from the descriptor collection till the indicator definition

Glass Eel thematic box 0Porto 6-7th ofJune 2006

Glass-Eel Thematic boxFrom the descriptor collection till

the indicator definition

Authors by alphabetic order:J.-C. Bouvet, N. Bru; M.-N de Casamajor; G. Castelnaud; S.

Dossou-Gbete et P. Prouzet


Descriptors are used to characterize, for a given biological stage, various contexts and features which will allow to define the indicators and to interpret them

Environmental and administrative contextsFishery contextBiological featuresAbundance Anthropogenic impacts


Environmental and administrativecontexts


Hydrodynamic and administrative contexts An example : The Adour river

NL-3 NL-1 NL+1NL+3 PQ-2 PQ PQ+2 PL-3 PL-1 PL+1 PL+3 DQ-2 DQ DQ+2LUNE

0

1

2

3

4

CPUE

Cm

oy

Moon phases and catches

0

2

4

6

8

10

12

14

16

18

01/11

/0106

/11/01

11/11

/0116

/11/01

21/11

/0126

/11/01

01/12

/0106

/12/01

11/12

/0116

/12/01

21/12

/0126

/12/01

31/12

/0105

/01/02

10/01

/0215

/01/02

20/01

/0225

/01/02

30/01

/0204

/02/02

09/02

/0214

/02/02

19/02

/0224

/02/02

01/03

/0206

/03/02

11/03

/0216

/03/02

21/03

/02

T°c

-4.00

-2.00

0.00

2.00

4.00

6.00

8.00

10.00

Diff

éren

tiel t

herm

ique

(°c)

T°c - mer T°c - estuaire Différentiel thermique

Thermal contrast

20

30

40

50

60

70

80

90

100

110

120

01/11

/1999

07/11

/1999

13/11

/1999

19/11

/1999

25/11

/1999

01/12

/1999

07/12

/1999

13/12

/1999

19/12

/1999

25/12

/1999

31/12

/1999

06/01

/2000

12/01

/2000

18/01

/2000

24/01

/2000

30/01

/2000

05/02

/2000

11/02

/2000

17/02

/2000

23/02

/2000

29/02

/2000

06/03

/2000

12/03

/2000

18/03

/2000

24/03

/2000

Saison 1999/2000

Coe

ffic

ient

de

mar

ée

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Déb

it en

m3.

s-1

COEF DEBITS

Tide coefficient & flow rate

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25 30 35Km

vite

sse

m/s

t:2.0ht:4.0ht:6.0ht:8.0ht:10.0ht:12.0ht:14.0ht:16.0ht:18.0h

Bayonne Urt

PM : 7h09 - 19h30BM : 0h53 - 13h19

Dynamic front tide

Salinity front

012

012

3,14,15,16,17,28,29,2

7,5 8,5 9,5 10,5 11,5 12,5 13,5

10 15 20 25 30 35Salinity (g/l)

Temperature (°C)

W E

Dep

th(m

)

50

Freshwater

Seawater

Maritime zone

River zonePush sieves

Hand sieves

0

200

400

600

800

1000

1200

1400

1711

2411 51

2

1112

1912

2912 80

1

1601

2201

3001 50

2

1302

Dates campagne 1997/1998

Déb

its e

n m

3/s

0

20

40

60

80

100

120

140

160

180

200

NTU

Débits Turbidité

Turbidity and flow rate


Fishery context


Descriptors and fisheries monitoring

The fishery descriptors and primary Socio Economic ones proceed from the fishing results, the fishing activity, and are linked to the fisheries monitoring systems which permit to collect the data; they are of 2 kinds:

1.Compulsory declaration ( logbook), from the whole population;2. if no existence, impossibility or for assessment:

Data obtained from a representative sample of professional fishermen ( equal to the cooperative sample used by Cemagrefsystem) ;

The (sophisticated) Socio-Economic Descriptors (SED) are coming from the Fishing enterprise (production factor = workers,vessels, gears and facilities) and from the market (trading, purchases); they involve socio-economic surveys.

