Lunar and seasonal variations in the catches of Macrobrachium fisheries of the Cross River Estuary, SE Nigeria

Monthly catches of the Macrobrachium fisheries were recorded at a commercial shrimp landing site on the coasts of Calabar (Nigeria), from April 1997 to August 1998. Catches fluctuated over an annual cycle, with two peaks occurring from May-July and November-December. These peaks represented periods of major activities, reproduction, recruitment or migration. Also, mean catches decreased in the months of February and August, corresponding to the peak of dry season and the so-called 'August break', respectively. Catches from active gears (seine, push net) varied among the moon phases too, with a main peak during full moon, and the minimum catch was recorded during the first moon quarter. However, the catch from passive gear (trap) depicted an inverse relationship, showing a peak during the first moon quarter. Variation in catches at different months and moon phases were significant at P:0.05. Recognize these variations and trends would help in management decisions such as defining closed seasons without adversely affecting the economy of the fisher

Ecology and fishery in the Cross River Estuary - a research project

A literature review of 50 titles including nearly all relevant publications ensures adequate basis on the present level of knowledge. The proposal includes (a) the determination of the biozoenosis and selected environmental factors, and (b) of fishery and stock data of the main fish and shellfish species. The ecological research studies physical and chemical variables of the estuarine waters (flow velocity and direction, water temperature, conductivity, pH, dissolved oxygen, salinity, nutrients such as ammonium, nitrite, phosphate, silicate, pollutants such as hybrocarbons, pesticides and heavy metals, biochemical oxygen demand, chemical oxygen demand), plankton (bacterio-phyto-and zooplankton), benthos, sediment. The fishery biological and fishery investigations include: number of villages and fishermen, number of boats and gears by type, length and weight data of the main fishery objects with concentration on the shrimps, species and numbers of fish parasites. The ecological variables were monitored at fixed stations on sections in the Cross-River Estuary, Calabar and Great Kwara Rivers two times per month during spring and neap tides. The fishery biological and fishery variables were obtained during spring and neap tide too. For the determination of the detailed methodology the ecological and fishery part of the progeamme should be started with frame surveys based on a larger number of stations. These frame surveys should be repeated from time to time. Both parts of the programme are based on three years duration. It seems already appropriate to continue the work with selected representative stations, villages and variables in form of a long-term data chai

Factors influencing the emigration of juvenile Bonga from the Cross River estuary

Studies were conducted to identify and quantify the proximate factors responsible for the emigration of juvenile bonga Ethmalosa fimbriata (Bowdich, 1825) from the Cross River estuary. A time series of bonga cpue, salinity, turbidity and plankton abundance was undertaken, juvenile bonga was abundant in the estuary when salinities ranged between 1 and 9ppt. at salinities outside this range, they were absent. We conclude that salinity is the proximate factor that initiates the emigration of juvenile bonga from the estuar

Towards optimization of pulsed sodium laser guide stars

Pulsed sodium laser guide stars (LGS) are useful because they allow for Rayleigh blanking and fratricide avoidance in multiple-LGS systems. Bloch-equation simulations of sodium-light interactions show that these may be able to achieve photon returns nearly equal to, and in some cases greater than, what is seen from continuous-wave (CW) excitation. In this work, we study the time-dependent characteristics of sodium fluorescence, and investigate the optimal format for the new fiber laser LGS that will be part of the upgraded adaptive optics (AO) system on the Shane telescope at Mt. Hamilton. Results of this analysis are examined in the context of their general applicability to other LGS systems and the potential benefits of uplink correction are considered. Comparisons of simulation predictions with measurements from existing LGS are also presented and discussed.Comment: 9 pages, 7 figures, accepted by JOSA

