Life-history traits in fish populations are highly correlated. A subset of these correlations are called allometric scaling, they refer to biological processes which can be described using body size as independent variable. Particularly, allometric scaling related with food consumption (Q) and biomass production (P) has gained the attention of ecologists for several decades. This thesis proposes a quantitative framework for food consumption, which allows both the identification of the mechanisms underlying the allometric scaling for Q and the development of a predictive model for consumption to biomass ratio (Q/B) in fish populations. This thesis is based on the fact that food consumption can be inferred from first principles underlying the von Bertalanffy growth model. In addition, it has been noticed in the literature that biomass production and food consumption show similar allometric scaling dependence, therefore, both can be derived from these first principles. Thus, a similar quantitative framework was used to produce models for P/B in fish populations. Once functional forms for production and food consumption were identified, a third model was developed for the ratio between production and consumption (P/Q). This ratio is usually named ecological efficiency because it determines how efficiently a population can transform ingested food into biomass. Several authors have noticed that P/Q remains invariant (independent of body size) across species. From a theoretical point of view, the results presented here allow the first quantitative explanation for the existence of the allometric scaling for Q/B and the invariance of P/Q across fish species. These results, together with the explanation for allometry in P/B reported in the literature, suggest that the regular across-species pattern for the trio {P/B,Q/B,P/Q} can be explained by basic principles that underpin life-history in fish populations. This quantitative framework for the trio {P/B,Q/B,P/Q} is based on an explicit dependence with body size, which simplifies the estimation of these quantities. Model complexity depends, in part, on which data are available. Models were applied to real data from commercially important species fished in Chile. Statistical properties of the new models were evaluated by an intensive resampling approach. The simplest possible model for the trio {P/B,Q/B,P/Q} rests on the assumption of a stable age distribution. These quantities have a key importance in ecosystem modelling because they determine population energetics in terms of food intake by predation and the transformation of this energy into population biomass of predators. Application of the new models produces results which were comparable to those given by standard methods. This thesis is a result of multidisciplinary research which attempts to make a contribution to the understanding of the mechanisms underlying the allometric scaling of food consumption and production in fish populations. It proposes models for the trio {P/B,Q/B,P/Q} and thus, has the potential to be widely applicable in fisheries science.

