1. Noëlle BRU Laboratoire de Mathématiques et ses Applications UMR CNRS 5132 Université de Pau et des Pays de l’Adour  : noelle.bru@univ-pau.fr Patrick PROUZET IFREMER LRHA Michel LEJEUNE Université Grenoble 2 As an example the Adour Estuary (Southwestern part of France)

2.  About management groups :  ICES (International Council for the Exploration of the sea): “the stock of European eel (Anguilla Anguilla L.) is outside safe biological limit and that current fisheries are not sustainable”.  18 September 2007: the Council of the European Union adopted a council regulation (EC 1100/2007) establishing measures for the recovery of stock of European eel.  November 2007 : the IUCN (International Union for Conservation of Nature) listed the European eel on its Appendix II and considered the eel as an endangered species.  Glass eel = young eel...  Passive migration…  During flood tide…  Mainly by night… Colloque ASP - Boulogne sur Mer 20082 General context… (source : IFREMER)

3. Colloque ASP - Boulogne sur Mer 20083  In European estuaries: constant decrease is observed for several years. Over-exploitation at the different phases of the biological cycle ? Inland habitat loss ? Climate and ocean current changes ? Diseases ? Degradation of continental environment and pollution ?…  An estimate of biomass is needed : To quantify the importance of this decrease To study the link with all the possible causes... But absolute fish abundance in an open ocean region is hard to obtain... General context… ?

4. Colloque ASP - Boulogne sur Mer 20084 Most methods : » Designed for a fixed stock within a given area » Geostatistical approaches » Hydroacoustics campaigns… A specific method :  in a particular environment : from the mouth of a estuary + an area of migration...  a species with a specific migratory behavior...  a method to compute an efficient estimate of glass eels abundance... Problems…

5. Colloque ASP - Boulogne sur Mer 20085 Used to propose biomass estimates… How and why to put together these datasets ?? About the talk... What are the data available to do so ? Historical time series of professional catches (by day, into the maritime area) Data from scientific in situ surveys Step 1 Step 2 Are they really good indicators of abundance ?

6. Step 1 of the method : Using data from scientific in situ surveys… Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment « Observed » glass eels biomass estimates (source IFREMER)

7. Colloque ASP - Boulogne sur Mer 20087 All samples are assumed to be simultaneous... 1 passage  30 min ( 8 passages max !!!) …… during the flood tide…. 5 min 10 min Right Bank MiddleLeft Bank Glass eel densities (in g/100m 3 ) s=1…S (=6)k=1,…, n(=8) Main Push-sieve fishery Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment The Adour estuary

8. Colloque ASP - Boulogne sur Mer 20088 Total biomass (in kg) for the flood tide period through vertical region R Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment J different schemes tested…

9. Colloque ASP - Boulogne sur Mer 20089 We need a functional form for each term!! Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment For the current speed v s (t)… A sinusoidal model depending on time A log-log linear model depending on the current speed For glass eels density d s (t)… An explicit form for the estimate + An evaluation of its variability to correct possible errors of measurement to evaluate the beginning and the end of the flood tide

10.  Finally, ◦ Simple method... With sparse data... ◦ Some approximations and hypothesis… ◦ More surveys than results... ◦ But “observed” biomasses seems “realistics” !  Method easily adaptable for other estuaries  Exploitation rates for push- sieve are derived by days... Colloque ASP - Boulogne sur Mer 200810 Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment SeasonDayBiomass (in Kg)push-sieve catches (in Kg) 98/99 12/01/19991386 14/01/19993798,2 22/01/199915711,2 28/01/1999424,5 11/02/1999794,6 17/02/199920614,5 17/03/199920313,5 99/00 09/12/1999159736,79 22/12/199966421,15 05/01/200040977,31 07/01/200082163,64 08/01/200076334,67 09/01/200099312,56 12/01/2000958,79 01/02/2000171536,18 08/02/20004641,2 00/01 14/12/20001523,2 21/12/200013414,7 03/01/2001283 10/01/20019711,5 12/01/20018118,1 24/01/200126464,5 26/01/200113245,9 02/03 03/01/20035530,4 22/01/2003822,6 03/04 26/11/2003808,2 21/01/2004378,2 04/05 09/11/200455010,3 18/11/200425733,8 23/11/2004371,5 08/12/200437513 14/12/200419817,6

11. Step 2 of the method : Using both information (« observed » estimates and professional catches) Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment for a fixed fishing season Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment

12. Colloque ASP - Boulogne sur Mer 200812 Model ? Dependent variable : rate of exploitation Explanatory variables : catches + environmental variables Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment Professional catches with push-sieves « observed » biomass Data concerning the same glass eel run !!

13.  Model : glm( Rate ~ TurbCod + Catches^0.646 + TideCod+ FlowCod * Moon+catches*Moon) ◦ Gamma distribution (with canonical link = inverse) ◦ Coded explanatory variables : Colloque ASP - Boulogne sur Mer 200813 Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment TurbCodTideCodFlowCod 1 if <13 NTU 2 otherwise. 1 if <60, 3 > 86 2 otherwise 1 if <250 m 3 /s, 3 > 400 m 3 /s 2 otherwise Degree of freedomDeviance Residual Degree of freedomF valuePr(F) NULL31 TurbCod19,5723018,7460,001 Catches^0,67813,185296,2370,024 TideCod20,939270,9190,419 FlowCod:Moon87,044191,7240,168 Catches:Moon31,295160,8450,489 With 32 observations…

14. Colloque ASP - Boulogne sur Mer 200814 « cleaned » values + A variability associated to each predicted value of the rate of exploitation ! Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment Values >100 or < 0 Predicted rate of exploitation <1,5% and catches >100kg tide 600m 3 /s

15. Colloque ASP - Boulogne sur Mer 200815 Smoothed biomass (by gaussian kernels) Predicted biomass + erreur « observed » biomass + error of prediction Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment With a estimated standard error around 7 T

16. Colloque ASP - Boulogne sur Mer 200816 + Glass eels recruitment for a fixed season ??? Known for every night (see before)unknown Hyp : mean value between two consecutive nights Fishing season Catckes with push- sieves in kg Total catches in kg Biomass in kg Rate of exploitation of push-sieves Glass eels recruitment in kg Overall rate of exploitation 1998/1999 1,655 ~ 6,000 28,200 5.9%53,47811.2% 1999/2000 4,579 ~15,000 96,900 4.7%181,3548.3% 2000/2001 1,446 1,983+F 15,500 9.3%32,990 2001/2002 770 2,395+F 20,600 3.7%43,307 2002/2003 388 0,594+F 3,100 12.5%6,231 2003/2004 1,093 2,969 8,700 12.6%17,55016.9% 2004/2005 1,398 7,183 27,700 5.0%59,29212.1% 2005/2006 686 3,531 7,870 8.7%15,71922.4% average 1,50226,070 7,85%51,240 median 1,24618,050 7,3%38,149 Step 1 : In situ scientific surveys… Sampling protocol and data Statistical method for estimation of « observed » glass eels biomass Results and discussion Step 2 : Using professional catches… Estimate of seasonal glass eels biomass migrating by night Estimate of glass eels recruitment

17.  Need to explicit the precision of each estimates at each step of the calculus.  The method is adaptable to other estuary but with the search of a model…  But the level of seasonal biomass is realistic !! Colloque ASP - Boulogne sur Mer 200817 Conclusions and perspectives…

18. Colloque ASP - Boulogne sur Mer 200818 Thanks to the numerous scientists and crew members who conducted the experimental campaigns because our analysis is based on their hard work !!!