Modelling the biophysical dynamics of sardine and anchovy ichthyoplankton in the Canary Upwelling System: continent-archipelago interactions

Transcription

1 Modelling the biophysical dynamics of sardine and anchovy ichthyoplankton in the Canary Upwelling System: continent-archipelago interactions Timothée Brochier, Eurocean PhD student, IRD Azeddine Ramzi Christophe Lett Eric Machu Santiago Hernández-León Pierre Fréon INRH, Morocco IRD, France IRD - INRH, Morocco ULPGC, Spain IRD, France

2 Summary. Issues: a. Filament-eddy system b. Spawning patterns (anchovy and sardine) c. Larval presence in Canary area II. Method: a. Hypotheses to test b. Modelling tools c. Simulation design III.Results and discussion

3 Filament-eddy system Connecting the coastal upwelling area with the archipelago and its associated eddy field Near-surface structures, ~ km wide, up to several hundred km long Filament + associated eddy = favourable fundamental triad for a reproductive habitat (Bakun, 99). --> cyclonic eddies may provide nursery grounds for neritic fish Major filaments Eddy field Adapted from Pelegri et al., image from Javier Aristegui

4 Spawning patterns (Sardine and anchovy) Upwelling Seasonality: maximum in summer, almost permanent south of Cap Juby Anchovy spawn mainly north of Cap Juby in summer and in the central area in winter Sardine spawn mainly south of Cap Juby in summer, and both north and south in winter Data from INRH cruise surveys from 99 to 999 Summer Sardine Winter Sardine Anchovy Anchovy Coastal Area Coastal Area Summer (eggs.m-) Winter (eggs.m-) 7 9 Berraho Amina, 7. Relations spatialisées entre milieu et ichtyoplancton des petits pélagiques de la côte Atlantique marocaine (Zones centrale et sud). Thèse de Doctorat, Univ. Mohamed V, Rabat, p. Anchovy Sardine

5 Larval presence near Canary archipelago No anchovy nor sardine eggs off the African shelf (Rodriguez et. al, ) Sardine larvae associated with filaments (Rodriguez et al., 999; Becognée et al. ) Anchovy larvae more frequent, not associated with filaments (Becognée et al. ) Similar vertical distribution, mainly in the upper m (Rodriguez et. al, ) Mean vertical concentrations of Engraulis encrasicolus larvae (Rodrıguez et al, ) Larval presence is associated with lunar cycle (Becognée et al. )

6 Hypotheses to test. Ichthyoplankton transport to Canary islands is associated with filaments of upwelled waters. Ichthyoplankton transport to Canary island coasts is more frequent from anchovy spawning areas than sardine spawning areas. Vertical migration of larvae impact their transport in filaments

7 Modelling tools We used a coupled IBM-hydrodynamic model: The hydrodynamic field is reproduced by a numerical model (ROMS) Eggs and larvae are released along Moroccan coast as Lagrangian particles at regular dates and places using an IBM (Ichthyop) ROMS SST Initial release days days

8 Ichthyop: A Lagrangian tool for modelling ichthyoplankton dynamics Download page:

9 Simulation design Transport success = being transported to one of the following areas: eastern islands, eastern eddy field, western islands, western eddy field Transport Duration = Larval stage duration: about month for anchovy and sardine Simu : passive tracers release depth levels (-m, -m, -m) repeats Simu : active individuals egg densities (.,.,.) vertical migration schemes (m, m, m, -m) particles released every month years of release areas of release (along the African shelf) Release and Recruitment areas

10 Result - Simu : passive tracers A- Transport from the upwelling area to the entire Canary area: 8 North 8 _nord _sud Release area. to.. to.. to. -m -m -m Release depth (m) depth South 8 8 Upwelling index Jan Mar May Jul Sep Nov Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Release month Month of release Replicate repeat Release areas - Maximum transport to Canary area: - from areas, and - for release near surface (-m) - during summer (July-August) - No variation between repeats Results consistent with field observations of filaments and with the upwelling index

11 Result - Simu : passive tracers B- Transport from the upwelling area to the specific Canary area: - Western archipelago: - No transport to the western islands (zone ) - Some transport to the western area (zone ) from the southern release areas - Eastern archipelago: - Transport to the eastern islands (zone ) max in March-April, coming from northern release areas - Transport to the eastern area (zone ) is max in summer, from the southern areas Recruitment area I (-; 7-8) Transport to Recruitment area (max 8%) (--7) (; 7-8) Release area (shelf) (-; 7-8) Month of maximum transport

12 Result - Simu : Active individuals Mar May 9 Relea Oct 97Nov Dec More transport to Canary area when larvae remain in the upper layer m!. to!. to!.!. m -m!. to!.!.!. -m Target depth (m) Release depth (m) m!. to!.!.!. m!. to!. Target depth (m)!. to! Release month target dataset$target_depth dataset$releasearea Release year Target depth (m) 99. Release year!. to!.!. to.!. m 98 More transport to Canary area for higher egg density Release year Sep 98. Aug Target depth 97. Jul Jun Dec Release month Vertical migration success (%) TransportTransport success (%) Nov. Apr 97 May Oct Nov Egg dentity Target depth (m) Sep Mar Sep Release month.. m Jul Release month Feb Aug Jan Jul Jun Dec May Nov _sud Oct Mar Apr Sep 8 Egg density Transport success (%) Feb Aug Release month. to!. ntity Jan Jul Time since spawning area Jun Jan 8 8 days Impact on the transport to Canary area: May _sud Release area Active larvae (vertical migration) 8 _nord days yolk sac larvae (passive) 8 spawn eggs (buoyant) 8 Simplified larval development model:

13 Conclusions The results comfort our hypotheses: The transport patterns correspond to filament characteristics (seasonality, location and depth structure) The sardine spawning area is exposed to transport toward the eddy field south of the islands (~8%), but rarely to the islands (<%) At the opposite, the anchovy spawning area is subject to transport towards the eastern islands (~%), but less to the southern eddy field (~%) No ichthyoplankton transport to the western islands Larval vertical migration can double the transport to the Canary area, from % (m) to % (m)

14 Questions?