Rainfed areas in the Dry-Zone of Sri Lanka are characteristic of extensive marginal agro-ecosystems known as the semi-arid tropics (SAT) populated by poor farming communities. In the Dry-Zone and elsewhere, the traditional response to seasonal water scarcity was to construct rainfall-harvesting devices known as ‘tanks’; created by building earthen dykes across ephemeral streams in undulating terrain. Most are held in common ownership by adjacent communities, who use them for multiple functions including irrigation, bathing and fishing. Storage efficiency is enhanced by arranging tanks in cascading sequence within watersheds so that drainage waters can be re-used. The aim of this study was to evolve improved collective strategies for the management of seasonal water bodies (focussing on aquatic production) in order to reduce the vulnerability of the poorest groups. Understanding of these complex systems requires a holistic approach which integrates hydrological, biological and socio-economic factors on a suitable (watershed) scale. Work commenced with a comprehensive situation analysis, culminating with the formulation of a participatory research agenda for action research based on low-input stocking enhancements. Village livelihoods have traditionally revolved around paddy cultivation as the primary tank function; however, in recent times, water-use strategies have responded to a range of demographic, economic and environmental pressures with implications for the sustainable management of natural resources, especially living aquatic organisms. Natural fish production in the most seasonal tanks relies on intermittent spill-events which link successive tanks; these provide migration routes which permit recruitment of stocks from lower perennial tanks. Rehabilitation initiatives that increase the storage / irrigation capacity of tanks or poorly designed surplus weirs that impede migration have negative impacts on fisheries, though they are rarely considered by planners. The fundamental concept of the purana complex (PC) as the smallest logical sub-component of the watershed for intervention is introduced. Within PC boundaries discrete community groups bound by ties of kinship and caste, control access to private and commonly held natural resources. PCs in the uppermost reaches of watersheds are distinguishable by the highly seasonal nature of their tanks and poor physical infrastructure relative to lower watershed communities. Such areas are also often buffer zones between as yet uninhabited hinterlands and settled areas where cultivation potentials are further restricted due to wild animal incursions. Consequently, these groups exhibit the greatest dependence on exploitation of the natural resource base. This often includes less seasonal tanks in lower PCs where fisheries are of less significance to local livelihoods. Such low-level ‘poaching’ is generally well tolerated, but potential for conflict exists where development efforts restrict hitherto free access to these resources. These findings were the basis for two phases of action research which involved the stocking of ten tanks belonging to seven communities in North West Province (2000-2001). Phase 1 trials encompassed a range of social and physical and settings from lower to upper watershed. Results indicated that the use of costly hatchery-produced seed was unlikely to be sustainable given (1) a background of highly erratic natural production (2) uncertain returns to individual effort and (3) a low priority accorded to fish production from village tanks given the availability of low-cost commercial production from perennial reservoirs. The second phase was restricted to low-caste communities in upper watershed areas and relied entirely on wild-fish stocks captured from perennial reservoirs lower in the watershed. Also emphasis was on intermittent ‘staggered’ harvesting using hook and line gears rather than the single intensive ‘collective harvests’ adopted in phase 1 trials. High yield potentials were demonstrated in the smallest tanks (<4ha) which were devoid of fish stocks during two pervious drought years. Results also indicate that sustainable adoption will be likely only where there is strong social cohesion and representative village leadership. An adaptive learning process which can demonstrate the net benefits of staggered harvesting in seasonal tanks is described. These stocking strategies combined with tank rehabilitation sympathetic to preservation of upstream hydrological linkages, are highly complementary enhancement steps. Results clearly show that together they have potential to maintain the wider aquatic ecosystem on which the poorest groups depend.

Throughout the Pacific, many species of echinoderms and molluscs have cultural value and are harvested extensively in subsistence fisheries. Many of these species are sedentary and often associated with distinct reef-top habitats. Despite the significance of reef habitats and their fauna for fisheries and biodiversity etc, little information has been available on the distribution of habitats and their influence on the reef-top fauna in the Cook Islands. This thesis developed a novel approach to assess the status of the shallow-water reef-tops of Rarotonga, Cook Islands, to provide critical information to fisheries and conservation managers. The approach used remote sensing (aerial photography with ground truthing) to map the spatial arrangement and extent of the entire reef-top habitats accurately, and historical wind data and coastline shape to determine the windward and leeward sides of the island. The benthic habitat maps and degree of wind exposure were used to design and undertake a stratified sampling programme to assess the distribution and abundance of the epibenthic macroinvertebrate fauna of the reef-top. I quantified the distribution and abundance of the epibenthic macroinvertebrates and how they varied with habitat, assessed the effectiveness of a traditional ra�ui (marine protected area) for conserving stocks of Trochus niloticus and other invertebrates, and investigated the reproductive biology and impacts of traditional gonad harvesting on Holothuria leucospilota. There were four major habitat types (rubble/rock, sand/coral matrix, algal rim and sand) identified, the most extensive being rubble/rock (45%) and sand/coral matrix (35%). The degree of exposure to winds was found to correlate with the reef development and habitat distribution. The assemblage composition of each major habitat type differed significantly from every other habitat. The rubble/rock habitat had the greatest substratum heterogeneity and structural complexity, and the highest number of species and individuals. The overall abundance of the fauna was dominated by holothurians (68%) and echinoids (30%), while Trochus niloticus and Tridacna maxima accounted for the remaining 2% of the total invertebrate assemblage. Clear habitat partitioning was also found for adult and juvenile Trochus niloticus and Tridacna maxima. In the traditional fishery for Holothuria leucospilota, the mature gonads of males are harvested by making an incision in the body-wall of the animal, removing the gonads and then returning the animal to the reef to allow regeneration. Monthly collections of H. leucospilota were used to describe the reproductive biology of this species. Gametogenesis and spawning were synchronous between the sexes and spawning occurred annually during summer, when water temperature and photoperiod were at their highest. Although the incision in the body-wall and gonad removal had no impact on the survival of H.leucospilota in experimental cages, their body weight, and general sheltering and feeding behaviors were affected. Gonads took at least 41 days to start regenerating, suggesting a considerable delay in the spawning of fished individuals. In 1998, five Rarotongan communities re-introduced the traditional ra�ui system of resource management, prohibiting all fishing and gathering from their reefs. The performance of the Nikao ra�ui, which had been put in place to allow trochus stocks to increase, was investigated. Comparisons of macroinvertebrate assemblage composition and species density were made between three fishing treatments, i.e. fished areas adjacent to the ra�ui, within the ra�ui after two years of protection, and in the ra�ui after it had been lifted for three weeks to allow a commercial trochus harvest. Analysis of variance on the count data for the twelve most abundant species, and non-metric multi-dimensional scaling indicated that there were no differences in the microhabitat or the invertebrate assemblage composition between the three fishing treatments. However, there were significant differences between the rubble/rock and sand/coral matrix habitat types. The results on the effectiveness of the Nikao ra�ui are equivocal, due to the small sample size, and the variability between samples which was highlighted by the wide confidence intervals. This study highlights the importance of habitat to the macroinvertebrate fauna of the reef-top and the need for accurate habitat maps to increase the cost-effectiveness of future resource surveys, to provide information to management, and for the design of Marine Protected Areas. The mapping and survey methods must be reliable and repeatable in terms of the limitations of time, and the availability of expertise, funding and resources. The results provide important information for fisheries and conservation managers of Rarotonga and other Pacific Islands to better design rigorous sampling programmes for monitoring the status of reef-top resources, and for evaluating and planning Marine Protected Areas.

