Diet of larval albacore Thunnus alalunga (Bonnaterre, 1788) off Mallorca Island (NW Mediterranean)

These are the first data on the feeding of larval albacore (Thunnus alalunga Bonnaterre, 1788) in the Mediterranean. Specimens were gathered from day-time bongo-hauls conducted over the SW Mallorcan (Balearic Islands) shelf-slope. Ninety eight percent of 101 individuals ranging from 2.65 to 9.4 mm standard length (SL) contained 1 to 15 prey items per gut. Mean number of prey/gut was 3.55 ± 2.19 (SD). A positive correlation was found between larval SL and the number of prey/gut. The analysis of frequency of occurrence (F), numerical frequency (N), weight frequency (W) and the Index of Relative Importance (IRI) showed a dominance of copepodites and nauplii in the smallest size-class. As larvae grew, cladocerans and Calanoida copepodites dominated the diet, and cladocerans and copepodites were important in F, N and W. Piscivory was observed after notochord flexion and was important in terms of W. A positive correlation between mean prey size and both SL and lower jaw length (LJL) was observed. The niche breadth (S) did not vary with LJL, but the raw prey size range did. Larger copepodites, the absence of nauplii and the incorporation of fish larvae and a larger number of cladocerans in the diet accounted for the increase in mean prey size through increased larval size.DIETA DE LAS LARVAS DE ALBACORA THUNNUS ALALUNGA (BONNATERRE, 1788) EN AGUAS DE MALLORCA (MEDITERRÁNEO NW). – Se ofrecen los primeros datos sobre la dieta de las larvas de albacora (Thunnus alalunga Bonaterre, 1788) en el Mediterráneo. Los especímenes se obtuvieron de pescas diurnas con bongo sobre la plataforma-talud al SW de Mallorca (Islas Baleares). El 98% de 101 individuos de entre 2.65 y 9.4 mm de longitud estándar (LE) contuvieron entre 1 y 15 presas por digestivo. La media de presas por larva fue de 3.55 ± 2.19 (DE), existiendo una correlación positiva entre el número de presas en el tubo digestivo y la LS. Los índices de frecuencia de ocurrencia (F), frecuencia numérica (N), frecuencia en peso (W) y el Índice de Importancia Relativa (IRI) mostraron un predominio de copepoditos y nauplius en larvas pequeñas, disminuyendo en importancia a lo largo del crecimiento en detrimento de cladóceros y copepoditos de Calanoida, que fueron importantes en F, N y W. Se observó piscivoría, importante en W, a partir de la flexión de la notocorda. Se detectó una correlación positiva entre el tamaño medio de las presas y tanto la LS como la longitud de la maxila (LJL) de las larvas. La amplitud del nicho alimentario (S) no varió con la LJL, aunque el rango total del tamaño de las presas sí lo hizo. El aumento de talla de los copepoditos, la desaparición progresiva de mauplius y la incorporación de larvas de peces y más cladóceros explica el aumento de la talla media de las presas a lo largo del crecimiento larvario.Versión del editor1,006

Size dependent predation in piscivorous larval stages of three tuna species

The bluefin tuna (Thunnus thynnus) is a heavily fished temperate tuna that spawns in the Mediterranean Sea; the area off the Balearic Islands is a key spawning area. Other abundant tunas, including albacore (Thunnus alalunga) and the small bullet tuna (Auxis rochei) spawn in the same area. The three species temporally overlap during the summer spawning period of the adults. Because they are clearly piscivorous already at very early larval stages, we expect strong interactions both in terms of a direct predator–prey relationship and as competitors for food resources. In this study, we focus on understanding the size dependent trophic interactions among the three species at the different developmental larval stages. First, we describe the environmental and biological scenarios where different size stages of the three species co-occur through the application of generalized additive model (GAM) analyses to field data collected during cruise surveys in 2004–2005. We then develop an individual_based model (IBM) to evaluate inter- and intraspecific predation rates considering size structured prey and predator fields in the framework of piscivorous behaviour. The results demonstrate how predation mortality rates influence the spawning location of the three speci

Seasonal differences in muscle fibre recruitment of pilchard larvae in the north-western Mediterranean

11 pages, 2 figures, 2 tablesThe recruitment of slow and fast myotomal muscle fibres with respect to growth in body length in European pilchard larvae Sardina pilchardus [(3.5–13.5mm standard length (LS)] was significantly higher in November 1998 than February 1999. This resulted in a significant seasonal difference in the relationship between fibre number and LS, particularly for the fast muscle. Mean sea surface temperature was c. 6º C higher in November than February, whereas the mean abundance of potential prey items (copepod nauplii) was comparable between cruises. Laboratory and field data obtained from other clupeid species have indicated the importance of early thermal experience on muscle fibre recruitment patterns. Differences in average sea temperature therefore provide a plausible mechanism for the observed seasonal differences in muscle growth characteristicsThis work was funded by the following research programmes: ‘‘Fil’’ Spanish CYTMAR, MAR97 09-02 and ‘‘Llucet’’ EU Contract FAIR CT-97-3522 (1998–2000)Peer reviewe

Adapting to the wild: the case of aquaculture-produced and released meagres Argyrosomus regius

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