2,437 t M. merluccius ghost fished off Algarve 30.
  Prominent decrease in number of IND after 30 days, gradual decrease until after 230 days, residual bycatch after 12 months when study stopped. 18 species of which most frequently by number Citharus linguatula (34.2-38.7%), Scorpaena notata (23.7%) in spring, Scomber scombrus (30.7%) in autumn, most frequently by weight Lophius piscatorius, Microchirus azevia, Scorpaena notata (in sum 58.1%) in spring, Scomber scombrus, Auxis rochei, Scyliorhinus canicula (in sum 68.1%) in autumn. After 8 months, almost exclusively BENTHIC species. Per year, estimated 20,367 IND or 5.2 t ghost fished off the southern Portuguese coast (the Algarve), equalling 17,213 Euro. Estimated ghost fishing impact of ~25 FISHES or 64.4 kg/100 m of net in ~430 days of active fishing life of the ghost net. To reduce ghost fishing and the loss of nets, the following measures are recommended: implementing a Code of Good Practice, closure of areas where active and passive gear interact for one gear at a time, biodegradable nets, lower number of nets, soak time, and vessels, making reporting of lost gear mandatory, regular gear recovery attempts, gear retrieval during DEMERSAL trawl surveys 31.
  • How to improve: prevent ghost fishing: implement a Code of Good Practice, close areas where active and passive gear interact for one gear at a time, use biodegradable nets, reduce number of nets, soak time, and vessels, make reporting of lost gear mandatory, regularly attempt gear recovery, apply gear retrieval during DEMERSAL trawl surveys

How much is this species targeted annually?

Authors: Jenny Volstorf, Joly Ghanawi

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 through contact with the gear, handling/dropping, and predation pressure. To avoid it during catching/hauling, a) prefer mesh size that assures good size selectivity and that reduces catching undersized IND or large sexually productive females given body ∅ in season and region, b) prefer 7 h soak time over 12 h. To avoid it during release from the gear, sorting, and storing, take more care to avoid a decrease in welfare, but best prefer immediate stunning followed by slaughter while still unconscious. Decreasing distance to neighbour is probably not an issue in set nets. Further research needed.

1.1 Barotrauma

• Catching depth with gillnets in 24-250 m, mostly <100 m 12, 38-327 m 20, 50-70 m 14 9, 65-78 m 6, 68-405 m 21, 95-256 m 8, 150-300 m 6, 500-700 m 10 and unknown speed of hauling in nets results in barotrauma 3 22 4 5 23. Further research needed on how to avoid this.
  • Catching step:  Catching

Ruptured swim bladder: no data found yet.

Bleeding: no data found yet.

1.2 Damages/abrasions/lacerations/wounds

Eye damage: no data found yet.

Skin damage: no data found yet.

Mouth damage: no data found yet.

Opercular/gill damage: no data found yet.

Scale loss: no data found yet.

Broken spine: no data found yet.

