Purse Seining Flashcards
How much does purse seining contribute to global catches?
30% of global catch
What is purse seining used to catch?
Dense mobile pelagic species
-Important to catch bulk of whiting (converted to fish meal for animal feeds)
-Species with high individual value, tuna
In Northern Europe (Mainly Scotland and Norway) what do pursers target?
-Mackerel
-Herring
-Scad
What do pursers catch in the Mediterranean?
-Sardines
-Anchovy
-Tuna
What are the advantages of purse seining?
-Capable of catching tonnes of fish in one haul
-Most efficient method of catching dense shoals of fish
What does purse seining success depends on?
-Fish being near surface
-Fine calm weather conditions
What do pursers target in tropical waters?
Tuna
(French and Spanish)
How long can ocean going seines be?
Over 100 m long
Describe the purse seine net
-Wall of vertical net fencing
-Size adapted to suit vessel size and target species
-Mesh size to suit target species
How big are purse seine nets?
200 - 400 m long
60 - 90 m deep
What is the function of headropes?
Carries numerous floats to keep net on the surface
Describe the physical structure of the purse seine net
-Lower frame rope of net is equipped with a lead line and rings (purse rings) through which a special cable (purse wire) is passed
What is the function of the purse wire?
Closes off the bottom of the net and prevents fish from escaping downwards
What are stages 1-6 using a purse seine net?
- Vessel acquires target shoal on sonar
- Launch a buoy or skiff that carries a wing of the net as the vessels encircles the shoal
- Encirclement complete, net deploys to depth
4.Pursing commences, preventing escape of fish
5.Shoal brought to vessels side ready for brailing - With net dried up, vessel is ready for next shot
What do sardines do when panicked?
Similar to behaviours of adult herring
-When panicked, they sound (dives to the bottom)
What does the term the net is dried mean?
It is progressively brought on board, reducing the portion in the water that contains fish to a minimum
What is a blunt in regards to purse seining?
Is the portion of the seine net still in the water after drying that is a concentrated pocket of fish
What is the function of brailers / fish pumps
Brailers - smaller meshed nets
Function of both is transport fish from the seine to the boat
Describe purse seiners (vessels)
-Built to steam faster to reach markets as quick as possible
-Stores catch in RSW tanks to ensure good quality
-New seiners are more versatile- can pelagic trawl and purse to cope with changing patterns of fish
What does FAD stand for?
Fish Aggregating Device
What is a Fish Aggregating Device?
Manmade floating / suspended structures
Why are FADs effective?
Various species of fish congregate or associate with floating objects in the sea
What are some major disadvantages of purse seining?
-Mostly small fish swim at surface
-High mortality of target species
-By-catch mortality
-Poor monitoring of fleets
-High costs
What are by-catch species of purse seining?
-Juvenile fish
-Megafuana
-Young bigeye and yellowfin tuna
-Sharks
-Rays
-Turtles
-Spotted and spinner dolphins (Eastern tropical Pacific)
How much of the world’s tuna catch is from purse seining?
75%
What is an issue with purse seining for skipjack tuna?
Skipjack tuna shoal together with young bigeye and yellowfin tuna
-Immature fish are harvested with goes against the whole principle of fisheries management