Fisheries survey in Cross River State, Nigeria

The survey was performed in the Calabar Municipality, Calabar South, Odukpani, Akpabio and New Bakassi Local Government Areas. Taken as indicator, number of canoes, the largest villages are situated in Akpabio and New Bakassi LGOs and the smallest in Calabar Municipality and Calabar South. The larger villages base economically apart from fishery on oil palm-dominated agriculture. There are villages where each man is a fisher and also a farmer and others, were these main professions are performed by different persons. In the larger villages, there are traditionally operating carpenters (boats builders), hunters, honey samplers and wood cutters. Nearly all women are engaged in fish trading and several as fish and shrimp processor (smoke-drying) and periwinkle sampler/processor. In the larger villages are three sizes of canoes, small for two, medium for seven and large for 10-15 crew members. The small canoes are mainly used for the gill net fishery system on juvenile bonga (ekpai) in the dry season and on croaker and other demersal and semi-demersal species mainly in the raining season and are common in all surveyed villages. They are also used for fisheries with trap, cast net and long line. With mediu sized canoes, it's mainly operated the anchor net for catch of estuarine shrimp and sometimes boat seine for adult bongo (ibat). The larger canoes are engaged in the purse seine fishery on ibat in the near-coastal waters. In most of the larger villages, it is a common expedition fisheries; fishermen leave for up to several weeks out of their homes and operate in the more productive outer estuary and near-coastal waters, mostly on an estuarine shrimp; they produce smoke-dried products in their camps. The mean catch per boat per day for the small about of 5kg, for the medium-sized 15kg and for the larger purse seine canoes more than 100kg. In Calabar Municipality and South LGAs, all catches are sold fresh in own small markets at the landing site. In other LGAs the catches are processing to smoke-dried product is common. However, by using the mostly existing road connections to Calabar, and also selling of fresh fish is performed. By estimation, the monthly mean income per fisher family in the larger villages is N30, 000, after paying for repairs of nets and outboard engine. On the daily income for fish processing and trading, women included N0-500 and the men, probably by N100 or less

Gear considerations in the artisanal shrimp fishery of the Cross River Estuary, Nigeria

The artisanal shrimp fishery of the Cross River Estuary, SE Nigeria is exploited with three main shrimping gears, viz: beach seine, push net and trap. While the beach seine and push net are active gears, the trap is passive. Catch composition from the three gears was analysed for species diversity, catch contribution in weight and sex ratio. The trap showed the lowest species diversity, with only three Macrobrachium (M. macrobrachion, M. vollenhovenii and M. equidens) species represented in the catch, while Callinectes crab and Eleotris were by-catch. The complete absence of Penaeus notialis from trap catches throughout the sampling period of eighteen months was remarkable, while M. equidens was very low in abundance. The beach seine and push net had similar species composition in their catches with more than thirteen shrimp species represented. The catch per unit effort for the three gears varied, with beach seine contributing 46.13%, push net 24.41 % and trap 29.46%, of the overall catch. The sex ratio (male: female) was 1 :2.2 (beach seine), 1 :2.1 (push net), 1:2.15 (trap) for M. macrobrachion, 1 :1.27 (beach seine), 1 :1.32 (push net) and 1 :1.64 (trap), for M. vollenhovenii. The size structure showed more juveniles (below 40 mm) in beach seine and push net. Analysis of catches from the three gears showed some complexities as active and passive gears manifested extreme characteristics in their selection. In managing this fishery, therefore, a middle-of-the road option would be necessary, and we recommend the closed season

Efficient optimization of hollow-core photonic crystal fiber design using the finite-element method

We employ a finite-element (FE) solver with adaptive grid refinement to model hollow-core photonic crystal fibers (HC-PCFs) whose core is formed from 19 omitted cladding unit cells. We optimize the complete fiber geometry for minimal field intensity at material/air interfaces, which indicates low loss and high damage threshold, using multidimensional optimization. Our approach has very high numerical efficiency and accuracy, and we confirm that the FE-method is particularly well suited to model HC-PCFs

Phase Statistics of Soliton

The characteristic function of soliton phase jitter is found analytically when the soliton is perturbed by amplifier noise. In additional to that from amplitude jitter, the nonlinear phase noise due to frequency and timing jitter is also analyzed. Because the nonlinear phase noise is not Gaussian distributed, the overall phase jitter is also non-Gaussian. For a fixed mean nonlinear phase shift, the contribution of nonlinear phase noise from frequency and timing jitter decreases with distance and signal-to-noise ratio.Comment: 8 pages, submitted to JOSA