Accelerating loss of seagrasses across the globe threatens coastal ecosystems

Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 square kilometers per year since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% per year before 1940 to 7% per year since 1990. Seagrass loss rates are comparable to those reported for mangroves, coral reefs, and tropical rainforests and place seagrass meadows among the most threatened ecosystems on earth.

A method for estimating the rate of shedding of tags from yellowfin tuna

ENGLISH: The present paper describes a new method for estimating the shedding rate of tags. The method utilizes not only data on tagging and recovery of fish marked with two tags but also data from those marked with one. One important advantage of the new technique is that the estimates of the shedding rates are free from distortion caused by variations in fishing intensity during the total recovery period. The idea of this method appears to be implicit in a short note by Gulland (1963). This technique has been applied to the data obtained by the Inter-American Tropical Tuna Commission in a tagging cruise off the west coast of southern Baja California, during June 1963, at which time both single and double-tagged yellowfin tuna were released. Details of the tagging procedure and equipment have been described by Fink (1965b). The results presented in the present paper are for yellowfin tuna tagged with dart tags. Estimates of shedding should be made separately for each species investigated and also for each type of tag used, since these rates may be variable and often unexpectedly high (Springer and McErlean 1961, Chadwick 1963). SPANISH: El presente estudio describe un nuevo método para estimar las tasas del desprendimiento de marcas. El método emplea no solamente los datos sobre la marcación y recobro de peces marcados con dos marcas, pero también datos de los peces marcados con una marca. Una ventaja importante de la nueva técnica, es que las estimaciones de las tasas de desprendimiento son libres de alteración, causada por las variaciones en la intensidad de pesca durante el período total de recobro. La idea de este método parece ser implícita en un breve apunte por Gulland (1963). Esta técnica se ha aplicado a los datos obtenidos por la Comisión Interamericana del Atún Tropical, en un crucero de marcación efectuado frente a la costa occidental al sur de Baja California, en junio de 1963, tiempo en el cual fueron liberados atunes aleta amarilla marcados tanto con una como con dos marcas. Los detalles del procedimiento de la marcación y del equipo usado han sido descritos por Fink (1965b). Los resultados presentados en este estudio, pertenecen al atún aleta amarilla marcado con marcas de dardo. Las estimaciones del desprendimiento deben efectuarse separadamente para cada especie que ha sido investigada y también para cada tipo de marca usado, ya que estas tasas pueden ser vaiables, y a menudo inesperadamente altas (Springer y McErlean 1961, Chadwick 1963). (PDF contains 20 pages.)

Some aspects of the temperature, oxygen and nutrient distributions in Monterey Bay, California. Annual Report, Part 1, 1973

Seasonal variations in temperature, dissolved oxygen, and nutrients in the nearshore areas and in the canyon area of Monterey Bay, California during 1971-1972 were similar~ During upwelling periods, however, water in the nearshore areas was higher in temperature and oxygen and lower in nutrients than water in the canyon area~ This was caused by upwelled water moving north and south of the canyon into counterclockwise and clockwise flow in the northern and southern ends of the bay respectively. The water was heated by insolation and depleted of its nutrients by photosynthesis during this movement. The residence time of water in the nearshore northern and southern bay during upwelling is estimated to be 3 to 8 days, and this fits well into the above circulation pattern and average measured current velocities of 10 to 15 cm/sec~ There is sorne evidence that this circulation pattern and the estimated residence time may be also valid for on-upwelling periods. Upwelling apparently occurred in Monterey Submarine Canyon at rates of 0.4 to 2.9 m/day and was stronger in 1971 than 1972. (PDF contains 107 pages)

