Feeding habits of European hake, Merluccius merluccius (Actinopterygii: Gadiformes: Merlucciidae), from the northeastern Mediterranean Sea

European hake, Merluccius merluccius (Linnaeus, 1758), is an important predator of deep Mediterranean upper shelf slope communities, being a nektobenthic species inhabiting a wide depth range (20–1000 m) throughout the Mediterranean Sea and the northeastern Atlantic region (Carpentieri et al. 2005). It is one of the chief commercial and most heavily exploited species of demersal fishery in all northern Mediterranean countries. Recent time-series studies referring to the western part of the Adriatic Sea have shown catches to be made up mainly of specimens shorter than 20 cm TL, with survey catch rates apparently increasing between 1985 and 1995 and decreasing in the following years both in the northern(Piccinetti and Piccinetti Manfrin 1971, Manfrin et al. 1998) and southern Adriatic Sea (Marano et al. 1998). In 2006, annual hake landings were estimated to be around 76 000 t in the Mediterranean (Anonymous 2008) and around 18 000 t in the Adriatic Sea (Anonymous 2007), with the species being the most abundant in the demersal group of the Adriatic Sea (Ungaro et al. 2001). As a rule, hake feeds predominantly on fish and crustaceans, and the proportion of piscivory increases with hake length; crustaceans appearing mostly in the stomach of <16 cm hakes in the northern-central Adriatic Sea (Karlovac 1959, Županovic 1968, Piccinetti and Piccinetti Manfrin 1971, Jukic 1972, Froglia 1973, Jardas 1976). The presently reported study analysed the diet of the hake in the northeast Mediterranean, which, given its abundance, plays an important role in comprehending the food chain dynamics. Despite hake's environmental and economic importance (Oliver and Massuti 1995) in the Mediterranean, much of its ACTA ICHTHYOLOGICA ET PISCATORIA (2011) 41 (4): 277–284 DOI: 10.3750/AIP2011.41.4.0

Feeding strategy and ontogenetic changes in diet of gurnards (Teleostea: Scorpaeniformes: Triglidae) from the Adriatic Sea

A multi-specific approach in fish diet studies provides insight into the complexity of trophic interactions in marine communities. The feeding habits of three gurnard species, Aspitrigla cuculus, Chelidonichthys lucerna and Eutrigla gurnardus (Scorpaeniformes: Triglidae), from the north-middle Adriatic Sea were studied to evaluate prey-resource partitioning amongst species and within species, comparing juveniles' and adults' diet for each gurnard species. A total of 1818 specimens (390 A. cuculus, 973 C. lucerna, 455 E. gurnardus) were collected by bottom trawling and they were assigned to size classes (juveniles or adults) on the basis of macroscopic evaluation of the gonads. Stomach contents were analysed. A common dietary preference for Crustacea was found in all species and size classes considered. Nevertheless, gurnards showed distinct feeding behaviour: C. lucerna and E. gurnardus were generalist-opportunistic predators, showing a varied diet based on epi-benthic, bentho-pelagic and necto-benthic preys belonging to different taxa such as Teleostei and Mollusca, while A. cuculus may be considered a specialist feeder, feeding almost exclusively on necto-benthic invertebrates. Morisita's index calculated for critical size classes (juveniles and adults) pointed out differences. At the inter-specific level, possible dietary competition between A. cuculus and E. gurnardus (C > 0.65) was found for all size classes combined, due to the prey abundance of Lophogaster typicus (Crustacea: Mysida). At the intra-specific level, high diet overlap was found between juveniles and adults of C. cuculus (C = 0.98) and between juveniles and adults of E. gurnardus (C > 0.84). In contrast, C. lucerna did not compete with increasing body size (C < 0.20), showing a clear change from crustaceans to fish in its diet preferences. The possibility that A. cuculus and E. gurnardus may compete for the same prey resources while C. lucerna shows food resource partitioning is discussed. Better understanding of the ecology of these coexisting predators should lead to improved conservation and improved fisheries management

Environmental infuence on calcifcation of the bivalve Chamelea gallina along a latitudinal gradient in the Adriatic Sea

Environmental factors are encoded in shells of marine bivalves in the form of geochemical properties, shell microstructure and shell growth rate. Few studies have investigated how shell growth is affected by habitat conditions in natural populations of the commercial clam Chamelea gallina. Here, skeletal parameters (micro-density and apparent porosity) and growth parameters (bulk density, linear extension and net calcification rates) were investigated in relation to shell sizes and environmental parameters along a latitudinal gradient in the Adriatic Sea (400 km). Net calcification rates increased with increasing solar radiation, sea surface temperature and salinity and decreasing Chlorophyll concentration in immature and mature shells. In immature shells, which are generally more porous than mature shells, enhanced calcification was due to an increase in bulk density, while in mature shells was due to an increase in linear extension rates. The presence of the Po river in the Northern Adriatic Sea was likely the main driver of the fluctuations observed in environmental parameters, especially salinity and Chlorophyll concentration, and seemed to negatively affect the growth of C. gallina