• Given the principle of set nets to catch IND 1 2 3 4 5 by the head region (called "snagging") 6, by the gills (called "gilling") 6 7 8 9, by the mid body (called “wedging”) 6 8 9, or by wrapping the whole body or attaching protruding body parts like teeth (called “entangling”) 6 7 8, hazard consequences are probable 0. Further research needed on types of hazard consequences.
  • Catching steps:  Catching Bycatch avoidance Emersion
• The following mesh sizes assure good size selectivity, i.e., the listed sizes of IND will have contact with the gear:
  Gillnets in 500-700 m depth after 7-12 h soak time: 81 mm mesh size (commercially used) caught IND of 30-65 cm TOTAL LENGTH and avoided catch of IND <27 cm minimum landing size, avoiding bycatch 10.
  Commercial gillnets in 150-300 m depth: decreasing number of IND and increasing catching length with increasing mesh size (69.5, 81, 88.5 mm), no difference between 88.5 mm commercial and 96.3 mm experimental mesh size. Decreasing number of males, increasing number of females with increasing length. Of 17-65 cm TOTAL LENGTH caught, increasing frequency of IND <27 cm minimal catch size with increasing mesh size (0.6-2.1%), but also lower number of IND <45.3 cm size at maturity 11↶6, prompting recommendation to increase minimum mesh size to 81 mm even though minimum mesh size cannot avoid entangling of small IND by teeth 6.
  Experimental gillnets in mostly <100 m depth: highest number and weight of IND at mesh size 60, 70, 80 mm with best combination at 70 mm; largest IND but lower number at 90 mm. Of 19-67 cm TOTAL LENGTH caught, 5% IND <27 cm (minimal landing size) at 60-80 mm mesh size 12. Corresponds with legally enforced mesh size ≥80 mm given maturity in females at 45.3 cm 11↶12.
  In experimental bottom-set gillnets after average 23.3 h soak time, tendency of increasing size of caught IND with increasing mesh size (80, 100, 120 mm) when caught by gills (majority of cases); no effect when caught by teeth. Lower catch rate at 140 mm mesh size. At 120 mm mesh size (commercial size), small frequency of IND <60 cm and majority of IND 70-85 cm, indicating good size selectivity of currently used mesh size 7.
  Experimental gillnets in 95-256 m depth: tendency of increasing weight and length and decreasing number of IND with increasing mesh size (53, 62.5, 70, 82 mm). Best combination and lowest risk for catching large sexually productive females at 62.5 mm – larger than the commercially used 53 mm mesh size 8.
  Bottom-set gillnets with 28, 30, 32 mm mesh size in 50-70 m depth after 22 h soak time: highest weight and number of IND caught and of 23.5-41.0 cm TOTAL LENGTH, tendency of lowest percentage (2.7%) of IND <25 cm minimal landing size 13↶14 at 30 mm mesh size (commercially used), indicating good size selectivity of currently used mesh size 14.
  With bottom gillnets in 50-70 m depth at soak time 20-22 h, no difference in catching size between mesh sizes 28, 30, 33 mm: 23.5-41 cm TOTAL LENGTH, indicating that commercial mesh size 30 mm assures exceeding minimal landing size 9 of 20 cm TOTAL LENGTH in Turkey 15↶9.
  • Catching steps:  Catching Bycatch avoidance
  • How to improve: prefer mesh size that assures good size selectivity given body ∅ in season and region
• The following mesh sizes potentially cause bycatch, i.e., they should be avoided to prevent those IND from having contact with the gear:
  70 mm commercial mesh size with highest number of IND caught, but also high number of IND <45.3 cm size at maturity 11↶6 and high discard and scavenging rate in gillnets in 150-300 m depth, prompting recommendation to cease using 70 mm mesh size commercially 6.
  Of 19-67 cm TOTAL LENGTH caught, IND <27 cm (minimal landing size) mainly at 40 mm mesh size in experimental gillnets in mostly <100 m depth, decreasing percentage with increasing mesh size 12.
  At 80 mm mesh size, IND <60 cm caught in experimental bottom-set gillnets after average 23.3 h soak time, increasing size of caught IND with increasing mesh size 7.
  No IND <20 cm minimal landing size and no males below size at maturity (19 cm TOTAL LENGTH 17↶8), but 32.5% immature females (<35.1 cm TOTAL LENGTH 17↶8) caught at 53 mm mesh size (commercially used). Higher number of larger (potentially very sexually productive) females than males at mesh sizes 70 and 82 mm mean potentially big risk to overexploitation of population in experimental gillnets in 95-256 m depth 8.
  Lowest number of IND and weight caught and tendency of highest percentage (4.4%) of IND <25 cm minimal landing size 13↶14 at 32 mm mesh size in bottom-set gillnets in 50-70 m depth after 22 h soak time 14.
  Assuming maturity in females at 21.5 cm, in males at 25.7-27.7 cm 18↶9 19↶9, females were caught above length at maturity, but males were caught below length at maturity in 4.5-8% at mesh sizes 28, 30, 32 mm with bottom gillnets in 50-70 m depth at soak time 20-22 h 9.
  • Catching steps:  Catching Bycatch avoidance