Nutrient distributions for Georges Bank and adjacent waters in 1979

In this report we describe the temporal and spatial distributions of inorganic nutrients over Georges Bank and in adjacent waters and discuss major features with respect to tbe nutrient environments of pbytoplankton. Nitrate and orthophosphorus were rapidly depleted from the surface layer of much of the study area in spring, but major differences were found between the shallow areas on Georges Bank and the surrounding stratified waters. In the "well-mixed" area of Georges Bank, the depletion encompassed the entire water column and ammonium became the dominant form of inorganic nitrogen throughout. Dissolved silicon was depleted slowly over central Georges Bank, reaching a minimum concentration in September while orthophosphorus gradually increased during the summer. The nutrient environment of phytoplankton over central Georges Bank may be described as vertically uniform but temporally changing in the relative availability of the various nutrients. In areas that undergo stratification (e.g., the central Gulf of Maine), a quasi-steady state was established as the surface water layer formed, consisting of declining nutrient gradients from below the euphotic layer to the top of the water column. These intergrading nutrient environments are relatively stable through time. Destratification reintroduced nutrients to depleted areas beginning in October; however, dissolved silicon was again depleted over shallow Georges Bank in late autumn though nitrate remained abundant. Slope water has been found to enter the bottom layer of the Gulf of Maine via the Northeast Channel. High nutrient concentrations observed in the bottom water of the Northeast Channel are consistent with this mechanism being the nutrient source for the Gulf of Maine. (PDF file contains 40 pages.)

Nutrient dynamics of seasonal tanks in the dry zone of Sri Lanka in relation to their hydrological regimes

Village tanks are put to a wide range of uses by the rural communities that depend on them for their survival. As the primacy of irrigation has decreased under these tanks due to a variety of climatic and economic reasons there is a need to reevaluate their use for other productive functions. The research presented in this paper is part of a programme investigating the potential to improve the management of living aquatic resources in order to bring benefits to the most marginal groups identified in upper watershed areas. Based on an improved typology of seasonal tanks, the seasonal changes and dynamics of various water quality parameters indicative of nutrient status and fisheries carrying capacity are compared over a period of one year. Indicators of Net (Primary) Productivity (NP): Rates of Dissolved Oxygen (DO) change, Total Suspended Solids (TSS): Total Suspended Volatile solids (TVSS) ratios are the parameters of principle interest. Based on these results a comparative analysis is made on two classes of ‘seasonal’ and ‘semi-seasonal’ tanks. Results indicate a broad correlation in each of these parameters with seasonal trends in tank hydrology. Highest productivity levels are associated with periods of declining water storage, whilst the lowest levels are associated with the periods of maximum water storage shortly after the NW monsoon. This variation is primarily attributed to dilution effects associated with depth and storage area. During the yala period, encroachment of the surface layer by several species of aquatic macrophyte also has progressively negative impacts on productivity. The most seasonal tanks show wider extremes in seasonal nutrient dynamics, overall, with less favourable conditions than the ‘semi-seasonal’ tanks. Never the less all the tanks can be considered as being highly productive with NP levels comparable to fertilised pond systems for much of the year. This indicates that nutrient status is not likely to be amongst the most important constraints to enhancing fish production. Other potential management improvements based on these results are discussed. [PDF contains 19 pages]

Recent Developments in In Situ Nutrient Sensors: applications and future directions, Savannah, Georgia, December 11-13, 2006: workshop proceedings

The Alliance for Coastal Technologies (ACT) convened a Workshop on "Recent Developments in In Situ Nutrient Sensors: Applications and Future Directions" from 11-13 December, 2006. The workshop was held at the Georgia Coastal Center in Savannah, Georgia, with local coordination provided by the ACT partner at the Skidaway Institute of Oceanography (University System of Georgia). Since its formation in 2000, ACT partners have been conducting workshops on various sensor technologies and supporting infrastructure for sensor systems. This was the first workshop to revisit a topic area addressed previously by ACT. An earlier workshop on the "State of Technology in the Development and Application of Nutrient Sensors" was held in Savannah, Georgia from 10-12 March, 2003. Participants in the first workshop included representatives from management, industry, and research sectors. Among the topics addressed at the first workshop were characteristics of "ideal" in situ nutrient sensors, particularly with regard to applications in coastal marine waters. In contrast, the present workshop focused on the existing commercial solutions. The in situ nutrient sensor technologies that appear likely to remain the dominant commercial options for the next decade are reagent-based in situ auto-analyzers (or fluidics systems) and an optical approach (spectrophotometric measurement of nitrate). The number of available commercial systems has expanded since 2003, and community support for expanded application and further development of these technologies appears warranted. Application in coastal observing systems, including freshwater as well as estuarine and marine environments, was a focus of the present workshop. This included discussion of possible refinements for sustained deployments as part of integrated instrument packages and means to better promote broader use of nutrient sensors in observing system and management applications. The present workshop also made a number of specific recommendations concerning plans for a demonstration of in situ nutrient sensor technologies that ACT will be conducting in coordination with sensor manufacturers.[PDF contains 40 pages]