Glass Eel thematic box 0Porto 6-7th ofJune 2006Fishery and Socio-Economic (primary) Descriptors

Fisheries statisticsSED and FD

Socio-economicobjective

Biologicalobjective

The aim is to collect descriptors in order to : estimate, under some requirements, the abundance of the species ; estimate the viability of the fishing enterprises ;provide information on biological processes ;compare the fisheries among catchments ;


Descriptors of fishing pressure (I) performance and economic viability (II)

Ratio per season between (examples):1) number of fishermen (by category and all categories)/ Total surface basin 2) production (idem)/ Colonized surf. by Glass eel 3) total surf. Scoop net/ Surf. technically fishableRatio per season between (examples):1) total turn over of the glass eel fisheries/ total turn over of the eel fisheries)2) total turn over of the glass eel fisheries / Total t.o. all species3) total turn over of the glass eel fisheries / Nber of fishermen 4) total turn over of the glass eel fisheries / Surf. technically fishable.

(I)

(II)


From rough to accurate: fishery Descriptors

- Capture: weight in kg for glass eel;

- Effort: season, Nber of fishermen, Nber of fishing days, Nber of gears, tot. surface of straining, tot. filtered volume (units: 1 fisherman-season, 1 day-fisherman, 1 gear, m2, m3 );

- CPUE: weight / season, weight / group of fishermen, weight / fishermen, weight / fishing day, weight / gear, weight / m2, weight/ m3 ….

They lead to recruitment index recruitment estimation(associated to scientific fishing experiments)

They need: historical seriesdata of good quality

Only possible in catchments where exploitation existsProblem of data availability and reliability


Biological features


Biological descriptorsLength (mm)

Weight (mg)

Pigmentation stage(Document de référence: Elie et al., 1982 ; Grellier et al., 1991)

Glass eel biometric descriptors

Validation of sampling protocol


Glass eel biometric descriptors

• Sampling conditionsHydrography locationTemporal frequencyPeriodicity of sampling Recommendation for

validation of descriptors

Each yearMonthly (New Moon)

50 individuals (minimum)Temperature + Salinity

Dynamic and salinity tide area• Quantity of individuals

Number of individualsMini 50 – if possible 100(according to the homogeneity of pigmentation stage in the sample)

• Environmental conditionsTemperatureSalinityTurbidity


Glass eel biometric indicatorsDistribution of the pigmentation stages

on two rivers

Isle

VB94%

VA6%

Loire


Example

Adour

Glass eel biometric indicatorsCondition factor of glass eel (w/alb)

Length – Weight

Monthly samplingOn new moon


How to determinate the glass eel abundance and its variation ?

0

20

40

60

80

100

120

140

01/1

1/19

98

08/1

1/19

98

15/1

1/19

98

22/1

1/19

98

29/1

1/19

98

06/1

2/19

98

13/1

2/19

98

20/1

2/19

98

27/1

2/19

98

03/0

1/19

99

10/0

1/19

99

17/0

1/19

99

24/0

1/19

99

31/0

1/19

99

07/0

2/19

99

14/0

2/19

99

21/0

2/19

99

28/0

2/19

99

07/0

3/19

99

14/0

3/19

99

21/0

3/19

99

Poid

s tot

al c

aptu

ré p

ar jo

ur (K

g)

Tamis à main Tamis poussé

Nov Dec Jan Feb1999 2000

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

*

* ****

*

*

*

Biomasse estimée sur certains joursBiomasse extrapolée sur la saisonBiomasse observée


From catches to abundanceCatch equation :Catch quantity equals to the product of q by effort intensity and bythe ratio of glass eel abundance on the size in space and time of the dispersion area.

So the catch per unit effort is proportional to the density of glass eel and proportional to abundance if the dispersion area remains the same from one year to another.