Strongly structured populations and reproductive habitat fragmentation increase the vulnerability of the Mediterranean starry ray Raja asterias (Elasmobranchii, Rajidae)

The Mediterranean starry ray (Raja asterias) populations within the Mediterranean Sea are susceptible to high rates of bycatch in the multispecies trawl fisheries. Understanding its population structure and identifying critical habitats are crucial for assessing species vulnerability and setting the groundwork for specific management measures to prevent population decline. To assess the population structure of R.&nbsp;asterias in the Mediterranean, the genetic variation in nine population samples at one mitochondrial marker and eight nuclear microsatellite loci was analysed. Moreover, 172 egg cases collected in the Strait of Sicily were identified at species level using integrated molecular and morphological approaches. Genetic analyses revealed that the Mediterranean starry ray comprises three distinct units inhabiting the western, the central-western, and the central-eastern areas of the Mediterranean. An admixture zone occurs in the Strait of Sicily and the Ionian Sea, where individuals of the central-western and central-eastern population units intermingle. The joint morphometric–genetic analyses of rajid egg cases confirmed the presence of more than one species in the admixture area, with a predominance of egg cases laid by R.&nbsp;asterias. DNA barcoding revealed that egg cases and embryos of R.&nbsp;asterias shared several haplotypes with adult individuals from the central-western and central-eastern Mediterranean Sea, revealing that females of both populations laid numerous eggs in this area. According to these findings, detailed taxonomic determination of egg cases, when combined with seasonal migration studies, could improve the capability to identify important spawning or nursery areas for the Mediterranean starry ray, particularly in those admixture zones relevant to maintaining genetic diversity. Finally, these new insights should be considered to update the Action Plan for the Conservation of Cartilaginous Fishes in the Mediterranean Sea with effective measures to reduce the impact of skate bycatch in trawling and safeguard egg cases in nursery areas

Genetic Structure of Bluefin Tuna in the Mediterranean Sea Correlates with Environmental Variables

Abstract Background Atlantic Bluefin Tuna (ABFT) shows complex demography and ecological variation in the Mediterranean Sea. Genetic surveys have detected significant, although weak, signals of population structuring; catch series analyses and tagging programs identified complex ABFT spatial dynamics and migration patterns. Here, we tested the hypothesis that the genetic structure of the ABFT in the Mediterranean is correlated with mean surface temperature and salinity. Methodology We used six samples collected from Western and Central Mediterranean integrated with a new sample collected from the recently identified easternmost reproductive area of Levantine Sea. To assess population structure in the Mediterranean we used a multidisciplinary framework combining classical population genetics, spatial and Bayesian clustering methods and a multivariate approach based on factor analysis. Conclusions FST analysis and Bayesian clustering methods detected several subpopulations in the Mediterranean, a result also supported by multivariate analyses. In addition, we identified significant correlations of genetic diversity with mean salinity and surface temperature values revealing that ABFT is genetically structured along two environmental gradients. These results suggest that a preference for some spawning habitat conditions could contribute to shape ABFT genetic structuring in the Mediterranean. However, further studies should be performed to assess to what extent ABFT spawning behaviour in the Mediterranean Sea can be affected by environmental variation.(undefined

Citharus linguatula. In: Sartor P., Mannini A., Carlucci R., Massaro E., Queirolo S., Sabatini A., Scarcella G., Simoni R. (eds), Sintesi delle conoscenze di biologia, ecologia e pesca delle specie ittiche dei mari italiani / Synthesis of the knowledge on biology, ecology and fishery of the halieutic resources of the Italian seas.

This species has an oval body and a pointed head with a slightly concave profile above the eye. Eyes are located on the left side of the body and the mouth is curved downward, with a prominent jaw and tip facing down. The upper edge of the preopercule is free and clearly visible. Vomerine teeth are strong, sharp and unequal: biseriate on the front side of each jaw and uniseriate on sides. The species is common throughout the Mediterranean and is preferably found on soft bottoms (with a strong muddy component) down to 300-400 m depths. C. linguatula is a predator; it preferably feeds on small teleosts, decapod crustaceans, mysids, whilst polychaetes and molluscs are secondary preys. The spotted flounder reaches a maximum size of 25 cm TL in the Italian seas and 30 cm TL in its range of distribution . Generally, the most represented sizes from trawl fishing catches are between 10 and 20 cm TL. Currently, the knowledge of period and size at first maturity of the species is scarce; catches of mature females were reported in March in the French Mediterranean or in autumn in the Gulf of Naples and in November-December in the central Adriatic. This species is a by catch of trawl fishery on the continental shelf. There is no assessment on the state of exploitation of this species, and no minimum size

Consideration on minimum commercial size of Chamelea gallina (L.)