  • How to improve: prefer mesh size that reduces catching undersized IND or large sexually productive females given body ∅ in season and region
• Given soak times of 1.5-3 h (end of lowering to end of picking up: 4.9-6.3 h), sometimes >12 h (end of lowering to end of picking up: 15-16.3 h) 21, 3-24+ h, mean 13-18 h 12, 5 h 8, 7-12 h 10, 10 h 4, average 17.2-22.1 h 20, or 20-22 h 14 9, hazard consequences are probable 0.
  In gillnets in 500-700 m depth, condition of IND decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h, probably due to scavenging crustaceans 10. Further research needed on types of hazard consequences.
  • Catching step:  Catching
  • How to improve: prefer 7 h soak time over 12 h
• No crowding step before hauling the net on board, but IND remained caught and with the same distance to other con-specifics under and above water when net was continuously hauled 1 2 3 4 5, probably not resulting in decreasing distance to neighbour 0.
  • Catching steps:  Catching Emersion
  • How to improve:
    • no risk of hazard consequences, as decreasing distance to neighbour is unlikely compared to catching methods with crowding step
    • continuous hauling instead of crowding the net prevents decreasing distance to neighbour
• During soaking, depredation rate by Tursiops truncatus 25%/haul 24. Given that depredated IND are discarded after manual disentangling 2, depradation should be avoided or at least decreased 0.
  In gillnets in 500-700 m depth, condition of IND decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h, probably due to scavenging crustaceans 10. Further research needed on types of hazard consequences.
  • Catching steps:  Catching Bycatch avoidance Discarding
  • How to improve: prefer 7 h soak time over 12 h
• Given short distance between water surface and aboard vessel and thus hardly any occasion 1 2 3 4 5, predation pressure during emersion is probably low 0. More time and more convenient occasion during soak time or hauling →3.7. Predation pressure.
  • Catching step:  Emersion
  • How to improve: low predation pressure during emersion, rather during soaking (→ 3.7. Predation pressure)
• When the net is hauled on board, IND may be catapulted on deck, and given how the effect of gravity interacts with the type of catching (snagging, gilling, wedging, entangling) and therefore how the net affects the skin and given contact with several reels along which the net is guided 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Emersion
• Given that during manual disentangling, IND may fall to the floor 5 and that after disentangling, IND are thrown into trays 1 3 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching steps:  Release from gear Sorting
• Given that manual disentangling happens fast and rough 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching steps:  Release from gear Sorting Discarding
• Given that undersized IND are discarded after manual disentangling 1 3 5, hazard consequences are probable 0. Further research needed on types of hazard consequences.
  • Catching steps:  Release from gear Sorting Discarding
  • How to improve: prefer mesh size that reduces catching undersized IND given body ∅ in season and region (→ 4.2. Contact with the gear 4.2. Contact with the gear)
• Gillnets in 500-700 m depth: 42% biomass of caught IND were discarded due to being partially or completely deteriorated by scavenging crustaceans. Condition decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h 10.
  • Catching step:  Discarding
  • How to improve: prefer 7 h soak time over 12 h
• IND were immediately gutted alive and placed in cleaning bath after disentangling and sorting 1 2 3. Given that in busy times with a full net, gutting might take place only after a waiting time in a holding container, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious
• IND were immediately gutted alive and placed in cleaning bath after disentangling and sorting, then transferred to storing containers initially without ice 1 2 3, eventually with ice 4. Given that IND are already dead when stored in containers, hazard consequences are improbable 0.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious
• Given that IND were immediately gutted alive after disentangling and sorting without prior stunning 1 2 3, hazard consequences are probable 0. Further research needed on types of hazard consequences and on quick and painless stunning methods.
  • Catching step:  Slaughter
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious
• IND were immediately gutted alive after disentangling and sorting without prior stunning 1 2 3 and placed in ice 4, which prevents live storage and prolonged suffering. Given that stunning is lacking, hazard consequences are probable 0. Further research needed on types of hazard consequences and on quick and painless stunning methods.
  • Catching step:  Slaughter
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious

