Fishery as a source of biodiversity loss
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Transcript of Fishery as a source of biodiversity loss
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
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 decussatusnative species
Tapes philippinarumnon-native species
Mechanical Clam fishery – target 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
N. target species:
N. discarded species:
% biomass discarded per commercial catch:
27 1
22 10
14% 139.8%
-
0.50
1.00
1.50
2.00
2.50
3.00
Conflicts
Artisanal fishery Landings (MT x 1000) from 1945 to 2001
Conflicts
1999 production
mechanical clam harvesting: 40,000 MT60 millions €
artisanal fishery 629 MT2.31 millions €
1971 -1981 production
mechanical clam harvesting: -
artisanal fishery: 2,100 MT8.5 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
Trophic level kCal/m²
VI 0.01V 0.42IV 9.29III 131.22II 393.62I 473.26Total 1007.82with Detritus 6714.28 I
II
III
IVV
Tapes area
Trophic Level
0
2
4
6
8
10
12
14
1,5 2 2,5 3 3,5 4 4,5 5
Trophic Level
Pri
ce
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
-0.70
-0.50
-0.30
-0.10
0.10
0.30
0.50
Ulv
ales
Sea
gras
ses
Oth
er M
acro
alga
e
Epip
hyte
s
Phyt
opla
nkto
n
Bac
terio
plan
kton
Zoo
plan
kton
Mic
ro-M
eiob
enth
os
Mac
robe
ntho
s de
triti
voro
us
Mac
robe
ntho
s he
rbiv
orou
s
Mac
robe
ntho
s fil
ter-
feed
ers
Man
ila c
lam
juv.
Man
ila c
lam
com
m.
Mac
robe
ntho
s m
ixed
-fee
ders
Mac
robe
ntho
s ca
rniv
orou
s
Mul
lets
juv.
Mul
lets
ad.
San
d sm
elt
Gra
ss g
oby
Nek
ton
carn
ivor
ous
bent
hic
feed
ers
Sea
brea
m ju
v.
Sea
brea
m a
d.
Sea
bass
juv.
Sea
bass
ad.
Bird
s
SO
M &
LO
M
Det
ritus
Art
isan
al f
ishe
ry
Cla
m f
ishe
ry (
catc
hes)
Cla
m f
ishe
ry (
resu
spen
sion
)
Mix
ed
Tro
phi
c Im
pa
ct
Manila clam juv. Manila clam comm.
Mixed Trophic Impact is an index which synthesize all the interactions, positive and negative, of each species upon each other
-400
-200
0
200
400
600
800
1000M
acr
ob
en
tho
s fil
ter-
fee
de
rs
Bir
ds
Cla
m f
ish
ery
(re
susp
en
sio
n)
Ma
nila
cla
m c
om
m.
Ma
nila
cla
m ju
v.
Ph
yto
pla
nkt
on
Mu
llets
ad
.
Se
ab
ass
juv.
Gra
ss g
ob
y
Sa
nd
sm
elt
Se
ab
ass
ad
.
Ma
cro
be
nth
os
carn
ivo
rou
s
Mu
llets
juv.
Ma
cro
be
nth
os
he
rbiv
oro
us
Ne
kto
n c
arn
ivo
rou
s b
en
thic
fe
ed
ers
Se
ag
rass
es
Se
ab
rea
m a
d.
Mic
ro-M
eio
be
nth
os
Ep
iph
yte
s
Art
isa
na
l fis
he
ry
Oth
er
Ma
cro
alg
ae
Ulv
ale
s
Cla
m f
ish
ery
(ca
tch
es)
Ba
cte
rio
pla
nkt
on
Se
ab
rea
m ju
v.
Ma
cro
be
nth
os
mix
ed
-fe
ed
ers
SO
M &
LO
M
De
tritu
s
Ma
cro
be
nth
os
de
triti
voro
us
Zo
op
lan
kto
n
Tot
al M
TI f
or im
pact
ing
grou
ps
TL value x MTI = Functional value
Valuations of externalities – functional value
1
3
2
4
Tro
ph
ic l
ev
el
Artisanal fishery Mechanical clamharvesting
Birds
Atherinaboyeri
Benthic detritus
Macrobenthoscarnivorous
Nektonbenthic feeder Mugilidae
juv
Sparusaurata juv Sparus
aurata
Zosterisessorophiocephalus
Dicentrarchuslabrax juv
Dicentrarchuslabrax
Zooplankton
Mugilidae
BacterioplanktonMicro-meio
benthos
Macrobenthosdetritivorous
SOM & LOM Phytoplankton Epiphyte
Macrobenthosherbivorous
Macrobenthosfilter feeder
Tapesphilippinarum
juveniles
SeagrassOther
macroalgaeUlva rigida
Tapesphilippinarum commercial
Macrobenthosomnivorous
Mixed Trophic Impact
Results
Discard
Artisanal fishery Mechanical clam fishery
biomasses:
Natural capital (TLValue):
Functional value (MTI value):
138.9%
13.6% 143%
12.4% 404%
14%
scenarios
Scenario a: 0% discard diesScenario b: 100% discard diesScenario 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: 121.2 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