Marine biology of the Sierra Leone River Estuary. 1. The physical environment

The Sierra Leone River Estuary is a relatively young drowned river valley, it is shallow except for a deep channel which passes close to the Freetown shoreline. The upper reaches merge into a network of creeks and channels fringed by large areas of mangrove swamps. It is a tidal estuary of the semi-mixed type with the saline oceanic water entering it on a diurnal cycle. The climate of Sierra Leone is marked by a very distinct change between a very wet rainy season and a dry season. The tidal range of the Estuary (spring 3.03m; neap 2.28m) does not impede normal use of the harbour. The tidal variations can be felt as far as 42 miles inland along the water courses of the Sierra Leone River and its tributaries. The volume of fresh water entering the Estuary is large during the rainy season and greatly reduced during the dry season. Consequently there is a marked fall in salinity during the rainy season and higher salinities due to the marine influence prevailing during the dry season. The nature of the shores and bottom, the hydrography and chemistry of the estuarine system have been outlined in relation to the prevailing climatic conditions.

Sim-Colmeia: ambiente de simulação da dinâmica de uma colmeia para o ensino de Biologia

As ferramentas computacionais estão apoiando, de maneira crescente, o processo de ensino e aprendizagem em diversas áreas. Elas aumentam as possibilidades do docente para ministrar um conteúdo e interagir com seus alunos. Neste grupo de ferramentas estão as simulações baseadas em sistemas multiagentes. Neste contexto, este trabalho tem como objetivo apresentar um ambiente de simulação do crescimento populacional de uma colmeia para o ensino de Biologia. As variáveis do sistema podem ser alteradas visando analisar os diferentes resultados obtidos. Aspectos como duração e tempo da florada das plantações, conhecidos como campos de flores, podem ser manipulados pelo aluno. A abordagem multiagentes em Inteligência Artificial Distribuída foi a solução escolhida, para que o controle das atividades do aplicativo fosse feito de maneira automatizada. A Realidade Virtual foi utilizada para acrescentar aspectos importantes do processo que não podem ser visualizados pela simulação matemática. Uma síntese da utilização de tecnologias na educação, em especial da Informática, é discutida no trabalho. Aspectos da aplicação no ensino de Biologia são apresentados, assim como resultados iniciais de sua utilização.

A review of IATTC research on the early life history and reproductive biology of scombrids conducted at the Achotines Laboratory from 1985 to 2005

English: For nearly a century, fisheries scientists have studied marine fish stocks in an effort to understand how the abundances of fish populations are determined. During the early lives of marine fishes, survival is variable, and the numbers of individuals surviving to transitional stages or recruitment are difficult to predict. The egg, larval, and juvenile stages of marine fishes are characterized by high rates of mortality and growth. Most marine fishes, particularly pelagic species, are highly fecund, produce small eggs and larvae, and feed and grow in complex aquatic ecosystems. The identification of environmental or biological factors that are most important in controlling survival during the early life stages of marine fishes is a potentially powerful tool in stock assessment. Because vital rates (mortality and growth) during the early life stages of marine fishes are high and variable, small changes in those rates can have profound effects on the properties of survivors and recruitment potential (Houde 1989). Understanding and predicting the factors that most strongly influence pre-recruit survival are key goals of fisheries research programs. Spanish: Desde hace casi un siglo, los científicos pesqueros han estudiado las poblaciones de peces marinos en un intento por entender cómo se determina la abundancia de las mismas. Durante la vida temprana de los peces marinos, la supervivencia es variable, y el número de individuos que sobrevive hasta las etapas transicionales o el reclutamiento es difícil de predecir. Las etapas de huevo, larval, y juvenil de los peces marinos son caracterizadas por tasas altas de mortalidad y crecimiento. La mayoría de los peces marinos, particularmente las especies pelágicas, son muy fecundos, producen huevos y larvas pequeños, y se alimentan y crecen en ecosistemas acuáticos complejos. La identificación los factores ambientales o biológicos más importantes en el control de la supervivencia durante las etapas tempranas de vida de los peces marinos es una herramienta potencialmente potente en la evaluación de las poblaciones. Ya que las tasas vitales (mortalidad y crecimiento) durante las etapas tempranas de vida de los peces marinos son altas y variables, cambios pequeños en esas tasas pueden ejercer efectos importantes sobre las propiedades de los supervivientes y el potencial de reclutamiento (Houde 1989). Comprender y predecir los factores que más afectan la supervivencia antes del reclutamiento son objetivos clave de los programas de investigación pesquera.

