Search

This study is based on the results of an extensive research carried out on silver scabbardfish Lepidopus caudatus from 2003 to 2005 in the Northern Aegean Sea (NAS). Data were collected from both commercial fisheries and research bottom trawl surveys. 264 specimens of silver scabbardfish, caught between 200 and 600 m depth, were processed for diet analysis. The silver scabbardfish diet covers different trophic levels, including euphausiids, decapods, fish and cephalopods. Overall, euphausiids were found to be the most important prey. Ontogenetically, the L.caudatus diet gradually changed from crustaceans, consumed by the smaller individuals to fish and cephalopods. During the sampling period, radical changes in the diet composition were observed: from euphausiids to fish between 2003 and 2004 and from fish to decapoda, euphausiids and cephalopods between 2004 and 2005. During 2004, feeding on high trophic level preys was attributed to lack of euphausiids. It was suggested that euphausiids play a crucial role in the energy transfer between lower and higher trophic levels in the deep demersal areas of the NAS.

We analysed data collected on board commercial purse seine vessels in the Aegean and Ionian Seas (eastern Mediterranean Sea, Greece) in 13 seasonal sampling periods from 2003 to 2008 in order to describe the composition of the retained and discarded catch and shed light on discarding practices. In each area, five species constituted the majority of the marketable catch (> 97%): sardine (Sardina pilchardus), anchovy (Engraulis encrasicolus), round sardinella (Sardinella aurita), bogue (Boops boops) (in both areas), mackerel (Scomber japonicus; in the Aegean Sea) and picarel (Spicara smaris; in the Ionian Sea). Discarded quantities were on average 4.6% and 2.2% of the total catch in terms of weight in the Aegean and Ionian Seas respectively. Discards on the marketable ratio fluctuated over years and seasons without showing any particular trend. At the species level, sardine and mackerel were seldom discarded while large amounts of anchovy were discarded only during its recruitment period (autumn), when juvenile fish dominate the population. The discarding ratio for bogue, picarel and round sardinella ranged from zero to total discarding because they constitute a supplementary source of income for the fishers. Discarded fish comprised mainly small individuals for all species considered with the exception of round sardinella. However, the lengths at which 50% of the individuals were discarded were generally small, often smaller than the species minimum landing sizes. Geographical coordinates and marketable catch explained part of the variability of the discarded quantities, as revealed by generalized additive models. Discarding practices and implications for management of purse seine fisheries are also discussed., Analizamos datos recogidos a bordo de pesqueros comerciales de cerco en el mar Egeo y el mar Jónico (Mediterráneo Oriental, Grecia) durante 13 estacionales de muestreo desde 2003 hasta 2008, con el objetivo de describir la composición de las capturas conservadas y de las descartadas con el fin de arrojar luz sobre la práctica del descarte. En cada zona, la mayor parte de la captura comercial (> 97%) consistía en cinco especies, a saber: la sardina (Sardina pilchardus), el boquerón (Engraulis encrasicolus), la alacha (Sardinella aurita), la boga (Boops boops) (en ambas zonas), la caballa (Scomber japonicus; en el mar Egeo) y el caramel (Spicara smaris; en el mar Jónico). Las cantidades descartadas representaban un promedio del 4.6% y 2.2% de la captura total en términos de peso, en el mar Egeo y en el Jónico respectivamente. La proporción de la captura descartada sobre la captura comercializable fluctuó mucho en todos los años y estaciones sin mostrar ninguna tendencia particular. Con respecto a las especies, en el caso de la sardina y de la caballa, los descartes ocurrieron raramente e incluso los individuos más pequeños se conservaron, mientras que grandes cantidades de boquerón fueron descartadas solamente durante su temporada de reclutamiento (otoño), cuando la población está dominada por peces jóvenes. La proporción descartada en el caso de la boga, del caramel y de la alacha fluctuó mucho, desde un descarte de cero hasta un descarte total, ya que estas especies representan una fuente de ingresos complementaria para los pescadores. Las coordenadas geográficas y la captura comercial explicaban parte de la variabilidad de las cantidades descartadas, como se demuestra con modelos aditivos generalistas. Asimismo, presentamos una discusión sobre la práctica del descarte así como de las consecuencias sobre la gestión de la pesca de cerco.

Faced to the actual global change, it appears to be of utmost importance to quantify and monitor the variability of community diversity and composition. In the present work, we have analysed the reproducibility of the empirical relationships between 11 diversity indices related to four major facets of species diversity (species richness, rarity, evenness and species taxonomy) in order to determine whether there is a general pattern of redundancy or complementarity that holds across years, areas and spatial scales. Variation of species composition at these different situations was investigated using the STATIS-CoA multitable method. We have applied this approach to groundfish diversity through the analysis of 2404 trawl hauls collected during the first large-scale annual surveys of the MEDITS program carried out using a single sampling design throughout the northern Mediterranean Sea. Our results highlight that, in contrast to what is still the usual practice, monitoring diversity should not be based on only one or two of the most widely used facets, even at large scale. Finally, the strong reproducibility of the relationships between indices we observed offers a basis for discussion of the feasibility and relevance of proposing a general shortlist of indices for monitoring diversity at different management scales.