ANfqC ×Δ×=Δ

AN

fC q ×=Δ

Δ

0

1 000

2 000

3 000

4 000

5 000

6 000

7 000

8 000

9 000

10 000

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Cap

ture

s (kg

)

0 .0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

kg / sortie

kg kg/sortie tamis kg/sortie pibalour

Glass Eel thematic box 0Porto 6-7th ofJune 2006Relevant descriptors for biomass

Two possibilities :

Computation and measurement system :

Ideal !!

More realistics…

Type of data collection

Calculated Observed

Exhaustive Number

Partial Glass eel density Number

• Glass eel fish ladders• Special fisheries

(below dams…)

• Section of fishing gears• Time span by fishing• Speed of filtration

Professional fishery statisticsScientific sampling surveys


Estimates of Glass eel density :Some examples of sampling protocol

El Minho (Portugal) The Adour river (France)

Professional catches Scientific sampling surveys

Tamis poussés (points d’échantillon--nage)

Fond

Surface

RDMRG

Aval

Courant

S1 S2 S3S4 S5 S6

Rive gauche Milieu Rive droite

Transect

S1,.. Compartiments

Tamis poussés (points d’échantillon--nage)

Fond

Surface

RDMRG

Aval

Courant

S1 S2 S3S4 S5 S6

Rive gauche Milieu Rive droite

Transect

S1,.. Compartiments


Vilaine River (France) Glass eel fish ladders

Professional catches below dam(strong catchability)

Glass eel counts :Some examples of sampling protocol

Counts through glass eel ladders


From glass eel density : From glass eel counts :

Computation of some biomass indicators

densitydensity ×× waterwater volume of volume of spreadingspreading

Sum Sum of of countscounts

i. Glass eel migratory behaviourii. Known hydroclimatic parametersiii. In a fixed part of the water colum :

be able to compute glass eel densities

Basic mathematical principle Basic mathematical principle

i. How to compute the part of the glass eel run coming through the glass eel fish ladders ?

Underlying constraints Underlying constraints

Absolute indicator of biomassVia observed

descriptorsVia calculated

descriptors

Glass Eel thematic box 0Porto 6-7th ofJune 2006Computations of glass eel biomass indicator : To estimate the fishery impact

01/11/1998 27/11/1998 24/12/1998 19/01/1999 15/02/1999

Date (jrs)

0

500

1000

1500

2000

Bio

mas

se jo

urna

lière

(kg)

0

200

400

600

Cap

ture

s pr

ofes

sion

nelle

s (k

g)

31/10/1999 30/11/1999 30/12/1999 29/01/2000 28/02/2000

Date (jrs)

0

1000

2000

3000

Bio

mas

se jo

urna

lière

(kg)

0

200

400

600

800

Cap

ture

pro

fess

ionn

elle

(kg)

01/11/2000 27/11/2000 24/12/2000 19/01/2001 15/02/2001

Date (jrs)

0

200

400

600

800

Bio

mas

se jo

urna

lière

(kg)

0

100

200

300

400

Cap

ture

s pr

ofes

sion

nelle

s (k

g)

Biomasse estiméeBiomasse estimée (lissage)Biomasse calculéeCaptures prof.


Rate of exploitation some examples for the Adour river

Fishing season 1998-1999Total catches = 1,65 tonsSeasonal rate of exploitation = 10,1% [6,5 – 17,1%]Mean daily rate of exploitation = 11,8% [6,5 – 17,1%] Seasonal biomass = 16,4 tons [14,9 – 17,8]Fishing season 1998-1999Total catches = 4,58 tonsSeasonal rate of exploitation = 7,8% [7,4 – 8,1%]Mean daily rate of exploitation = 12,1% [8,8 – 15,3%] Seasonal biomass = 59,2 tons [56,7 – 61,6]Fishing season 1998-1999Total catches = 1,45 tonsSeasonal rate of exploitation = 22,9% [19,4 – 25,5%]Mean daily rate of exploitation = 23,2% [17,2 – 29,2%] Seasonal biomass = 6,6 tons [5,7 – 7,5]


Thank You

from the descriptor collection till the indicator definition

Documents