Modifying Fishing Gears to Achieve Ecosystem Objectives

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Modifying Fishing Gears to Achieve Ecosystem
Objectives
Directed readingChapter 3, 5 and 13Jennings,
Kaiser Reynolds 2001

• John Willy Valdemarsen, FAO
• Petri Suuronen, Finland

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Where did the name otter trawl originate?

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How fishing gears affect the ecosystem

• Removal of organisms that, for various reasons
  should not been taken (e.g. juveniles, threaten
  species)
• Alteration of the habitat that may be negative to
  the organisms living there
• Injure benthic organisms
• Reduce habitat complexities
• Reduce biodiversity

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Harvesting pattern of Baltic Cod today
Mortality other than fishery (M)
Too few spawners!
Spawning stock size
Catch consisting mainly of small fish and
large part of them are discarded! (estimated
discard rate 12-20 in numbers)
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Examples of gear modifications that reduce
unwanted by-catch

• Turtle Excluder Device (TED)
• Shrimp-fish separators
• Size selective grids
• Square mesh windows
• Medina panel/ Backdown principle to avoid
  dolphins in tuna purse seining
• Bird scaring lines in longline fishing
• Selective trap nets

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Turtle Excluder Device for Shrimp trawls

• Releases Turtles
• Retains target shrimps
• Debris blocking the grid can cause some loss of
  catch
• TEDs are mandatory in many tropical shrimp
  fisheries
• Further developments are directed to also avoid
  fish bycatch

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Nordmøre grid for separating shrimp and fish

• Retains shrimp
• Releases fish by-catch
• Improves quality of target catch
• Reduces sorting work onboard
• Increases yields of non-targets for other
  fisheries
• Mandatory in a number of fisheries

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Size sorting grid

• Small, juvenile fish are released
• Size sorting with grids is less dependant on high
  catch rates than meshes
• Properly designed and used size sorting grids
  may allow fishing to continue in areas where the
  abundance of young fish is high

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Square mesh window to release small fish

• Square meshes stay open during towing
• Square mesh panels are cheap and simple size
  selective devices
• Square mesh windows are mandatory in some
  fisheries

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By-catch while purse seining

• Incidental catch of dolphins while purse seining
  for tuna species (350 000 taken in the Pacific
  fisheries in the 1960s)
• Capture of juvenile tuna and other non-target
  fish while fishing with Fish Aggregating Devices
  (FADs)

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Medina Panel and backdown principle to release
dolphins
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Modified salmon trap to avoid seal capture

• Grid in the entrance prevents seals from entering
  the trap
• Strong outside netting also prevents seals from
  breaking into the trap
• The captured salmon is safe from seal attack and
  seals are not trapped

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Bird-Scaring line to reduce seabird capture
during longline fishing

• Seabirds try to take bait from hooks during
  setting of longlines and might self be hooked
• This is particularly a problem for albatrosses
  and petrels in Southern Oceans
• Mitigations tools such as scaring lines
  significantly reduce the problem

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How fishing gears impact the ecosystem
Coral bottom
Sandy/stony bottom
Muddy bottom
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Overall effect of various fishing gears on bottom
habitats

• Dredges (-----)
• Bottom otter trawls (---)
• Beam trawls (--)
• Demersal seines (--)
• Bottom-set gillnets (-)
• Demersal longlines (-)
• Traps and pots (-)

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Trawldoor track on sandy/stony bottom
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Smart trawling technology

• Reduced bottom impact of trawl gears can be
  achieved by
• Lifting the trawl doors from bottom
• Using dropper chain instead of roller gear to
  keep bottom contact
• Other ground gear designs (size, material, and
  construction of rollers)

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Change of fishing practise

• Close the most sensitive areas for fishing
  (Monitor activity with VMS)
• Concentrating fishing effort where density of
  fishing objects are highest (High CPUE)
• Replace harmful fishing gears with gears that are
  less harmful to the bottom habitat, like a fish
  pot!!!