Biology and Management of the American Shad and Status of the Fisheries, Atlantic Coast of the United States, 1960

This paper summarizes current information on the American shad, Alosa sapidissima, and describes the species and its fishery. Emphasis is placed on (1) life history of the fish, (2) condition of the fishery by State and water areas in 1960 compared to 1896 when the last comprehensive description was made, (3) factors responsible for decline in abundance, and (4) management measures. The shad fishery has changed little over the past three-quarters of a century, except in magnitude of yield. Types of shad-fishing gear have remained relatively unchanged, but many improvements have been made in fishing techniques, mostly to achieve economy. In 1896 the estimated catch was more than 50 million pounds. New Jersey ranked first in production with about 14 million pounds, and Virginia second with 11 million pounds. In 1960 the estimated catch was slightly more than 8 million pounds. Maryland ranked first in production with slightly more than 1.5 million pounds, Virginia second with slightly less than 1.4 million pounds, and North Carolina third with about 1.3 million pounds. Biological and economic factors blamed for the decline in shad abundance, such as physical changes in the environment, construction of dams, pollution, over-fishing, and natural cycles of abundance, are discussed. Also discussed are methods used for the rehabilitation and management of the fishery, such as artificial propagation, installation of fish-passage facilities at impoundments, and fishing regulations. With our present knowledge, we can manage individual shad populations; but, we probably cannot restore the shad to its former peak of abundance.

Computational study of the vortex path variation with the VG height

An extensive range of conventional, vane-type, passive vortex generators (VGs) are in use for successful applications of flow separation control. In most cases, the VG height is designed with the same thickness as the local boundary layer at the VG position. However, in some applications, these conventional VGs may produce excess residual drag. The so-called low-profile VGs can reduce the parasitic drag associated to this kind of passive control devices. As suggested by many authors, low-profile VGs can provide enough momentum transfer over a region several times their own height for effective flow-separation control with much lower drag. The main objective of this work is to study the variation of the path and the development of the primary vortex generated by a rectangular VG mounted on a flat plate with five different device heights h = delta, h(1) = 0.8 delta, h(2) = 0.6 delta, h(3) = 0.4 delta and h(4) = 0.2 delta, where delta is the local boundary layer thickness. For this purpose, computational simulations have been carried out at Reynolds number Re = 1350 based on the height of the conventional VG h = 0.25m with the angle of attack of the vane to the oncoming flow beta = 18.5 degrees. The results show that the VG scaling significantly affects the vortex trajectory and the peak vorticity generated by the primary vortex.

Aspects of the biology and population dynamics of freshwater mussels in Lake Kariba and Lake McIlwaine

The essential aim of this study was to provide a broad foundation of biological knowledge upon which a programme of mussel utilization and management could be built. Results of the study are presented in three main sections. Part 1 describes the stock of Lake Kariba and Lake McIlwaine; part 2 describes various aspects of the breeding biology of the three species; and part 3 presents the results of morphological, biochemical and age analyses - aspects which are used for initial standing crop and production calculations. The final discussion concludes the thesis with a general examination in ecological terms of the factors which have influenced the development and nature of the mussel faunas of the two lakes under consideration.

Reproductive biology of blue marlin (Makaira nigricans) in the western Pacific Ocean

The reproductive biology of blue marlin (Makaira nigricans) was assessed from 1001 fish (ranging from 121 to 275 cm in eye-to-fork length; EFL) caught by Taiwanese offshore longliners in the western Pacific Ocean from September 2000 to December 2001 and from 843 gonad samples from these fish, The overall sex ratio of the catch was approximately 1:1 dur ing the sampling period, but blue marlin are sexually dimorphic; females are larger than males. Reproductive activity (assessed by histology), a gonadosomatic index, and the distribution of oocyte diameters, indicated that spawning occurred predominantly from May to September. The estimated sizes-at-maturity (EFL50) were 179.76 ±1.01 cm (mean ±standard error) for females and 130 ±1 cm EFL for males. Blue marlin are multiple spawners and oocytes develop asynchronously. The proportion of mature females with ovaries containing postovulatory follicles (0.41) and hydrated oocytes (0.34) indicated that the blue marlin spawned once every 2–3 days on average. Batch fecundity (BF) for 26 females with the most advanced oocytes (≥1000 μm), but without postovulatory follicles, ranged from 2.11 to 13.50 million eggs (6.94 ± 0.54 million eggs). The relationships between batch fecundity (BF, in millions of eggs) and EFL and round weight (RW, kg) were BF = 3.29 × 10 –12 EFL5.31 (r2 = 0.70) and BF = 1.59 × 10–3 RW 1.73 (r2= 0.67), respectively. The parameters estimated in this study are key information for stock assessments of blue marlin in the western Pacific Ocean and will contribute to the conservation and sustainable yield of