Thesis (M.M.S.)--Memorial University of Newfoundland, 2002. / "October 2002." Bibliography: leaves 56-66.

published_or_final_version / Biological Sciences / Master / Master of Philosophy

No description available.

Το πρόβλημα της αυξημένης σύλληψης υπομεγεθών ατόμων τσιπούρας (Sparus aurata, Linnaeus 1758) στις ιχθυοσυλληπτικές εγκαταστάσεις της λιμνοθάλασσας Μεσολογγίου-Αιτωλικού τις τελευταίες δεκαετίες έχει αποκτήσει σοβαρές διαστάσεις. Το φαινόμενο αυτό εκτός του ότι συνιστά περιβαλλοντική απειλή έχει επιφέρει σημαντική μείωση της εμπορικής αξίας του αλιεύματος με αποτέλεσμα τη συρρίκνωση του εισοδήματος των αλιέων. Η παρούσα εργασία μελετά την επιλεκτικότητα νέων τροποποιημένων ιχθυοπαγίδων που έχουν εγκατασταθεί στη λιμνοθάλασσα στο πλαίσιο μιας πρωτοβουλίας για την αντιμετώπιση του συγκεκριμένου προβλήματος. Η παρακολούθηση αυτής της πρωτοβουλίας έδειξε ότι οι νέες ιχθυοπαγίδες συμβάλλουν στη διαφυγή των υπομεγεθών ψαριών, οπότε και στη μείωση των ποσοτήτων των απορριπτόμενων ψαριών διασφαλίζοντας έτσι τη βιωσιμότητα του ιχθυοπληθυσμού. Επίσης, αυξάνονται τα έσοδα της αλιευτικής εκμετάλλευσης και βελτιώνεται η καθημερινότητα των αλιέων δεδομένου ότι δε μεσολαβεί το στάδιο του διαχωρισμού των μη εμπορεύσιμων από τα εμπορεύσιμα ψάρια. Οι διαφυγές των ψαριών από τις ιχθυοπαγίδες φάνηκε να επηρεάζονται από την αφθονία του αλιεύματος και πιο συγκεκριμένα σε περιπτώσεις μεγάλης αφθονίας παρατηρήθηκε να δυσχεραίνεται η διαφυγή των υπομεγεθών ψαριών από τις ιχθυοπαγίδες. Ενδεχομένως, αυτό να δημιουργεί την ανάγκη επέκτασης της τροποποιημένης επιφάνειας των ιχθυοπαγίδων. Η παρούσα εργασία αποτελεί πηγή σημαντικών πληροφοριών στη λήψη μέτρων με στόχο τη βελτίωση του προτύπου της αλιευτικής εκμετάλλευσης της λιμνοθάλασσας. / The problem of increased capture of undersized individuals of gilthead seabream (Sparus aurata, Linnaeus, 1758) at the Messolonghi - Etoliko lagoon fish traps, the last decades has become serious. This phenomenon apart from the ecological threat has decreased the commercial value of the catch thus leading to a reduction of the fishermen income. The present study investigates the selectivity of new fish traps installed in the lagoon in order to deal with this problem. It was found that modified traps contribute to the escapement of undersized individuals thus decreasing the discards as well as ensuring the sustainability of fish population. Furthermore, new traps exploitation leads to an increase of the income. Also, there is no need to sort undersized fish from the catch thus improving the daily lives of the fishermen. Fish escapement was found to be affected by the abundance of fish catch. In more details, high abundance was observed to make fish escapement difficult. Perhaps, this highlights the need of modified area extension. The present study reflects a source of useful information to take into consideration for the improvement of the lagoon fishery exploitation.