1.3 Ecchymosis

Bruising and discoloration of the skin due to squeezing: no data found yet.

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 through contact with the gear, lack of oxygen, handling/dropping, and predation pressure. To avoid it during catching/hauling, a) prefer mesh size that assures good size selectivity and that reduces catching undersized IND or large sexually productive females given body ∅ in season and region, b) prefer 7 h soak time over 12 h. To avoid it during emersion, further research needed. To avoid it during release from the gear, sorting, and storing, take more care to avoid a decrease in welfare, but best prefer immediate stunning followed by slaughter while still unconscious. Decreasing distance to neighbour is probably not an issue in set nets. Further research needed.

Cortisol, glucose, lactate, other physiological stress parameters: no data found yet.

Opercular movement: no data found yet.

• Given the principle of set nets to catch IND 1 2 3 4 5 by the head region (called "snagging") 6, by the gills (called "gilling") 6 7 8 9, by the mid body (called “wedging”) 6 8 9, or by wrapping the whole body or attaching protruding body parts like teeth (called “entangling”) 6 7 8, hazard consequences are probable 0. Further research needed on types of hazard consequences.
  • Catching steps:  Catching Bycatch avoidance Emersion
• The following mesh sizes assure good size selectivity, i.e., the listed sizes of IND will have contact with the gear:
  Gillnets in 500-700 m depth after 7-12 h soak time: 81 mm mesh size (commercially used) caught IND of 30-65 cm TOTAL LENGTH and avoided catch of IND <27 cm minimum landing size, avoiding bycatch 10.
  Commercial gillnets in 150-300 m depth: decreasing number of IND and increasing catching length with increasing mesh size (69.5, 81, 88.5 mm), no difference between 88.5 mm commercial and 96.3 mm experimental mesh size. Decreasing number of males, increasing number of females with increasing length. Of 17-65 cm TOTAL LENGTH caught, increasing frequency of IND <27 cm minimal catch size with increasing mesh size (0.6-2.1%), but also lower number of IND <45.3 cm size at maturity 11↶6, prompting recommendation to increase minimum mesh size to 81 mm even though minimum mesh size cannot avoid entangling of small IND by teeth 6.
  Experimental gillnets in mostly <100 m depth: highest number and weight of IND at mesh size 60, 70, 80 mm with best combination at 70 mm; largest IND but lower number at 90 mm. Of 19-67 cm TOTAL LENGTH caught, 5% IND <27 cm (minimal landing size) at 60-80 mm mesh size 12. Corresponds with legally enforced mesh size ≥80 mm given maturity in females at 45.3 cm 11↶12.
  In experimental bottom-set gillnets after average 23.3 h soak time, tendency of increasing size of caught IND with increasing mesh size (80, 100, 120 mm) when caught by gills (majority of cases); no effect when caught by teeth. Lower catch rate at 140 mm mesh size. At 120 mm mesh size (commercial size), small frequency of IND <60 cm and majority of IND 70-85 cm, indicating good size selectivity of currently used mesh size 7.
  Experimental gillnets in 95-256 m depth: tendency of increasing weight and length and decreasing number of IND with increasing mesh size (53, 62.5, 70, 82 mm). Best combination and lowest risk for catching large sexually productive females at 62.5 mm – larger than the commercially used 53 mm mesh size 8.
  Bottom-set gillnets with 28, 30, 32 mm mesh size in 50-70 m depth after 22 h soak time: highest weight and number of IND caught and of 23.5-41.0 cm TOTAL LENGTH, tendency of lowest percentage (2.7%) of IND <25 cm minimal landing size 13↶14 at 30 mm mesh size (commercially used), indicating good size selectivity of currently used mesh size 14.
  With bottom gillnets in 50-70 m depth at soak time 20-22 h, no difference in catching size between mesh sizes 28, 30, 33 mm: 23.5-41 cm TOTAL LENGTH, indicating that commercial mesh size 30 mm assures exceeding minimal landing size 9 of 20 cm TOTAL LENGTH in Turkey 15↶9.
  • Catching steps:  Catching Bycatch avoidance
  • How to improve: prefer mesh size that assures good size selectivity given body ∅ in season and region
• The following mesh sizes potentially cause bycatch, i.e., they should be avoided to prevent those IND from having contact with the gear:
  70 mm commercial mesh size with highest number of IND caught, but also high number of IND <45.3 cm size at maturity 11↶6 and high discard and scavenging rate in gillnets in 150-300 m depth, prompting recommendation to cease using 70 mm mesh size commercially 6.
  Of 19-67 cm TOTAL LENGTH caught, IND <27 cm (minimal landing size) mainly at 40 mm mesh size in experimental gillnets in mostly <100 m depth, decreasing percentage with increasing mesh size 12.
  At 80 mm mesh size, IND <60 cm caught in experimental bottom-set gillnets after average 23.3 h soak time, increasing size of caught IND with increasing mesh size 7.
  No IND <20 cm minimal landing size and no males below size at maturity (19 cm TOTAL LENGTH 17↶8), but 32.5% immature females (<35.1 cm TOTAL LENGTH 17↶8) caught at 53 mm mesh size (commercially used). Higher number of larger (potentially very sexually productive) females than males at mesh sizes 70 and 82 mm mean potentially big risk to overexploitation of population in experimental gillnets in 95-256 m depth 8.
  Lowest number of IND and weight caught and tendency of highest percentage (4.4%) of IND <25 cm minimal landing size 13↶14 at 32 mm mesh size in bottom-set gillnets in 50-70 m depth after 22 h soak time 14.
  Assuming maturity in females at 21.5 cm, in males at 25.7-27.7 cm 18↶9 19↶9, females were caught above length at maturity, but males were caught below length at maturity in 4.5-8% at mesh sizes 28, 30, 32 mm with bottom gillnets in 50-70 m depth at soak time 20-22 h 9.
  • Catching steps:  Catching Bycatch avoidance
  • How to improve: prefer mesh size that reduces catching undersized IND or large sexually productive females given body ∅ in season and region
