Die Entwicklung des atlantischen Kabeljaubestandes vor Grönland in der zweiten Hälfte des 20. Jahrhunderts

Based on the results of an analytical assessment, the Atlantic cod stock off Greenland collapsed already in the late 60s and, since then, reached rarely the 10 % level of its size in 1955. Applying the concept of a self-sustaining stock, the drastic harvesting strategy of the past four decades must be considered inadequate. The stock collapse was therefore found consistent with annual exploitation rates being not adjusted to conservative management options and exceeding the productivity of the stock by far. The results of a multiplicative model explained the following recruitment failure based on significant effects of spawning stock size as well as temperature. Certainly, cold periods have negatively affected the recruitment process and consequently contributed to the stock collapse. However, such ecological effects should not be itemized causal but must be taken into account regarding appropriate stock management. Till today, the spawning stock remained severely depleted causing a low probability of a successful recruitment and a substantial stock recovery.

Watershed monitoring and the TMDL modeling to assess bacterial loading in estuarine environments to improve management

Shellfish bed closures along the North Carolina coast have increased over the years seemingly concurrent with increases in population (Mallin 2000). More and faster flowing storm water has come to mean more bacteria, and fecal indicator bacterial (FIB) standards for shellfish harvesting are often exceeded when no source of contamination is readily apparent (Kator and Rhodes, 1994). Could management reduce bacterial loads if the source of the bacteria where known? Several potentially useful methods for differentiating human versus animal pollution sources have emerged including Ribotyping and Multiple Antibiotic Resistance (MAR) (US EPA, 2005). Total Maximum Daily Load (TMDL) studies on bacterial sources have been conducted for streams in NC mountain and Piedmont areas (U.S. EPA, 1991 and 2005) and are likely to be mandated for coastal waters. TMDL analysis estimates allowable pollutant loads and allocates them to known sources so management actions may be taken to restore water to its intended uses (U.S. EPA, 1991 and 2005). This project sought first to quantify and compare fecal contamination levels for three different types of land use on the coast, and second, to apply MAR and ribotyping techniques and assess their effectiveness for indentifying bacterial sources. Third, results from these studies would be applied to one watershed to develop a case study coastal TMDL. All three watershed study areas are within Carteret County, North Carolina. Jumping Run Creek and Pettiford Creek are within the White Oak River Basin management unit whereas the South River falls within the Neuse River Basin. Jumping Run Creek watershed encompasses approximately 320 ha. Its watershed was a dense, coastal pocosin on sandy, relic dune ridges, but current land uses are primarily medium density residential. Pettiford Creek is in the Croatan National Forest, is 1133 ha. and is basically undeveloped. The third study area is on Open Grounds Farm in the South River watershed. Half of the 630 ha. watershed is under cultivation with most under active water control (flashboard risers). The remaining portion is forested silviculture.(PDF contains 4 pages)

Resource utilization practices and sustainable development at the Lake Chad basin

The paper examines the resource utilization practices of the Lake Chad in view of the need for sustainable development of the natural resources of the area, which are being recklessly exploited. The issues of obnoxious fishing practices, inappropriate agricultural practices, indiscriminate grazing, reckless fuel-wood harvesting, water pollution etc were discussed. There are clear indications that the current resources utilization practices are pushing the natural resources of the area beyond the limit of their regenerative capacity. This is traceable to institutional weakness and inadequate management strategies at the Lake Chad basin. Suggestions were made towards witnessing a change of attitude to resource use, exploitation and management strategies

Tympanotonus fuscatus - its potential and abundance in the mangrove swamps of the upper Bonny River, River State

The Shellfish Tympanotonus fuscatus fisheries was studied in the upper Bonny River of River State. Abundance and size distribution were evaluated through collection of the Shellfish from 4 sampling stations along the River System. Shell size differences were observed between the sampling stations. The periwinkles, which were harvested heavily by local women, were smaller. The results do suggest that the population of Tympanotonus fuscatus in the Mangrove swamps of the upper Bonny River Creeks are strongly influenced by the harvesting

