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