• Given soak times of 1.5-3 h (end of lowering to end of picking up: 4.9-6.3 h), sometimes >12 h (end of lowering to end of picking up: 15-16.3 h) 21, 3-24+ h, mean 13-18 h 12, 5 h 8, 7-12 h 10, 10 h 4, average 17.2-22.1 h 20, or 20-22 h 14 9, hazard consequences are probable 0.
  In gillnets in 500-700 m depth, condition of IND decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h, probably due to scavenging crustaceans 10. Further research needed on types of hazard consequences.
  • Catching step:  Catching
  • How to improve: prefer 7 h soak time over 12 h
• No crowding step before hauling the net on board, but IND remained caught and with the same distance to other con-specifics under and above water when net was continuously hauled 1 2 3 4 5, probably not resulting in decreasing distance to neighbour 0.
  • Catching steps:  Catching Emersion
  • How to improve:
    • no risk of hazard consequences, as decreasing distance to neighbour is unlikely compared to catching methods with crowding step
    • continuous hauling instead of crowding the net prevents decreasing distance to neighbour
• During soaking, depredation rate by Tursiops truncatus 25%/haul 24. Given that depredated IND are discarded after manual disentangling 2, depradation should be avoided or at least decreased 0.
  In gillnets in 500-700 m depth, condition of IND decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h, probably due to scavenging crustaceans 10. Further research needed on types of hazard consequences.
  • Catching steps:  Catching Bycatch avoidance Discarding
  • How to improve: prefer 7 h soak time over 12 h
• Given short distance between water surface and aboard vessel and thus hardly any occasion 1 2 3 4 5, predation pressure during emersion is probably low 0. More time and more convenient occasion during soak time or hauling →3.7. Predation pressure.
  • Catching step:  Emersion
  • How to improve: low predation pressure during emersion, rather during soaking (→ 3.7. Predation pressure)
• Given that when the net is hauled on board, IND are exposed to air 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Emersion
• When the net is hauled on board, IND may be catapulted on deck, and given how the effect of gravity interacts with the type of catching (snagging, gilling, wedging, entangling) and therefore how the net affects the skin and given contact with several reels along which the net is guided 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Emersion
• Given that when the net is hauled on board 1 2 3 4 5, IND are exposed to gravity and given no evolutionary adaptation to experiencing own weight in air 25, hazard consequences following emersion are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Emersion
• Given that during manual disentangling, IND are exposed to air 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching steps:  Release from gear Sorting Discarding
• Given that during manual disentangling, IND may fall to the floor 5 and that after disentangling, IND are thrown into trays 1 3 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching steps:  Release from gear Sorting
• Given that manual disentangling happens fast and rough 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching steps:  Release from gear Sorting Discarding
• Given that undersized IND are discarded after manual disentangling 1 3 5, hazard consequences are probable 0. Further research needed on types of hazard consequences.
  • Catching steps:  Release from gear Sorting Discarding
  • How to improve: prefer mesh size that reduces catching undersized IND given body ∅ in season and region (→ 4.2. Contact with the gear 4.2. Contact with the gear)
• Given that surviving discarded IND will have to return to their natural living depth, vertical displacement is probable 25. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Discarding
• Gillnets in 500-700 m depth: 42% biomass of caught IND were discarded due to being partially or completely deteriorated by scavenging crustaceans. Condition decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h 10.
  • Catching step:  Discarding
  • How to improve: prefer 7 h soak time over 12 h
• Given that surviving discarded IND are probably disoriented, stressed, and weakened after the catching process and release, and given that seabirds and other predators might gather near fishing boats, predation pressure is probable 25. Further research needed on how to avoid or decrease this.
  • Catching step:  Discarding
• IND were immediately gutted alive and placed in cleaning bath after disentangling and sorting 1 2 3. Given that in busy times with a full net, gutting might take place only after a waiting time in a holding container, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious
• IND were immediately gutted alive and placed in cleaning bath after disentangling and sorting, then transferred to storing containers initially without ice 1 2 3, eventually with ice 4. Given that IND are already dead when stored in containers, hazard consequences are improbable 0.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious
• Given that IND were immediately gutted alive after disentangling and sorting without prior stunning 1 2 3, hazard consequences are probable 0. Further research needed on types of hazard consequences and on quick and painless stunning methods.
  • Catching step:  Slaughter
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious
• IND were immediately gutted alive after disentangling and sorting without prior stunning 1 2 3 and placed in ice 4, which prevents live storage and prolonged suffering. Given that stunning is lacking, hazard consequences are probable 0. Further research needed on types of hazard consequences and on quick and painless stunning methods.
  • Catching step:  Slaughter
  • 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 during storing is probably not an issue in set nets, as IND are likely already dead. To be sure, prefer immediate stunning followed by slaughter while still unconscious. Further research needed.

