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Indicang. Indicang. Indicang – Interreg III. Situation of European eel in the Oria river basin and progress of the project. Characteristics of the basin :. Item Zero. - Mean basin discharge: 942 hm 3 /year. - Length: 75 km. - Mean rainfall: 1.650 mm. - Mean Temperature: 12,4 ºC.
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Indicang Indicang Indicang – Interreg III Situation of European eel in the Oria river basin and progress of the project
Characteristics of the basin : Item Zero - Mean basin discharge: 942 hm3/year - Length: 75 km - Mean rainfall: 1.650 mm - Mean Temperature: 12,4 ºC - Maximum height: 1.260 m - 126.000 people through river axis - Valleys fit in V
Eel fisheries in the basin Item Zero - More than a century of fishery activity and sale. - Decline in the stock: intuitively, no any historical data series. - Launch of fisheries monitoring plan. 2001 - New regulation issued. 2003. Agreed with the fishermen. License and daily catches report
Situation of the habitat Item Zero - Poor habitat quality - More than 100 obstacles, 1-3 m high - 24 % of total riverbank affected by hard bank reinforcement -10 Native or non defined origin fish species, 3 introduced fish species - Poor water quality in general, pollution
Item Zero 90 80 70 60 50 Eels/1000 m 40 30 20 10 0 10 20 30 40 50 60 70 Distance to mouth (km)) Yellow and silver eel abundance and distribution in Oria Basin
Results glass eel Catches report 2003/2004 First time we have data! Problems Solutions Low response Data from 40,3% of fishermen It is obligatory to deliver the catches report to obtain the new license. Apply it. Lack of precision of data Underestimation of catches Validation with samplings and data of distribution companies
Results glass eel 80 70 60 50 Fishers 40 30 20 10 0 Oct. Nov. Dec. Jan. Feb. March Trawling Sieve Wave Boat Total Date Description of fisheries 2003/2004 - Fishermen/gear - More fishermen in January - More fishermen in boat and sieve
Results glass eel 0,180 0,160 0,140 0,120 0,100 0,080 CPUEs (kg/h) 0,060 0,040 0,020 0,000 Oct. Nov. Dec. Jan. Feb. March Trawling Sieve Wave Boat Total Description of fisheries 2003/2004 - Catches/Fishing effort • Highest CPUEs in December but no significant differences among • months in each modality - - Significant differences in CPUES among fishing gears (p=0,0003), higher in boat and sieve
Results glass eel Precipitation Air temperature High tide level Water temperature E component wind Flow N component wind Turbidity N component deep current E component deep current Days before new moon Swell period Days of fishing season Temperature in depth Description of fisheries 2003/2004 Catch/day: preliminary approachStepwise forward multiple regression Independent variables: River variables: Marine variables: Boat fishing: p=0, r2=.545 n=87 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 Sieve land fishing: p=0, r2=.471 n=79 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
Results glass eel No validation Experimental samplings - In the mouth - With a motor boat, two fishermen and two sieves of 1.60 diameter (surface and depth) - Temperature, salinity, turbidity , water current speed • Just three samplings because: - started in December - Only when high entrance: change of strategy - Upstream - Samples given by the fishermen
Results glass eel Upstream In the mouth VA VB 0,93 VIA0 VIA1 0,9 VIA2 0,87 Log (size) 0,84 0,81 0,78 0,07 0,09 0,11 0,13 0,15 0,17 0,19 Log (weight+1) Mouth Log (size) = -0,437976 + 0,65796*Log(weigth+1) r2= .748 Upstream: Log (size) = -0,55478 + 0,802235*Log(weigth+1) r2=.883 Experimental samplings - Comparison of mouth and upstream glass eels • According to the pigmentation levels glass eels are in a more advanced stage upstream as we expected • No significant differences between size/weight relations (ANCOVA p=0.0764): NO SLIMMING
Results glass eel No validation this year Experimental samplings - Trap: It has just worked properly in 25 % of the days (just one sample obtained): Cause Solution High flow variability: • Flooding and silting • Not enough water to reach the base of the sample. • ???? • To increase the ramp Leafs obstruct the entrance Installation of a gadget to keep clear the entrance
Results yellow and silver eel Specific sampling stations 2004 Nº Station River Distance to mouth 1 Zubieta Oria 15 Km 2 Andoain Oria 22 Km 3 Leitzaran Andoain Leitzaran 23 Km 4 Olazar Leitzaran 25 Km 5 A. ab. Andatza San Pedro 4 Km 6 Desemb. San Pedro San Pedro 1,5 Km
Results yellow and silver eel • Zubieta: no constant catchability • Leitza Olazar : no valid sampling
Results yellow and silver eel 2 passes- Seber & Le Cren (1967) Zubieta Andoain Leitzaran 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 CT 188 160 173 18 177 394 Ninf./Ha 1877 1203 1962 55 3549 9750 N/Ha 2531 1441 2854 177 3928 11142 Nsup./Ha 3185 1679 3746 299 4307 12534 Var (N) 1239.41 275.63 1702.63 72.00 96.61 1036.03 P 0.459 0.571 0.427 0.500 0.669 0.535 Failure condition 56.996 139.377 38.927 8 408.888 243.732 • Zubieta: valid sampling but underestimated (see 3 passes) • Leitzaran Olazar : no valid sampling • In stations with high catchability the estimations are better when passing • three times
Results yellow and silver eel 3.790 eels /Ha – Distance to mouth: 15 Km 1.669 eels /Ha – Distance to mouth: 22 Km Eel population structure. Zubieta station. Oria river. Summer 2004 Eel population structure. Andoain station. Oria river. Summer 2004 . . % num. % num. 10 10 9 8 8 7 6 6 5 4 4 3 2 2 1 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Length (cm) Length (cm) Density decrease, 3 dams between the two points
Results yellow and silver eel 214 eels /Ha – Distance to mouth:25 Km 2.406 eels /Ha – Distance to mouth:23 Km Eel population structure. Leitzaran station. Leitzaran river. Summer 2004 Eel population structure. Olazar station. Leitzaran river. Summer 2004 . % num. % num. 14 14 13 12 12 11 10 10 9 8 8 7 6 6 5 4 4 3 2 2 1 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Length (cm) Length (cm) 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 Eel population structure. Ab. Adantza station. San Pedroriver. Summer 2004 Eel population structure. San Pedro station. San Pedroriver. Summer 2004 . . 10.953 eels /Ha – Distance to mouth1,5 Km 4.289 eels /Ha – Distance to mouth4 Km % num. % num. 10 10 9 9 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Length (cm) Length (cm) Stream that flows in the estuary with high recruitment
Results yellow and silver eel - The stations with higher area and depth (Zubieta, Andoain, Olazar): • Low catchability, when passing two times population underestimated • (sometimes even with three) • The stations with lower area and depth (S.P. Andatza, S.P.Desem- • bocadura, Leitzaran Andoain): - High catchability, passing three times better estimations than with two, tighter confidence limits - Litter stations: 3 passes Bigger stations: what method would fit better in these cases?