Nutrient-phytoplankton interrelationships in the Eastern Tropical Pacific Ocean

ENGLISH: Near surface nutrient distributions in the eastern tropical Pacific Ocean, using data from the EASTROPAC Expedition of 1967-68 and pre~EASTROPAC data, are described. Nutrient concentrations were maximal along the equator, in the Peru Current and its offshore extension, and in the Costa Rica Dome and westward tensions of this feature. Nutrient-poor water was found north of the equator well offshore. In this water nitrate was often undetectable (<0.1 µg-at/liter) at the surface, but phosphate and silicic acid concentrations were moderate. Enrichment experiments showed that nitrogen was the primary limiting nutrient in poor water even though large amounts of organic N were found. Half saturation constants (K s ) were determined for ammonium-supported phytoplankton growth. These data were used to calculate near-surface primary productivity values which compared favorably with 14C values. Assimilation ratio measurements indicated that algae were not extremely nitrogen-deficient. Laboratory-determined K, values for phosphate and silicic acid indicated that these nutrients were rarely limiting. In rich water, chlorophyll levels were less than expected from nutrient levels, and this anomaly may be related to limitation by nutrients other than nitrogen (N), phosphorus (P), or silicon (Si), or to grazing. SPANISH: Se describe la distribución subsuperficial de los nutrientes en el Océano Pacífico oriental tropical, empleando los datos de la Expedición EASTROPAC de 1967~68 y datos anteriores a éstos. La concentración de nutrientes fue máxima a lo largo del ecuador, en la Corriente del Perú, en su prolongación mar afuera, en el Domo de Costa Rica y en las prolongaciones occidentales de esta característica. Se encontraron aguas pobres en nutrientes al norte del ecuador y bastante mar adentro. En estas aguas el nitrato era casi imperceptible (<0.1 µg-at/litro) en la superficie, pero las concentraciones de fosfato y ácido silícico fueron moderadas. Los experimentos de enriquecimiento indicaron que el nitrógeno era el principal nutriente limitante en aguas pobres, aun cuando se encontraron grandes cantidades de nitrógeno orgánico. Se determinaron las constantes de saturación media (K s ) para el desarrollo del fitoplancton sostenido por el amonio. Estos datos se emplearon para calcular los valores de la productividad primaria cerca a la superficie que pueden compararse favorablemente con los valores del 14C. Las medidas de la proporción de asimilación indican que las algas no tenían una deficiencia extremada de nitrógeno. Los valores determinados en el laboratorio de K, para el fosfato y ácido silícico indicaron que estos nutrientes limitaron rara vez la producción. En aguas ricas, los niveles de clorofila fueron inferiores a lo esperado según los niveles nutritivos y esta anomalía puede relacionarse a la alimentación o a la escasez de otros nutrientes distintos al nitrógeno (N), fósforo (P) o silicio (Si).

