Indicang – Interreg III

Séminaire Indicang 18 et 19 mai 2005

Indicang – Interreg III

Situation of European eel in the Oria river basin and progress of the project


Characteristics of the basin :

- Valleys fit in V

- 126.000 people through river axis

- Maximum height: 1.260 m

- Mean Temperature: 12,4 ºC

- Mean rainfall: 1.650 mm

- Mean basin discharge: 942 hm3/year

- Length: 75 km

Item Zero


Eel fisheries in the basin

- Launch of fisheries monitoring plan. 2001

- New regulation issued. 2003. Agreed with the fishermen.License and daily catches report

- Decline in the stock: intuitively, no any historical data series.

- More than a century of fishery activity and sale.

Item Zero


Situation of the habitat

-10 Native or non defined origin fish species, 3 introduced fish species

- 24 % of total riverbank affected by hard bank

reinforcement

- More than 100 obstacles, 1-3 m high

Item Zero

- Poor habitat quality

- Poor water quality in general, pollution

Séminaire Indicang 18 et 19 mai 2005 Item Zero

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10 20 30 40 50 60 70Distance to mouth (km))

Eel

s/10

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Yellow and silver eel abundance and distribution

in Oria Basin


Catches report 2003/2004

Validation with samplings and data of distribution companies

Lack of precision of data

Underestimation of catches

It is obligatory to deliver the catches report to obtain the new license. Apply it.

Low response

Data from 40,3% of fishermen

SolutionsProblems

First time we have data!

Results glass eel


Description of fisheries 2003/2004

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Oct. Nov. Dec. Jan. Feb. March

Date

Fis

he

rs

Trawling

Sieve

Boat

Wave

Total

- Fishermen/gear

- More fishermen in January

- More fishermen in boat and sieve

Results glass eel



- Catches/Fishing effort

- Significant differences in CPUES among fishing gears (p=0,0003),higher in boat and sieve

-

Trawling

Sieve

Boat

Wave

Total0,000

0,020

0,040

0,060

0,080

0,100

0,120

0,140

0,160

0,180

Oct. Nov. Dec. Jan. Feb. March

CP

UE

s (k

g/h

)

-Highest CPUEs in December but no significant differences among months in each modality

Results glass eel



preliminary approach Stepwise forward multiple regression

Sieve land fishing: p=0, r2=.471 n=79

Independent variables:

Days before new moonDays of fishing season

Catch=91606,8-205,04*days of fishing season-599,67*days before new moon+6990,* High tide level-6952,37*Temperature in depth- Precipitation*117,808 +380,184* N component wind

Catch/day:

Precipitation

FlowTurbidity

Water temperatureAir temperature

High tide level

Temperature in depth

N component windE component wind

Swell periodE component deep currentN component deep currentMarine variables:

River variables:

Catch=14424,8-28,01*days of fishing season-104,334*days before new moon+725,09* High tide level-1022,3* Temperature in depth+7.13*Turbidity

Boat fishing: p=0, r2=.545 n=87

Results glass eel


Experimental samplings

- With a motor boat, two fishermen and two sieves of 1.60 diameter (surface and depth)

- Just three samplings because:

- Temperature, salinity, turbidity , water current speed

- In the mouth

- Upstream

- Samples given by the fishermen

- Only when high entrance: change of strategy

- started in December

No validation

Results glass eel


Experimental samplings

-According to the pigmentation levels glass eels are in a more advanced stage upstream as we expected

VAVBVIA0VIA1VIA2

In the mouth Upstream

- Comparison of mouth and upstream glass eels

0,07 0,09 0,11 0,13 0,15 0,17 0,19Log (weight+1)

0,78

0,81

0,84

0,87

0,9

0,93

Lo

g (

size

)

Upstream: Log (size) = -0,55478 + 0,802235*Log(weigth+1) r2=.883

Mouth Log (size) = -0,437976 + 0,65796*Log(weigth+1) r2= .748

-No significant differences between size/weight relations (ANCOVA p=0.0764): NO SLIMMING

Results glass eel


Experimental samplings- Trap:

Installation of a gadget to keep clear the entrance

Leafs obstruct the entrance

????To increase the ramp

High flow variability:Flooding and siltingNot enough water to reach the base of the sample.