Indigenous knowledge use in identifying artisanal fishing zones is the core issue in this dissertation. It seeks, on one hand, to show the potentially of this knowledge and to establish the relationships between indigenous and scientific knowledge in fishing zones identification and, on other the hand, it is also a trend for alleviating those fishing zones surrounding beaches, estuaries and bays highly exploited by artisanal fishermen. Pushing artisanal fishermen upward offshore and/or into the open sea, they will fish more quality and high economic value fish contributing to enhance their income. By so doing, artisanal fishermen will uplift their living standard and, at the same time, they will contribute to sustainable artisanal fisheries management. Angoche District in Nampula province, north of Mozambique is the study area. The study was carried out to describe the logical sequence underlying on the process of identifying artisanal fishing zones using indigenous knowledge. The relationship between indigenous and scientific knowledge is treated with particular attention. The nature of the study is descriptive and analytical based on qualitative and quantitative data. The method used for data collection was face-to-face interviews using structured and semi-structured open-ended questions. Data on socioeconomic, traditional and cultural practices, technological and climate characteristics were collected, analyzed and discussed. Factors underlying artisanal fishing zones were studied. Spatial and non-spatial information for artisanal fishing zones identification was recorded applying Global Positioning Systems (GPS) and, later, processed and analyzed employing Geographical Information Systems (GIS). Finally, a map showing the localization and distribution of the identified fishing zones in the study area was produced. Results from the research show that identification of fishing zones offshore or open sea can be done simply based on local indigenous knowledge. The GIS technology employment facilitates the inclusion of indigenous knowledge into other knowledge which can be used for local decision making. Sustainable fisheries management can only be achieved by developing a science based on the priorities of local people, and creating a technological base that includes both traditional and modern approaches to problem-solving. / Thesis (M.Env.Dev.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

The depletion of a great many conventional fish stocks is urgent testimony for fisheries management to evaluate risk and uncertainty in an interpretable manner. We propose a novel decision based approach to time-series analysis that explores the spectrum of alternative population trajectories, each of which can be formulated as hypotheses about the state of the fishery. In the first chapter, we evaluate the ability of different regions of the surplus production state space to describe the true state of three North American fisheries: Pacific cod, porbeagle shark and yellowtail flounder. We consider how environmental variability and life history traits may alter our assumptions about population productivity, and we lay the foundation for a decision based age-structured analysis. In the second chapter, the approach is extended further into the ecological realm by considering how community interactions between Atlantic cod and harp seals can be represented in state space. Our results indicate that since the fishing moratorium in 1992, harp seals have potentially lowered cod productivity, preventing their recovery.

