Odnos dužine i maksimalnog obujma za 24 riblje vrste u sjevernom Egejskom moru (istočno Sredozemno more)

The knowledge of morphological relationships and particularly of those concerning fish body girth (G) with total length (TL) is necessary in gear selectivity and specifically the technical measures to avoid capture of undersized individuals. This study concerns 24 marine species exploited by the small-scale coastal fleet in the Aegean Sea (eastern Mediterranean Sea), for 6 of which, the TL-G relationships are mentioned for the first time in the Mediterranean Sea and the adjacent seas. Samples were collected seasonally, from April 2016 to February 2017. The coefficients of the linear regression of body girth in three body positions, (Geye, posterior to the eye; Ghead at the posterior end of the operculum; Gmax at the maximum body depth), with the total length were estimated for each species and for the groups formatted when Geye, Ghead and Gmax were plotted against total length for all the species combined. Statistically significant differences among the three groups were detected (ANCOVA, P<0.001). Comparison of the total length-body girth relationships for 18 species previously studied in different geographic areas of the Mediterranean and the adjacent seas, showed differences mainly with the results from Portuguese waters for certain species populations. Based on the resulted equations, the maximum girth (G max) corresponding to the Minimum Conservation Reference Size (MCRS) and to the total length at maturity (L m) were calculated for each species. Identified mesh sizes respective to G max values were quite larger than the minimum legal mesh size for gillnets and the inner sheet of trammel nets, indicating that the relevant current fisheries regulations cannot meet the requirements for sustainable exploitation of fish resources.Poznavanje morfoloških odnosa, a posebno onih koji se tiču maksimalnog obujma tijela ribe (G) s ukupnom dužinom (TL) potrebito je za određivanje selektivnosti alata, a posebno za tehničke mjere za izbjegavanje hvatanja nedoraslih jedinki. Ova studija se odnosi na 24 morske vrste koje se iskorištavaju u priobalnoj ribolovnoj floti u Egejskom moru (istočno Sredozemno more), za 6 od kojih se TL-G odnosi prvi put spominju u Sredozemnom moru i susjednim morima. Uzorci su prikupljani sezonski, od travnja 2016. do veljače 2017. Koeficijenti linearne regresije obujma tijela u tri položaja tijela (G eye, posteriorno od oka; G head na stražnjem kraju operkuluma; Gmax na maksimalnoj visini tijela), s ukupnom duljinom procijenjene su za svaku vrstu i za skupine oblikovane kada su Geye, Ghead i Gmax ucrtani u odnosu na ukupnu duljinu za sve vrste zajedno. Utvrđene su statistički značajne razlike između tri skupine (ANCOVA, P<0,001). Usporedba odnosa ukupne duljine i obujma tijela za 18 vrsta koje su prethodno istraživane u različitim geografskim područjima Sredozemlja i susjednih mora, pokazala je razlike uglavnom s rezultatima iz portugalskih voda za određene populacije vrsta. Na temelju dobivenih jednadžbi izračunat je maksimalni obujam (Gmax) koji odgovara minimalnoj referentnoj veličini očuvanja (MCRS) i ukupnoj dužini pri zrelosti (Lm) za svaku vrstu. Identificirane veličine oka koje odgovaraju Gmax vrijednostima bile su dosta veće od minimalne zakonske veličine oka za mreže stajačice i unutarnju ploču troslojnih mreža, što ukazuje da relevantni trenutačni propisi o ribarstvu ne mogu ispuniti zahtjeve za održivo iskorištavanje ribljih resursa

New developments in the analysis of catch time series as the basis for fish stock assessments: The CMSY++ method