Modelling soil erosion and transport in the Burrishoole catchment, Newport, Co. Mayo, Ireland

The Burrishoole catchment is situated in County Mayo, on the northwest coast of the Republic of Ireland. Much of the catchment is covered by blanket peat that, in many areas, has become heavily eroded in recent years. This is thought to be due, primarily, to the adverse effects of forestry and agricultural activities in the area. Such activities include ploughing, drainage, the planting and harvesting of trees, and sheep farming, all of which are potentially damaging to such a sensitive landscape if not managed carefully. This article examines the sediment yield and hydrology of the Burrishoole catchment. Flow and sediment concentrations were measured at 8-hourly intervals from 5 February 2001 to 8 November 2001 with an automatic sampler and separate flow gauge, and hourly averages were recorded between 4 July 2002 and 6 September 2002 using an automatic river monitoring system [ARMS]. The authors describe the GIS-based model of soil erosion and transport that was applied to the Burrishoole catchment during this study. The results of these analyses were compared, in a qualitative manner, with the aerial photography available for the Burrishoole catchment to see whether areas that were predicted to contribute large proportions of eroded material to the drainage network corresponded with areas where peat erosion could be identified through photo-interpretation.

Proceedings of the first world meeting on bigeye tuna

The annual catches of big eye are exceeded by those of only two other species of tuna, skipjack, Katsuwonus pelamis, and yellowfin, Thunnus albacares. However, because most of the bigeye caught are consumed fresh, whereas most of the skipjack and yellowfin caught are canned, the economic value of big eye exceeds that of any other species of tuna. Despite its importance, less is known of the biology of bigeye than of the biology of any of the other principal market species of tunas. Historically, bigeye have been harvested mostly by longlines, which take only medium to large fish. During recent years, however, greater amounts of small bigeye have been caught by purse seines and other surface gear. This is a matter of concern for several reasons. First, long line fishermen are concerned that the harvesting of small bigeye will decrease the amounts of medium to large bigeye available to them. Second, since small bigeye are canned, rather than eaten fresh, consumers are concerned about the possible decrease in the supply of high-quality fresh fish. Third, economists are concerned about the possible economic loss associated with harvesting fish at less than their maximum economic value. Fourth, biologists are concerned about the possibility that harvesting of small bigeye could decrease the overall catches of that species. These concerns cannot be properly addressed until more knowledge of the biology of big eye is available. The purposes of the meeting were to review and discuss the information available and to make recommendations for further research.

Report on the workshop of tuna-dolphin interactions

ENGLISH: In April 1981 the IATTC convened a working group of scientists in Managua, Nicaragua to discuss the tuna-dolphin association and to suggest priorities for future research which would enable the effects of any interaction to be detected or quantified. The yellowfin tuna, Thunnus albacares, fishery in the eastern tropical Pacific is unique in that a significant proportion of the catch is of fish found in association with one or more species of dolphins. This association has never been fully understood but for many years tuna fishermen have used the more visible and more easily herded dolphin schools to help them locate and capture the tuna. In recent years, the concept of managing renewable resources in relation to their environments has been more fully developed. Any renewable resource is closely linked to other components in its general system and it is becoming increasingly more apparent that the harvesting of one resource affects another. This is the case with yellowfin tuna and dolphins in the eastern tropical Pacific, although the dolphins are killed incidental to the fishery and are not harvested. There would seem to be obvious advantages in managing the tuna-dolphin complex as a whole. To do this it is necessary to understand the effect that tuna and dolphins have on each other and the causal mechanisms of the interactions. SPANISH: En abril de 1981, la CIAT convoco un grupo de trabajo de investigadores en Managua (Nicaragua), para deliberar sobre la asociación atún-delfín e indicar prioridades referentes a una investigación futura que pueda facilitar la cuantificación o el reconocimiento de los efectos de cualquier interacción. La pesca del atún aleta amarilla Thunnus albacares en el Pacifico oriental tropical, es única, ya que una proporción importante de su captura es de peces encontrados en asociación con una o mas especies de delfines. No se ha logrado comprender cabalmente esta asociación, pero por varios anos los pescadores atuneros han utilizado los cardúmenes de delfines que son mas visibles y que pueden agruparse mas fácilmente para poder localizar y capturar los atunes. En los últimos anos, el concepto de administrar los recursos renovables con relación a su ambiente, ha tenido mas auge. Cualquier recurso renovable se vincula estrechamente a otros componentes en el sistema general y actualmente es mas evidente que la explotación de un recurso afecta otro. Este es el caso del atún aleta amarilla y de los delfines en el Pacifico oriental tropical aunque los delfines mueren incidentalmente con relación a la pesca y no son explotados. Parece que se obtendr1an ventajas evidentes si se administrara como un todo el conjunto atún-delfín. Para realizar esto es necesario comprender los efectos que tienen los atunes y delfines los unos sabre los otros y los mecanismos causantes de la interacción.

