Evaluation of approaches to estimate fish catches on Lake Victoria: a case study using CAS and frame data from Uganda

Since 2005, harmonized catch assessment surveys (CASs) have been implemented on Lake Victoria in the three riparian countries Uganda, Kenya, and Tanzania to monitor the commercial fish stocks and provide their management advice. The regionally harmonized standard operating procedures for CASs have not been wholly followed due to logistical difficulties. Yet the new approaches adopted have not been documented. This study investigated the alternative approaches used to estimate fish catches on the lake with the aim of determining the most reliable one for providing management advice and also the effect of current sampling routine on the precision of catch estimates provided. The study found the currently used lake-wide approach less reliable and more biased in providing catch estimates compared to the district based approach. Noticeable differences were detected in catch estimates between different months of the year. The study recommends future analyses of CAS data collected on the lake to follow the district based approach. Future CASs should also consider seasonal variations in the sampling design by providing for replication of sampling. The SOPs need updating to document the procedures that deviate from the original sampling design.

Symposium on participatory approaches to reservoir fisheries management: issues, challenges and policies. Dambulla, Sri Lanka, 04-06 Oct. 2004 Session I. Community-based fisheries management; experience in other countries: presentation on STREAM Vietnam’s experience

Established in early 2002, STREAM Vietnam has so far attained a number of good experiences and lessons in using participatory approaches for its work. The Country Office has been able to link to a wide range of stakeholders, and is working hard to build close relationships amongst them, so that institutional entities can better support the livelihoods of poor aquatic resources users, and support disadvantaged groups of people to improve their living standards by themselves. Reservoir fisheries and co-management are at early stage in Vietnam, but in certain places and industries co-management has brought about successful results by involving proactive participation of communities. Situated on the same continent and having many similarities, the interaction in agriculture and fisheries sector between Vietnam and Sri Lanka has brought the two countries closer. Being members of the STREAM family, there are great opportunities for exchange of experiences and lessons towards sustainable management of reservoir resources. (PDF has 11 pages.)

Approaches to national fish breeding programs: pointers from a tilapia pilot study

Details are given of a framework for developing breeding programmes using experience from the Genetic Improvement of Farmed Tilapias project which focussed on Nile tilapias (Oreochromis niloticus ). The following aspects are outlined: Analysis of targeted production and marketing systems; Breeding goals; Systematic documentation and evaluation of available genetic resources and choice and genetic base; Number of strains; Breeding strategy; Selection criteria and evaluation; Production and dissemination of improved strains; and, social, economic and environmental impacts.

Approaches to the evaluation and management of the fish stock in Kainji Lake, Nigeria

Estimates of potential yield for Kainji Lake, and the methods of analysis by earlier workers are discussed. Also summarized is the state of the fishery after impoundment, between 1969 and 1971, based on experimental gillnet catches. Recent sampling of the young of the year along the littoral margin indicates that most of the commercially important species have spawned successful1y in the lake. An intense fishing mortality of juvenile fish, owing to the use of small mesh nets by local fishermen, presents a possible threat to the future establishment of the fish in the lake. The results of gill-net selection studies based on HOLT'S (1957) method are given. The data have been extracted from experimental gill-net catches with graded fleets of nets between 1969 and 1971. Recommendations based on the above studies have been made to ensure a successful establishment of the fish species in the lake and an increase in catch-per~unit effort in subsequent years.

The Use of Herbicides to Control Hydrilla and the Effects on Young Largemouth Bass Population Characteristics and Aquatic Vegetation in Lake Seminole, Georgia

