1 / 18

Noëlle BRU Laboratoire de Mathématiques et ses Applications UMR CNRS 5132

Daily and seasonal biomasses estimates of glass eels runs ( Anguilla anguilla L.) in an opened estuary. As an example the Adour Estuary (Southwestern part of France). Noëlle BRU Laboratoire de Mathématiques et ses Applications UMR CNRS 5132 Université de Pau et des Pays de l’Adour.

kenneth-mooney
Télécharger la présentation

Noëlle BRU Laboratoire de Mathématiques et ses Applications UMR CNRS 5132

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Daily and seasonal biomasses estimates of glass eels runs (Anguilla anguilla L.) in an opened estuary As an example the Adour Estuary (Southwestern part of France) 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

  2. General context… • 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… (source : IFREMER) Colloque ASP - Boulogne sur Mer 2008

  3. General context… • 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... Colloque ASP - Boulogne sur Mer 2008

  4. Problems… • 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... Colloque ASP - Boulogne sur Mer 2008

  5. Used to propose biomass estimates… 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 Are they really good indicators of abundance ? How and why to put together these datasets ?? Step 2 Colloque ASP - Boulogne sur Mer 2008

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

  7. Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion • Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment 1 passage  30 min ( 8 passages max !!!) …… during the flood tide…. The Adour estuary 10 min 5 min 5 min 5 min Right Bank Middle Left Bank Main Push-sieve fishery Glass eel densities (in g/100m3) s=1…S (=6) k=1,…, n(=8) Colloque ASP - Boulogne sur Mer 2008 All samples are assumed to be simultaneous...

  8. Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion • Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment Total biomass (in kg) for the flood tide period through vertical region R J different schemes tested… Colloque ASP - Boulogne sur Mer 2008

  9. Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion • Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment We need a functional form for each term!! For glass eels density ds(t)… For the current speed vs(t)… A sinusoidal model depending on time A log-log linear model depending on the current speed • to correct possible errors of measurement • to evaluate the beginning and the end of the flood tide An explicit form for the estimate + An evaluation of itsvariability Colloque ASP - Boulogne sur Mer 2008

  10. Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion • Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment • 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 2008

  11. Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion • Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment 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

  12. Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment • Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion « observed » biomass Dependent variable : rate of exploitation Explanatory variables :catches + environmental variables Model ? Data concerning the same glass eel run !! Professional catches with push-sieves Colloque ASP - Boulogne sur Mer 2008

  13. Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment • Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion • Model : glm( Rate ~ TurbCod + Catches^0.646 + TideCod+ FlowCod * Moon+catches*Moon) • Gamma distribution (with canonical link = inverse) • Coded explanatory variables : With 32 observations… Colloque ASP - Boulogne sur Mer 2008

  14. Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment • Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion « cleaned » values Values >100 or < 0 Predicted rate of exploitation <1,5% and catches >100kg tide < 60 and rate of flow >600m3/s + A variability associated to each predicted value of the rate of exploitation ! Colloque ASP - Boulogne sur Mer 2008

  15. Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment • Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion Smoothed biomass (by gaussian kernels) Predicted biomass + erreur « observed » biomass + error of prediction With a estimated standard error around 7 T Colloque ASP - Boulogne sur Mer 2008

  16. Step 2 : Usingprofessional catches… • Estimate of seasonal glass eelsbiomassmigrating by night • Estimate of glass eelsrecruitment • Step 1 : In situ scientific surveys… • Sampling protocol and data • Statistical method for estimation of « observed » glass eels biomass • Results and discussion Glass eels recruitment for a fixed season ??? + Known for every night (see before) unknown Hyp : mean value between two consecutive nights Colloque ASP - Boulogne sur Mer 2008

  17. Conclusions and perspectives… • 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 2008

  18. Merci... Thanks to the numerous scientists and crew members who conducted the experimental campaigns because our analysis is based on their hard work !!! Colloque ASP - Boulogne sur Mer 2008

More Related