Premiers résultats sur l'excrétion et la production du zooplancton de la Lagune Ebrié (Côte d'Ivoire)

Biomass and metabolic rates (total nitrogen and phosphorus excretion and respiration) were measured at 4 stations, representative of the lagoon environment, during high-water (Oct-Nov), dry (Dec-Jan) and rainy (July) seasons. In low-salinity waters (4o/oo) Acartia clausi is almost the only species, whereas a marine and diversified fauna is brought in from the ocean during the dry season. O/NT and O/PT atomic ratios between respiration (O) and total nitrogen (NT) and phosphorus (PT) excretions are high (15.1 and 111, respectively) and show a marked hydrocarbon feeding of zooplankton. Production was assessed from excretion via the net growth efficiency coefficient, K2 , calculated from N/P ratios for particles (a1), zooplankton excretion (a2) and constitution (a3). Daily productivity indices (i.e. daily production/biomass ratio) are high and equivalent to 1.2-3.8 day turn-over times. These high values may be ascribed to high temperatures (26.5-30 C) and phytoplankton richness (surface chlorophyll 'a' concentrations are always greater than 4 mg/m-3). Finally, the paper deals with trophic relationships between phyto- and zooplankton (ingestion /primary production ratio and transfer coefficient) and the question of relationships between zooplankton and predators.

Biological productivity and fishery potential in the coastal waters off Bombay

Fishery potential of the nearshore waters of Bombay is estimated from the observed values of biological productivity at different trophic levels. The rate of primary and secondary production is relatively higher in the polluted coastal waters of Versova, Mahim and Thana. Observed mean benthic standing stock in the polluted creek waters is far less than the relatively unpolluted coastal regions off Bombay. Results suggest that the higher productivity at the lower trophic levels due to pollution, may not end up with high tertiary production. Therefore, such polluted regions are to be classified as special ecosystems where the transfer coefficient may be far less than the assumed 10% conversion factor.

Contribution of zooplankton to the fishery of Dharamtar Creek, adjoining Bombay Harbour

The rich zooplankton standing stock of Dharamtar Creek showed a variation of 8 to 5261 (av. 1032) mg C/100 m super(3)/d which led to a turnover of 29 tonnes C/km super(2)/y. The estimated fishery potential from zooplankton production was 0.079 tonnes C/km super(2) or 29.00 tonnes/km/y. The worked out yield in terms of wet weight of fish was 0.059 tonnes/km2u2/d. Experimental trawling within the creek showed a potential of 0.19 tonnes/km super(2)/d suggesting a transfer coefficient of only 31.4% form secondary to tertiary level. Fish eggs and larvae were very common in the area but contributed collectively only 1% to the total zooplankton population. On an average the outer zone sustained relatively higher population of fish eggs and larvae than the interior zone. The mean population density of larvae (334/100 m super(3)) was 3.5 times higher than fish eggs (93/100 m super(3)) suggesting the good survival rate and a congenial environment for larvae to thrive.

Variations in year-class strength and estimates of the catchability coefficient of yellowfin tuna, Thunnus albacares, in the Eastern Pacific Ocean

