67 research outputs found
Reburial potential and survivability of the striped venus clam (Chamelea gallina) in hydraulic dredge fisheries
No full textThe striped venus clam (Chamelea gallina) is the main edible bivalve living in Italian waters. According
to Regulation (EU) 2020/2237, undersized specimens (total length of the shell, < 22 mm) must be
returned to the sea. C. gallina specimens of different size classes that had undergone hydraulic
dredging and mechanized sorting were analysed for reburial ability in a laboratory tank and for
survivability in the laboratory (135 clams, 21 days) and at sea (320 clams, 15 days). In the tank
experiments, the reburial times (
T50 and T90)
and the upper (+) and lower (−) confidence intervals (CIs)
of the whole sample were about 4 h (CI+ 4.4, CI− 3.6) and 8 h (CI+ 8.2, CI− 7.7), respectively, and were
significantly shorter for the medium-sized clams (22–24.9 mm) than for the smallest (< 21.9 mm) and
the largest (> 25 mm) specimens. For the field survivability experiments, clams under and above the
minimum conservation reference size were placed in separate metal cages. Survival rates were 94.8%
and 96.2% respectively in the laboratory and at sea, without significant differences between the two
experiments or among size classes. These findings conclusively demonstrate that C. gallina specimens
returned to the sea have a very high survival probability and that they can contribute to mitigate the
overexploitation of natural populations
Crisio of capitalism
No full textThere are some fundamental questions that must be answered if we want to fully understand capitalism, in the various forms that it has been taking in the present phase of its planet-wide expansion: How is the work process organized? How do markets work? What determines the share that goes to profits and the share that goes to wages? What is the role of technology? Why some workers earn more than others? What is a crisis, and when does it takes a structural rather than conjunctural character? What is the connection between the financial crisis and the general economic crisis, and when and how does this last take the character of a systemic crisis? Is it possible to overcome a structural crisis by means of Keynesian policies? What does the passage from the Keynesism of the social state to private, entrepreneurial and military Keynesism means?
The answers to the above questions largely depend upon the type of theory we use to interpret economic reality. We have chosen the standpoint of Marx’s critique of political economy. Marxian theory, and then Marxism, does not have the typical characteristics of the so-called “bourgeois sciences”. Marxism interprets the laws of the natural, social and economic sciences as aspects of concrete reality, almost always quite independent from the will of single individuals. Historical facts depend on sets of interconnections, the power relationships between classes and the modalities of the capital – labour conflict in each given historical period.
The profound transformation that the planet has undergone with the so-called globalization of the economic and social processes which characterizes the present imperialist phase of global competition has shown with clarity the limits of many theoretical paradigms. Every economic theory is the outcome of the period in which it was created, and theories that are lucky enough to be dominant are constantly struggling with new approaches.
The scope and aim of this book (which is a compendium of “Trattato di Economia Applicata”, Jaca Book, 2007, by the same author) is delimited in time and space. It is not a work in “pure economics”, but rather a guide to the understanding of the present phase of planet-wise expansion of the social production and reproduction of the capitalist form, and to its structural and systemic crisis. We refer to the theory of the capitalist mode of production as a process. In this sense this is a work of applied economics, although not in the reductive academic meaning of applying economics to, say, the environment, engineering, sociology and so on. To produce an applied economics in our sense we need Marx’s toolkit. Following Marx’s own procedure, we must first appropriate the tools of political economy, in order to then criticize them; this leads us to produce, with a scientific approach, a complex theory that is capable to go beyond political economy and, as a consequence, beyond the capitalist mode of production itself
Dredge selectivity in a Mediterranean striped venus clam (Chamelea gallina) fishery
No full textThe striped venus clam Chamelea gallina is the target of a large fleet of hydraulic dredgers, which represent an
important fishing sector in terms of income and landings in the Mediterranean Sea. Although there is information
on the catch rates, impact and discards related to this fishery, the size selection process carried out by the dredge
during trawl under commercial conditions is practically unknown. The present study aimed to fill this gap,
assessing the selectivity of the gear at different haul durations. We demonstrated that 25% of the clams entering
the dredge were not size selected by it. Clams with a length (i.e. maximum distance between anterior and
posterior margins) of 18.9 mm had 50% retention probability and tow duration did not affect the size selection
process in the dredge. The dredge catch efficiency was 79% in numbers of clams and 89% in weight. 58% of the
clams caught were below the minimum conservation reference size of 25 mm. The study demonstrates that to
land only the legal sizes of clams, the additional size selection process carried out on board the fishing vessels by
the sorting sieves is necessary
Meiobenthic assemblages as ecological indicator of natural variability induced by ecosystem engineers
No full textIndonesia is biologically one of the most diverse areas in the world. Nevertheless, its biodiversity is
underestimated, and this is particularly evident for meiobenthic assemblages. Seagrass meadows are
known to be ecosystem engineers that can significantly modify the habitat heterogeneity and, thereby,
increase the meiobenthic diversity. Therefore, a study on the meiobenthic distribution and biodiversity
was conducted in two seagrass meadows around Siladen Island (Bunaken Marine National Park): Barat
and Lagoon, characterized by different sedimentary regimes, as well as by different anthropogenic
impact. An overall high level of diversity indices and richness were recorded (H′: 1.19–1.69; J: 0.46–
0.67; number of taxa: 9–14), with meiobenthic abundances ranging between 770 and 2529 ind.