A model of the pelagic ecossystem in the eastern tropical Pacific Ocean

English: Recent calls for a more holistic approach to fisheries management have motivated development of trophic mass-balance models of ecosystems that underlie fisheries production. We developed a model hypothesis of the pelagic ecosystem in the eastern tropical Pacific Ocean (ETP) to gain insight into the relationships among the various species in the system and to explore the ecological implications of alternative methods of harvesting tunas. We represented the biomasses of and fluxes between the principal elements in the ecosystem with Ecopath, and examined the ecosystem's dynamic, time-series behavior with Ecosim. We parameterized the model for 38 species or groups of species, and described the sources, justifications, assumptions, and revisions of our estimates of the various parameters, diet relations, fisheries landings, and fisheries discards in the model. We conducted sensitivity analyses with an intermediate version of the model, for both the Ecopath mass-balance and the dynamic trajectories predicted by Ecosim. The analysis showed that changes in the basic parameters for two components at middle trophic levels, Cephalopods and Auxis spp., exert the greatest influence on the system. When the Cephalopod Q/B and Auxis spp. P/B were altered from their initial values and the model was rebalanced, the trends of the biomass trajectories predicted by Ecosim were not sensitive, but the scaling was sensitive for several components. We described the review process the model was subjected to, which included reviews by the IATTC Purse-seine Bycatch Working Group and by a working group supported by the National Center for Ecological Analysis and Synthesis. We fitted the model to historical time series of catches per unit of effort and mortality rates for yellowfin and bigeye tunas in simulations that incorporated historical fishing effort and a climate driver to represent the effect of El Niño-Southern Oscillation-scale variation on the system. The model was designed to evaluate the possible ecological implications of fishing for tunas in various ways. We recognize that a model cannot possibly represent all the complexity of a pelagic ocean ecosystem, but we believe that the ETP model provides insight into the structure and function of the pelagic ETP. Spanish: Llamamientos recientes hacia un enfoque más holístico al ordenamiento de la pesca han motivado el desarrollo de modelos tróficos de balance de masas de los ecosistemas que sostienen la producción pesquera. Desarrollamos una hipótesis modelo del ecosistema pelágico en el Océano Pacífico oriental tropical (POT) con miras a mejorar los conocimientos de las relaciones entre las distintas especies en el sistema y explorar las implicaciones ecológicas de métodos alternativos de capturar atunes. Con Ecopath representamos las biomasas de los elementos principales en el ecosistema, y los flujos entre los mismos, y con Ecosim examinamos el comportamiento dinámico del ecosistema con el tiempo. Parametrizamos el modelo para 38 especies o grupos de especies (denominados “componentes” del modelo), y describimos las fuentes, justificaciones, supuestos, y revisiones de nuestras estimaciones de los distintos parámetros, relaciones basadas en dieta, capturas retenidas de las pesquerías, y descartes de las mismas en el modelo. Realizamos análisis de sensibilidad con una versión intermedia del modelo, para el balance de masas de Ecopath y las trayectorias dinámicas predichas por Ecosim también. El análisis demostró que cambios en los parámetros básicos para dos componentes en niveles tróficos medianos, Cefalópodos y Auxis spp., ejercieron la mayor influencia sobre el sistema. Cuando se alteraron el Q/B de los Cefalópodos y el P/B de los Auxis spp. de sus valores iniciales y se balanceó el modelo de nuevo, las tendencias de las trayectorias de la biomasa predichas por Ecosim no fueron sensibles, pero la escala fue sensible para varios componentes. Describimos el proceso de revisión al que fue sujeto el modelo, inclusive revisiones por el Grupo de Trabajo sobre Captura Incidental de la CIAT y un grupo de trabajo apoyado por el Centro Nacional para Síntesis y Análisis Ecológicos. Ajustamos el modelo a series de tiempo históricas de capturas por unidad de esfuerzo y tasas de mortalidad de atunes aleta amarilla y patudo en simulaciones que incorporaron esfuerzo de pesca histórico e impulsos climáticos para representar el efecto de variaciones a escala de El Niño-Oscilación del Sur sobre el sistema. El modelo fue diseñado para evaluar las posibles implicaciones ecológicas de la pesca atunera de varias formas. Reconocemos la imposibilidad de que el modelo represente toda la complejidad de un ecosistema oceánico pelágico, pero creemos que el modelo del POT mejora los conocimientos de la estructura y función del POT pelágico.