• IND were immediately gutted alive and placed in cleaning bath after disentangling and sorting, then transferred to storing containers initially without ice 1 2 3, eventually with ice 4. Given that IND are already dead when stored in containers, hazard consequences are improbable 0.
  • 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. Further research needed for ways to avoid it.

• In ca 25 m depth, low salinity (ca 18 ppt) water from Black Sea meets high salinity (ca 38 ppt) water from Mediterranean. By fishing depth of 50-70 m 9, IND are hauled from one layer to the other, and hazard consequences are probable 0. Further research needed on the rate M. merluccius adapts to osmotic changes without decreasing welfare and on reports of osmoregulatory distress after gillnetting.
  • Catching step:  Catching

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.

Unspecified: no data found 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 from emersion on. To avoid it, prefer immediate stunning followed by slaughter while still unconscious. Further research needed.

Behaviour indicating lack of oxygen (gulping, tail beating, etc.): no data found yet.

• Given that when the net is hauled on board, IND are exposed to air 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Emersion
• Given that during manual disentangling, IND are exposed to air 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching steps:  Release from gear Sorting Discarding
• IND were immediately gutted alive and placed in cleaning bath after disentangling and sorting 1 2 3. Given that in busy times with a full net, gutting might take place only after a waiting time in a holding container, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Storing
  • How to improve: prefer immediate stunning followed by slaughter while still unconscious

Unspecified: no data found yet.

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?

There is no conclusion yet.

Inactivity/low vitality: no data found yet.

Oxidative stress: no data found yet.

Unspecified: 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?

There is no conclusion yet.

9.1 Fear (continuum up to panic)

Freeze: no data found yet.

Avoidance behaviour: no data found yet.

Startling behaviour: no data found yet.

Unspecified: no data found yet.

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 through contact with the gear and predation pressure. To avoid it during catching/hauling, a) prefer mesh size that assures good size selectivity and that reduces catching undersized IND or large sexually productive females given body ∅ in season and region, b) prefer 7 h soak time over 12 h. If bycatch and discards cannot be avoided, longlines may be the better choice compared to gillnets. Further research needed.

