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 people through river axis - Maximum height: m - Mean Temperature: 12,4 ºC - Mean rainfall: mm - Mean basin discharge: 942 hm 3 /year - Length: 75 km Item Zero

Séminaire Indicang 18 et 19 mai 2005 Eel fisheries in the basin - Launch of fisheries monitoring plan New regulation issued 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 Distance to mouth (km)) Eels/1000 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/ 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/ Catches/Fishing effort - Significant differences in CPUES among fishing gears (p=0,0003), higher in boat and sieve - -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, r 2 =.471 n=79 Independent variables: Days before new moon Days 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, ,184* N component wind Catch/day: Precipitation Flow Turbidity Water temperature Air temperature High tide level Temperature in depth N component wind E component wind Swell period E component deep current N component deep current Marine 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, r 2 =.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 VA VB VIA0 VIA1 VIA2 In the mouth Upstream - Comparison of mouth and upstream glass eels 0,070,090,110,130,150,170,19 Log (weight+1) 0,78 0,81 0,84 0,87 0,9 0,93 Log (size) Upstream: Log (size) = -0, ,802235*Log(weigth+1) r 2 =.883 Mouth Log (size) = -0, ,65796*Log(weigth+1) r 2 =.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 silting  Not 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 ,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 passes- Carle & Strub (1978) (MEMAPO) ZubietaAndoain Leitzaran Andoain Leitzaran Olazar S.P. Andatza S.P. Desemb. Width (m) Depth (cm) C1C C2C C3C CTCT Ninf./Ha N/Ha Nsup./Ha Var (N) P χ2χ g.l. 1; χ 2 0, valid.Var (N) > Zubieta: no constant catchability Leitza Olazar : no valid sampling Results yellow and silver eel

Séminaire Indicang 18 et 19 mai 2005 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 Results yellow and silver eel

Séminaire Indicang 18 et 19 mai Length (cm) % num. Eel population structure. Olazar station. Leitzaran river. Summer eels /Ha – Distance to mouth:25 Km Length (cm) % num. Eel population structure. Leitzaran station. Leitzaran river. Summer 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 Length (cm) % num. Eel population structure. Ab. Adantza station. San Pedro river. Summer eels /Ha – Distance to mouth4 Km. Eel population structure. San Pedro station. San Pedro river. Summer Length (cm) % num eels /Ha – Distance to mouth1,5 Km Results yellow and silver eel

Séminaire Indicang 18 et 19 mai 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