A 4500-year time series of Pacific cod (Gadus macrocephalus) size and abundance: archaeology, oceanic regime shifts, and sustainable fisheries

A 4500-year archaeological record of Pacific cod (Gadus macrocephalus) bones from Sanak Island, Alaska, was used to assess the sustainability of the modern fishery and the effects of this fishery on the size of fish caught. Allometric reconstructions of Pacific cod length for eight prehistoric time periods indicated that the current size of the nearshore, commercially fished Pacific cod stocks is statistically unchanged from that of fish caught during 4500 years of subsistence harvesting. This finding indicates that the current Pacific cod fishery that uses selective harvesting technolog ies is a sustainable commercial fishery. Variation in relative Pacific cod abundances provides further insights into the response of this species to punctuated changes in ocean climate (regime shifts) and indicates that Pacific cod stocks can recover from major environmental perturbations. Such palaeofisheries data can extend the short time-series of fisheries data (<50 yr) that form the basis for fisheries management in the Gulf of Alaska and place current trends within the context of centennial- or millennial-scale patterns.

Efficiency and catch dynamics of collapsible square and conical pots used in the red king crab (Paralithodes camtschaticus) fishery

We compared the capture efficiency and catch dynamics of collapsible square and conical pots used in resource assessment and harvesting of red king crabs (Paralithodes camtschaticus [Tilesius, 1815]) in the Barents Sea. After two days of soaking, square pots caught three times as many crabs as conical pots, and their catches consisted of a higher proportion of male crabs and male crabs larger than 160 mm carapace length compared to the catches in the conical pots. Catches in the square pots did not increase as soak times were increased beyond two days, which indicates equilibrium between the rate of entries into and the rate of exits from the pots. Catches in conical pots, however, increased with increasing soak times up to eight days, the longest soak time examined in this study. These findings demonstrate the higher efficiency of square pots and the importance of understanding catch dynamics when making population assessments based on catchper-unit-of-effort data. The favorable catch characteristics and handling properties of the collapsible square pot may make this pot design suitable for other crab fisheries, as well.

