Séminaire Indicang 18 et 19 mai 2005
Indicang – Interreg III
Situation of European eel in the Oria river basin and progress of the project
Séminaire Indicang 18 et 19 mai 2005
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
Séminaire Indicang 18 et 19 mai 2005
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
Séminaire Indicang 18 et 19 mai 2005
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
00 m
Yellow and silver eel abundance and distribution
in Oria Basin
Séminaire Indicang 18 et 19 mai 2005
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
Séminaire Indicang 18 et 19 mai 2005
Description of fisheries 2003/2004
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80
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
Séminaire Indicang 18 et 19 mai 2005
Description of fisheries 2003/2004
- 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
Séminaire Indicang 18 et 19 mai 2005
Description of fisheries 2003/2004
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
Séminaire Indicang 18 et 19 mai 2005
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
Séminaire Indicang 18 et 19 mai 2005
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
Séminaire Indicang 18 et 19 mai 2005
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
Séminaire Indicang 18 et 19 mai 2005
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
Séminaire Indicang 18 et 19 mai 2005
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
Results yellow and silver eel
Séminaire Indicang 18 et 19 mai 2005
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)
Results yellow and silver eel
Séminaire Indicang 18 et 19 mai 2005
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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Length (cm)
% num.
3.790 eels /Ha – Distance to mouth: 15 Km
Results yellow and silver eel
Séminaire Indicang 18 et 19 mai 2005
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Length (cm)
% num.
Eel population structure. Olazar station. Leitzaran river. Summer 2004
214 eels /Ha – Distance to mouth:25 Km
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Length (cm)
% num.
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
Results yellow and silver eel
Séminaire Indicang 18 et 19 mai 2005
Stream that flows in the estuary with high recruitment
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Length (cm)
% num.
Eel population structure. Ab. Adantza station. San Pedro river. Summer 2004
4.289 eels /Ha – Distance to mouth4 Km
.
Eel population structure. San Pedro station. San Pedro river. Summer 2004
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Length (cm)
% num.10.953 eels /Ha – Distance to mouth1,5 Km
Results yellow and silver eel
Séminaire Indicang 18 et 19 mai 2005
- 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?
Results yellow and silver eel