10 cm−2. The lowest meiobenthic abundance and diversity (i.e. Shannon-diversity, number of taxa)
were reported at Barat meadow, probably in response to sedimentological modifications and higher
anthropogenic pressure at this site. Differences in meiobenthic assemblage structures were particularly
evident when only rare taxa were considered (i.e taxa found in low abundances and characterized by
a sporadic distribution in the study area). This result underlines the role of rare species as possible
indicators of spatial variability generated by engineer species and different environmental conditions
Multi-benthic size approach to unveil different environmental conditions in a Mediterranean harbor area (Ancona, Adriatic Sea, Italy)
No full textHarbors are hubs of human activity and are subject to the continuous discharge and release of industrial, agricultural, and municipal waste and contaminants. Benthic organisms are largely known to reflect environmental conditions they live in. Despite meio- and macrofauna interacting within the benthic system, they are ecologically distinct components of the benthos and as such may not necessarily respond to environmental conditions and/or disturbances in the same way. However, in a few field studies the spatial patterns of meio- and macrofauna have been simultaneously compared. In the present study, we assess the response and patterns in the abundance, diversity, and distribution of the two benthic size classes to the different environmental conditions they live in (i.e., sediment concentrations of selected trace metals and polycyclic aromatic hydrocarbons (PAHs); organic matter contents and grain size) characterizing the Ancona Harbor (Adriatic Sea). Meio- and macrofauna provided partially similar types of information depending on the indices used (univariate measures or community structure/species composition) and the different ‘response-to-stress’. The community structure (i.e., taxa composition) of both benthic size components clearly showed differences among sampling stations located from inside to outside the harbor, reflecting the marked environmental heterogeneity and disturbance typically characterizing these systems. Notwithstanding, the univariate measures (i.e., meio- and macrofauna total abundance, diversity indices and equitability) didn’t show similar spatial patterns. Meiofauna were likely to be more sensitive to the effects of environmental features and contaminants than macrofauna. Overall, trace metals and PAHs affected the community composition of the two benthic components, but only the meiofauna abundance and diversity were related to the environmental variables considered (i.e., quantity and quality of organic matter). Our results pinpoint the importance of studying both meio- and macrofauna communities, which could provide greater insight into the processes affecting the investigated area and reveal different aspects of the benthic ecosystems in response to harbor conditions
Morphometric analysis revealed two different Mediterranean horse mackerel (Trachurus mediterraneus) stocks in the Adriatic Sea
No full textPhenotypical differentiation among individuals of Mediterranean horse mackerel Trachurus mediterraneus in the Adriatic Sea was investigated through the analysis of several morphometric characters. Overall, 426 individuals of Mediterranean horse mackerels were sampled from the northern, central and southern Adriatic Sea during the summers of 2012 and 2013. Forty-six morphometric characters were measured for each individual and then compared using multivariate techniques (linear discriminant analysis). Based on the morphometric characteristics, at least two different Mediterranean horse mackerel were identified: one comprising the northern and central Adriatic, and the other formed by individuals from the southern Adriatic basin. The northern and central areas showed stable populations, overlapping both in space and time. The southern area seemed to be more variable over the years, with a low degree of overlapping both in space and time. A possible hypothesis for this, to be further investigated, could be the flow of individuals from the Ionian and Aegean Seas populations through the Otranto Channel. The main differences between the two stocks were associated with the head characters of the fish. In particular, the northern and central Adriatic Sea individuals had shorter and thicker heads than the southern ones. This could be due to different feeding habits: the former mainly feed on small fishes, the latter mainly on euphausiids. A short mouth could reduce the power of suction of bigger preys, while a long mouth could increase the volume of water to be filtered to feed on small planktonic crustaceans. From this study, it becomes clear that the Mediterranean horse mackerel should not be managed as a single stock in the Adriatic Sea as it was evident that at least two morphologically different stocks are present in the basin
Estimating selectivity of experimental diamond (T0) and turned mesh (T90) codends in multi-species Mediterranean bottom trawl
No full textThis paper evaluates the effect of changing from a diamond mesh codend (T0) to a 90° turned mesh codend (T90) on the size selectivity of seven commercially important species in the Mediterranean bottom trawl fishery. In sea trials conducted in the north-western Adriatic, two experimental codends made of 54 mm nominal mesh size netting and differing only in mesh configuration were alternately mounted on the same trawl. Overall, the T90 mesh significantly improved codend size selection for all the species analysed. The difference in the predicted average L50 values between the T90 and T0 codend was particularly marked in European hake (Merluccius merluccius, 21.26 vs 11.26 cm total length), common squid (Loligo vulgaris, 12.06 vs 7.88 cm mantle length) and mantis shrimp (Squilla mantis, 20.78 vs 13.35 mm carapace length). Both codends showed an excessive size selectivity, which involves a commercial loss, especially for red mullet (Mullus barbatus), Mediterranean horse mackerel (Trachurus mediterraneus) and whiting (Merlangius merlangus). These findings demonstrate the efficiency of the T90 configuration in excluding undersized specimens, especially of hake, whose average L50 was above the minimum conservation reference size of 20 cm. The adoption of this practical and inexpensive solution can contribute to improve the management of the demersal resources targeted by the Mediterranean bottom trawl fishery
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Spatio-temporal variability of plant features and motile invertebrates in Posidonia oceanica seagrass meadows
No full textspatio-temporal Variability of Plant features and Motile Invertebrates in Posidonia oceanica Seagrass Meadows
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