Nutrient digestibility and growth response of rainbow trout (Salmo gairdneri ) fed different carbohydrate types

Seven groups of fingerling rainbow trout (S. gairdneri ) were fed for 10 weeks on 0%, 10%, 20% and 30% of cassava or rice in isonitrogenous diets. Optimum growth and food utilization was at 20% dietary cassava. High fiber content of the control diet did not suppress protein digestibility in this group. Rather, at all levels, protein digestibility was good and remained between 84.4% and 90.1%. However, in the control group, carbohydrate digestibility was very poor. The cassava diets which had the highest digestible energy as carbohydrate produced the best growth performance, food utilization and protein sparing. At the levels studied, the dietary carbohydrates produced no hyperglycamic effect on the fish

The influence of some environmental variables on the apparent abundance of skipjack tuna, Katsuwonus pelamis, in the Eastern Pacific Ocean

ENGLISH: The abundance of skipjack larvae in the central and western Pacific approximately doubled for every 1°C increase in sea-surface temperature (SST) from 23°C to a maximum of about 29°C, and then usually decreased with further increases in SST. Skipjack larvae are scarce in the eastern Pacific Ocean (EPO), so most skipjack recruits and adults in this area are believed to have originated in the central and, possibly, the western Pacific. The catch per unit of effort (CPUE), in short tons per day's fishing, and the catch rate, in number of fish per day's fishing, are estimates of apparent abundance in a fishery. The logarithm of the annual CPUE for skipjack for international baitboats in the EPO for the 1934-1960 period was positively correlated with SST in the spawning area in the central Pacific 18 months earlier (r2 0.31), during the July-June period when most of the recruits in each cohort were presumed to have been spawned. Adequate data for other environmental variables were not available for testing with the baitboat data. The other environmental variables available and selected for testing for correlation with estimates of skipjack abundance for purse seiners for the 1961-1984 period and the reasons for their selection are as follows. 1)Wind-mixing index (WMI). The degree of mixing in the upper layers of the ocean is proportional to the cube of the wind speed, called WMI. The degree of mixing in the spawning areas of the central and the western Pacific may affect the concentration of organisms that skipjack larvae feed upon, thereby influencing their survival, and ultimately determining cohort strength and the number of recruits to the eastern Pacific fishery. 2) SST in the fishing areas at the time of fishing (SST). The CPUE for yellowfin tuna has been shown to be inversely related to SST in the fishing areas, and there are indications that skipjack CPUE is lower during EI Nino events when SST is higher than normal. 3) North-south SST gradient across the thermal front off the Gulf of Guayaquil. This is a measure of the degree of upwelling and nutrient enrichment of the upper waters south of the front and ultimately of the production of food for tunas. 4) Speed of the North Equatorial Countercurrent (NECC). Young skipjack may migrate from the central Pacific to the EPO in the eastward flowing NECC; if so, the number of recruits might be affected by variations in the speed of the current. The logarithm of the annual catch rate of skipjack recruits by international purse seiners in the EPO for the 1961-1984 period was positively correlated with SST in the spawning area of the central Pacific 18 months earlier (r2 = 0.21),and inversely correlated with WMI in the spawning area 18 months earlier (r2 0.46). The logarithm of CPUE for purse seiners in the area off the Gulf of Guayaquil was not correlated with SST in the spawning area 18 months earlier, but was inversely correlated with WMI in the spawning area 18 months earlier (r2 = 0.19), and