Few records on cetaceans’ distribution are available for the North Aegean Sea and no research on diet has been attempted up to now. The present study, based on stomach content analysis of stranded animals, aims to fill the lack of data on cetaceans’ feeding habits in the area. Out of the 32 cetaceans stranded since 2002 from Strimonikos Gulf in Chalkidiki to Alexandroupoli on the Turkish border, stomachs’ samples were collected whenever possible. The stranded specimens belong to five species: Bottlenose dolphin (Tursiops truncatus), Common dolphin (Delphinus delphis), Striped dolphin (Stenella coeruleoalba), Risso’s dolphin (Grampus griseus) and Harbour porpoise (Phocoena phocoena)., N/A

Age, growth, mortality, reproduction and feeding habits were analysed for Lithognathus mormyrus collected in the coastal waters of the Thracian Sea from November 1997 to September 1999. Specimens ranged from 42 to 341 mm in total length. Weight increased with size allometrically (b = 3.242) for immature individuals and isometrically (b = 2.960) for males, females and intersexuals. Growth was described by the standard form of the von Bertalanffy growth equation and the estimated parameters were k = 0.21, t0 = –0.996 and L? = 309.4. Total and natural instantaneous rate of mortality was found to be Z = 0.79 year-1 and M = 0.61 year-1. Sex inversion occurred mainly between 210 and 300 mm (4-9 age classes). Males reached sexual maturity at 162.1 mm (2.5 years) and females at 190.40 mm (3.6 years). The spawning period occurred from May to September, while the gamete emission peaked in June-August. Stomach content analysis revealed that L. mormyrus is a carnivorous species feeding on benthic invertebrates, mainly polychaeta and bivalve molluscs. Ontogenetic variation in the diet composition showed that while growing, the fish become more generalist feeders. We also found that in the summer season the fish become more selective feeders., La edad, crecimiento, reproducción y alimentación de Lithognathus mormyrus capturados en aguas costeras del mar de Trácia entre noviembre 1997 y septiembre 1999 han sido analizadas. La talla total de los especímenes osciló entre 42 y 341 mm. El peso aumentó con la talla alométricamente (b=3.242) para los individuos inmaduros e isométricamente (b=2.960) para machos, hembras e intersexuales. El crecimiento ha sido descrito mediante la forma estándar de la ecuación de crecimiento de von Bertalanffy; los parámetros estimados han sido: k=0.21, t0 =–0.996 y L? =309.4. La tasa instantánea de mortalidad total y natural ha sido Z=0.79 año-1 y M=0.61 año-1. La inversión de sexo tuvo lugar principalmente entre 210 y 300 mm (clases de edad 4-9). Los machos alcanzaron la madurez sexual a 162.1 mm (2.5 años) y las hembras a 190.4 mm (3.6 años). El período de puesta tuvo lugar entre mayo y septiembre, con un pico en junio-agosto. El análisis de contenidos estomacales reveló que L. mormyrus es una especie carnívora que se alimenta de invertebrados bentónicos, principalmente de poliquetos y moluscos bivalvos. La variación ontogenética en la composición de la dieta mostró que a lo largo del crecimiento los individuos devienen generalistas. Estacionalmente, se ha encontrado que en verano los individuos devienen más selectivos.

Species composition, abundance and diversity of fish larvae were assessed in the Strymonikos and Ierissos Gulfs (northern Aegean Sea, Greece). Both gulfs are affected by the freshwater input of the Rivers Strymon and Rihios; water depth does not exceed 80 m. Samples were collected using a bongo net sampler (250 µm mesh size) over a grid of 35 stations in six cruises between June 1997 and May 1998. A total of 48 taxa of fish larvae (36 species, 5 genera and 7 families) were identified. The majority of identified fish larvae taxa consisted of demersal species that included larvae of Bothidae, Gobiidae, Callionymidae, Sparidae and Serranidae. The highest number of species occurred in the warm season (May, June, July, September) and this was attributed to the summer spawners that start their reproduction period during spring/early summer. The European anchovy (Engraulis encrasicolus) was the dominant species between July and September, and the European sardine (Sardina pilchardus) between November and March. Two distinct seasons (warm and cold) were identified by multivariate analysis, highlighting the importance of seasonality in shaping the community structure. The absence of well-defined larval fish associations revealed the importance of depth in the identification of different spatial patterns in an area., Se evaluaron la composición, abundancia y diversidad de las larvas de peces en los golfos de Strymonikos y Ierissos (norte del mar Egeo, Grecia). Ambos golfos están afectados por la llegada de agua dulce de los ríos Strymon y Rihios y, en ellos, la profundidad no supera los 80 m. Las muestras se recolectaron en seis campañas realizadas entre los meses de junio de 1997 y mayo de 1998, sobre una parrilla de 35 estaciones, utilizando una red Bongo (con malla de 250 µm). Entre las larvas de peces se identificó un total de 48 taxa (36 especies, 5 géneros y 7 familias). La mayoría de las larvas identificadas correspondieron a especies demersales de las familias Bothidae, Gobiidae, Callionymidae, Sparidae y Serranidae. El número más alto de especies apareció durante la estación cálida (mayo, junio, julio y septiembre) y esto se atribuyó a los ponedores de verano que inician su periodo de reproducción en primavera/principio de verano. La anchoa europea (Engraulis encrasicolus) fue la especie dominante de julio a septiembre, y la sardina europea (Sardina pilchardus) de noviembre a marzo. Mediante análisis multivariante se identificaron dos estaciones distintas (cálida y fría), destacando la importancia de la estacionalidad en la estructuración de la comunidad. La ausencia de asociaciones de larvas bien definidas reveló la importancia de la profundidad en la identificación de diferentes patrones espaciales en el área.