Modifying Fishing Gear to Achieve Ecosystem Objectives in Ecosystem-based Management

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					Modifying Fishing Gears to Achieve Ecosystem Objectives

John Willy Valdemarsen, FAO & Petri Suuronen, Finland

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

Harvesting pattern of Baltic Cod today:
Mortality other than fishery (M)

Spawning stock size

Too few spawners!

Catch consisting mainly of small fish and …

large part of them are discarded!
(estimated discard rate 12-20% in numbers)

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

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

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

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

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

By-catch while purse seining
• Incidental catch of dolphins while purse seining for tuna species (350 000 taken in the Pacific fisheries in the 60ies) • Capture of juvenile tuna and other nontarget fish while fishing with Fish Aggregating Devices (FADs)

Medina Panel and backdown principle to release dolphins

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

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

How fishing gears impact the ecosystem
• Alteration of the habitat that may be negative to the organisms living there
> Injure benthic organisms > Reduce habitat complexities > Reduce biodiversity

Three examples of bottom habitats
Muddy bottom

Sandy/stony bottom

Coral bottom

Overall effect of various fishing gears on bottom habitats
• • • • • • • Bottom otter trawls (---) Beam trawls (----) Dredges (-----) Demersal seines (--) Bottom-set gillnets (-) Demersal longlines (-) Traps and pots (-)

Possible technical gear modifications
• Lifting gear parts off the bottom • Use electrical stimuli to scare target objects off the bottom

Trawldoor track on sandy/stony bottom

“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)

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!!!

Fish pot

Conclusions (1)
• Modifications of fishing gears has significantly helped to reduce by-catches • Techniques that are not practical or increase costs will most likely fail • Economic rewards should be offered for the creation and use of gear modifications that reduce by-catches and minimize impacts on habitats • Co-operation between fishing industry, scientists and other stake holders is fundamental

Conclusions (2)
• Characteristics of various trawls grounds should be better known to focus the development and implementation of proper technologies and practises • Reduction of impact on grounds that has a “rich” biodiversity should be given highest priority • Areas with a complex biodiversity, like corals, should be closed for sensitive fishing like trawling and dredging • Fishing practice that has reduced bottom interaction should be promoted on grounds with an intermediate type of biodiversity

THANK YOU


				
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posted:8/4/2008
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