Hazard function models to estimate mortality rates affecting fish populations with application to the sea mullet (Mugil cephalus) fishery on the Queensland coast (Australia)

Fisheries management agencies around the world collect age data for the purpose of assessing the status of natural resources in their jurisdiction. Estimates of mortality rates represent a key information to assess the sustainability of fish stocks exploitation. Contrary to medical research or manufacturing where survival analysis is routinely applied to estimate failure rates, survival analysis has seldom been applied in fisheries stock assessment despite similar purposes between these fields of applied statistics. In this paper, we developed hazard functions to model the dynamic of an exploited fish population. These functions were used to estimate all parameters necessary for stock assessment (including natural and fishing mortality rates as well as gear selectivity) by maximum likelihood using age data from a sample of catch. This novel application of survival analysis to fisheries stock assessment was tested by Monte Carlo simulations to assert that it provided un-biased estimations of relevant quantities. The method was applied to data from the Queensland (Australia) sea mullet (Mugil cephalus) commercial fishery collected between 2007 and 2014. It provided, for the first time, an estimate of natural mortality affecting this stock: 0.22 $\pm$ 0.08 year$^{-1}$

Environmental and fishing effects on the dynamic of brown tiger prawn (Penaeus esculentus) in Moreton Bay (Australia)

This analysis of the variations of brown tiger prawn (Penaeus esculentus) catch in the Moreton Bay multispecies trawl fishery estimated catchability using a delay difference model. It integrated several factors responsible for variations in catchability: targeting of fishing effort, increasing fishing power and changing availability. An analysis of covariance was used to define fishing events targeted at brown tiger prawns. A general linear model estimated inter-annual variations of fishing power. Temperature induced changes in prawn behaviour played an important role in the dynamic of this fishery. Maximum likelihood estimates of targeted catchability ($3.92 \pm 0.40 \ 10^{-4}$ boat-days$^{-1}$) were twice as large as non-targeted catchability ($1.91 \pm 0.24 \ 10^{-4}$ boat-days$^{-1}$). The causes of recent decline in fishing effort in this fishery were discussed.Comment: revised manuscript following reviewers comments + adding data and code for reader

A maximum likelihood estimate of natural mortality for brown tiger prawn (Penaeus esculentus) in Moreton Bay (Australia)

The delay difference model was implemented to fit 21 years of brown tiger prawn (Penaeus esculentus) catch in Moreton Bay by maximum likelihood to assess the status of this stock. Monte Carlo simulations testing of the stock assessment software coded in C++ showed that the model could estimate simultaneously natural mortality in addition to catchability, recruitment and initial biomasses. Applied to logbooks data collected from 1990 to 2010, this implementation of the delay difference provided for the first time an estimate of natural mortality for brown tiger prawn in Moreton Bay, equal to $0.031 \pm 0.002$ week$^{-1}$. This estimate is approximately 30\% lower than the value of natural mortality (0.045 week$^{-1}$) used in previous stock assessments of this species

Use of a proposed antimicrobial susceptibility testing method for Haemophilus parasuis

The aim of this study was to examine the antimicrobial susceptibility of 97 Haemophilus parasuis cultured from Australian pigs. As there is no existing standard antimicrobial susceptibility technique available for H. parasuis, methods utilising the supplemented media, BA/SN for disc diffusion and test medium broth (TMB) for a microdilution technique, were initially evaluated with the reference strains recommended by the Clinical and Laboratory Standards Institute. The results of the media evaluation suggested that BA/SN and TMB can be used as suitable media for susceptibility testing of H. parasuis. The proposed microdilution technique was then used with 97 H. parasuis isolates and nine antimicrobial agents. The study found that Australian isolates showed elevated minimum inhibitory concentrations (MICs) for ampicillin (1%), penicillin (2%), erythromycin (7%), tulathromycin (9%), tilmicosin (22%), tetracycline (31%) and trimethoprim-sulfamethoxazole (40%). This study has described potential antimicrobial susceptibility methods for H. parasuis and has detected a low percentage of Australian H. parasuis isolates with elevated antimicrobial MICs

