Observations de la temperature et des courants sur le plateau continental ivoirien

The Centre de Recherches Océanographiques d'Abidjan has carried out the HYDROBIOCLIMAT program in order to study the seasonal and interannual fluctuations of the physical and biological parameters over the continental shelf of Ivory Coast ; two subsurface moorings with from one to three AANDERAA current meters fixed on the lines, were deployed in front of Abidjan and San Pedro. Temperature and current measurement records are presented at these two locations.

Seasonality in the coastal ocean of North America, 35°N - 48°N [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): The seasonal cycles of coastal wind stress, adjusted sea level height (ASL), shelf currents and water temperatures off the west coast of North America (35°N to 48°N) were estimated by fitting annual and semiannual harmonics to data from 1981-1983. Longer records of monthly ASL indicate that these two harmonics adequately represent the long-term monthly average seasonal cycle, and that the current measurement period is long enough to define the seasonal cycles, with relatively small errors in magnitude and phase.

Development of an electric shrimp trawl 1. Reaction of shrimps to low volt direct current

Preliminary attempts were made to assess the effect of direct current on shrimps and to see whether the shrimp could be guided in large numbers into the fishing net by using a current of appropriate voltage without scattering them away as it happens at present. This communication is the first in the series of studies and primarily deals with laboratory equipment and experimental procedures followed.

Monitoring fish populations in Lower Lough Erne, Northern Ireland: applicability of current methods and implications for future monitoring under the EC Water Framework Directive

The proposed EC Water Framework Directive (WFD) will require member states to monitor both biotic and abiotic components of lake environments. With adoption of the WFD some measurement of fish populations will also be required. This paper describes work carried out since 1971, and particularly since 1991, on the status of fish populations in Lower Lough Erne, Northern Ireland, with an emphasis on defining change over time due to human impacts on the lake. This offers a reasonable starting point from which to develop a monitoring programme suitable for the needs of the WFD in this lake. The implications for as yet unmonitored fish populations in lakes are also determined.

Electric fishing survey of the gravel addition sites on the River Wyre, Grizedale Beck and Joshua's Beck.

Although geographically the River Wyre lies between two rivers containing major migrations of adult salmon and sea trout, its rod & line fisheries have for a number of years produced exceptionally low catches. In order to determine the causes of this the Wyre Salmon and Sea trout Restoration Group (WSSRG) was conceived in 1994 as a partnership between the then National Rivers Authority (now Environment Agency), local landowners, angling clubs and interested parties. Two studies of 1994 and 1995 stated that there is a shortage of useable spawning gravels on the river. This is compounded by Abbeystead Reservoir acting as a gravel trap, the siltation of gravels on several side becks and problems with access to available gravels by returning adults. There was also perceived to be a need for accurate fishery data from the river encompassing redd counts, catch data and surveys of fry populations. The 1995 report suggested a number of management proposals which might be adopted in order to improve and create available spawning habitat for migratory salmonids. Funding was made available to create three spawning gravels on each of two side becks (Grizedale Beck and Joshua's Beck) and the addition of gravels to a site oh the main river below Abbeystead Reservoir. Modifications were also made to the fish pass at Abbeystead to allow easier passage of fish. These improvements were made in the autumn of 1995. Salmonid spawning redd counting was undertaken on the whole Wyre catchment in 1995/1996 and specific surveys by electric fishing on the gravel enhancement sites in the summer of 1996. This report details the current state of the improvement works that were undertaken and presents the results of electric fishing surveys in September 1996. A number of lessons have been learnt which will be of great benefit to the Fisheries Function in other parts of the Wyre catchment and the Central Area in general.

Effect of analytical conditions in wavelength dispersive electron microprobe analysis on the measurement of strontium-to-calcium (Sr/Ca) ratios in otoliths of anadromous salmonids

The use of strontium-to-calcium (Sr/Ca) ratios in otoliths is becoming a standard method to describe life history type and the chronology of migrations between freshwater and seawater habitats in teleosts (e.g. Kalish, 1990; Radtke et al., 1990; Secor, 1992; Rieman et al., 1994; Radtke, 1995; Limburg, 1995; Tzeng et al. 1997; Volk et al., 2000; Zimmerman, 2000; Zimmerman and Reeves, 2000, 2002). This method provides critical information concerning the relationship and ecology of species exhibiting phenotypic variation in migratory behavior (Kalish, 1990; Secor, 1999). Methods and procedures, however, vary among laboratories because a standard method or protocol for measurement of Sr in otoliths does not exist. In this note, we examine the variations in analytical conditions in an effort to increase precision of Sr/Ca measurements. From these findings we argue that precision can be maximized with higher beam current (although there is specimen damage) than previously recommended by Gunn et al. (1992).

Preliminary observations on the effect of a. c. current on Catla catla and Ophicephalus punctatus

In order to evolve suitable electrical fishing gear for inland waters, preliminary experiments have been conducted to observe effect of a. c. currents on Catla catla at voltages of 30, 90 and 120, pH 7.3 and 8.4, temperature 48°F, 78°F and 105°F, distance between electrodes 25 cm, 50 cm and 75 cm, size range of fish 100 mm, to 235 mm. Apparatus used was a 5 kw; a. c. 60 cycles generator with resistance control. Larger sizes of fish were more prone to electric shock. Higher temperature increases the intensity of the shock, while variation of pH between 7.3 to 8.4 did not materially affect the intensity of the shock. Fishing with a mixed population of Catla catla and Ophicephalus punctatus gave a greater percentage of mortality for the latter.

Instrument for the measurement of the fore and aft tilt of otterboards

A portable self-contained instrument has been designed and developed for the measurement of the Fore and Aft tilt of otter boards within the range —22° to + 22° with an accuracy of ± 1°. An underwater transducer fitted on the otter board converts its tilt into corresponding electrical resistance which is measured in an ohmmeter on board, both being connected by electric cable.

Stray current corrosion of copper sheathing and keel cooling pipe of a 36' trawler

The results of investigations into the cause of an accelerated corrosion of copper sheathing and keel cooling pipe of a 36' wooden trawler are reported. The corrosion is attributed to the stray electric currents originating from the electrical wiring system. The sources of stray currents and the remedial measures have been suggested.