800 resultados para strategic courtship


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In the past stock assessment surveys were generally reactive in response to a particular problem e.g. a pollution incident and as such were limited in the information they provided. A programme of strategic stock assessment would be more beneficial, providing up to date information on the status and composition of the stock. On a national level this could reveal trends in population dynamics and enable comparisons to be made between key rivers and between regions. The Stock Assessment Task Group (1991) has recommended annual strategic surveys for juvenile salmonids and triennial strategic surveys for coarse fish and non- migratory salmonids. The aim of this pilot study was to gain information on species distribution and their relative abundance within the River Lune catchment, and to compare the findings with the surveys carried out between 1981-1985. This would provide valuable information on the current status of the stock and provide an indication of the resources required to conduct such strategic surveys on other river catchments in the North West Region of the National Rivers Authority.

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Many species of reef f ish agg regate seasonally in large numbers to spawn at predictable times and sites (Johannes, 1978; Sadovy, 1996; Domeier and Colin, 1997). Although spawning behavior has been observed for many reef fish in the wild (Wicklund, 1969; Smith, 1972; Johannes, 1978; Sadovy et al., 1994; Aguilar Perera and Aguilar Davila, 1996), few records exist of observations on the courtship or natural spawning for the commercially important family Carangidae (jacks) (von Westernhagen, 1974; Johannes, 1981; Sala et al., 2003). In this study, we present the first observations on the natural spawning behavior of the economically-valuable permit (Trachinotus falcatus)(Linnaeus, 1758) from the full to new moon period at reef promontories in Belize, with notes on the spawning of the yellow jack (Carangoides bartholomaei) (Cuvier, 1833), and the courtship of five other carangid species.

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This is the report on the strategic stock assessment survey of the Colton Beck catchment in 1994 with particular reference to salmonids in Colton Beck, River Ea, River Gilpin and Rusland Pool. This report forms one part of the third year of a triennial survey programme for the South West Cumbria and South Cumbria catchments. It was produced by the National Rivers Authority in 1994. Colton Beck had excellent densities of sea trout (Salmo trutta) and a small population of salmon (Salmo salar) in its lowest reaches. The total productivity was very good throughout the catchment. Stocking of sea trout fry in 1993 has enhanced the population with survivors through to parr probably adding to the scoring of double class A at two sites in the survey in 1994. Stocking was not undertaken in 1994, but the population appears to be maintaining itself at a very high level.

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This is the report on the strategic fisheries stock assessment survey of the minor catchments in South West Cumbria 1996 with particular reference to salmonids, produced by North West Water in 1994. The 1996 Minor Catchment survey indicates variations in salmonid production within these catchments. Survey results indicate that production may be reaching its limit in certain areas whilst others are underachieving and others are unsuitable for salmonid production. Trout production within the catchments is higher and more widespread than that of salmon. Water quality levels vary considerably between catchments and intra-annually within individual catchments. The need for selective habitat surveys, with a view to habitat improvement schemes (H.I.S) is discussed. This report formed a basis for subsequent reports, thus, allowing data comparisons and analysis of production level fluctuations. It was the most extensive assessment of these catchments to date, taking into account comparisons with the new National Database on salmonid production in England and Wales.

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This is the report on the strategic fisheries stock assessment survey of the River Winster 1995 together with a coarse fish survey in 1994 and reference to the 1995 drought, produced by the Environment Agency North West in 1996. Salmonid production within the Winster catchment was dominated by trout although good densities of salmon juveniles were found on some main river sites. Despite suffering drought conditions for much of 1995, only salmon fry production appeared to have been affected. Coarse fish populations once found in the lower reaches of the Winster appear to have declined to very low levels with no fish sampled. This may be partly due to broken tidal gates allowing saline intrusion. It seems that the lower river was suited to the development of a recreational coarse fishery, now that the gates have been repaired. This report completes the strategic stock assessment surveys planned for the period 1992-1995. It represents the last major catchment that was surveyed to determine the current status of fisheries in the South and South West Cumbria areas.

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This is the Brown trout habitat assessment on the River Bela catchment produced by the Environment Agency North West in 1997. The Environment Agency (EA) and its predecessor the National Rivers Authority undertook strategic fish stock assessments in 1992 and 1995 on the River Bela catchment. These surveys found low numbers of brown trout {Salmo trutta) at some sites. Following this, habitat evaluation assessments were undertaken on the eleven poorest sites Factors probably responsible for declining trout populations on the three main tributaries of the Bela catchment include: Overgrazing by farm stock; Lack of suitable cover for parr; the absence of suitable spawning areas; existing potential of certain areas within the catchment not being utilised, due to poor dispersal. Habitat Improvement Schemes (H.I.S) are discussed and prioritised.