Following an introduction to the nature of fisheries catches and their information content, a new development of CMSY, a data-limited stock assessment method for fishes and invertebrates, is presented. This new version, CMSY++, overcomes several of the deficiencies of CMSY, which itself improved upon the “Catch-MSY” method published by S. Martell and R. Froese in 2013. The catch-only application of CMSY++ uses a Bayesian implementation of a modified Schaefer model, which also allows the fitting of abundance indices should such information be available. In the absence of historical catch time series and abundance indices, CMSY++ depends strongly on the provision of appropriate and informative priors for plausible ranges of initial and final stock depletion. An Artificial Neural Network (ANN) now assists in selecting objective priors for relative stock size based on patterns in 400 catch time series used for training. Regarding the cross-validation of the ANN predictions, of the 400 real stocks used in the training of ANN, 94% of final relative biomass (B/k) Bayesian (BSM) estimates were within the approximate 95% confidence limits of the respective CMSY++ estimate. Also, the equilibrium catch-biomass relations of the modified Schaefer model are compared with those of alternative surplus-production and age-structured models, suggesting that the latter two can be strongly biased towards underestimating the biomass required to sustain catches at low abundance. Numerous independent applications demonstrate how CMSY++ can incorporate, in addition to the required catch time series, both abundance data and a wide variety of ancillary information. We stress, however, the caveats and pitfalls of naively using the built-in prior options, which should instead be evaluated case-by-case and ideally be replaced by independent prior knowledge

Choosing from skyline sets

The skyline operator has been proposed to bridge the gap between traditional and multimedia database systems by finding the optimal objects according to the notion of Pareto dominance. According to the notion of Pareto dominance an object dominates another if it is better in one attribute and equal in all others. Skyline sets end up being pretty large because of the "curse of dimensionality". Many skyline reduction algorithms have been proposed to choose "interesting" objects from skyline sets in order to reduce their size. The purpose of this master thesis is to propose a new way of using reduction algorithms, that is to summarize datasets. A framework is proposed for interactive query refinement that will give users an overview of their query results provided by a skyline reduction algorithm. On the grounds of summarizing datasets different reduction algorithms will be compared against each other and a new novel reduction algorithm will be proposed that will hopefully summarize better query results.Electrical Engineerin

