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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
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
Fishing activities in Venice Lagoon
Artisanal fishery
1940: 25 types of net and fishing techniques
Artisanal fishery
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
Artisanal fishery – discard species
n. discard species = 22
Discard biomass vs commercial catch biomass = 14%
Fishing activities in Venice Lagoon
Mechanical Clam fishery – target species
Tapes decussatus
native species
Tapes philippinarum
non-native species
Mechanical Clam fishery – fishing technique
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 fishery
Mechanical clam
fishery
27
1
N. discarded species:
22
10
% biomass discarded
per commercial catch:
14%
139.8%
N. target species:
Conflicts
Artisanal fishery Landings (MT x 1000) from 1945 to 2001
3.00
2.50
2.00
1.50
1.00
0.50
01
20
97
19
93
19
89
19
85
19
81
19
77
19
73
19
69
19
65
19
61
19
57
19
53
19
49
19
19
45
-
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 €
Conflicts
Artisanal employes 15 time more people than mechanical
clam harvesting per weight of landings,
or 5 time more people per unit value
Aims - Valuations of externalities
The aims of the study are:
- to assign a preliminary monetary value to unmarketable
species (to estimate the natural capital);
Trophic Level
- to roughly estimate the functional value of the species
involved, basing on the previous value and on an ecological
index (to estimate functional value);
Mixed Trophic Impact
- to apply these values for assessing the externalities of
fishing effects on non-target species (discard), comparing two
different kinds of fishing activities.
Discard of fishing activities
Trophic Level
Trophic Level
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.
14
12
Price
10
TL Value
8
6
4
2
0
1,5
2
2,5
3
3,5
Trophic Level
4
4,5
5
-0.70
Clam fishery (resuspension)
Clam fishery (catches)
Artisanal fishery
Detritus
SOM & LOM
Birds
Seabass ad.
Seabass juv.
Seabream ad.
Seabream juv.
Nekton carnivorous benthic feeders
Grass goby
Sand smelt
Mullets ad.
Manila clam juv.
Mullets juv.
Macrobenthos carnivorous
Macrobenthos mixed-feeders
Manila clam comm.
Manila clam juv.
Macrobenthos filter-feeders
Macrobenthos herbivorous
Macrobenthos detritivorous
Micro-Meiobenthos
Zooplankton
Bacterioplankton
Phytoplankton
Epiphytes
Other Macroalgae
Seagrasses
Ulvales
Mixed Trophic Impact
Mixed Trophic Impact
Mixed Trophic Impact is an index which synthesize all the
interactions, positive and negative, of each species upon each other
0.50
Manila clam comm.
0.30
0.10
-0.10
-0.30
-0.50
-400
Zooplankton
Macrobenthos detritivorous
Detritus
SOM & LOM
Macrobenthos mixed-feeders
Seabream juv.
Bacterioplankton
Clam fishery (catches)
Ulvales
Other Macroalgae
Artisanal fishery
Epiphytes
Micro-Meiobenthos
Seabream ad.
Seagrasses
Nekton carnivorous benthic feeders
Macrobenthos herbivorous
Mullets juv.
Macrobenthos carnivorous
Seabass ad.
Sand smelt
Grass goby
Seabass juv.
Mullets ad.
Phytoplankton
-200
Manila clam juv.
Manila clam comm.
Clam fishery (resuspension)
Birds
Macrobenthos filter-feeders
Total MTI for impacting groups
Valuations of externalities – functional value
1000
800
600
400
200
0
TL value x MTI = Functional value
Mixed Trophic Impact
Artisanal fishery
Mechanical clam
harvesting
Birds
4
Zosterisessor
ophiocephalus
Dicentrarchus
labrax
Trophic level
Nekton
benthic feeder
Atherina
boyeri
Dicentrarchus
labrax juv
Mugilidae
juv
Sparus
aurata juv
Sparus
aurata
Macrobenthos
carnivorous
3
Mugilidae
Macrobenthos
omnivorous
Macrobenthos
detritivorous
Zooplankton
Micro-meio
benthos
Bacterioplankton
Benthic detritus
SOM & LOM
Macrobenthos
Tapes
filter feeder
philippinarum
Tapes
juveniles
philippinarum
commercial
Macrobenthos
herbivorous
2
1
Phytoplankton
Epiphyte
Seagrass
Other
macroalgae
Ulva rigida
Results
Artisanal fishery
Mechanical clam
fishery
Discard
14%
138.9%
Natural capital (TLValue):
13.6%
143%
Functional value
(MTI value):
12.4%
404%
biomasses:
scenarios
Scenario a: 0% discard dies
Scenario b: 100% discard dies
Scenario c: 50% discard dies
Artisanal fishery
Scenario b:
100% discard dies
Mechanical clam
fishery
Scenario c:
50% discard dies
scenarios
Mechanical clam
fishery
Scenario c: 50% discard dies
1 € of landing
0.72 € natural capital loss
2.02 € functional value loss
Artisanal fishery
Scenario b: 100% discard dies
1 € of landing
0.13 € natural capital loss
0.12 € functional value loss
scenarios
1999
Mechanical clam
fishery
Total landing value: 60 millions €
Natural capital loss: 43.2 millions €
Functional value loss: 121.2 millions €
Artisanal fishery
Total landing value: 2.31 millions €
Natural capital loss: 0.3 millions €
Functional value loss: 0.27 millions €
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