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 outline

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

Fishing activities in Venice Lagoon

Artisanal fishery 1940: 25 types of net and fishing techniques

Today only 2 types of net and fishing techniques Artisanal fishery

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

Artisanal fishery – target species Grass goby Sand smelt Cuttlefish

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

Fishing activities in Venice Lagoon

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

Mechanical Clam fishery – fishing technique

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

Fishing impacts - discard Artisanal fisheryMechanical clam fishery N. target species: N. discarded species: % biomass discarded per commercial catch: %139.8%

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

Conflicts 1999 production mechanical clam harvesting: 40,000 MT 60 millions € artisanal fishery629 MT 2.31 millions € production mechanical clam harvesting: - artisanal fishery:2,100 MT 8.5 millions € 1

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

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. Aims - Valuations of externalities Trophic Level Mixed Trophic Impact Discard of fishing activities

Trophic Level

Valuations of externalities – natural capital 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. the same energy quantity is required to sustain two different species having the same TL; TL Value

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

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

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

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

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

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

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

Conclusions value as a tool in management of fishery 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 not the habitat restoration price a value for cost-benefit analysis