Knowledge Networks in Organic Fruit Production across Europe: A Survey Study

Limited data regarding the resources and methods used by organic fruit growers to learn about production practices are available, even though this information is crucial to improving the efficacy of knowledge transfer. Therefore, a survey to gain information from knowledge networks dealing with organic fruit production about their structural organisation, tasks and methods of communication was carried out in twenty-one countries from Europe and the Mediterranean basin. A total of 56 networks representing about 42,500 professionals were identified as a result of the survey. The vast majority of them were only active at the regional or national level and were composed of farmers, advisors and researchers. About 3/4 of the networks were developing improved strategies for agronomic practices and about half of them were also involved in different knowledge-transfer activities between their members. Personal contact was the most used method to exchange and disseminate information within the networks as well as to elaborate improved strategies. The findings were analysed in view of the methods and practices commonly used to share both explicit (scientific) and implicit (practical) knowledge among practitioners. It was concluded that knowledge networks play an important role in the development of more resilient organic cropping systems, frequently making organic fruit growers the drivers of innovation. Networking for knowledge exchange was considered a process that encourages the active involvement of farmers in experimentation and innovation applying a method of knowledge sharing that is rooted in the very foundation of organic philosophy. Some recommendations and future research were suggested to further foster the development and functioning of networks for knowledge exchange

Hazard Function Models to Estimate Mortality Rates Affecting Fish Populations with Application to the Sea Mullet (Mugil cephalus) Fishery on the Queensland Coast (Australia)

Fisheries management agencies around the world collect age data for the purpose of assessing the status of natural resources in their jurisdiction. Estimates of mortality rates represent a key information to assess the sustainability of fish stocks exploitation. Contrary to medical research or manufacturing where survival analysis is routinely applied to estimate failure rates, survival analysis has seldom been applied in fisheries stock assessment despite similar purposes between these fields of applied statistics. In this paper, we developed hazard functions to model the dynamic of an exploited fish population. These functions were used to estimate all parameters necessary for stock assessment (including natural and fishing mortality rates as well as gear selectivity) by maximum likelihood using age data from a sample of catch. This novel application of survival analysis to fisheries stock assessment was tested by Monte Carlo simulations to assert that it provided unbiased estimations of relevant quantities. The method was applied to the data from the Queensland (Australia) sea mullet (Mugil cephalus) commercial fishery collected between 2007 and 2014. It provided, for the first time, an estimate of natural mortality affecting this stock: 0.22±0.08 year −1

Rising temperatures increased recruitment of brown tiger prawn (Penaeus esculentus) in Moreton Bay (Australia)

Abiotic factors are fundamental drivers of the dynamics of wild marine fish populations. Identifying and quantifying their influence on species targeted by the fishing industry is difficult and very important for managing fisheries in a changing climate. Using multiple regression, we investigated the influence of both temperature and rainfall on the variability of recruitment of a tropical species, the brown tiger prawn (Penaeus esculentus), in Moreton Bay which is located near the southern limit of its distribution on the east coast of Australia. A step-wise selection between 60 environmental variables identified temperature as the most important environmental factor to explain the variations of recruitment between 1990 and 2014. Including temperature into the Beverton and Holt stock–recruitment relationship explained 69% of the recruitment variability compared with 9.5% when omitted. This analysis indicates that increasing temperatures have increased recruitment of brown tiger prawn in Moreton Bay

A study on compatibilization mechanisms of nanocomposites with engineering polymer blends for the upgrade of critical properties