Throughout the Pacific, many species of echinoderms and molluscs have cultural value and are harvested extensively in subsistence fisheries. Many of these species are sedentary and often associated with distinct reef-top habitats. Despite the significance of reef habitats and their fauna for fisheries and biodiversity etc, little information has been available on the distribution of habitats and their influence on the reef-top fauna in the Cook Islands. This thesis developed a novel approach to assess the status of the shallow-water reef-tops of Rarotonga, Cook Islands, to provide critical information to fisheries and conservation managers. The approach used remote sensing (aerial photography with ground truthing) to map the spatial arrangement and extent of the entire reef-top habitats accurately, and historical wind data and coastline shape to determine the windward and leeward sides of the island. The benthic habitat maps and degree of wind exposure were used to design and undertake a stratified sampling programme to assess the distribution and abundance of the epibenthic macroinvertebrate fauna of the reef-top. I quantified the distribution and abundance of the epibenthic macroinvertebrates and how they varied with habitat, assessed the effectiveness of a traditional ra�ui (marine protected area) for conserving stocks of Trochus niloticus and other invertebrates, and investigated the reproductive biology and impacts of traditional gonad harvesting on Holothuria leucospilota. There were four major habitat types (rubble/rock, sand/coral matrix, algal rim and sand) identified, the most extensive being rubble/rock (45%) and sand/coral matrix (35%). The degree of exposure to winds was found to correlate with the reef development and habitat distribution. The assemblage composition of each major habitat type differed significantly from every other habitat. The rubble/rock habitat had the greatest substratum heterogeneity and structural complexity, and the highest number of species and individuals. The overall abundance of the fauna was dominated by holothurians (68%) and echinoids (30%), while Trochus niloticus and Tridacna maxima accounted for the remaining 2% of the total invertebrate assemblage. Clear habitat partitioning was also found for adult and juvenile Trochus niloticus and Tridacna maxima. In the traditional fishery for Holothuria leucospilota, the mature gonads of males are harvested by making an incision in the body-wall of the animal, removing the gonads and then returning the animal to the reef to allow regeneration. Monthly collections of H. leucospilota were used to describe the reproductive biology of this species. Gametogenesis and spawning were synchronous between the sexes and spawning occurred annually during summer, when water temperature and photoperiod were at their highest. Although the incision in the body-wall and gonad removal had no impact on the survival of H.leucospilota in experimental cages, their body weight, and general sheltering and feeding behaviors were affected. Gonads took at least 41 days to start regenerating, suggesting a considerable delay in the spawning of fished individuals. In 1998, five Rarotongan communities re-introduced the traditional ra�ui system of resource management, prohibiting all fishing and gathering from their reefs. The performance of the Nikao ra�ui, which had been put in place to allow trochus stocks to increase, was investigated. Comparisons of macroinvertebrate assemblage composition and species density were made between three fishing treatments, i.e. fished areas adjacent to the ra�ui, within the ra�ui after two years of protection, and in the ra�ui after it had been lifted for three weeks to allow a commercial trochus harvest. Analysis of variance on the count data for the twelve most abundant species, and non-metric multi-dimensional scaling indicated that there were no differences in the microhabitat or the invertebrate assemblage composition between the three fishing treatments. However, there were significant differences between the rubble/rock and sand/coral matrix habitat types. The results on the effectiveness of the Nikao ra�ui are equivocal, due to the small sample size, and the variability between samples which was highlighted by the wide confidence intervals. This study highlights the importance of habitat to the macroinvertebrate fauna of the reef-top and the need for accurate habitat maps to increase the cost-effectiveness of future resource surveys, to provide information to management, and for the design of Marine Protected Areas. The mapping and survey methods must be reliable and repeatable in terms of the limitations of time, and the availability of expertise, funding and resources. The results provide important information for fisheries and conservation managers of Rarotonga and other Pacific Islands to better design rigorous sampling programmes for monitoring the status of reef-top resources, and for evaluating and planning Marine Protected Areas.