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Fishery as a source of biodiversity loss

outline. Fishery as a source of biodiversity loss. The case study: Venice Lagoon. fishing gears commercial catch discard catch conflicts. The methodology. Trophic Levels – natural capital Mixed Trophic Impact – functional value. Results. Fishery as a source of biodiversity loss.

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Fishery as a source of biodiversity loss

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  1. outline Fishery as a source of biodiversity loss The case study: Venice Lagoon • fishing gears • commercial catch • discard catch • conflicts The methodology • Trophic Levels – natural capital • Mixed Trophic Impact – functional value Results

  2. Fishery as a source of biodiversity loss fishing impacts: species community ecosystem Discard catch: that portion of the catch returned to the sea as a result of economic, legal, or personal considerations

  3. Fishing activities in Venice Lagoon

  4. Artisanal fishery 1940: 25 types of net and fishing techniques

  5. Artisanal fishery Today only 2 types of net and fishing techniques

  6. Artisanal fishery

  7. Artisanal fishery – target species 27 target species = 6 resident species + 21 migrant species

  8. Artisanal fishery – target species Grass goby Sand smelt Cuttlefish

  9. Artisanal fishery – discard species n. discard species = 22 Discard biomass vs commercial catch biomass = 14%

  10. Fishing activities in Venice Lagoon

  11. Mechanical Clam fishery – target species Tapes decussatus native species Tapes philippinarum non-native species

  12. Mechanical Clam fishery – fishing technique

  13. Mechanical Clam fishery – fishing technique

  14. Mechanical Clam fishery – discard species n. discard species = 10 Discard biomass vs commercial catch biomass = 139.8%

  15. Mechanical clam fishery Fishing impacts - discard Artisanal fishery N. target species: 27 1 10 N. discarded species: 22 % biomass discarded per commercial catch: 14% 139.8%

  16. Conflicts Artisanal fishery Landings (MT x 1000) from 1945 to 2001

  17. Conflicts 1971 -1981 production mechanical clam harvesting: - artisanal fishery: 2,100 MT 8.5 millions €1 1999 production mechanical clam harvesting: 40,000 MT 60 millions € artisanal fishery 629 MT 2.31 millions €

  18. Conflicts Artisanal employes 15 time more people than mechanical clam harvesting per weight of landings, or 5 time more people per unit value

  19. Aims - Valuations of externalities • The aims of the study are: • to assign a preliminary monetary value to unmarketable species (to estimate the natural capital); • to roughly estimate the functional value of the species involved, basing on the previous value and on an ecological index (to estimate functional value); • to apply these values for assessing the externalities of fishing effects on non-target species (discard), comparing two different kinds of fishing activities. Trophic Level Mixed Trophic Impact Discard of fishing activities

  20. Trophic Level

  21. Trophic Level

  22. TL Value Valuations of externalities – natural capital the same energy quantity is required to sustain two different species having the same TL; As described by other authors a relationship between TL and prices of species landed exist, even if prices are greatly influenced by a lot of variables.

  23. Mixed Trophic Impact Mixed Trophic Impact is an index which synthesize all the interactions, positive and negative, of each species upon each other

  24. Valuations of externalities – functional value TL value x MTI = Functional value

  25. Artisanal fishery Mechanical clam harvesting Birds 4 Zosterisessor ophiocephalus Dicentrarchus labrax Atherina boyeri Sparus aurata juv Nekton benthic feeder Dicentrarchus labrax juv Sparus aurata Macrobenthos carnivorous Mugilidae juv 3 Mugilidae Macrobenthos omnivorous Macrobenthos filter feeder Macrobenthos detritivorous Zooplankton Tapes philippinarum juveniles Tapes philippinarum commercial Micro-meio benthos Bacterioplankton Macrobenthos herbivorous 2 Trophic level Benthic detritus Other macroalgae Ulva rigida SOM & LOM Phytoplankton Epiphyte Seagrass 1 Mixed Trophic Impact

  26. Mechanical clam fishery Results Artisanal fishery Discard 14% 138.9% biomasses: 13.6% Natural capital (TLValue): 143% Functional value (MTI value): 12.4% 404%

  27. Mechanical clam fishery scenarios Scenario a: 0% discard dies Scenario b: 100% discard dies Scenario c: 50% discard dies Artisanal fishery Scenario b: 100% discard dies Scenario c: 50% discard dies

  28. Mechanical clam fishery Artisanal fishery scenarios Scenario c: 50% discard dies 1 € of landing 0.72 € natural capital loss 2.02 € functional value loss Scenario b: 100% discard dies 1 € of landing 0.13 € natural capital loss 0.12 € functional value loss

  29. Mechanical clam fishery Artisanal fishery scenarios 1999 Total landing value: 60 millions € Natural capital loss: 43.2 millions € Functional value loss: 121.2 millions € Total landing value: 2.31 millions € Natural capital loss: 0.3 millions € Functional value loss: 0.27 millions €

  30. Conclusions discard species value are here calculated respect to natural capital and functionality • externalities due to the fishing activities • mechanical clam fishery as a high income activity value as a tool in management of fishery • not the habitat restoration price • a value for cost-benefit analysis

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