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Theses

Interactions entre comportement et variations de la croissance des juvéniles de la sole (Solea solea) dans les nourriceries des pertuis Charentais.

Abstract : This thesis aimed to identify and analyse processes involved in the functioning of sole Solea solea (L.)
nurseries in the Pertuis Charentais, the most important oyster cultivation basin in Europe and a major nursery for
the Bay of Biscay sole. Juveniles concentrate in coastal and estuarine habitats, which are essential in the biological
cycle of this species but implies (i) adaptation to environmental variability and (ii), accessibility to habitat resources.
Assuming that effective nurseries account for what fish must perform in response to habitat constraints, especially
in selecting feeding, resting or refuge areas, we used both field works and mesocosm experiments to obtain
integrative indicators of the nursery quality (growth rate, Fulton's condition index, endocrine status), and
behavioural responses of how sole use space (acoustic telemetry techniques) and food (feeding regime and
carbon daily ration estimates) in a habitat influenced by shellfish culture.
Juvenile growth curves in the pertuis Breton were close to the species maximum in summer but they tended to a
plateau around the autumn equinox. A mesocosm experiment confirmed that in situ temperatures could not explain
this growth arrest. At the same time, juveniles had low condition indices, the weakest thyroid hormone levels and
the lowest feeding activity. This status suggested various constraints, which could be specific to Pertuis, semienclosed
bays under moderate river plume influence. It seemed that the Pertuis environment is less favourable at
the end of summer and/or that cumulated effects on the trophic web do not allow the entire 0 group soles to grow
according to species potentialities. Nevertheless, in the present climatic context, some of these juveniles were
shown to over-winter in these nurseries, where they recovered high hormonal levels and restored their feeding
activity. Under the Pertuis environmental constraints, sole growth was modulated, but behaviour did not appear
modified. A mesocosm experiment, whose results still need field assessment, demonstrated that access to areas
under oyster culture influence was not restricted, either by oyster-trestle effects or by water and bottom changes
due to shellfish biological activity. From two 30h sampling cycles performed in the Pertuis d'Antioche, we
demonstrated that young sole were able to adjust their activity rhythm and feeding rates, probably due to
hydrodynamics, in relation to fortnightly tide cycles or wind stress. These cycles allowed us to evaluate the daily
ration of organic carbon of sole juveniles, results which would contribute to the development of trophic web models.
Finally, as spin-off of this thesis, a heavy infestation of the Pertuis Charentais by bucephalid metacercariae was
revealed. Cercariae being propagated by mussel culture, this parasitosis gave a new point of view concerning the
interaction between nursery function in coastal habitats and shellfish culture.
Document type :
Theses
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https://tel.archives-ouvertes.fr/tel-00080739
Contributor : Pascal Laffargue <>
Submitted on : Tuesday, June 20, 2006 - 2:05:26 PM
Last modification on : Tuesday, March 30, 2021 - 12:26:04 PM
Long-term archiving on: : Monday, April 5, 2010 - 11:09:16 PM

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  • HAL Id : tel-00080739, version 1

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Pascal Laffargue. Interactions entre comportement et variations de la croissance des juvéniles de la sole (Solea solea) dans les nourriceries des pertuis Charentais.. Ecologie, Environnement. Université de La Rochelle, 2004. Français. ⟨tel-00080739⟩

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