From 1997 to 2003, we examined the impacts of two aquatic herbicides, fluridone (Sonar; 1-methyl-3-phenyl-5-[3-(trifluromethl) phenyl]-4(1H)-pyridinone), and dipotassium salt of endothall (Aquathol K; 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid), used to control dense hydrilla (Hydrilla verticillata L. f. Royle), on population characteristics of juvenile largemouth bass (Micropterus salmoides Lacepede) in small coves (<10 ha) in Lake Seminole, Georgia. In addition, we estimated areal coverage and species composition of submersed aquatic vegetation (SAV) communities in each cove. Fish and plants were sampled in both control (hydrilla infested)and herbicide treated coves in November and March- April each year. Electrofishing catch-per-effort for both number and weight of age-0 and age-1 fish for the 1997 to 2002 year classes was either the same or higher (p < 0.05) in herbicide treated than in control coves. Age-0 fish were larger (p <0.05) in treated, than in control coves in November, but at age-1 in the following spring, fish were slightly longer (p <0.05) in the control coves. Higher age-0 catches were associated with greater percent reductions in numeric catch between age-0 and age-1 and reduced lengths of fish in November indicating density-dependent effects. Age-0 fish lengths were also negatively correlated to percent cover of both total and native SAV. Total or native SAV coverages were not associated with catch-per-unit effort for number and weight, but nearly all control and herbicide treated coves had total SAV coverage greater than 40%. Applications of both Sonar and Aquathol K reduced total SAV coverage and hydrilla, permitted the establishment of native SAVs, and had either neutral or positive impacts on young largemouth bass in small coves in Lake Seminole. (PDF contains 7 pages.)

Poverty and aquatic resources in Vietnam: an assessment of the role and potential of aquatic resource management in poor people's livelihoods

This report seeks to discuss a variety of approaches to poverty in order to illustrate the diversity of poor people, and the range of ways in which people are poor, facilitating a broader understanding of poverty and the significance of aquatic resources in poor people’s livelihoods. This is intended to provide a balance to the general neglect of the poor in the pursuit of aquaculture development within the Fisheries sector. It is also intended that this approach to poverty will assist in the planning and targeting of aquatic resource interventions that aim to promote poverty alleviation. In its many different forms, poverty remains a persistent problem with a great number of people facing deprivation and vulnerable livelihoods. Rates of poverty alleviation also differ; whereas the Red River Delta has achieved the greatest reductions in poverty, the Mekong Delta has achieved the smallest improvements, with possible indications that inequality has increased (see 2.4). Inequality between regions persists despite progress in all regions. (PDF has 37 pages.)

EcoGIS – GIS tools for ecosystem approaches to fisheries management

Executive Summary: The EcoGIS project was launched in September 2004 to investigate how Geographic Information Systems (GIS), marine data, and custom analysis tools can better enable fisheries scientists and managers to adopt Ecosystem Approaches to Fisheries Management (EAFM). EcoGIS is a collaborative effort between NOAA’s National Ocean Service (NOS) and National Marine Fisheries Service (NMFS), and four regional Fishery Management Councils. The project has focused on four priority areas: Fishing Catch and Effort Analysis, Area Characterization, Bycatch Analysis, and Habitat Interactions. Of these four functional areas, the project team first focused on developing a working prototype for catch and effort analysis: the Fishery Mapper Tool. This ArcGIS extension creates time-and-area summarized maps of fishing catch and effort from logbook, observer, or fishery-independent survey data sets. Source data may come from Oracle, Microsoft Access, or other file formats. Feedback from beta-testers of the Fishery Mapper was used to debug the prototype, enhance performance, and add features. This report describes the four priority functional areas, the development of the Fishery Mapper tool, and several themes that emerged through the parallel evolution of the EcoGIS project, the concept and implementation of the broader field of Ecosystem Approaches to Management (EAM), data management practices, and other EAM toolsets. In addition, a set of six succinct recommendations are proposed on page 29. One major conclusion from this work is that there is no single “super-tool” to enable Ecosystem Approaches to Management; as such, tools should be developed for specific purposes with attention given to interoperability and automation. Future work should be coordinated with other GIS development projects in order to provide “value added” and minimize duplication of efforts. In addition to custom tools, the development of cross-cutting Regional Ecosystem Spatial Databases will enable access to quality data to support the analyses required by EAM. GIS tools will be useful in developing Integrated Ecosystem Assessments (IEAs) and providing pre- and post-processing capabilities for spatially-explicit ecosystem models. Continued funding will enable the EcoGIS project to develop GIS tools that are immediately applicable to today’s needs. These tools will enable simplified and efficient data query, the ability to visualize data over time, and ways to synthesize multidimensional data from diverse sources. These capabilities will provide new information for analyzing issues from an ecosystem perspective, which will ultimately result in better understanding of fisheries and better support for decision-making. (PDF file contains 45 pages.)

