An acoustic telemetry study of seabream (Sparus aurata L.): first results on activity rhythm,effects of environmental variables and space utilization

The movements of seabream (Sparus aurata L) were recorded in two earthen ponds (250 m² and 400 m²) by tracking fish tagged with miniature acoustic transmitters. Five seabreams, 500 g in weight, were tracked for periods of four or five days. Fish positions were recorded continuously using an acoustic telemetry system. Each of the five tagged seabreams were tracked individually. Two fishes were released schooled with numerous other individuals, two others were released in isolation and one was grouped with three other individuals.The schooled seabreams were more active in general and, in the large school they were diurnal; isolated fishes however, were more active at night. Temperature influences significantly and progressively the fish activity. Activity decreases at night and increases during daylight. Oxygen saturation also influences swimming activity with a general positive relationship.The horizontal distribution of this species was not uniform. Its resting area was generally located around some particular landmarks such as inlet or outlet pipes in the ponds. No feverish feeding competition was observed between individuals of the same school. The feeding area was cleaned rapidly, in less than 10 minutes, without subsequent returns from the resting area to the feeding area.

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Résumé Les déplacements de la daurade (Sparus aurata L.) ont été enregistrés dans deux bassins en terre (250 m² et 400 m²) en suivant des poissons marqués avec des émetteurs acoustiques miniaturisés. Cinq daurades d'un poids individuel de 500 g furent suivies durant des périodes de 4 ou 5 jours. Les positions des poissons ont été enregistrées en continu avec un systéme de télémétrie acoustique. Chacun des cinq poissons marqués fut suivi individuellement. Deux poissons furent regroupés avec de nombreux autres individus, deux autres furent laissés seuls et le dernier fut mis avec trois autres individus.Les daurades groupées étaient en général plus actives et, en grand banc, étaient diurnes; les poissons isolés étaient toutefois plus actifs durant la nuit. La température influence significativement et progressivement l'activité des poissons. L'activité décroît durant la nuit et augmente pendant le jour. Le pourcentage de saturation en oxygéne agit aussi, de façon positive, sur l'activité de nage.La distribution horizontale de cette espéce n'est pas uniforme. Son aire de repos est généralement localisée dans quelques zones particuliéres comme les arrivées et les sorties d'eau. Aucune compétition alimentaire fébrile n'a été observée entre les individus d'un même banc. L'aire de nourrissage est rapidement nettoyée, en moins de 10 minutes, sans retours ultérieurs depuis la zone de repos jusqu' à la zone de nourrissage.

     

Feeding Responses of Hatchery-Reared Gilthead Sea Bream (Sparus aurata L.) to a Commercial Diet and Natural Prey Items

Many fish species have evolved feeding mechanisms and behaviours enabling them to feed on specific prey. However, such mechanisms may not be optimal for feeding on commercial-pelleted diets in aquaculture. Gilthead sea bream chew and occasionally eject pellets or parts of pellets from the mouth when feeding on commercial diets. This may result in an increase in nutritional waste from the intensive culture of this species. In this study we examined the prevalence of this food processing behaviour in two sizes of sea bream, feeding on three types of natural prey items in comparison to a commercial pellet, to give an insight into the circumstances in which excess chewing and ejection of food items from the mouth occurred. These included two hard-textured food items (commercial pellet and hard-shelled prey) and two soft-textured food items (larvae and small crustacean). Both sizes of sea bream frequently consumed the soft-textured food types, however large sea bream also frequently consumed hard-textured pellets. Hard-textured food required longer handling times and elicited more chewing and the ejection of food items from the mouth. These results suggest that future investigations on the food processing behaviour and consequent waste when fed commercial diets differing in texture could give an insight into improving diets and feeding efficiency for intensively cultivated gilthead sea bream.     

Swimming activity of seabass: comparing patterns obtained in natural environment and in re-circulating tanks under high density

Seabass ( Dicentrarchus labrax ) swimming activity was compared between natural environments and aquaculture facilities. Behaviour under natural conditions was assessed in a saltmarsh pond (250 m², 18 × 14 × 0·8 m) using acoustic telemetry. From several surveys, we documented the diel activity rhythm and demonstrated group effects on swimming patterns and amplitudes by comparing activity of solitary fish with that of a fish living in a group of 60. Consequences of weather variability were also analysed and revealed a high sensitivity of fish to atmospheric conditions for both swimming and demand‐feeding behaviour. Behaviour in fish tanks was also studied using acoustic telemetry, as part of the EUREKA EU1 960 'Aqua‐Maki 2' project investigating aspects of fish culture in re-circulating tanks under high density. A re-circulating hexagonal tank (5·4 × 5·4 m, 1·8 m depth, 48 m³) was equipped with positioning and demand‐feeding systems, oxygen and temperature probes. Initial density was 50 kg m³ in March and rose to 90 kg m³ at the end of the experiment in May. During this period, the movements of nine fish were continuously recorded for 24 h each, reaching a total of six 24 h episode at eight days interval. Swimming activity was analysed in terms of activity rhythms and space occupation specially around feeding events. The two data set and main results will be presented and compared to assess seabass behavioural plasticity and sensitivity to husbandry conditions.     

Comparison of Solea solea macroparasites between two nursery-continental shelf systems in the Bay of Biscay and the Portuguese coast

Digenean metacercariae of 0 year group common sole Solea solea ( n = 70) were more abundant in the embayed nursery of the Pertuis Charentais than in the Tagus estuary nursery. Macroparasite assemblages of adult sole ( n = 119) displayed only one species in common between the Bay of Biscay and the Portuguese coast continental shelves. These data highlighted the potential use of macroparasites as biological tags in various aspects of common sole ecology.     

Importance of soil nutrients in the distribution of forest communities on a large geographical scale

Aim Soil nutrient content plays a key role in plant growth through mineral nutrition and toxicity. Its impact on plant species and community distribution is studied on a large geographical scale through surrogates like topography or geology. We investigated the importance of soil pH and C:N ratio, as direct nutritional gradients, to determine, with climatic factors, the spatial distribution of plant communities over large territories. Location We studied the distribution of six beech habitats of the NATURA 2000 network throughout France (550,000 km²). Methods Models were calibrated with 2108 floristic plots classified in the NATURA 2000 system and including climatic and topographic variables and soil nutritional measurements carried out in a laboratory. Logistic regression was used to model habitat distribution according to environmental variables. Climatic layers, a digital elevation model and maps of soil pH and nitrogen content, created using plant indicator values and large floristic databases, were used to map the sites suitable for beech communities. Distribution models were evaluated with an independent set of 2091 phytosociological plots. Results pH and nitrogen supply were the key distribution drivers for four of the six beech communities on a national scale. Their use in the distribution models distinguished within homogeneous climatic territories a gradient of nutritional conditions from acidic areas, suitable for nutrient‐poor beech communities, to calcareous areas suitable for nutrient‐rich ones. Predicted maps of beech habitats fit the spatial distribution of validation plots. Main conclusions Soil pH and nitrogen supply strongly improve predictions of forest community distribution carried out with climatic variables on a broad geographical scale. They allow delineation of areas with nutritional conditions suitable for each community, as well as the realization of predictive high‐resolution maps over large areas useful for sustainable and conservation management. Nomenclature Tutin & Heywood (2001 ) Flora Europaea. Cambridge University Press, Cambridge.