Improving productivity in tropical lakes and reservoirs

Freshwater aquaculture, Inland fisheries

Balanced exploitation and coexistence of interacting, size-structured, fish species

This paper examines some effects of exploitation on a simple ecosystem containing two interacting fish species, with life histories similar to mackerel (Scomber scombrus) and cod (Gadus morhua), using a dynamic, size-spectrum model. Such models internalize body growth and mortality from predation, allowing bookkeeping of biomass at a detailed level of individual predation and growth and enabling scaling up to the mass balance of the ecosystem. Exploitation set independently for each species with knife-edge, size-at-entry fishing can lead to collapse of cod. Exploitation to achieve a fixed ratio of yield to productivity across species can also lead to collapse of cod. However, harvesting balanced to the overall productivity of species in the exploited ecosystem exerts a strong force countering such collapse. If balancing across species is applied to a fishery with knife-edge selection, size distributions are truncated, changing the structure of the system and reducing its resilience to perturbations. If balancing is applied on the basis of productivity at each body size as well as across species, there is less disruption to size-structure, resilience is increased, and substantially greater biomass yields are possible. We note an identity between the body size at which productivity is maximized and the age at which cohort biomass is maximized. In our numerical results based on detailed bookkeeping of biomass, cohort biomass reaches its maximum at body masse

Engaging local communities in aquatic resources research and activities: a technical manual

This document is part of a series of 5 technical manuals produced by the Challenge Program Project CP34 “Improved fisheries productivity and management in tropical reservoirs”. The objective of this technical manual is to relay the field experience of a group of scientists who have worked extensively in small fisheries in sub-Sahara Africa and Asia and lay out a series of simple and pragmatic pointers on how to establish and run initiatives for community catch assessment. The manual relies in particular on practical experience gained implementing Project 34 of the Challenge Programme on Water and Food: Improved Fisheries Productivity and Management in Tropical Reservoirs. (PDF contains 26 pages

Sustainable fishing of inland waters

Sustainability in fisheries has over the past decades evolved from a single species maximization concept to covering ecosystem and biodiversity considerations. This expansion of the notion, together with increased evidence that the targeted removal of selected components of the fish community may have adverse ecological consequences, poses a serious dilemma to the conventional fisheries management approach of protecting juveniles and targeting adults. Recently, the idea of balanced harvest, harvesting all components in the ecosystem in proportion to their productivity, has been promoted as a unifying solution in accordance the ecosystem approach to fisheries, but this will require a fundamental change to management. In this paper, we review theoretical background, and practicalities of securing high yielding fisheries in inland waters, with empirical examples freshwater fisheries which satisfy the extended objectives of minimal impact on community and ecosystem structure. We propose framework of ecological indicators to assess these objectives

Growth, mortality, maturity and length-weight parameters of fishes in Lake Kariba, Africa

This preliminary compilation presents vital parameters for 22 species of freshwater fish from Lake Kariba. The majority of the growth parameters are derived from tables in Balon and Coche's "Lake Kariba: a man-made tropical ecosystem in central Africa". The rest of the parameters are compiled from more recent sources and unpublished data

Growth, mortality, maturity and length-weight parameters of fishes in Lake Kariba, Africa

This preliminary compilation presents vital parameters for 22 species of freshwater fish from Lake Kariba. The majority of the growth parameters are derived from tables in Balon and Coche's "Lake Kariba: a man-made tropical ecosystem in central Africa". The rest of the parameters are compiled from more recent sources and unpublished data.Fish, Length-weight relationships, Africa, Kariba L.,

Identification of Important Factors Affecting Use of Digital Individualised Coaching and Treatment of Type 2 Diabetes in General Practice: A Qualitative Feasibility Study

Most type 2 diabetes patients are treated in general practice and there is a need of developing and implementing efficient lifestyle interventions. eHealth interventions have shown to be effective in promoting a healthy lifestyle. The purpose of this study was to test the feasibility, including the identification of factors of importance, when offering digital lifestyle coaching to type 2 diabetes patients in general practice. We conducted a qualitative feasibility study with focus group interviews in four general practices. We identified two overall themes and four subthemes: (1) the distribution of roles and lifestyle interventions in general practice (subthemes: external and internal distribution of roles) and (2) the pros and cons for digital lifestyle interventions in general practice (subthemes: access to real life data and change in daily routines). We conclude that for digital lifestyle coaching to be feasible in a general practice setting, it was of great importance that the general practitioners and practice nurses knew the role and content of the intervention. In general, there was a positive attitude in the general practice setting towards referring type 2 diabetes patients to digital lifestyle intervention if it was easy to refer the patients and if easily understandable and accessible feedback was implemented into the electronic health record. It was important that the digital lifestyle intervention was flexible and offered healthcare providers in general practice an opportunity to follow the type 2 diabetes patient closely