200 σ.Σκοπός της παρούσας διπλωματικής εργασίας ήταν η μελέτη μηχανισμών συμβατοποίησης νανοσυνθέτων με μίγματα μηχανολογικών πολυμερών (ABS/PC) για αναβάθμιση κρίσιμων, ρεολογικών, μηχανικών και θερμικών, ιδιοτήτων. Επίσης, σκοπός ήταν η λήψη μέσω των πραγματοποιηθέντων πειραμάτων συμπερασμάτων σχετικά με τις δυνατότητες ανακύκλωσης μιγμάτων ABS/PC προερχόμενων από απορρίμματα ηλεκτρικού και ηλεκτρονικού εξοπλισμού (ΑΗΗΕ). Τα ABS και PC συναντώνται σε υψηλά ποσοστά στα ΑΗΗΕ, ενώ όταν αναμιγνύονται συνδυάζονται οι καλές μηχανικές και θερμικές ιδιότητες του PC με την επεξεργασιμότητα του ABS. Όμως, η μηχανική ανακύκλωση των πολυμερών έχει ως αποτέλεσμα την υποβάθμιση ορισμένων ιδιοτήτων τους, κυρίως λόγω της θερμοοξειωτικής αποδόμησης που λαμβάνει χώρα. Έτσι. για να αναβαθμιστούν οι ιδιότητες των πολυμερικών μιγμάτων ABS/PC εξετάστηκε η χρήση δύο προσθέτων, τoυ συμβατοποιητή ABS-g-MAH και της οργανικά τροποποιημένης ορυκτής αργίλου Cloisite 30B. Μετά την πραγματοποίηση της εκβολής και την κοκκοποίηση των μιγμάτων, τα δείγματα των διαφόρων συστάσεων ABS/PC (100/0, 70/30. 50/50 και 30/70 w/w) εξετάσθηκαν ως προς τη δομή και τη μορφολογία τους μέσω XRD, SEM και DSC, ενώ ταυτόχρονα εξετάστηκαν οι μηχανικές (πειράματα εφελκυσμού), οι ρεολογικές (MFI) και οι θερμικές ιδιότητές τους (ΤGA, μέτρηση ανώτερης θερμογόνου δύναμης), με σκοπό τη συσχέτιση των μικροσκοπικών ιδιοτήτων με τις εμφανισθείσες μακροσκοπικές. Η μερική συμβατότητα των δύο πολυμερών, για την οποία δόθηκαν ενδείξεις μέσω της ανάλυσης με DSC, επιβεβαιώθηκε και μέσω SEM. Συγκριτικά, όσον αφορά τη μορφολογία των πολυμερικών μιγμάτων, η προσθήκη Cloisite 30B φαίνεται να έχει καλύτερα αποτελέσματα σε σχέση με το ΑΒS-g-MAH, γεγονός που αποδεικνύει τη συμβατοποιητική δράση που έχει ο οργανικά τροποποιημένη ορυκτή άργιλος. Η συνδυασμένη δράση της οργανικά τροποποιημένης ορυκτής αργίλου ως συμβατοποιητή και μέσου ενίσχυσης είχε ως αποτέλεσμα την αναβάθμιση της πλειοψηφίας των ιδιοτήτων των εξετασθέντων μιγμάτων ABS/PC. Συγκεκριμένα, η προσθήκη Cloisite 30B είχε ως αποτέλεσμα την βελτίωση της αντοχής σε εφελκυσμό και του μέτρου ελαστικότητας, καθώς και την αύξηση του ιξώδους των μιγμάτων. Όσον αφορά τις θερμικές ιδιότητες, η συνολική βελτίωση που παρατηρήθηκε, μετά την προσθήκη Cloisite 30B, μπορεί πιθανώς να αποδοθεί: (α) στο «φαινόμενο φράγματος», η ισχυροποίηση του οποίου εξαρτάται από το βαθμό διασποράς των πλακιδίων του ΟΜΜΤ και (β) από την αλλαγή του μηχανισμού θερμικής αποδόμησης, αφού μέσω των πειραμάτων TGA παρατηρήθηκε ότι τα νανοσύνθετα των πλούσιων σε PC μιγμάτων αποδομούνται σε δύο διακριτά στάδια. Τα δεδομένα αυτά οδηγούν στο συμπέρασμα ότι η βελτίωση των θερμικών ιδιοτήτων, η οποία πραγματοποιείται μέσω αλλαγής του μηχανισμού αποδόμησης και της εμφάνισης του «φαινομένου φράγματος», πιθανώς να βασίζεται στην αλληλεπίδραση της ορυκτής αργίλου με το PC, καθώς και στην προστασία των νησίδων του PC από τα πλακίδια της ορυκτής αργίλου που έχουν συγκεντρωθεί στη διεπιφάνεια των ABS/PC. Η καλύτερη θερμική σταθερότητα των μιγμάτων επαληθεύθηκε και μέσω των πειραμάτων μέτρησης της ανώτερης θερμογόνου δύναμης. Αντίθετα, η προσθήκη του ABS-g-MAH δεν είχε κάποια ιδιαίτερη επίδραση στις μηχανικές και θερμικές ιδιότητες των μιγμάτων, αλλά απλά μία μικρή αύξηση στο ιξώδες τους. Επίσης, η δράση των ABS-g-MAH και Cloisite 30B δεν είναι αθροιστική, αφού η προσθήκη συμβατοποιητή στα νανοσύνθετα δε βελτίωσε, αλλά μάλλον υποβάθμισε, τις ιδιότητές τους. Συμπερασματικά, η οργανικά τροποποιημένη ορυκτή άργιλος Cloisite 30B κρίνεται ως καλύτερο πρόσθετο σε σχέση με το ABS-g-MAH, αφού η συνδυασμένη της δράση ως συμβατοποιητή και μέσο ενίσχυσης είχε ως αποτέλεσμα την εμφάνιση βελτιωμένων ιδιοτήτων, κυρίως μηχανικών και θερμικών, στη πλειοψηφία των πολυμερικών μιγμάτων