inversely correlated with the north-south SST gradient in the fishing area at the time of fishing (r2 0.32). Neither of these estimates of apparent abundance from purse seiners were correlated with SST in the fishing areas, or with the speed of the NECC at earlier times. SPANISH: La abundancia de larvas de barrilete en el Pacífico central y occidental se multiplicó por dos, aproximadamente, por cada aumento de 1°Cen la temperatura de la superficie del mar (TSM) entre 23°C y un máximo de unos 29°C, y luego generalmente disminuyó con más aumentos en la TSM. Las larvas de barrilete son escasas en el Océano Pacífico oriental (OPO), y por lo tanto se cree que la mayoría de los reclutas y adultos en esta zona surgieron del Pacífico central, y posiblemente también del Pacífico occidental. La captura por unidad de esfuerzo (CPUE), en toneladas cortas por día de pesca, y la tasa de captura, en número de peces por día de pesca, son estimaciones de la abundancia aparente en una pesquería. El logaritmo de la CPUE anual de barrilete lograda por barcos de carnada en el OPO en el período 1934-1960 se correlacionó positivamente con la TSM en la zona de desove en el Pacífico central de 18 meses antes (r2 = 0.31), durante el período de junio-julio en el cual se cree que nació la mayoría de los reclutas en cada cohorte. No se dispuso de datos suficientes sobre otras variables ambientales para comprobarlos con los datos de los barcos de carnada. Las demás variables ambientales disponibles y seleccionadas para someterlas a pruebas de correlación con las estimaciones de la abundancia del barrilete de barcos cerqueros en el período 1961-1984, y las razones por su selección, son las siguientes: 1) Indice de mezcla por el viento (IMV). El grado de mezcla en las capas superiores del océano es proporcional al cubo de la velocidad del viento, llamado IMV. Es posible que el grado de mezcla en las zonas de desove del Pacífico central y occidental afecte la concentración de los organismos que alimentan a las larvas del barrilete, afectando así la supervivencia de éstas, y finalmente determinando el tamaño de las cohortes y el número de reclutas a la pesquería del OPO. 2) TSM en la zona de pesca al realizarse la pesca (TSM). Se ha mostrado que la relación de la CPUE del atún aleta amarilla a la TSM en la zona de pesca es inversa, y existen indicaciones que la CPUE de barrilete es inferior durante eventos del Niño, cuando las TSM son superiores a lo normal. 3) Gradiente norte-sur de las TSM a través del frente térmico frente al Golfo de Guayaquil. Esto es una medida del grado de afloramiento y enriquecimiento nutritivo del nivel superior de las aguas al sur de dicho frente, y finalmente de la producción de alimento para los atunes. 4) La velocidad de la Contracorriente Ecuatorial del Norte (CCEN). Es posible que los bariletes juveniles migren del Pacífico central al Pacífico oriental en la CCEN, que fluye hacia el este; de ser así, es posible que la cantidad de reclutas se vea afectada por variaciones en la velocidad de la corriente. El logaritmo de la tasa anual de captura de reclutas de barrilete por cerqueros de varias banderas en el OPO en el período 1961-1964 estuvo correlacionado de forma positiva con las TSM en la zona de desove del Pacífico central de 18meses antes (r2 0.21),y de forma inversa con el IMV de la zona de desove de 18 meses antes (r2 0.46). El logaritmo de la CPUE de los cerqueros en la zona frente al Golfo de Guayaquil no estuvo correlacionado con las TSM en la zona de desove de 18 meses antes, pero sí estuvo correlacionado de forma inversa con el IMV en la zona de desove de 18 meses antes (r2 0.19),y con el gradiente norte-sur de las TSM en la zona de pesca al realizarse la pesca (r2 0.32). Ninguna de estas estimaciones de abundancia aparente provenientes de barcos cerqueros estuvo correlacionada con las TSM en las zonas de pesca o con la velocidad de la CCEN en épocas anteriores. (PDF contains 140 pages.)

