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This challenge is addressed
through a major study of the bay of Biscay. 2001 was spent opening the
project, creating its structure and implementing studies. The first phase
plans to update knowledge about species, human activities and the climate
in order to identify what determines their behaviours. Concurrently, the
monitoring network for the bay will be set up and technological
developments for its instruments will be implemented. Outstanding results
were obtained in three fields: interference between climatic forcing and
human activities determining species production, driving economic forces
for catches, and technology. |
Effetcs of climatic and
anthropogenic forcing
Studies on hydrological structures, nutrient stocks,
chlorophyllous biomasses and water-sediment interface exchanges began in
the northern part of the bay with the Nutrigas survey (aboard Thalassa,
from 23 February to 3 March 2001). This cruise took place in the high
winter flow period. It showed major freshening extending to the middle of
the continental shelf, on the latitude of the Loire river. Fluorescence
measurements revealed phytoplancton growth over a large part of the area
investigated, up to a hundred kilometres from the coast. Phytoplancton
development was probably slowed by higher turbidity along the coast.
Chlorophyll concentrations reached several micrograms per litre,
indicating diatom production made possible by nutrient inputs (nitrogen,
phosphorus, silicon) from land-based activities. Ocean colour images from
the SeaWiFS satellite, processed using Ifremer's algorithm, confirmed and
specified the extension of this primary production.
River flow and sole juvenile abundance in the bay of the Vilaine river
over the past two decades were analysed, establishing a relationship
between the abundance of these juveniles, i.e., recruitment, and the
climatic regime at the start of the year. The benthic community which
provides food for these juveniles is behind this relationship, since the
extension of estuarine plumes conditions the surface area and food
production for benthic invertebrates, notably annelid worms.
Anchovy larval drift from their spawning sites on the French shelf to
south of 46°30N were assessed using the extended hydrodynamic model for
the bay of Biscay. Juveniles found off the Spanish coast are thought to
originate in spawns on the French shelf. Anchovy larva growth indexes vary,
depending on whether the larvae develop in spawning zones in the Gironde
river plume or in the Azores (Pégase 1998 cruise). According to a
hydrodynamic model reconstitution of larval transport towards nursery
areas, the juveniles recruited may come from fast-growing larvae (Plagia
1999 and Juveus 1999 cruises). However, the spawning ground distribution
shows significant interannual variability (Pelgas 2000 and 2001 cruises).
So, hydroclimatic disturbance regimes have proved to be determining
factors, acting both as a vector to disperse anthropogenic inputs and as a
control of the population dynamics for fish species and plancton algae. |
Economic components
Economic components are taken into account in order to
better understand the way use evolves over time and space, as a function
of economic agents. 2001 was devoted to setting up an economic data
acquisition network on fishing companies plying the bay. These data
provide a detailed analysis of companies' costs and revenues and improve
our knowledge of their activity's economic stakes. Professional fishermen
cooperated to set up the network. In 2001, it supplied essential results,
both on the scale of the bay and for smaller coastal regions. For
instance, an operational assessment of the spiny lobster fleet in the bay
was made for the Ministry of Agriculture and Fisheries, combining
information about the vessels' activity and their economic situation. Data
acquisition should continue in 2002, in order to improve the base data
required for this part of the programme.
Instrumentation
Numerical modelling is needed if we are to understand
how the ecosystem works and predict biological resource trends in the bay
of Biscay. To correctly simulate reality and be capable of predicting how
the system will evolve, these models must be validated and supplemented by
measurements at sea. Their systematic collection requires developing
appropriate and innovative ways to take measurements.
Therefore, for better fish stock assessments, an entirely new multibeam
echo sounder was designed in 2001. It will be the equivalent of some
thirty conventional sounders and will provide 3D views of schools of fish.
This will considerably improve the performances and accuracy of surveys at
sea. This instrument is slated to be put into use aboard the Thalassa in
2004. |