• Given the principle of set nets to catch IND 1 2 3 4 5 by the head region (called "snagging") 6, by the gills (called "gilling") 6 7 8 9, by the mid body (called “wedging”) 6 8 9, or by wrapping the whole body or attaching protruding body parts like teeth (called “entangling”) 6 7 8, hazard consequences are probable 0. Further research needed on types of hazard consequences.
  • Catching steps:  Catching Bycatch avoidance Emersion
• The following mesh sizes assure good size selectivity, i.e., the listed sizes of IND will have contact with the gear:
  Gillnets in 500-700 m depth after 7-12 h soak time: 81 mm mesh size (commercially used) caught IND of 30-65 cm TOTAL LENGTH and avoided catch of IND <27 cm minimum landing size, avoiding bycatch 10.
  Commercial gillnets in 150-300 m depth: decreasing number of IND and increasing catching length with increasing mesh size (69.5, 81, 88.5 mm), no difference between 88.5 mm commercial and 96.3 mm experimental mesh size. Decreasing number of males, increasing number of females with increasing length. Of 17-65 cm TOTAL LENGTH caught, increasing frequency of IND <27 cm minimal catch size with increasing mesh size (0.6-2.1%), but also lower number of IND <45.3 cm size at maturity 11↶6, prompting recommendation to increase minimum mesh size to 81 mm even though minimum mesh size cannot avoid entangling of small IND by teeth 6.
  Experimental gillnets in mostly <100 m depth: highest number and weight of IND at mesh size 60, 70, 80 mm with best combination at 70 mm; largest IND but lower number at 90 mm. Of 19-67 cm TOTAL LENGTH caught, 5% IND <27 cm (minimal landing size) at 60-80 mm mesh size 12. Corresponds with legally enforced mesh size ≥80 mm given maturity in females at 45.3 cm 11↶12.
  In experimental bottom-set gillnets after average 23.3 h soak time, tendency of increasing size of caught IND with increasing mesh size (80, 100, 120 mm) when caught by gills (majority of cases); no effect when caught by teeth. Lower catch rate at 140 mm mesh size. At 120 mm mesh size (commercial size), small frequency of IND <60 cm and majority of IND 70-85 cm, indicating good size selectivity of currently used mesh size 7.
  Experimental gillnets in 95-256 m depth: tendency of increasing weight and length and decreasing number of IND with increasing mesh size (53, 62.5, 70, 82 mm). Best combination and lowest risk for catching large sexually productive females at 62.5 mm – larger than the commercially used 53 mm mesh size 8.
  Bottom-set gillnets with 28, 30, 32 mm mesh size in 50-70 m depth after 22 h soak time: highest weight and number of IND caught and of 23.5-41.0 cm TOTAL LENGTH, tendency of lowest percentage (2.7%) of IND <25 cm minimal landing size 13↶14 at 30 mm mesh size (commercially used), indicating good size selectivity of currently used mesh size 14.
  With bottom gillnets in 50-70 m depth at soak time 20-22 h, no difference in catching size between mesh sizes 28, 30, 33 mm: 23.5-41 cm TOTAL LENGTH, indicating that commercial mesh size 30 mm assures exceeding minimal landing size 9 of 20 cm TOTAL LENGTH in Turkey 15↶9.
  • Catching steps:  Catching Bycatch avoidance
  • How to improve: prefer mesh size that assures good size selectivity given body ∅ in season and region
• The following mesh sizes potentially cause bycatch, i.e., they should be avoided to prevent those IND from having contact with the gear:
  70 mm commercial mesh size with highest number of IND caught, but also high number of IND <45.3 cm size at maturity 11↶6 and high discard and scavenging rate in gillnets in 150-300 m depth, prompting recommendation to cease using 70 mm mesh size commercially 6.
  Of 19-67 cm TOTAL LENGTH caught, IND <27 cm (minimal landing size) mainly at 40 mm mesh size in experimental gillnets in mostly <100 m depth, decreasing percentage with increasing mesh size 12.
  At 80 mm mesh size, IND <60 cm caught in experimental bottom-set gillnets after average 23.3 h soak time, increasing size of caught IND with increasing mesh size 7.
  No IND <20 cm minimal landing size and no males below size at maturity (19 cm TOTAL LENGTH 17↶8), but 32.5% immature females (<35.1 cm TOTAL LENGTH 17↶8) caught at 53 mm mesh size (commercially used). Higher number of larger (potentially very sexually productive) females than males at mesh sizes 70 and 82 mm mean potentially big risk to overexploitation of population in experimental gillnets in 95-256 m depth 8.