ENGLISH: Year-class composition of catch, virtual population size and yearclass strength were determined from serial samples of size composition of catches and catch records. Murphy's Solution to the catch equation, which is free from the effects caused by changes in fishing pressure, was used to estimate year-class strength, i.e. the total population of fish age 3/4 years. The resultant estimates indicated that the X55, X56, X57, X62 and X63 year classes were above average and the X58, X59, X60, X61 and X64 year classes were below average. The year-class designation refers to the year of actual entry or presumed year of entry into the commercial fishery (at approximately 1 year of age). The strongest and poorest year classes were the X57 and X61 classes, respectively. The ratio of the strongest to the weakest year class was 2.6. This amount of variation is small compared to that found for other species of fish. It was found that the relationship between stock size and yearclass strength is of no value in predicting year-class strength. As a by-product of the analysis, estimates of the catchability coefficients (qN) of the age groups in the fishery were obtained, These estimates were found to vary with age and time. Age-two fish apparently showed the greatest vulnerability to fishing gear, followed by ages three and one, respectively. The average estimate of the catchability coefficient in weight was calculated and found to compare favorably with Schaefer's estimate. The influence of sea-surface water temperature upon year-class strength was investigated to determine whether the latter can be predicted from a knowledge of sea-surface temperatures prevailing during and following spawning. No correlation was evident. SPANISH: La composición de la clase anual en la captura, el tamaño de la población virtual y la fuerza de clase anual, fueron determinados según una serie de muestras de la composición de tamaño de las capturas y de los registros de captura. La Solución de Murphy de la ecuación de captura, que está libre de los efectos causados por los cambios de la presión de pesca, fue usada para estimar la fuerza de la clase anual, i.e. la población total de peces de 3/4 años. Las estimaciones resultantes indican que las clases anuales X55, X56, X57, X62 y X63 fueron superiores al promedio y que las clases anuales X58, X59, X60, X61 y X64 fueron inferiores al promedio. La designación de la clase anual se refiere al año actual de entrada o al año supuesto de entrada en la pesca comercial (aproximadamente a la edad de 1 año). Las clases anuales más fuertes y más pobres fueron la X57 y X61 respectivamente. La razón de la clase anual más fuerte en relación a la más débil fue 2.6. Esta cantidad de variación es pequeña comparada con la encontrada para otras especies de peces. Se encontró que la relación entre en tamaño del stock y la fuerza de la clase anual no tiene valor en predecir la fuerza de la clase anual. Se obtuvieron estimaciones de los coeficientes de capturabilidad (qN) de los grupos de edad en la pesquería como un producto derivado del análisis. Se encontraron que estas estimaciones variaron con la edad y tiempo. Los peces de edad dos aparentemente presentaron la vulnerabilidad más grande en relación al arte pesquero, seguidos por las edades tres y una, respectivamente. La estimación promedio del coeficiente de capturabilidad en peso fue calculada y se encontró que podía compararse favorablemente con la estimación de Schaefer. La influencia de la temperatura del agua superficial del mar sobre la fuerza de la clase anual fue investigada para determinar si se podía predecir esta última según el conocimíento de las temperaturas superficiales del mar prevalecientes durante el desove y después de éste. No hubo correlación evidente. (PDF contains 44 pages.)

Transfer of Medical Sensor Technologies to Environmental Monitoring, Solomons, Maryland, April 6-8, 2005: workshop proceedings

(pdf contains 23 pages)

Strategies for transfer of aquaculture technology to small-scale fish farmers in Nigeria

There is increasing awareness of aquaculture in Nigeria today for a number of reasons namely: water pollution, declining catch and the awareness of the attractiveness of aquaculture as an investment area and a pivotal point for national development. The development of aquaculture in Nigeria, requires the building up of institutions at the grassroot level and the formulation of policies and programmes for the small fishfarmer. This of course would be backed up by a sound technology generation, verification and packaging, dissemination and use programme

Aquaculture research: technology transfer for rural development in Nigeria

Conventional aquaculture has been promoted in Nigeria for the past five decades with minimal impact on rural communities: from the findings of Maclearen (1949) where he popularized the use of culturable fish predators Lutjanus sp; Pomades sp; Tarpon adanticus; Chrysichthys nigrodigitatus in earthen ponds near Onikan-Lagos, Nigeria; to the finding of Zwilling, 1963, who reported common carp, Cyprinus carpio propagation and culture in Panyan Fish Farm, near Jos; to the findings of FAO, 1965, when the potential culture of marine mullets culture in brackish water ponds in Buguma, Rivers State was presented. The work of other researchers Sivalingam, (1970; 1973), Ezenwa (1976), development officers and extension officers contributed to the development of aquaculture in few rural areas of the country and informed on public and private owned fish farm infrastructures. Despite a moderate long history of aquaculture research and development in Nigeria, an annual production level of 25,000 metric tons was recorded in 1999. This situation calls for a more sustainable approach for a stronger link between aquaculture research and technology transfer for the development of rural communities of Nigeria. This paper therefore examines some of the issues involved in the continuous flow of the new aquaculture technology in the improvement of fish protein output, standard of living of rural farmers and prevention of urban migration by the youth