Sorting sieve selectivity experiments were carried out on a hydraulic dredge fishery exploiting the clam, Chamelea gallina (Mollusca: Veneroida, Linneus, 1758). Six sieves (from 20 to 23 mm) were tested. The material collected shows that all sieves capture undersized clams. As it is impossible, with current sorting techniques, to avoid presence of undersized clams, the alternative approach “number per kilogram” has been proposed. The result of the study shows in 220 the allowed number of clams per kilogram

Assessment of reproductive cycle in common sole by citometry.

The common sole Solea solea (L., 1758) is one of the most valuable resources and it is a target fishery species in Mediterranean water, but guidelines about the resource management are generally lacking. In order to increase the scarce knowledge on the annual maturative cycle of the ovary, in the Adriatic Sea, histological and cytological analyses of ovary obtained from monthly captures of sole were carried out. Cytometric analysis was carried out by a computerized image analysis system Leica Qween. The gonad-somatic index (GSI determined on the basis of the ovary to body weight ratio), supported by histological and cytological data, describe the spawning period from December to March. The GSI increased rapidly during the reproductive season, when the majority of oocyte growth (diameter &gt; 200 mm) occurred. The range of germinal cells is comprised between 8 mm (oogonia) and 1.360 mm (hydrated oocytes immediately before spawning). The cytological study of oocyte size distribution showed only previtellogenic oocytes (diameter &lt; 200 mm), during the period April-November, but also vitellogenic oocytes (diameter &gt; 200 mm), during the period December-March. Before ten years ago, the oocyte size distribution in the mature ovaries was rarely studied in populations of common sole and the data obtained were often conflicting. In conclusion, the cytological approach applied throughout the ovary maturation cycle in common sole is a good \u201cassessment environmental test\u201d as gonad maturation is closely dependent on environmental conditions

ASSESSMENT OF REPRODUCTIVE CYCLE IN COMMON SOLE BY CITOMETRY

The common sole Solea solea (L., 1758) is one of the most valuable resources and it is a target fishery species in Mediterranean water, but guidelines about the resource management are generally lacking. In order to increase the scarce knowledge on the annual maturative cycle of the ovary, in the Adriatic Sea, histological and cytological analyses of ovary obtained from monthly captures of sole were carried out. Cytometric analysis was carried out by a computerized image analysis system Leica Qween. The gonad-somatic index (GSI determined on the basis of the ovary to body weight ratio), supported by histological and cytological data, describe the spawning period from December to March. The GSI increased rapidly during the reproductive season, when the majority of oocyte growth (diameter &gt; 200 mm) occurred. The range of germinal cells is comprised between 8 mm (oogonia) and 1.360 mm (hydrated oocytes immediately before spawning). The cytological study of oocyte size distribution showed only previtellogenic oocytes (diameter &lt; 200 mm), during the period April-November, but also vitellogenic oocytes (diameter &gt; 200 mm), during the period December-March. Before ten years ago, the oocyte size distribution in the mature ovaries was rarely studied in populations of common sole and the data obtained were often conflicting. In conclusion, the cytological approach applied throughout the ovary maturation cycle in common sole is a good \u201cassessment environmental test\u201d as gonad maturation is closely dependent on environmental conditions

Size at maturity of triglid fishes in the Adriatic Sea, northeastern Mediterranean

Aspitrigla cuculus (red gurnard), Chelidonichthys lucerna (tub gurnard) and Eutrigla gurnardus (grey gurnard) (Scorpaeniformes, Triglidae) occur in the Mediterranean Sea and in the eastern Atlantic. These gurnard species were included in the list of target species from the Coordination of the International bottom trawl survey in the Mediterranean Sea (MEDIT project) (Relini et al., 2008). This project, under grant since 1994 by the European Union, is carried out in the Mediterranean Sea to monitor the abundance and distribution of Mediterranean commercial demersal resources. Despite abundance and importance as economic resource of these triglids, there is a lack of knowledge of their basic biology and their stock composition and population dynamics (Olim and Borges, 2006; Marriott et al., 2010), particularly in the Italian Seas (Colloca et al., 2003; Vallisneri et al., 2010). Knowledge of the reproductive features of fish stocks, such as size at maturity, is important for the estimation of the spawning biomass in stock assessment models. Thus the objectives of this study was to estimate the size at first maturity, which is one of the key parameter related to the reproductive strategy of red gurnard, tub gurnard and grey gurnard in the coastal waters of the Adriatic Sea