Management of natural animal populations and the risk of extinction

The basic question posed in this thesis concerns the survival and conservation strategies deployed by natural animal populations, under the specific conditions of the Mediterranean - type ecosystems. Our null hypothesis is that populations develop their life-history strategies in interaction with their environment, through mechanisms associating demography with the main environmental features. In order to examine the life - history strategies for the Mediterranean animal populations, we suggest a time - variant, stochastic, stage - structured and Leslie - type metapopulation model, which incorporates the basic characteristics of the Mediterranean - type ecosystems. The model is applied on an ideal - species population of a terrestrial arthropod, using data which are appropriate for Mediterranean populations. Model simulations are used to examine population dynamics under spatially heterogeneous conditions and stochastically fluctuating environmental and demographical variables, the role of dispersal in the dynamics of these animals and life - history strategies under these conditions. In the third chapter we focus on the phenology of the Mediterranean arthropods, in the variety of the phenological responses that species deploy in order to weather the environmental severities, as well as the life - history strategies alterations in relation with their demography. Our results suggest that Mediterranean populations have developed a well - organized life - history program, based on conservative and conformistic life - cycle traits, a fact which also becomes obvious through their response to the stochastic phenomena affecting their dynamics. These adaptations allow the optimal exploitation of the limited and seasonally fluctuating resources, and through that the conservation of the populations in the field despite the constraints of the Mediterranean environment. Understanding the underlying mechanisms that form life history - strategies for mediterranean populations are of crucial importance when we apply conservation practices in order to diminish the risk of extinction in threatened species.Το βασικό επιστημονικό ζήτημα που πραγματεύεται η διδακτορική αυτή διατριβή αφορά τις στρατηγικές επιβίωσης και διατήρησης των φυσικών πληθυσμών των ζώων υπό τις ιδιαίτερες συνθήκες του Μεσογειακού οικοσυστήματος. Ως υπόθεση εργασίας θέτουμε ότι οι πληθυσμοί αναπτύσσουν τις στρατηγικές ιστορίας ζωής σε αλληλεπίδραση με το περιβάλλον τους, μέσα από μηχανισμούς που συνδέουν τη δημογραφία τους με τα βασικά χαρακτηριστικά του περιβάλλοντος. Προκειμένου να εξετάσουμε τις στρατηγικές ιστορίας ζωής των μεσογειακών πληθυσμών ζώων προτείνουμε ένα χρονομεταβλητό, στοχαστικό, μεταπληθυσμιακό μοντέλο τύπου Leslie το οποίο ενσωματώνει τα βασικά χαρακτηριστικά των Μεσογειακών οικοσυστημάτων. Η εφαρμογή του μοντέλου γίνεται επί ενός πρότυπου πληθυσμού εδαφικού αρθροπόδου, με δεδομένα που έχουν επιλεγεί κατάλληλα ώστε να του προσδίδουν τα βασικά χαρακτηριστικά των μεσογειακών πληθυσμών. Μέσα από προσομοιώσεις του μοντέλου, εξετάζουμε τη δυναμική των μεσογειακών πληθυσμών υπό συνθήκες χωρικής ετερογένειας (μεταπληθυσμιακό μοντέλο) και τυχαιότητας (περιβαλλοντική και δημογραφική στοχαστικότητα), το ρόλο της διασποράς στη δυναμική των εδαφικών αρθροπόδων, καθώς και τις στρατηγικές επιβίωσης που ακολουθούν οι πληθυσμοί αυτοί. Στο τρίτο κεφάλαιο εστιάζουμε στη φαινολογία των μεσογειακών αρθροπόδων, στην ποικιλία των φαινολογικών αντιδράσεων που εμφανίζουν τα είδη προκειμένου να ανταπεξέρθουν στις αντιξοότητες του περιβάλλοντος, καθώς και στο πως μεταβάλλονται οι στρατηγικές τους σε σχέση με τη δημογραφία τους. Τα αποτελέσματά μας υποδηλώνουν ότι οι μεσογειακοί πληθυσμοί έχουν αναπτύξει ένα καλά οργανωμένο πρόγραμμα ιστορίας ζωής βασιζόμενα στα συντηρητικά και τα κομφορμιστικά στοιχεία του κύκλου ζωής τους, γεγονός που γίνεται εμφανές και από την απόκρισή τους στα στοχαστικά φαινόμενα που επιδρούν επί της δυναμικής τους. Οι προσαρμογές αυτές επιτρέπουν τη βέλτιστη εκμετάλλευση των περιορισμένων και εποχικά μεταβαλλόμενων πόρων, και μέσω αυτής τη διατήρηση των πληθυσμών στο πεδίο υπό τους περιορισμούς του μεσογειακού περιβάλλοντος. Η γνώση σχετικά με τις στρατηγικές ιστορίας ζωής των μεσογειακών πληθυσμών αποτελεί απαραίτητο στοιχείο προκειμένου να είναι εύστοχες και αποδοτικές οι διαχειριστικές πρακτικές που εφαρμόζονται για τη μείωση του κινδύνου εξαφάνισής τους

Evaluation of Marine Recreational Fisheries and Their Relation to Sustainability of Fisheries Resources in Greece

During 2019, Greece conducted a nationwide telephone survey in order to estimate the number of marine recreational fishers (MRF), to identify the main fishing methods, to estimate their effort, economic aspects of their activity and to evaluate certain perceptions of marine recreational fishing. MRF are estimated to be 7.93% of the country&rsquo;s resident population. Three main fishing methods were identified, fishing from the shore, fishing by boat and spearfishing. It is estimated that Greek MRF carry out approximately 11,461,765 fishing trips/year, their total catch is 9350 t/year and the total yearly expenditure is 132,186,000 Euros. Marine recreational catches constitute one-third of the reported small scale coastal fisheries&rsquo; catches, with their main catches belonging to the Sparidae family. The majority of MRFs are aware of the rules and limits associated with their activity, however a significant percentage seems to ignore or deny their existence. The results of the study indicate the social and economic importance of the activity in Greece and clearly demonstrates the need for regular monitoring and field work in order to properly evaluate marine recreational fisheries and sustainably manage both the activity and fisheries resources in the country