SolutionCause

It has just worked properly in 25 % of the days (just one sample obtained):

No validation this year

Results glass eel


1,5 KmSan PedroDesemb. San Pedro6

4 KmSan PedroA. ab. Andatza5

25 KmLeitzaranOlazar4

23 KmLeitzaranLeitzaran Andoain3

22 KmOriaAndoain2

15 KmOriaZubieta1

Distance to mouth

RiverStationNº

Specific sampling stations 2004

Results yellow and silver eel


3 passes- Carle & Strub (1978) (MEMAPO)

Zubieta AndoainLeitzaran Andoain

Leitzaran Olazar

S.P. Andatza

S.P. Desemb.

Width (m) 30 34 14 13 4 4

Depth (cm) 30 - 120 30 - 120 30 - 40 30 - 120 20 - 30 20 - 30

C1 122 112 110 12 133 269

C2 66 48 63 6 44 125

C3 68 35 22 6 26 55

CT 256 195 195 24 203 449

Ninf./Ha 2774 1488 2209 123 4050 10420

N/Ha 3790 1669 2406 214 4289 10953

Nsup./Ha 4807 1851 2602 304 4527 11487

Var (N) 2994.42 160.14 82.62 39.52 38.43 152.01

P 0.290 0.477 0.530 0.421 0.595 0.548

χ2 5.1360 2.4196 2.1542 1.0542 2.5326 0.0710

g.l. 1; χ20,95 3.841

valid.Var (N) 9.665 24.601 32.286 2.164 45.780 81.398

> 6.042 2.919 2.274 3.704 1.610 2.074

•Zubieta: no constant catchability

•Leitza Olazar : no valid sampling



243.732408.888838.927139.37756.996Failure

condition

0.5350.6690.5000.4270.5710.459P

1036.0396.6172.001702.63275.631239.41Var (N)

125344307299374616793185Nsup./Ha

111423928177285414412531N/Ha

9750354955196212031877Ninf./Ha

39417718173160188CT

125446634866C2

26913312110112122C1

20 - 3020 - 3030 - 12030 - 4030 - 12030 - 120Depth (cm)

441314 3430Width (m)

S.P. Desemb.

S.P. Andatza

Leitzaran Olazar

Leitzaran AndoainAndoainZubieta

2 passes- Seber & Le Cren (1967)

•Leitzaran Olazar : no valid sampling

• In stations with high catchability the estimations are better when passing

three times

•Zubieta: valid sampling but underestimated (see 3 passes)



Density decrease, 3 dams between the two points

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Length (cm)

% num.

Eel population structure. Andoain station. Oria river. Summer 2004

1.669 eels /Ha – Distance to mouth: 22 Km

Eel population structure. Zubieta station. Oria river. Summer 2004

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3.790 eels /Ha – Distance to mouth: 15 Km



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Eel population structure. Olazar station. Leitzaran river. Summer 2004

214 eels /Ha – Distance to mouth:25 Km

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Eel population structure. Leitzaran station. Leitzaran river. Summer 2004

2.406 eels /Ha – Distance to mouth:23 Km

Strong decrease between 1,5 and 2kms. A nearly insuperable dam.

Upstream few eels and the population structure does not fit to this point



Stream that flows in the estuary with high recruitment

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Length (cm)

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Eel population structure. Ab. Adantza station. San Pedro river. Summer 2004

4.289 eels /Ha – Distance to mouth4 Km

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Eel population structure. San Pedro station. San Pedro river. Summer 2004

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% num.10.953 eels /Ha – Distance to mouth1,5 Km



- The stations with higher area and depth (Zubieta, Andoain, Olazar):

-The stations with lower area and depth (S.P. Andatza, S.P.Desem-bocadura, Leitzaran Andoain):

- Litter stations: 3 passes

-Low catchability, when passing two times population underestimated (sometimes even with three)

- High catchability, passing three times better estimations than with two, tighter confidence limits

Bigger stations: what method would fit better in these cases?


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Indicang – Interreg III