που εξετάστηκαν. Τέλος, βάση των παραπάνω συμπερασμάτων κρίνεται ιδιαίτερα σημαντική η διαχείριση ενός μέρους των προερχόμενων από ΑΗΗΕ πολυμερών μέσω μηχανικής ανακύκλωσης των μιγμάτων τους, με ταυτόχρονη προσθήκη προσθέτων τέτοιων ώστε να καθίσταται δυνατή η περαιτέρω χρήση τους σε ανάλογες με τις αρχικές εφαρμογές. Όμως, η ανομοιογένεια του πλαστικού κλάσματος των ΑΗΗΕ και οι προσμίξεις που αυτά περιέχουν καθιστούν απαραίτητο το συνδυασμό διαφόρων μεθόδων διαχείρισης τους. Έτσι, παρόλο που η ανώτερη θερμογόνος δύναμή των μιγμάτων ABS/PC είναι μικρότερη αυτής που παρουσιάζουν τα πλαστικά αστικά απορρίμματα, η καύση αποτελεί μία καλή εναλλακτική λύση για την ολοκληρωμένη διαχείρισή τους.Blends of acrylonitrile–butadiene–styrene copolymer (ABS) and polycarbonate (PC) are a class of the largest selling commercial polymers, as they are widely applicable in automobile, home appliance and computer fields. This increased popularity is due to their relatively good mechanical properties, processibilty and heat resistance. However, the components of this alloy present poor compatibility and, therefore, compatibilization is often applied in industrial practice, in order to promote miscibility. This technique involves the use of third component, such as costly core-shell compatibilizer, as an additive to the blend system1. Balakrishnan et al.2 mixed PC with maleic anhydride (MAH) grafted ABS and attributed the improved interfacial interaction to the chemical reaction between the anhydride group of MAH and the terminal OH group of PC. Elmaghor et al.3 proposed that the role of MAH grafting is the compatibilization between two kinds of segments of ABS. More specifically, the grafting of styrene/butadiene segments helps them to enwrap the styrene/acrylonitrile segments and thus moderate the repulsion between those polar segments and the non-polar PC ones. In the present study, in order to improve the performance of ABS/PC blends, organically modified montmorillonite (OMMT) nanoparticles were incorporated into this mixture by melt mixing in a twin screw extruder. In addition, the effect of a compatibilizer, ABS-g-MAH, on the immiscibility, morphology and properties of ABS/PC blends and their nanocomposites was examined. The prepared hybrids were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction Analysis (XRD), Thermogravimetric Analysis (TGA), Dynamic mechanical Analysis (DMA) and Tensile test measurements. The addition of OMMT influences the thermal degradation mechanism and properties of ABS/PC blends with compositions 50/50 and 30/70 w/w in comparison with the respective unreinforced blends. The incorporation of organoclay nanofiller seems to inhibit thermal degradation of the PC phase, maybe due to the settlement of nanoclay at the ABS/PC interface and the formation of a protective layer. This layer insulates the underlying material leading to the formation of char with a multilayered carbonaceous-silicate structure on the surface during burning. Significant improvement was also recorded for modulus of elasticity during tensile tests, as well as for the storage modulus G’ of ABS/PC blends. The reduction of the average microdomain size of PC by OMMT addition suggests that nanoclay improves compatibility of ABS/PC blends. ABS-g-MAH compatibilzer, although improving the intercalation process of ABS/PC nanocomposites, does not have substantial effect on the thermal stability and mechanical properties of the investigated systems. References 1. S. Balakrishnan, N.R. Neelakantan, Journal of Materials Science 34: 5181-5185 (1999). 2. S. Balakrishnan, N.R. Neelakantan, D. Nabi Saheb, J.P. Jog, Polymer 39: 5765-5771 (1998). 3. F. Elmahhor, L. Zhang, R. Fan, H. Li, Polymer 45: 6719-6724 (2004).Εμμανουήλ Μ. Χατζηγιαννάκη