Gill/Drift Netting Flashcards
What is the oldest form of fishing?
Gill netting
Used for thousands of years to catch herring and pilchard
What are more efficient methods of fishing compared to gill netting?
Purse seining and pair trawling
What is gill netting?
Is sheets of thin netting allowed to drift with the tide or current to catch fish by enmeshing or entangling them
Why is gill netting nicknamed ‘walls of death’?
They are often made invisible by monofilament nylon strands
Where does gill netting take place the most?
North Adriatic region of the Mediterranean Sea
How does gill nets function?
-Long curtain of net suspended from surface by floats
-Upper corners are attached by ropes to these floats
-Net held in vertical plane by ropes fastened at their lower corners to a heavy cable/weight and anchored to sea-bed
How long are gill nets?
Up to 80m long
How wide are gill nets?
approx. 15m from top to bottom
Can gill netting be joined together?
Yes, and form walls of netting as long as 1-2km
What are gill nets used to catch in shallow water?
Mullet and mackerel
What are gill nets used to catch in deeper water?
Set on sea floor to catch sharks, nearer to surface to catch tuna
Is gill netting active or passive?
Yes,
Entangles species that move into them
How do fishers improve catches using gill netting?
Placing gear on
-Migration routes
-Across or with tidal currents
-Close proximity to refuges used by target species
What is the most selective type of fishing gear?
Gill netting
How is gill netting very selective?
-Meshes are uniform in size and shape
-Undersized fish swim through net
-Larger fish don’t get entangled
-Mesh sizes depend on target species
What is the mesh size ranges of gill netting?
50mm (smaller pelagics) to 400mm (monks, rays and swordfish)
What are the Northeast Atlantic mesh sizes for gill nets tailored for?
-Turbot
-Sole
-Bass
-Hake
What mesh size for gill netting is used to catch herring?
50 - 60mm
How does gill netting catch fish? (eg. herring)
Just wide enough to allow the herring to go so far into to the net, so that when the fish trys to retreat, the threads of meshes catch under the gill covers and prevent escape
What is gilling?
Bony fish swim into it and are caught by their gill covers (opercula)
(sharks)
What is snagging?
Parts of mouth, teeth, parts of head stuck in net
What is wedging?
Around fishes body as far as the dorsal fin
What is entangling?
Fins or other parts of body become entangled in net
How are gill nets characterised?
-Size of panels
-Number of panels
-Filament used
-Thickness of twine (visibility to target species)
What do fishers need to account for when using gill netting?
-Quality of their catch
-Time fish left in gear/water
-Risks of depredations by seals and crustacean scavengers
-Cost of retrieval vs catch rate vs losses due to decomposition and predation
What types of gill netting is there?
-Surface
-Mid-water
-Bottom-set
-Tangle nets
-Trammel nets (mainly on seabed)
What different types of gill sets are there?
-Drift
-Surface set
-Mid-water set
-Bottom set
Describe a drift set.
Not anchored, set or fixed
Describe surface sets
-Strong floats
-Top of the net is usually 2-3m below the surface
Describe mid-water sets?
Suspended mid-depth by lines
Describe bottom sets.
Anchored to bottom like a fence
-Catch rate will vary depending on the state of the tide
What is the deployment procedure of gill nets?
-Drop anchor
-Play out untangled net
-Drop anchor
What is the retrieval procedure for gill nets?
-Star from downwind
-Remove fish
-Into tub in coils
Describe tangle nets
-Single-walled nets
-Loose hung net that entangles fish rather than gilling
-Shorter nets with less floatations
-Flatfish, rays and monkfish
Describe trammel nets
-Mainly set on seabed
-3-walled net
-Inner small meshed net sandwiched between layers of large-meshed net
How does trammel nets catch fish?
Fish swims through the larger outer mesh and becomes entrapped within a pocket of netting
What species are caught in trammel nets?
Broad selection
Flatfish, rays and crustaceans
What is the hanging ratio?
Main determinant of the range of lengths of fish caught by gill nets
What is the hanging ratio formula?
Length of headline/ length of stretched mesh
What happens if the hanging ratio is low?
<50%, the net will hang slack in the water
-Net less selective
What is soak time?
Length of time that the gear remains in the water
What should maximum soaking time not exceed?
Not more than 18 hours
What is a disadvantage of long nets?
Longer time period to haul and clean it
Why should soak times not exceed 18 hours?
-Catch rates decrease after 12hrs -24 hrs
-Significant numbers are spoilt and unfit for human consumption
-Depends on water temperature
Is there significant advantages to gill netting?
-Not a lot in terms of advantages
What regulations govern gill netting?
-In general, there is few restrictions of gill nets
-Current ban on driftnetting for salmon at sea since 2006
-SW Ireland spurdog fishery collapsed in 1980s due to excessive gill netting
What was banned to 1992?
Global UN moratorium on large-scale drift nets on the high sea exceeding 2.5 km
What was banned in 2002?
EU wide ban on drift nets
-Fisheries for tuna, shark and swordfish in all EU waters except the Baltic and all EU vessels on the high seas
-Ban only applies to pelagic drift netting
What are acoustic pingers?
They are devices that emit sounds underwater at various intervals and are currently mandated in certain fisheries (EC Regulation 812/2004)
What is the purpose of acoustic pingers?
Alarms that alert dolphins and porpoises to the presence of fishing gear
-Decreases chances of entanglement
What are the disadvantages of drill netting?
-A single vessel can scoop half a ton of fish per day
-Extremely wasteful method of fishing, 40 -50 % fish escape net when hauling and some are injured in net and die later
-Evidence of illegal dumping of sheet netting
What countries heavily used gill nets in the 1980s?
Japan, South Korea and Taiwan to target tuna
What species are caught as by-catch by gill nets?
Green turtles
Leatherback turtles
Hawksbill turtle
Sharks
How much estimated fishing gear is lost per trip?
Anecdotal evidence suggests up to 30km of gear are discarded per trip