The growth and survival rate of Oreochromis niloticus fries fed (private) with varying percentages of Leucaena leucocephala leaf meal based diets

A-ten-week feeding trial was carried out to evaluate the growth and survival rate of Oreochromis niloticus fed with varying percentage levels of Leucaena leucocephala leaf meal based diets. The substitution rates of L.leucocephala leaf meal for groundnut cake in the various diets were 0% - Diet 1, 25% - Diet 2, 50% - Diet 3 and 75% - Diet 4. Ten fries with an average weight of 0.44g were stocked at the rate of 10 fish per bowl and fed at 5% body weight. Diet 1 with 0% inclusion of Leucaena leaf meal gave a significant difference (P>0.05) in growth and survival rate compared with diets 2, 3 and 4. The water quality parameters recorded were appropriate for fish culture

Water quality and nutrient dynamics - Lake Victoria, Kenya

Limnological studies in Lake Victoria (Kenyan portion) have been sporadic. Water quality and nutrient dynamics studies are being undertaken in fifteen sampling sites that have been divided into four ecological zones namely: Nyanza Gulf, Rusinga Channel, open waters inshore and open waters. The ongoing study will show how the physical and chemical paramenters affect fish distribution and abundance.

The growth and survival rate of (private) Oreochromis niloticus fingerlings fed with varying percentages of Leucaena leucocephala leaf meal based diets

A-ten-week feeding trial was carried out to evaluate the growth and survival rate of Oreochromis niloticus fed with varying percentage levels of Leucaena leucocephala leaf meal as a substitute for groundnut cake. The levels in the various diets were 0% - Diet 1, 25% - Diet 2, 50% - Diet 3 and 75% - Diet 4. Ten fingerlings with an average weight of 0.44g were stocked at the rate of 10 fish per bowl and fed at 5% body weight. Diet 1 with 0% inclusion of leucaena leaf meal gave a significant difference (P>0.05) in growth and survival rate compared with diets 2, 3 and 4. The water quality parameters recorded were appropriate for fish culture

Limnology in relation to fisheries in Tanzanian waters

The study of limnology is important to understand ecosystem dynamics and the ecological basis for fish production in the Lake Victoria which is important for fisheries resources use, planning and management. Physical, chemical and biological parameters are important and known to influence fish population production. Energy fixed by primary producers, e.g. algae, is transfered to higher trophic levels, e.g fish. Factors which influence the dynamics of phytoplankton and zooplankton population, e.g nutrient availability and uptake, growth rate, species composition and biomass, ultimately affect fish production. The commercial fisheries of Lake Victoria consists mainly of piscivorous Lates niloticus (L>), algivorous Oreochromis niloticus (L.) and zooplanktivorous Rastrineobola argentea (Pellegrin)

Growth performance of Clarias gariepinus fingerlings fed earthworm meal (Lumbricus terrestis)

An investigative study was carried out on the growth performance and nutrient utilization of (Clarias gariepinus) fingerlings fed earthworm meal as a replacement for fish meal. A large collection of earthworm was done during the peak of rainy season (July-August) within the University environment. They were then ovens dried. Used as test ingredients were 0% (Diet 1) 50% (Diet 2) and 1000% (Diet u). The trials were conducted in plastic bowls (40-L capacity) under laboratory conditions. The diets were fed at 5% body weight to fish; the fish were stocked at 10 fish per bowl. The evaluation of the growth parameters showed that there was no significant difference (P>0.05) in mean weight gain (MWG) specific growth rate (SGR) food conversion ratio (FCR), protein efficiency ration (PER) and survival among the fish fed the experimental diets

Growth response, feed conversion rate and cost benefits of hybrid catfish fed maggot meal based diets in outdoor tanks

The growth response, feed conversion ratio and cost benefits of hybrid catfish, Heterobranchus longifilis x Clarias gariepinus fed five maggot meal based diets were evaluated for 56 days in outdoor concrete tanks. Twenty-five fingerlings of the hybrid fish were stocked in ten outdoor concrete tanks of dimension 1.2mx0.13mx0.18m and code MM sub(1)-MM sub(5) in relation to their diet name. Five isonitrogenous and isocaloric maggot meal based diets namely MM sub(1)-0% maggot meal, MM sub(2)-25% maggot meal, MM sub(3)-50% maggot meal, MM sub(4-)75% maggot meal and MM sub(5-) 100% maggot meal were used for the experiment. The higher the proportion of maggot in the meal, the higher the ether extract and crude fiber. No significance difference P>0.05 exists between ash content of the experimental diets. Diet MM sub(2) had the best growth performance and highest MGR with a significant difference P<0.05 with other diets fed fish. No significance differences P>0.05 exists between the growth parameters for diets MM sub(1), MM sub(3), and MM sub(4). A positive correlation (r=1.0) exists (P<0.05, 0.25) between the growth parameters for the different experimental diets. Highest correlation r super(2)=0.9981 exists P<0.05 between MGR within the treatments. However, there no significant (P>0.05) difference in expenditure but there is between the profit indices and incidence of cost between the trials. MM sub(2) has the best yield cost and net profit. Without any reservation, inclusion of maggot based meal diet is recommended as feed of hybrid catfish to 75% inclusion for growth and profit incidence