A Morphometric and Karyological Study of the <i>Anthemis macedonica</i> Group (Asteraceae, Anthemideae) Reveals a New Species from Greece

A recent study of the Anthemis collections in the Balkans indicated that the taxa of the Anthemis macedonica group (A. macedonica subsp. macedonica, A. macedonica subsp. thracica, A. meteorica, A. orbelica) exhibit noteworthy morphological patterns not evaluated before. We applied morphometric approaches (principal components analysis, PCA; factor analysis on mixed data, FAMD) by considering 19 qualitative and 20 quantitative morphological characters, together with three ratios, in 26 populations of this group. Furthermore, the chromosome numbers and karyotype morphology were investigated in eight populations of the group, covering the taxa participating in the study. Our results revealed that the southernmost populations of the group represent a hitherto unknown species confined to serpentine: it is described here as Anthemis serpentinica Goula & Constantinidis. The morphological evidence supports the proximity of A. macedonica and A. orbelica, which would be better considered as subspecific entities of the same species. On the contrary, A. meteorica and A. thracica are retained as independent entities at species level. All taxa share the same diploid chromosome number of 2n = 2x = 18 with similar but not identical karyotypes. A brief description of all taxa, based on recent new collections, and a dichotomous key are presented. Lectotypes are designated for Anthemis macedonica and A. meteorica

Estimation of selectivity parameters for target and bycatch fishes of the trammel net fisheries in the northern Aegean Sea (eastern Mediterranean Sea)

The size selectivity of trammel nets was investigated in the northern Aegean Sea using 10 different inner-panel mesh sizes ranging from 16 to 70 mm nominal mesh size (bar length). Selectivity estimates were made for the eight most abundant target and bycatch fish species, namely black scorpionfish, Scorpaena porcus Linnaeus, 1758; annular seabream, Diplodus annularis (Linnaeus, 1758); red mullet, Mullus barbatus Linnaeus, 1758; surmullet, Mullus surmuletus Linnaeus, 1758; round sardinella, Sardinella aurita Valenciennes, 1847; European hake, Merluccius merluccius (Linnaeus, 1758); greater weever, Trachinus draco Linnaeus, 1758; and blotched picarel, Spicara flexuosum Rafinesque, 1810, which accounted for 51.5% by number and 42.7% by weight of the fish caught with trammel nets in the sea trials. The SELECT method was used to estimate the selectivity parameters. Five different selectivity functions (i.e., normal scale, normal location, gamma, log-normal, and bi-normal) were applied with the bi-normal function providing the best fit as it had the lowest deviance value for all species and the lowest values for the dispersion parameter (D/df). The mesh size of 16 mm in most of the cases retained specimens below the size at first maturity (Lm). The mesh size of 19 mm seems more appropriate for red mullet, surmullet, and blotched picarel, the mesh size of 22 mm for annular seabream and round sardinella, while for European hake and black scorpionfish, the mesh size larger than 26 mm would be more appropriate

Vegetation coverage change in the EU: patterns inside and outside Natura 2000 protected areas

EU conservation policy is primarily based on the Natura 2000 network of protected areas (PAs). We analyzed the land-cover changes between 2000 and 2006 inside 25,703 Natura 2000 sites in 24 EU Member States, and compared them with those observed outside the PAs. At the EU level, ‘Artificial surfaces’ and ‘Agricultural areas’ exhibit lower rates of transformation within PAs than outside. ‘Forests and semi-natural areas’ marginally increased inside PAs, while they marginally decreased outside. In States that joined the EU before 2000, landscape transformation rates were low, and inside PAs ‘Forest’ preservation was accompanied with a shift from intensive agricultural practices ‘Permanent arable land’ to more diverse ‘Agricultural mosaics’. In new Member States (most of them located in Eastern Europe), there was agricultural abandonment, with conversion to ‘Artificial surfaces’ or ‘Natural vegetation’, both within and outside PAs. Broad scale EU policies (like the Common Agricultural Policy) and socio-economic drivers (like the transition from planned to market economy) seem to be dominant factors in explaining land-cover transformations, while conservation policies may moderate these trends inside PAs