Acute toxicity of atrazine to Oreochromis niloticus fingerlings

Acute toxicity of atrazine to Oreochromis niloticus was undertaken to find the lethal concentration (LC) 50 of atrazine using fingerlings. Different concentrations were prepared in mg/L. There were six different concentrations with a control and each treatment was replicated three times. A total number of twenty-one aquaria were used. The highest concentration was 30mg/L. Ten test organisms were used in each aquarium. At 24, 48, 72 and 96 hours there were LC 50 of 15.6mg/L, 14mg/L, 11mg/L and 9.4, respectively. At 24, 48, 72 and 96 hours there were mean survivals of 49.0%, 34.3%, 28.6% and 28.1%, respectively

The impact of year-to-year changes in the weather on the seasonal dynamics of lakes

The methods currently used to monitor and model lakes were developed when weather conditions were very different to what they are today. Most are based on samples collected at weekly or fortnightly intervals and cannot quantify the effects of short-term, more extreme, variations in the weather. In this article, the author presents some examples to show the importance of developing new monitoring methods using case studies from a number of lakes in the English Lake District. The impact of year-to-year changes and short-term changes on the dynamics of of lakes are highlighted.

Estimating species and size composition of rockfishes to verify targets in acoustic surveys of untrawlable areas

Rockfish (Sebastes spp.) biomass is difficult to assess with standard bottom trawl or acoustic surveys because of their propensity to aggregate near the seafloor in highrelief areas that are inaccessible to sampling by trawling. We compared the ability of a remotely operated vehicle (ROV), a modified bottom trawl, and a stereo drop camera system (SDC) to identify rockfish species and estimate their size composition. The ability to discriminate species was highest for the bottom trawl and lowest for the SDC. Mean lengths and size distributions varied among the gear types, although a larger number of length measurements could be collected with the bottom trawl and SDC than with the ROV. Dusky (S. variabilis), harlequin (S. variegatus), and northern rockfish (S. polyspinis), and Pacific ocean perch (S. alutus) were the species observed in greatest abundance. Only dusky and northern rockfish regularly occurred in trawlable areas, whereas these two species and many more occurred in untrawlable areas. The SDC was able to resolve the height of fish off the seafloor, and some of the rockfish species were observed only near the seafloor in the acoustic dead zone. This finding is important, in that fish found exclusively in the acoustic dead zone cannot be assessed acoustically. For these species, methods such as bottom trawls, long-lines, or optical surveys using line transect or area swept methods will be the only adequate means to estimate the abundance of these fishes. Our results suggest that the selection of appropriate methods for verifying targets will depend on the habitat types and species complexes to be examined.

Biochemical and morphometric approaches to characterize farmed tilapias

Biochemical (electrophoresis and mitochondrial DNA) and morphological analysis are important tools for the characterization of strains. Reference is made to studies conducted in the framework of the Genetic Improvement of Farmed Tilapias project to establish a new base tilapia population for culture purposes, describing the basic concepts of electrophoresis and morphometric analysis.

Crab fisheries in Cambodia and the development of crab banks

The crab (swimming crab; Portunus pelagicus) fishery in coastal Cambodia appears to have declined in recent years due to over-fishing and a growth in the number of fishermen, but remains an important source of income for households along the coast. Several initiatives have started since 2007, with support from NGOs, international organizations and the Fisheries Administration (FiA), to test stock enhancement techniques through the release of crab larvae. The so-called “crab bank” initiative involves keeping harvested gravid crabs alive in cages for a few days until they spawn, instead of immediately selling them for consumption or processing. In Cambodia, this initiative has developed within the framework of Community Fisheries (CFis) and thus implies a communitybased approach. The FiA has promoted the continuation of such initiatives; however, the nature of crab fisheries and the results from crab bank initiatives have not been documented in detail. The scope of this study was to understand the diversity of approaches to crab bank development in Cambodia, as well as their operational status and the challenges faced at differen

The effect of increase in the number of fishing trips on the economic efficiency of 9.82 m and 11 m fishing trawlers along Kerala coast

Cost-benefit analysis of a 9.82 m and 11 m fishing trawlers based on the number of fishing trips is presented. The number of fishing trips per year determines the profit and loss of the trawler. With the increase in the number of fishing trips, the profit also increase for both the sizes of trawlers. The minimum quantity of prawn and fish to be landed for 0-20% profit for varying number of fishing trips are worked out. The break-even for 9.82 and 11m trawlers was observed to be 185 and 210 fishing trips respectively during 1980-81.