Local solutions to challenges of West Indian Ocean fisheries development

The West Indian Ocean is rich in biodiversity and marine resources. This paper gives an overview of fisheries development and resource management in the region. There are many shared issues that must be addressed within countries and at the regional level. These are illustrated by examples from three countries. In Mozambique the issues of lack of information about artisanal fisheries, excessive harvesting of juveniles and conflicts between artisanal and commercial sectors are highlighted. Elements in addressing this include targeted research and decision-making support tools. The challenges faced in Somalia stem primarily from the political instability that contributed to an absence of sound fisheries policy. An example of a highly participatory process to develop the policy provides a model for other countries. In Tanzania, the issue of dynamite fishing was addressed by local communities initiating a program to promote wise use of the resources. There is a clear opportunity for better collaboration and greater integration of fisheries research and management on a regional basis. There is also much to be learnt by the sharing of experiences between countries. This has been initiated by some recently launched regional cooperation projects, but there are still many challenges facing this region.

The evolution of body muscle composition of the African catfish (Clarias gariepinus) (Burchell 1822)

Changes in body muscle composition of Clarias gariepinus were studied in fish reared from 1.08 g to 383 g mean body weight in a 201-day culture period. Changes in the amount of protein content, dry matter and ash free dry matter in the muscle tissue can be described as a function of body weight. The percentage of protein content was observed to be higher in bigger fish. Fat content was low throughout the fingerling stage. Specific growth rate decreased significantly at 400 g mean body weight (P<0.05) while feed conversion rate increased. The conclusion, based on the culture conditions in this study, is that the optimal weight for harvesting C. gariepinus is 400 g.

Aquaculture technology transfer to smallholder farmers in Malawi, Southern Africa

Details are given of activities conducted in Zomba, Malawi, in order to demonstrate new aquaculture technologies and encourage their use by smallholder fish farmers. The following technologies were introduced: napier grass as a pond output; use of a reed fence for harvesting fish; developing a high-quality compost as a pond input; vegetable-pond integration; chicken-pond integration; smoking kiln; pond stirring; and rice-fish integration. The reactions of the farmers to these technologies and their testing by the farmers are outlined briefly.

Economics and management strategies for restocking sandfish in Vietnam

This paper assesses the costs and benefits of a proposed project for restocking sandfish (Holothuria scabra) in Khanh Hoa Province, Vietnam. It identifies the key stakeholders, institutional framework, management and financing required for its implementation. The recommended management strategy includes a 50 percent harvest at optimum size. Limiting the number of boats fishing an area, possibly through licensing, can control the number of sandfish removed. The easiest way to prevent harvesting of undersized sandfish is to control the size of processed sandfish from processors. The potential benefits of restocking are shown by the rapid changes in selected indicators, particularly the net present value, the internal rate of return, and the benefit-cost ratio. Probability analysis is used to estimate the uncertainties in the project calculations. Based on a conservative estimate, the restocking of sandfish is expected to be profitable, although cost-benefit analyses are sensitive to the survival of restocked sandfish and their progeny, and the number of boats fishing for sandfish in the release area.

Management of wetland resources in the lower Mekong Basin: issues and future directions

The Lower Mekong Basin has extensive wetlands and these are being threatened by numerous problems. Most of these problems are interdependent and interact with one another. The lack of an appropriate definition of wetlands applicable to the region, pervasive inefficiencies and chronic lack of funds among riparian governments, and the poor appreciation of the true economic importance of wetlands and its resources are among the most prominent. The current definition, based on the Convention on Wetlands (Ramsar, Iran, 1971), is too broad when compared to the understanding of wetlands as being swamps, marshes and the like, and was developed specifically for wetlands with international importance as waterfowl habitats. Furthermore, wetlands are composed of different types of resources, which require different modes of management. Often, institutional competition, overlapping mandates and sometimes jealousies occur between government departments when they try to assert their authority on a particular wetland resource and use, and put forward their development plans without considering how these may conflict with other wetlands uses. Finally, effective wetland management requires reliable statistics or information on rate of harvest of natural resources such as fish and others, fishing/harvesting methods over time in order to determine the level of exploitation, and the status of the natural resources. This information is needed to identify opportunities for expansion, to establish historical trends, and to determine when management interventions are necessary to protect the resources from being overused by other developments. In order to address these issues, ICLARM - The World Fish Center has launched a project, the aim of objectives of which are described in this paper.