  Lowest number of IND and weight caught and tendency of highest percentage (4.4%) of IND <25 cm minimal landing size 13↶14 at 32 mm mesh size in bottom-set gillnets in 50-70 m depth after 22 h soak time 14.
  Assuming maturity in females at 21.5 cm, in males at 25.7-27.7 cm 18↶9 19↶9, females were caught above length at maturity, but males were caught below length at maturity in 4.5-8% at mesh sizes 28, 30, 32 mm with bottom gillnets in 50-70 m depth at soak time 20-22 h 9.
  • Catching steps:  Catching Bycatch avoidance
  • How to improve: prefer mesh size that reduces catching undersized IND or large sexually productive females given body ∅ in season and region
• Given soak times of 1.5-3 h (end of lowering to end of picking up: 4.9-6.3 h), sometimes >12 h (end of lowering to end of picking up: 15-16.3 h) 21, 3-24+ h, mean 13-18 h 12, 5 h 8, 7-12 h 10, 10 h 4, average 17.2-22.1 h 20, or 20-22 h 14 9, hazard consequences are probable 0.
  In gillnets in 500-700 m depth, condition of IND decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h, probably due to scavenging crustaceans 10. Further research needed on types of hazard consequences.
  • Catching step:  Catching
  • How to improve: prefer 7 h soak time over 12 h
• During soaking, depredation rate by Tursiops truncatus 25%/haul 24. Given that depredated IND are discarded after manual disentangling 2, depradation should be avoided or at least decreased 0.
  In gillnets in 500-700 m depth, condition of IND decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h, probably due to scavenging crustaceans 10. Further research needed on types of hazard consequences.
  • Catching steps:  Catching Bycatch avoidance Discarding
  • How to improve: prefer 7 h soak time over 12 h
• Given short distance between water surface and aboard vessel and thus hardly any occasion 1 2 3 4 5, predation pressure during emersion is probably low 0. More time and more convenient occasion during soak time or hauling →3.7. Predation pressure.
  • Catching step:  Emersion
  • How to improve: low predation pressure during emersion, rather during soaking (→ 3.7. Predation pressure)
• When the net is hauled on board, IND may be catapulted on deck, and given how the effect of gravity interacts with the type of catching (snagging, gilling, wedging, entangling) and therefore how the net affects the skin and given contact with several reels along which the net is guided 1 2 3 4 5, hazard consequences are probable 0. Further research needed on types of hazard consequences and on how to avoid or decrease them.
  • Catching step:  Emersion
• Given that undersized IND are discarded after manual disentangling 1 3 5, hazard consequences are probable 0. Further research needed on types of hazard consequences.
  • Catching steps:  Release from gear Sorting
  • How to improve: prefer mesh size that reduces catching undersized IND given body ∅ in season and region (→ 4.2. Contact with the gear 4.2. Contact with the gear)
• Gillnets in 500-700 m depth: 42% biomass of caught IND were discarded due to being partially or completely deteriorated by scavenging crustaceans. Condition decreased with increasing soak time: from 77% IND in good condition after 7 h soak time to 35% in good condition after 12 h 10.
  • Catching step:  Discarding
  • How to improve: prefer 7 h soak time over 12 h
• Given that surviving discarded IND are probably disoriented, stressed, and weakened after the catching process and release, and given that seabirds and other predators might gather near fishing boats, predation pressure is probable 25. Further research needed on how to avoid or decrease this.
  • Catching step:  Discarding
• Higher discard rate from gillnetting than longline (42% versus 7% biomass) in 500-700 m depth, together with lower catch and yield and lower quality, led to ban of gillnets in favour of longlines 10.
  • Catching step:  Discarding
  • How to improve: potentially prefer longlines over gillnets (further research needed)

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?

There is no conclusion yet.

Unspecified: no data found yet.